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000
FXAK68 PAFC 222145
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT MON SEP 22 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN TODAY HAS A TROUGH ALONG THE ALCAN BORDER
WITH AN UPPER LEVEL RIDGE OVER THE EASTERN BERING SEA AND WESTERN
ALASKA. FARTHER WEST THERE IS A CUT OFF LOW CLOSE TO ATTU. THE 250
MB JET STREAM CONTINUES TO RUN SOUTH OF THE AREA.
A COLD UPPER LEVEL TROUGH IS MOVING INTO NORTHWEST ALASKA OFF THE
CHUKCHI SEA.
AT THE SURFACE THERE IS A WEAK TROUGH ALONG THE NORTH GULF COAST
AS WELL AS A WEAK LOW IN THE EASTERN COPPER RIVER BASIN. THESE
FEATURES ARE THE REMNANTS OF THE LOW THAT WAS IN THE EASTERN GULF
YESTERDAY. ANOTHER INTERESTING SURFACE FEATURE IS A MESO-LOW THAT
HAS DEVELOPED JUST SOUTH OF KODIAK ISLAND. THIS FEATURE CAN BE
SEEN BEST ON THE VISIBLE SATELLITE AS IT IS TOO LOW TO BE SEEN
WELL ON THE IR SATELLITE.
HIGH PRESSURE IS OVER THE EASTERN BERING SEA AND SOUTHWEST ALASKA
AND THIS RIDGE EXTENDS INTO THE INTERIOR OF THE STATE AS WELL. A
LOW COMPLEX REMAINS NEAR THE WESTERN BERING SEA AND WESTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT INTO WEDNESDAY BUT THEN THERE ARE
SIGNIFICANT PROBLEMS THAT SHOW UP OVER BOTH THE GULF OF ALASKA
AND BERING SEA. WHILE ALL THE MODELS KEEP THE HIGH PRESSURE OVER
THE MAINLAND PART OF THE STATE THROUGH THE WEEK THE TWO LOWS ON
THE PERIPHERY OF THE HIGH PRESSURE ARE THE ISSUE. ON THURSDAY A
LOW SOUTHEAST OF THE GULF OF ALASKA IS DETECTED BY ALL MODELS BUT
THERE IS A DISCREPANCY OF OVER 450 MILES BETWEEN THE NAM AND GEM
SOLUTIONS. THE ECMWF AND GFS ARE GENERALLY SPLITTING THE DIFFERENCE
AND THEY ARE LIKELY TO VERIFY BETTER. IN THE BERING SEA THE MODEL
DIFFERENCES ARE LARGER AND WILL HAVE MORE IMPACT ON THE FORECASTS.
WHILE THE DIFFERENCE IN THE LOW NEAR THE GULF CAN BE BLENDED OUT
TO GET A REASONABLE SOLUTION THE DIFFERENCES BETWEEN THE MODELS
PRECLUDES THIS. THE BASIC ISSUE REVOLVES AROUND WHETHER THE
INCOMING LOW WILL HAVE MULTIPLE CENTERS ALONG A BROAD TROUGH OR
WHETHER THE LOW WILL COALESCE INTO A SINGLE STRONG CENTER. THIS
SECOND SOLUTION IS ONE THAT THE ECMWF HAS INSISTED ON THE PAST FEW
RUNS. THE NAM AND GFS AND GEM SHOW A SOLUTION MORE LIKE THE FIRST
SCENARIO BUT WITH VERY DIFFERENT DETAILS. IN SHORT, THE FORECAST
IN THE BERING SEA AND ALEUTIANS FOR THE SECOND HALF OF THE WEEK
HAS A GREATER UNCERTAINTY THAN USUAL.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE REMNANTS OF THE GULF LOW PERSIST OVER THE COPPER RIVER BASIN
WITH ENOUGH DYNAMICS FOR SOME RAIN IN THE CENTRAL PART OF THE
BASIN AND SNOW TO THE EAST TOWARD MENTASTA PASS. MOST OF THIS WET
SNOW APPEARED TO BE MELTING AS IT HIT THE GROUND.
THE REST OF SOUTH CENTRAL ALASKA HAS CLEARED OUT QUITE WELL WITH
HIGH PRESSURE OVER THE INTERIOR AND SOUTHWEST ALASKA BRINGING IN
DRY AIR. THE EXCEPTION IS THE EASTERN AND SOUTHERN PARTS OF KODIAK
ISLAND ARE UNDER SOME CLOUD COVER DUE TO THE MESO-LOW JUST SOUTH
OF THE ISLAND. KODIAK NORMALLY HAS CLEAR SKIES UNDER THE NORTHWEST
FLOW ALOFT BUT THIS SURFACE LOW IS ENOUGH TO BRING IN THE CLOUDS
UNTIL IT PULLS FARTHER SOUTH LATE THIS EVENING. THE RIDGE COMBINED
WITH THE TROUGH ALONG THE NORTH GULF COAST HAS CREATED A PRESSURE
GRADIENT TIGHT ENOUGH FOR GUSTY OUTFLOW WINDS THROUGH CHANNELED
TERRAIN...ESPECIALLY RIGHT ALONG THE GULF COAST. THESE WINDS WILL
DIMINISH TOMORROW AS THE GRADIENT WEAKENS BUT THEN INCREASE AGAIN
ON TUESDAY NIGHT THROUGH WEDNESDAY NIGHT AS THE GRADIENT INCREASES
AGAIN.
THE CLEAR SKIES WILL ALSO USHER IN THE COLDEST OVERNIGHT
TEMPERATURES SO FAR THIS SEASON THE NEXT FEW NIGHTS.


SOUTHWEST ALASKA...
SOUTHWEST ALASKA IS UNDER THE HIGH PRESSURE AND HAS CLEAR SKIES
OVER MUCH OF THE AREA. THERE ARE A FEW STRATUS CLOUDS RIDING OVER
THE TOP OF THE RIDGE THAT ARE BEING DRAWS TOWARD THE UPPER LEVEL
TROUGH IN NORTHWEST ALASKA. THIS WILL BRING IN MORE CLOUDINESS TO
THE KUSKOKWIM VALLEY AND DELTA TOMORROW. THIS WILL BE SHORT LIVED
AS THE RIDGE WILL REMAIN OVER THE AREA UNTIL LATE THIS WEEK.

BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA AND ALASKA PENINSULA HAS LARGE AREAS OF
CLEAR SKIES TODAY UNDER THE RIDGE.
THE WESTERN ALEUTIANS HAVE A COMPLEX LOW IN THE AREA WITH AREAS OF
SHOWERS IN THE OCCLUSIONS AROUND IT. THE COLD AIR ALOFT IS
SIGNIFICANT ENOUGH THAT THERE WERE SOME THUNDERSTORMS BETWEEN
ADAK AND AMCHITKA THIS AFTERNOON. THESE STORMS WILL LIKELY NOT
LAST LONG INTO THE EVENING BUT THEY SHOW HOW UNSTABLE THE
ATMOSPHERE IS IN THAT REGION WITH COLD AIR ALOFT AND RELATIVELY
WARM AIR OVER THE BERING SEA.

&&

.LONG TERM FORECAST...
AFTER A DRY WEEK FOR MOST OF ALASKA...THE PATTERN WILL BEGIN TO
SHIFT AS A TROUGH ACROSS THE BERING AND NORTH PACIFIC SHIFTS EAST
INTO THE GULF OF ALASKA. MUCH UNCERTAINTY RIDDLES THE BEGINNING OF
THE EXTENDED FORECAST...HOWEVER...AS THE NUMERICAL GUIDANCE
STRUGGLES MIGHTILY WITH A COMPLEX WAVE MERGER OVER THE BERING SEA.
THE DIFFERENCES LIKELY COME DOWN TO MODEL PHYSICS AND
PARAMETERIZATIONS...WITH THE ECMWF FAVORING A FULL WAVE MERGER
WHILE THE GEM...NAM...AND GFS ARE MUCH LESS BULLISH. THE NET
RESULT IS THE ECMWF IS STRONGER AND FASTER WITH THE LOW AND
ASSOCIATED FRONT AS IT PROGRESSES INTO THE GULF OF ALASKA AS EARLY
AS FRIDAY. FOR THIS FORECAST...A MORE MODEST AND SLOW WAVE
PROGRESSION FAVORING THE GEM AND GFS WAS UTILIZED AS THERE IS NOT
HIGH CONFIDENCE IN THE OUTLIER ECMWF SOLUTION AT THIS TIME. WITH
THAT SAID...CLOUDS AND PRECIP CHANCES WILL BEGIN TO IMPACT
SOUTHERN ALASKA BY LATE WEEK INTO THIS WEEKEND...BUT TIMING AND
THE NORTHWARD EXTENT REMAINS HIGHLY UNCERTAIN.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

SEP 14




000
FXAK68 PAFC 222145
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT MON SEP 22 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN TODAY HAS A TROUGH ALONG THE ALCAN BORDER
WITH AN UPPER LEVEL RIDGE OVER THE EASTERN BERING SEA AND WESTERN
ALASKA. FARTHER WEST THERE IS A CUT OFF LOW CLOSE TO ATTU. THE 250
MB JET STREAM CONTINUES TO RUN SOUTH OF THE AREA.
A COLD UPPER LEVEL TROUGH IS MOVING INTO NORTHWEST ALASKA OFF THE
CHUKCHI SEA.
AT THE SURFACE THERE IS A WEAK TROUGH ALONG THE NORTH GULF COAST
AS WELL AS A WEAK LOW IN THE EASTERN COPPER RIVER BASIN. THESE
FEATURES ARE THE REMNANTS OF THE LOW THAT WAS IN THE EASTERN GULF
YESTERDAY. ANOTHER INTERESTING SURFACE FEATURE IS A MESO-LOW THAT
HAS DEVELOPED JUST SOUTH OF KODIAK ISLAND. THIS FEATURE CAN BE
SEEN BEST ON THE VISIBLE SATELLITE AS IT IS TOO LOW TO BE SEEN
WELL ON THE IR SATELLITE.
HIGH PRESSURE IS OVER THE EASTERN BERING SEA AND SOUTHWEST ALASKA
AND THIS RIDGE EXTENDS INTO THE INTERIOR OF THE STATE AS WELL. A
LOW COMPLEX REMAINS NEAR THE WESTERN BERING SEA AND WESTERN
ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT INTO WEDNESDAY BUT THEN THERE ARE
SIGNIFICANT PROBLEMS THAT SHOW UP OVER BOTH THE GULF OF ALASKA
AND BERING SEA. WHILE ALL THE MODELS KEEP THE HIGH PRESSURE OVER
THE MAINLAND PART OF THE STATE THROUGH THE WEEK THE TWO LOWS ON
THE PERIPHERY OF THE HIGH PRESSURE ARE THE ISSUE. ON THURSDAY A
LOW SOUTHEAST OF THE GULF OF ALASKA IS DETECTED BY ALL MODELS BUT
THERE IS A DISCREPANCY OF OVER 450 MILES BETWEEN THE NAM AND GEM
SOLUTIONS. THE ECMWF AND GFS ARE GENERALLY SPLITTING THE DIFFERENCE
AND THEY ARE LIKELY TO VERIFY BETTER. IN THE BERING SEA THE MODEL
DIFFERENCES ARE LARGER AND WILL HAVE MORE IMPACT ON THE FORECASTS.
WHILE THE DIFFERENCE IN THE LOW NEAR THE GULF CAN BE BLENDED OUT
TO GET A REASONABLE SOLUTION THE DIFFERENCES BETWEEN THE MODELS
PRECLUDES THIS. THE BASIC ISSUE REVOLVES AROUND WHETHER THE
INCOMING LOW WILL HAVE MULTIPLE CENTERS ALONG A BROAD TROUGH OR
WHETHER THE LOW WILL COALESCE INTO A SINGLE STRONG CENTER. THIS
SECOND SOLUTION IS ONE THAT THE ECMWF HAS INSISTED ON THE PAST FEW
RUNS. THE NAM AND GFS AND GEM SHOW A SOLUTION MORE LIKE THE FIRST
SCENARIO BUT WITH VERY DIFFERENT DETAILS. IN SHORT, THE FORECAST
IN THE BERING SEA AND ALEUTIANS FOR THE SECOND HALF OF THE WEEK
HAS A GREATER UNCERTAINTY THAN USUAL.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE REMNANTS OF THE GULF LOW PERSIST OVER THE COPPER RIVER BASIN
WITH ENOUGH DYNAMICS FOR SOME RAIN IN THE CENTRAL PART OF THE
BASIN AND SNOW TO THE EAST TOWARD MENTASTA PASS. MOST OF THIS WET
SNOW APPEARED TO BE MELTING AS IT HIT THE GROUND.
THE REST OF SOUTH CENTRAL ALASKA HAS CLEARED OUT QUITE WELL WITH
HIGH PRESSURE OVER THE INTERIOR AND SOUTHWEST ALASKA BRINGING IN
DRY AIR. THE EXCEPTION IS THE EASTERN AND SOUTHERN PARTS OF KODIAK
ISLAND ARE UNDER SOME CLOUD COVER DUE TO THE MESO-LOW JUST SOUTH
OF THE ISLAND. KODIAK NORMALLY HAS CLEAR SKIES UNDER THE NORTHWEST
FLOW ALOFT BUT THIS SURFACE LOW IS ENOUGH TO BRING IN THE CLOUDS
UNTIL IT PULLS FARTHER SOUTH LATE THIS EVENING. THE RIDGE COMBINED
WITH THE TROUGH ALONG THE NORTH GULF COAST HAS CREATED A PRESSURE
GRADIENT TIGHT ENOUGH FOR GUSTY OUTFLOW WINDS THROUGH CHANNELED
TERRAIN...ESPECIALLY RIGHT ALONG THE GULF COAST. THESE WINDS WILL
DIMINISH TOMORROW AS THE GRADIENT WEAKENS BUT THEN INCREASE AGAIN
ON TUESDAY NIGHT THROUGH WEDNESDAY NIGHT AS THE GRADIENT INCREASES
AGAIN.
THE CLEAR SKIES WILL ALSO USHER IN THE COLDEST OVERNIGHT
TEMPERATURES SO FAR THIS SEASON THE NEXT FEW NIGHTS.


SOUTHWEST ALASKA...
SOUTHWEST ALASKA IS UNDER THE HIGH PRESSURE AND HAS CLEAR SKIES
OVER MUCH OF THE AREA. THERE ARE A FEW STRATUS CLOUDS RIDING OVER
THE TOP OF THE RIDGE THAT ARE BEING DRAWS TOWARD THE UPPER LEVEL
TROUGH IN NORTHWEST ALASKA. THIS WILL BRING IN MORE CLOUDINESS TO
THE KUSKOKWIM VALLEY AND DELTA TOMORROW. THIS WILL BE SHORT LIVED
AS THE RIDGE WILL REMAIN OVER THE AREA UNTIL LATE THIS WEEK.

BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA AND ALASKA PENINSULA HAS LARGE AREAS OF
CLEAR SKIES TODAY UNDER THE RIDGE.
THE WESTERN ALEUTIANS HAVE A COMPLEX LOW IN THE AREA WITH AREAS OF
SHOWERS IN THE OCCLUSIONS AROUND IT. THE COLD AIR ALOFT IS
SIGNIFICANT ENOUGH THAT THERE WERE SOME THUNDERSTORMS BETWEEN
ADAK AND AMCHITKA THIS AFTERNOON. THESE STORMS WILL LIKELY NOT
LAST LONG INTO THE EVENING BUT THEY SHOW HOW UNSTABLE THE
ATMOSPHERE IS IN THAT REGION WITH COLD AIR ALOFT AND RELATIVELY
WARM AIR OVER THE BERING SEA.

&&

.LONG TERM FORECAST...
AFTER A DRY WEEK FOR MOST OF ALASKA...THE PATTERN WILL BEGIN TO
SHIFT AS A TROUGH ACROSS THE BERING AND NORTH PACIFIC SHIFTS EAST
INTO THE GULF OF ALASKA. MUCH UNCERTAINTY RIDDLES THE BEGINNING OF
THE EXTENDED FORECAST...HOWEVER...AS THE NUMERICAL GUIDANCE
STRUGGLES MIGHTILY WITH A COMPLEX WAVE MERGER OVER THE BERING SEA.
THE DIFFERENCES LIKELY COME DOWN TO MODEL PHYSICS AND
PARAMETERIZATIONS...WITH THE ECMWF FAVORING A FULL WAVE MERGER
WHILE THE GEM...NAM...AND GFS ARE MUCH LESS BULLISH. THE NET
RESULT IS THE ECMWF IS STRONGER AND FASTER WITH THE LOW AND
ASSOCIATED FRONT AS IT PROGRESSES INTO THE GULF OF ALASKA AS EARLY
AS FRIDAY. FOR THIS FORECAST...A MORE MODEST AND SLOW WAVE
PROGRESSION FAVORING THE GEM AND GFS WAS UTILIZED AS THERE IS NOT
HIGH CONFIDENCE IN THE OUTLIER ECMWF SOLUTION AT THIS TIME. WITH
THAT SAID...CLOUDS AND PRECIP CHANCES WILL BEGIN TO IMPACT
SOUTHERN ALASKA BY LATE WEEK INTO THIS WEEKEND...BUT TIMING AND
THE NORTHWARD EXTENT REMAINS HIGHLY UNCERTAIN.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

SEP 14





000
FXAK68 PAFC 221416
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
616 AM AKDT MON SEP 22 2014

.ANALYSIS AND UPPER LEVELS...
AN ELONGATED UPPER LEVEL TROUGH STRETCHES ALONG EASTERN ALASKA
AND SOUTH ACROSS THE GULF OF ALASKA. TWO SEPARATE LOW CENTERS CAN
BE SEEN ON WATER VAPOR EARLY THIS MORNING WITH ONE SPINNING NEAR
YAKUTAT AND THE OTHER CENTERED 400 MILES SOUTH OF THIS ONE OVER
THE GULF WATERS. A SURFACE LOW IN THE NORTHERN GULF...ASSOCIATED
WITH THE UPPER LOW NEAR YAKUTAT...IS THE FOCUS FOR SHOWER ACTIVITY
ALONG THE NORTHEASTERN GULF WITH ISOLATED SHOWERS MOVING INTO THE
COPPER RIVER VALLEY. RAIN AND SNOW DEVELOPED OVERNIGHT ALONG THE
EASTERN AREAS OF THE COPPER RIVER VALLEY AS UPPER LEVEL WAVES OF
ENERGY ENHANCED PRECIPITATION ALONG THE TROUGH AXIS.

THE REST OF SOUTH CENTRAL AND THE WESTERN GULF WERE UNDER
CLEARING SKIES WHICH ALLOWED RADIATIONAL COOLING ACROSS THE
MAINLAND TO DROP TEMPERATURES INTO THE LOWER 30S. OFFSHORE FLOW
KEPT GUSTY WINDS OVERNIGHT ACROSS CHANNELED TERRAIN ALONG THE
GULF.

TO THE WEST...AN UPPER RIDGE IS CENTERED ALONG THE EASTERN BERING
BLOCKING AN UPPER LOW SPINNING OVER THE KAMCHATKA PENINSULA. THIS
IS KEEPING THE SOUTHWESTERN MAINLAND WITH IN A COOLER AND DRIER
NORTHERLY FLOW PATTERN. A WARMER AIR MASS REMAINS OVER THE THE
WESTERN BERING WITH A FRONT MOVING RAIN INTO THE WESTERN ALEUTIANS.


&&

.MODEL DISCUSSION...
MODELS ARE IN RELATIVELY GOOD AGREEMENT WITH THE GENERALSYNOPTIC
PATTERN THROUGH EARLY WEDNESDAY AND THEN BEGIN TO DIVERGE IN
SOLUTIONS. THE FAVORED MODELS WERE NAM AND GFS AS THEY HAVE BEEN
FAIRLY CONSISTENT WITH THE PATTERN SHIFT MID WEEK. THE SUBTROPICALJET
STREAM REMAINS ZONAL THROUGH EARLY TUESDAY AND THEN AMPLIFIES WITH
A RIDGING PATTERN JUST SOUTH OF THE CENTRAL ALEUTIANS ON
WEDNESDAY. THIS SETS THE CURRENT PATTERN INTO AN EASTWARD SHIFT.
MODELS HAVE STRUGGLED WITH HANDLING THIS SHIFT...THUS CONFIDENCE
DECREASES IN OUTCOMES FOR MID WEEK. THE BASIC PATTERN SHIFT BRINGS
THE UPPER KAMCHATKA LOW CENTER OVER THE CENTRAL ALEUTIANS BY EARLY
THURSDAY WHICH SHIFTS THE RIDGE EAST OVER THE MAINLAND.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
LOW PRESSURE OVER THE COPPER RIVER WILL CONTINUE TO BRING A MIX OF
RAIN AND SNOW TODAY AND THEN TAPER OFF TONIGHT WITH A FEW SHOWERS
LINGERING THROUGH TUESDAY AFTERNOON. THE GAP WINDS WILL TAPER OFF
BY EARLY AFTERNOON TODAY...HOWEVER ANOTHER COLD FRONT WILL PUSH
FROM THE NORTHWEST TUESDAY NIGHT BRINGING ANOTHER ROUND OF GUSTY
WINDS THROUGH CHANNELED TERRAIN AND GAPS LOCATIONS ALONG THE
COAST. THIS FRONT WILL ALSO BRING INCREASED PRECIPITATION CHANCES
ACROSS THE SOUTHERN MAINLAND WITH SNOW POSSIBLE ACROSS THE
NORTHERN AREAS OF THE SUSITNA AND COPPER RIVER VALLEYS.

SOUTHWEST ALASKA...
DRIER AND COOLER CONDITIONS PREVAIL THROUGH MID WEEK AS ANOTHER
COLD FRONT MOVES IN FROM THE NORTHWEST ON TUESDAY. THE FRONT
MOVING INTO THE WESTERN ALEUTIANS TODAY WASHES OUT AS IT SWINGS
TOWARD THE ALASKA PENINSULA...SCATTERED SHOWERS MAY MAKE IT TO THE
WESTERN PENINSULA TUESDAY NIGHT BEFORE DIMINISHING.


BERING SEA/ALEUTIANS...
A FRONT BRINGS RAIN INTO THE WESTERN BERING TODAY AND PUSHES
SLOWLY INTO THE CENTRAL BERING AND EASTERN ALEUTIANS EARLY
TUESDAY AND THEN DIMINISHES AS RIDGING PRESIDES TO THE EAST.

&&

.LONG TERM FORECAST...
THE PATTERN SHIFTS TOWARD THE END OF THE WEEK AS THE UPPER LOW
MOVES FROM THE WESTERN BERING. RIDGING OVER THE MAINLAND WILL
BREAKDOWN ALLOWING THE LONGWAVE TO SHIFT TO THE GULF OF ALASKA
THIS WEEKEND. HOWEVER...MODELS ARE NOT YET LOCKING ON TO A
SOLUTION. THE LONG TERM FORECAST THURSDAY INTO THE WEEKEND
CONTINUES WITH A BIT OF UNCERTAINTY THE OVERALL PATTERN


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

KH SEP 14




000
FXAK68 PAFC 221416
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
616 AM AKDT MON SEP 22 2014

.ANALYSIS AND UPPER LEVELS...
AN ELONGATED UPPER LEVEL TROUGH STRETCHES ALONG EASTERN ALASKA
AND SOUTH ACROSS THE GULF OF ALASKA. TWO SEPARATE LOW CENTERS CAN
BE SEEN ON WATER VAPOR EARLY THIS MORNING WITH ONE SPINNING NEAR
YAKUTAT AND THE OTHER CENTERED 400 MILES SOUTH OF THIS ONE OVER
THE GULF WATERS. A SURFACE LOW IN THE NORTHERN GULF...ASSOCIATED
WITH THE UPPER LOW NEAR YAKUTAT...IS THE FOCUS FOR SHOWER ACTIVITY
ALONG THE NORTHEASTERN GULF WITH ISOLATED SHOWERS MOVING INTO THE
COPPER RIVER VALLEY. RAIN AND SNOW DEVELOPED OVERNIGHT ALONG THE
EASTERN AREAS OF THE COPPER RIVER VALLEY AS UPPER LEVEL WAVES OF
ENERGY ENHANCED PRECIPITATION ALONG THE TROUGH AXIS.

THE REST OF SOUTH CENTRAL AND THE WESTERN GULF WERE UNDER
CLEARING SKIES WHICH ALLOWED RADIATIONAL COOLING ACROSS THE
MAINLAND TO DROP TEMPERATURES INTO THE LOWER 30S. OFFSHORE FLOW
KEPT GUSTY WINDS OVERNIGHT ACROSS CHANNELED TERRAIN ALONG THE
GULF.

TO THE WEST...AN UPPER RIDGE IS CENTERED ALONG THE EASTERN BERING
BLOCKING AN UPPER LOW SPINNING OVER THE KAMCHATKA PENINSULA. THIS
IS KEEPING THE SOUTHWESTERN MAINLAND WITH IN A COOLER AND DRIER
NORTHERLY FLOW PATTERN. A WARMER AIR MASS REMAINS OVER THE THE
WESTERN BERING WITH A FRONT MOVING RAIN INTO THE WESTERN ALEUTIANS.


&&

.MODEL DISCUSSION...
MODELS ARE IN RELATIVELY GOOD AGREEMENT WITH THE GENERALSYNOPTIC
PATTERN THROUGH EARLY WEDNESDAY AND THEN BEGIN TO DIVERGE IN
SOLUTIONS. THE FAVORED MODELS WERE NAM AND GFS AS THEY HAVE BEEN
FAIRLY CONSISTENT WITH THE PATTERN SHIFT MID WEEK. THE SUBTROPICALJET
STREAM REMAINS ZONAL THROUGH EARLY TUESDAY AND THEN AMPLIFIES WITH
A RIDGING PATTERN JUST SOUTH OF THE CENTRAL ALEUTIANS ON
WEDNESDAY. THIS SETS THE CURRENT PATTERN INTO AN EASTWARD SHIFT.
MODELS HAVE STRUGGLED WITH HANDLING THIS SHIFT...THUS CONFIDENCE
DECREASES IN OUTCOMES FOR MID WEEK. THE BASIC PATTERN SHIFT BRINGS
THE UPPER KAMCHATKA LOW CENTER OVER THE CENTRAL ALEUTIANS BY EARLY
THURSDAY WHICH SHIFTS THE RIDGE EAST OVER THE MAINLAND.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
LOW PRESSURE OVER THE COPPER RIVER WILL CONTINUE TO BRING A MIX OF
RAIN AND SNOW TODAY AND THEN TAPER OFF TONIGHT WITH A FEW SHOWERS
LINGERING THROUGH TUESDAY AFTERNOON. THE GAP WINDS WILL TAPER OFF
BY EARLY AFTERNOON TODAY...HOWEVER ANOTHER COLD FRONT WILL PUSH
FROM THE NORTHWEST TUESDAY NIGHT BRINGING ANOTHER ROUND OF GUSTY
WINDS THROUGH CHANNELED TERRAIN AND GAPS LOCATIONS ALONG THE
COAST. THIS FRONT WILL ALSO BRING INCREASED PRECIPITATION CHANCES
ACROSS THE SOUTHERN MAINLAND WITH SNOW POSSIBLE ACROSS THE
NORTHERN AREAS OF THE SUSITNA AND COPPER RIVER VALLEYS.

SOUTHWEST ALASKA...
DRIER AND COOLER CONDITIONS PREVAIL THROUGH MID WEEK AS ANOTHER
COLD FRONT MOVES IN FROM THE NORTHWEST ON TUESDAY. THE FRONT
MOVING INTO THE WESTERN ALEUTIANS TODAY WASHES OUT AS IT SWINGS
TOWARD THE ALASKA PENINSULA...SCATTERED SHOWERS MAY MAKE IT TO THE
WESTERN PENINSULA TUESDAY NIGHT BEFORE DIMINISHING.


BERING SEA/ALEUTIANS...
A FRONT BRINGS RAIN INTO THE WESTERN BERING TODAY AND PUSHES
SLOWLY INTO THE CENTRAL BERING AND EASTERN ALEUTIANS EARLY
TUESDAY AND THEN DIMINISHES AS RIDGING PRESIDES TO THE EAST.

&&

.LONG TERM FORECAST...
THE PATTERN SHIFTS TOWARD THE END OF THE WEEK AS THE UPPER LOW
MOVES FROM THE WESTERN BERING. RIDGING OVER THE MAINLAND WILL
BREAKDOWN ALLOWING THE LONGWAVE TO SHIFT TO THE GULF OF ALASKA
THIS WEEKEND. HOWEVER...MODELS ARE NOT YET LOCKING ON TO A
SOLUTION. THE LONG TERM FORECAST THURSDAY INTO THE WEEKEND
CONTINUES WITH A BIT OF UNCERTAINTY THE OVERALL PATTERN


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

KH SEP 14





000
FXAK68 PAFC 212157
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
157 PM AKDT SUN SEP 21 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN THAT HAS BEEN IS PLACE THE PAST NUMBER OF
DAYS IS SHIFTING EASTWARD TODAY. THE HIGH OVER THE EASTERN BERING
SEA IS BUILDING OVER THE SOUTHWEST AND WESTERN COAST OF THE STATE
WHICH IS PUSHING THE LONGWAVE TROUGH EASTWARD. THIS UPPER LEVEL
TROUGH HAS DEVELOPED A CUT OFF LOW OVER THE GULF OF ALASKA. THE
250 MB JET STREAM IS RUNNING SOUTH OF THE ALEUTIANS BETWEEN 40N
AND 45N AND THEN CURVES AROUND THE CUT OFF LOW IN THE GULF AND IS
RUNNING DUE NORTH TO SOUTH OVER THE PANHANDLE BEFORE TURNING
SHARPLY TO THE EAST OVER THE YUKON. THE JET STREAM IS IMPORTANT
TODAY AS IT IS WHAT IS RAPIDLY INTENSIFYING A SURFACE LOW RUNNING
NORTHWARD OVER THE EASTERN GULF OF ALASKA. DUE TO THE JET CURVING BACK
TO THE EAST THIS LOW WILL LOSE ITS UPPER LEVEL SUPPORT TONIGHT AND
THEN RAPIDLY WEAKEN AS THE MAIN SURFACE LOW MOVES TOWARD MONTAGUE
ISLAND AS A LEE SIDE SURFACE LOW DEVELOPS IN THE YUKON WITH THE
UPPER LEVEL SUPPORT.
IN THE WESTERN BERING SEA THERE IS ANOTHER LOW THAT WILL REMAIN IN
THE AREA FOR THE NEXT FEW DAYS BUT NOT MAKING MUCH EASTWARD
PROGRESS DUE TO THE RIDGE IN THE EASTERN BERING SEA.

&&

.MODEL DISCUSSION...
COMPUTER MODELS CONTINUE TO STRUGGLE WITH THE LOW MOVING THROUGH
THE EASTERN GULF OF ALASKA. THE ECMWF AND GEM SEEM TO HAVE PICKED
UP ON THE WAY THE LOW IS RAPIDLY STRENGTHENING THIS
AFTERNOON...AND THEN WILL RAPIDLY WEAKEN OVERNIGHT AS ITS ENERGY
SPLITS WITH SOME OF THE UPPER LEVEL SUPPORT MOVING INTO THE YUKON
AND THE MAIN SURFACE LOW HEADS TOWARD MONTAGUE ISLAND OVERNIGHT.
THE GFS AND NAM DO HAVE A SIMILAR TRACK BUT THEY AND NOT DETECTING
THE INITIAL STRENGTH OF THIS LOW AS THE NEARBY OBSERVATIONS ARE
ALREADY 10 PLUS MB LOWER THAN THE GFS INDICATES AND WELL BELOW THE
NAM SOLUTION AS WELL. AFTER THIS LOW MOVES THROUGH THE MODELS ARE
ALL VERY MUCH IN AGREEMENT WITH THE RIDGE IN THE BERING SEA MOVING
EASTWARD SO IT STRETCHES FROM SOUTH OF THE ALASKA PENINSULA INTO
SOUTHWEST ALASKA AND THEN CURVES OVER THE INTERIOR AND SOUTH
CENTRAL ALASKA. THERE WILL ALSO BE THE DEVELOPMENT OF A TROUGH OF
LOW PRESSURE ALONG THE NORTH GULF COAST.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
TWO WEATHER FEATURES WILL BE IMPACTING THE AREA OVER THE NEXT DAY.
THE FIRST IS A COLD FRONT MOVING THROUGH THE SUSITNA VALLEY AND
UPPER COOK INLET THIS AFTERNOON WHICH WILL MOVE TO THE ALCAN
BORDER BY MONDAY AFTERNOON. THERE ARE SOME SHOWERS THAT HAVE
DEVELOPED AHEAD OF THIS FRONT AND THE FREEZING LEVEL IS LOW
ENOUGH THAT THE MORE INTENSE SHOWERS COULD HAVE SOME SMALL HAIL IN
THEM. BEHIND THIS COLD FRONT THE WINDS WILL TURN TO THE NORTHWEST
AND GET BREEZY WITH THE COLDER AND DRIER AIR MOVING IN. GAPS IN
THE ALASKA RANGE WILL BE ESPECIALLY GUSTY OVERNIGHT INTO TOMORROW.
THE SECOND FEATURE IS THE LOW IN THE EASTERN GULF THAT IS MOVING
TO THE NORTH WHICH WILL TURN NORTHWEST IN ITS MOTION THIS
EVENING. MOST OF THE RAINFALL WITH THIS SYSTEM WILL BE RELEGATED
TO THE GULF COAST FROM PRINCE WILLIAM SOUND EASTWARD.

SOUTHWEST ALASKA...
THE RIDGE BUILDING INTO THE AREA IS KEEPING NORTHERLY WINDS AND
MOSTLY CLEAR SKIES INTO TOMORROW. SOME CLOUDS WILL MOVE THROUGH
THE KUSKOKWIM VALLEY AND DELTA MONDAY NIGHT INTO TUESDAY DUE TO A
SHORT WAVE MOVING ACROSS THE AREA BUT NOTHING MORE THAN A FEW
PASSING SHOWERS IS EXPECTED AS FAR AS PRECIPITATION.

BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA IS SEEING A DECREASE INT CLOUDS DUE TO THE
CIRCULATION OF THE RIDGE BRINGING DRIER AIR FROM THE MAINLAND
OVER THE AREA. THE WESTERN BERING SEA AND WEST AND CENTRAL
ALEUTIANS WILL SEE SOME PERIODS OF LIGHT RAINFALL WITH THE LOW
PRESSURE IN THAT AREA.
EASTERN ALEUTIANS WILL REMAIN UNDER NORTHERLY FLOW WHICH WILL
KEEP SOME SHOWERS AROUND THROUGH THE NIGHT.
THE ALASKA PENINSULA WILL SEE SOME PARTIAL CLEARING FROM
NORTHEAST TO SOUTHWEST AS THE DRIER AIR FROM THE MAINLAND FILTERS
INTO THE AREA.

&&

.LONG TERM FORECAST...
THERE IS NO CHANGE TO THE GENERAL PATTERN EXPECTED WITH AN
UNSEASONALY DRY AND PLEASANT AUTUMN PATTERN DOMINATING THE STATE
AS A SPLIT UPPER LEVEL JET PATTERN CONTINUES. SOME UNCERTAINTY
STILL EXISTS WITH THE DEVELOPMENT OF A TROUGH ACROSS THE NORTH
CENTRAL PACIFIC...AND ITS EVENTUAL TRACK INTO THE GULF OF ALASKA.
THE ECMWF REMAINS THE MOST BULLISH IN TRACKING THE FRONT INTO THE
NORTH GULF COAST...BUT IT HAS DRAMATICALLY BACKED OFF ITS PREVIOUS
SOLUTIONS. THE GENERAL THINKING IS THE LOW WILL MAINLY IMPACT
COASTAL LOCATIONS...ALTHOUGH SOME CLOUDS AND PRECIP WILL
POTENTIALLY MOVE INTO THE COPPER BASIN OVER THE WEEKEND. AS A
WHOLE...HOWEVER...LARGELY DRY AND QUIESCENT WEATHER FOR ALASKA
WILL LIKELY CONTINUE THROUGH THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

SEP 14





000
FXAK68 PAFC 212157
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
157 PM AKDT SUN SEP 21 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN THAT HAS BEEN IS PLACE THE PAST NUMBER OF
DAYS IS SHIFTING EASTWARD TODAY. THE HIGH OVER THE EASTERN BERING
SEA IS BUILDING OVER THE SOUTHWEST AND WESTERN COAST OF THE STATE
WHICH IS PUSHING THE LONGWAVE TROUGH EASTWARD. THIS UPPER LEVEL
TROUGH HAS DEVELOPED A CUT OFF LOW OVER THE GULF OF ALASKA. THE
250 MB JET STREAM IS RUNNING SOUTH OF THE ALEUTIANS BETWEEN 40N
AND 45N AND THEN CURVES AROUND THE CUT OFF LOW IN THE GULF AND IS
RUNNING DUE NORTH TO SOUTH OVER THE PANHANDLE BEFORE TURNING
SHARPLY TO THE EAST OVER THE YUKON. THE JET STREAM IS IMPORTANT
TODAY AS IT IS WHAT IS RAPIDLY INTENSIFYING A SURFACE LOW RUNNING
NORTHWARD OVER THE EASTERN GULF OF ALASKA. DUE TO THE JET CURVING BACK
TO THE EAST THIS LOW WILL LOSE ITS UPPER LEVEL SUPPORT TONIGHT AND
THEN RAPIDLY WEAKEN AS THE MAIN SURFACE LOW MOVES TOWARD MONTAGUE
ISLAND AS A LEE SIDE SURFACE LOW DEVELOPS IN THE YUKON WITH THE
UPPER LEVEL SUPPORT.
IN THE WESTERN BERING SEA THERE IS ANOTHER LOW THAT WILL REMAIN IN
THE AREA FOR THE NEXT FEW DAYS BUT NOT MAKING MUCH EASTWARD
PROGRESS DUE TO THE RIDGE IN THE EASTERN BERING SEA.

&&

.MODEL DISCUSSION...
COMPUTER MODELS CONTINUE TO STRUGGLE WITH THE LOW MOVING THROUGH
THE EASTERN GULF OF ALASKA. THE ECMWF AND GEM SEEM TO HAVE PICKED
UP ON THE WAY THE LOW IS RAPIDLY STRENGTHENING THIS
AFTERNOON...AND THEN WILL RAPIDLY WEAKEN OVERNIGHT AS ITS ENERGY
SPLITS WITH SOME OF THE UPPER LEVEL SUPPORT MOVING INTO THE YUKON
AND THE MAIN SURFACE LOW HEADS TOWARD MONTAGUE ISLAND OVERNIGHT.
THE GFS AND NAM DO HAVE A SIMILAR TRACK BUT THEY AND NOT DETECTING
THE INITIAL STRENGTH OF THIS LOW AS THE NEARBY OBSERVATIONS ARE
ALREADY 10 PLUS MB LOWER THAN THE GFS INDICATES AND WELL BELOW THE
NAM SOLUTION AS WELL. AFTER THIS LOW MOVES THROUGH THE MODELS ARE
ALL VERY MUCH IN AGREEMENT WITH THE RIDGE IN THE BERING SEA MOVING
EASTWARD SO IT STRETCHES FROM SOUTH OF THE ALASKA PENINSULA INTO
SOUTHWEST ALASKA AND THEN CURVES OVER THE INTERIOR AND SOUTH
CENTRAL ALASKA. THERE WILL ALSO BE THE DEVELOPMENT OF A TROUGH OF
LOW PRESSURE ALONG THE NORTH GULF COAST.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
TWO WEATHER FEATURES WILL BE IMPACTING THE AREA OVER THE NEXT DAY.
THE FIRST IS A COLD FRONT MOVING THROUGH THE SUSITNA VALLEY AND
UPPER COOK INLET THIS AFTERNOON WHICH WILL MOVE TO THE ALCAN
BORDER BY MONDAY AFTERNOON. THERE ARE SOME SHOWERS THAT HAVE
DEVELOPED AHEAD OF THIS FRONT AND THE FREEZING LEVEL IS LOW
ENOUGH THAT THE MORE INTENSE SHOWERS COULD HAVE SOME SMALL HAIL IN
THEM. BEHIND THIS COLD FRONT THE WINDS WILL TURN TO THE NORTHWEST
AND GET BREEZY WITH THE COLDER AND DRIER AIR MOVING IN. GAPS IN
THE ALASKA RANGE WILL BE ESPECIALLY GUSTY OVERNIGHT INTO TOMORROW.
THE SECOND FEATURE IS THE LOW IN THE EASTERN GULF THAT IS MOVING
TO THE NORTH WHICH WILL TURN NORTHWEST IN ITS MOTION THIS
EVENING. MOST OF THE RAINFALL WITH THIS SYSTEM WILL BE RELEGATED
TO THE GULF COAST FROM PRINCE WILLIAM SOUND EASTWARD.

SOUTHWEST ALASKA...
THE RIDGE BUILDING INTO THE AREA IS KEEPING NORTHERLY WINDS AND
MOSTLY CLEAR SKIES INTO TOMORROW. SOME CLOUDS WILL MOVE THROUGH
THE KUSKOKWIM VALLEY AND DELTA MONDAY NIGHT INTO TUESDAY DUE TO A
SHORT WAVE MOVING ACROSS THE AREA BUT NOTHING MORE THAN A FEW
PASSING SHOWERS IS EXPECTED AS FAR AS PRECIPITATION.

BERING SEA/ALEUTIANS...
THE EASTERN BERING SEA IS SEEING A DECREASE INT CLOUDS DUE TO THE
CIRCULATION OF THE RIDGE BRINGING DRIER AIR FROM THE MAINLAND
OVER THE AREA. THE WESTERN BERING SEA AND WEST AND CENTRAL
ALEUTIANS WILL SEE SOME PERIODS OF LIGHT RAINFALL WITH THE LOW
PRESSURE IN THAT AREA.
EASTERN ALEUTIANS WILL REMAIN UNDER NORTHERLY FLOW WHICH WILL
KEEP SOME SHOWERS AROUND THROUGH THE NIGHT.
THE ALASKA PENINSULA WILL SEE SOME PARTIAL CLEARING FROM
NORTHEAST TO SOUTHWEST AS THE DRIER AIR FROM THE MAINLAND FILTERS
INTO THE AREA.

&&

.LONG TERM FORECAST...
THERE IS NO CHANGE TO THE GENERAL PATTERN EXPECTED WITH AN
UNSEASONALY DRY AND PLEASANT AUTUMN PATTERN DOMINATING THE STATE
AS A SPLIT UPPER LEVEL JET PATTERN CONTINUES. SOME UNCERTAINTY
STILL EXISTS WITH THE DEVELOPMENT OF A TROUGH ACROSS THE NORTH
CENTRAL PACIFIC...AND ITS EVENTUAL TRACK INTO THE GULF OF ALASKA.
THE ECMWF REMAINS THE MOST BULLISH IN TRACKING THE FRONT INTO THE
NORTH GULF COAST...BUT IT HAS DRAMATICALLY BACKED OFF ITS PREVIOUS
SOLUTIONS. THE GENERAL THINKING IS THE LOW WILL MAINLY IMPACT
COASTAL LOCATIONS...ALTHOUGH SOME CLOUDS AND PRECIP WILL
POTENTIALLY MOVE INTO THE COPPER BASIN OVER THE WEEKEND. AS A
WHOLE...HOWEVER...LARGELY DRY AND QUIESCENT WEATHER FOR ALASKA
WILL LIKELY CONTINUE THROUGH THE WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

SEP 14




000
FXAK68 PAFC 211222
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 AM AKDT SUN SEP 21 2014

.ANALYSIS AND UPPER LEVELS...
THE MAJOR FEATURE EVIDENT ON WATER VAPOR IMAGERY THIS MORNING IS A
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC. THIS BAROCLINIC
LEAF IS ON THE DOWNSTREAM SIDE OF THE PERSISTENT LONG-WAVE OVER
SOUTHERN ALASKA WHICH IS BEING FORCED TO PROPAGATE EASTWARD BY THE
DEVELOPING SYSTEM AS WELL AS UPPER RIDGING IMPINGING FROM THE
WEST. WHAT IS LEFT OF THE UPPER TROUGH DOES NOT LOOK IMPRESSIVE
WITH NO AREAS OF SIGNIFICANT LIFT EVIDENT...ONLY DECAYING PLUMES
OF MOISTURE ASSOCIATED WITH DIURNAL CONVECTION WHICH ARE QUICKLY
FADING AWAY. A STRONGER WAVE IS SHOWING UP OVER CENTRAL/NORTHERN
ALASKA THAT WILL SKIRT OUR NORTHERN ZONES BUT IS BEING KEPT AT
BAY BY THE UPPER RIDGE NOSING IN FROM THE WEST. FURTHER OUT
WEST...THE KAMCHATKA LOW LOOKS SPENT AND ILL-DEFINED WITH A BROAD
ANTI- CYCLONIC CIRCULATION OVER MUCH OF THE BERING SEA. THE JET
STREAM IS WELL TO THE SOUTH IN THE MID-LATITUDES AND VERY ZONAL IN
NATURE.

&&

.MODEL DISCUSSION...
GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE PATTERN ALOFT FOR THE
NEXT FEW DAYS WILL LITTLE DISCREPANCY FROM MODEL TO MODEL. THE
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC HAS INTRODUCED SOME
SLIGHT DIFFERENCES IN STRENGTH AND TIMING...ESPECIALLY WITH THE
GFS WHICH DOES NOT DEVELOP THE SYSTEM NEARLY AS MUCH AS THE OTHER
GUIDANCE. THE SYSTEM WILL MISS MOST OF THE SOUTHCENTRAL AS IT
MOVES INTO THE YUKON BUT EASTERN PORTIONS OF THE COPPER RIVER
BASIN COULD BE AFFECTED. THE BIGGEST EFFECT WILL BE ON THE LOW
LEVEL WIND FIELD AS TROUGHING SETTING UP ALONG THE COAST WILL
INDUCE SOME VERY WINTER-LIKE OUTFLOW WINDS ALONG THE GULF COAST.
BOTH DOMAINS PREFERRED THE ECMWF WITH THE CURRENT FORECAST
PACKAGE.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WHILE THE TROUGH ALOFT HAS WEAKENED
SIGNIFICANTLY...A POOL OF COLD AIR ALOFT AND A DISTURBANCE
SKIRTING THE ALASKA RANGE WILL KEEP AT LEAST SOME SHOWERY ACTIVITY
ACROSS THE AREA. A FRONT ALOFT ASSOCIATED WITH A TROUGH OVER THE
BROOKS RANGE WILL BRING MORE STABLE AIR ALOFT WHICH WILL SUPRESSCONVECTION.
THE QUESTION IS HOW MUCH CLEARING WILL THERE BE AHEAD OF THE FRONT
TO ENCOURAGE SURFACE HEATING? THE BEST WINDOW WILL BE IN THE MID
TO LATE AFTERNOON DURING PEAK SURFACE HEATING JUST AS THE TAIL OF
THE UPPER TROUGH SWINGS THROUGH. THE 00Z SOUNDING OVER ANCHORAGE
YIELDED 600 J/KG OF INSTABILITY WITH A CONVECTIVE TEMPERATURE OF
62F. THE ENVIRONMENT TODAY SHOULD BE JUST AS CONDUCIVE AS WE WILL
NOT HAVE SOUTHEAST WINDS OFF THE SURFACE AND LESS CLOUD COVER.

EXPECT AFTERNOON SHOWERS FROM THE WESTERN KENAI THROUGH THE
SUSITNA VALLEY...ESPECIALLY EAST. WINDS WILL REMAIN LIGHT BEFORE
SWITCHING TO THE NORTHWEST WITH SOME GUSTS. THE NEXT COUPLE DAYS
WILL BE COOLER AND DRIER AS RIDGING ALOFT BUILDS OVER THE AREA.

SOUTHWEST ALASKA...DRY CONDITIONS AND DECREASING CLOUDS CAN BE
EXPECTED TODAY. SOME GUSTY NORTHERLY WINDS WILL DEVELOP IN THE
AFTERNOON FOR INTERIOR BRISTOL BAY BEFORE DIMINISHING ON MONDAY.

BERING SEA/ALEUTIANS...A FRONTAL BOUNDARY WILL WASH OUT OVER THE
CENTRAL ALEUTIANS TODAY BRINGING SOME SPOTTY SHOWERS. AN UPPER LOW
PRESSURE DRIFTS EASTWARD THROUGH THE WEEK KEEPING SCATTERED
SHOWERS IN THE FORECAST.


&&

.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON WEDNESDAY...THE REGION WILL BE
UNDER THE INFLUENCE OF A SPLIT JET STREAM REGIME...WITH A DISTINCT
POLAR JET TO OUR NORTH...AND A MUCH STRONGER AND ACTIVE
SUBTROPICAL JET STREAM ACROSS THE NORTH PACIFIC. THIS WILL BE A
SOMEWHAT LARGE SHIFT FROM THE PREVIOUS TWO WEEKS WHERE THE
SUBTROPICAL JET STREAM WAS IN PHASE WITH THE POLAR JET...HELPING
TO PROMOTE A VERY ACTIVE PATTERN FOR ALASKA. THIS SPLIT JET STREAM
PATTERN WILL LINGER THROUGH FRIDAY...WITH UPPER LEVEL DISTURBANCES
TRACKING THROUGH NORTHERN AND CENTRAL ALASKA. THE NET EFFECT WILL
BE COOLER AND DRY AIR OCCASIONALLY DRIVING SOUTHWARD INTO THE GULF
OF ALASKA. OTHERWISE...THIS WILL LIKELY REPRESENT THE DRIEST AND
OVERALL MOST PLEASANT STRETCH OF WEATHER IN SEPTEMBER OVER THE
PAST THREE YEARS. OUTFLOW GAP WINDS INTO THE GULF OF ALASKA WILL
PEAK WEDNESDAY AND THEN POSSIBLY AGAIN ON SATURDAY. EXPECT THE
COLDEST TEMPERATURES OF THE YEAR ACROSS MANY LOCATIONS AS
OVERNIGHT TEMPERATURES PLUMMET WITH FAVORABLE RADIATIONAL COOLING.
BY FRIDAY...THE ECMWF IS HINTING AT A NORTH PACIFIC LOW TRACKING
INTO SOUTHWEST AND EVENTUALLY SOUTHCENTRAL...BUT CURRENTLY THAT IS
A LOW PROBABILITY SOLUTION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

MTL/JA SEP 14




000
FXAK68 PAFC 211222
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 AM AKDT SUN SEP 21 2014

.ANALYSIS AND UPPER LEVELS...
THE MAJOR FEATURE EVIDENT ON WATER VAPOR IMAGERY THIS MORNING IS A
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC. THIS BAROCLINIC
LEAF IS ON THE DOWNSTREAM SIDE OF THE PERSISTENT LONG-WAVE OVER
SOUTHERN ALASKA WHICH IS BEING FORCED TO PROPAGATE EASTWARD BY THE
DEVELOPING SYSTEM AS WELL AS UPPER RIDGING IMPINGING FROM THE
WEST. WHAT IS LEFT OF THE UPPER TROUGH DOES NOT LOOK IMPRESSIVE
WITH NO AREAS OF SIGNIFICANT LIFT EVIDENT...ONLY DECAYING PLUMES
OF MOISTURE ASSOCIATED WITH DIURNAL CONVECTION WHICH ARE QUICKLY
FADING AWAY. A STRONGER WAVE IS SHOWING UP OVER CENTRAL/NORTHERN
ALASKA THAT WILL SKIRT OUR NORTHERN ZONES BUT IS BEING KEPT AT
BAY BY THE UPPER RIDGE NOSING IN FROM THE WEST. FURTHER OUT
WEST...THE KAMCHATKA LOW LOOKS SPENT AND ILL-DEFINED WITH A BROAD
ANTI- CYCLONIC CIRCULATION OVER MUCH OF THE BERING SEA. THE JET
STREAM IS WELL TO THE SOUTH IN THE MID-LATITUDES AND VERY ZONAL IN
NATURE.

&&

.MODEL DISCUSSION...
GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE PATTERN ALOFT FOR THE
NEXT FEW DAYS WILL LITTLE DISCREPANCY FROM MODEL TO MODEL. THE
DEVELOPING SYSTEM IN THE NORTHEASTERN PACIFIC HAS INTRODUCED SOME
SLIGHT DIFFERENCES IN STRENGTH AND TIMING...ESPECIALLY WITH THE
GFS WHICH DOES NOT DEVELOP THE SYSTEM NEARLY AS MUCH AS THE OTHER
GUIDANCE. THE SYSTEM WILL MISS MOST OF THE SOUTHCENTRAL AS IT
MOVES INTO THE YUKON BUT EASTERN PORTIONS OF THE COPPER RIVER
BASIN COULD BE AFFECTED. THE BIGGEST EFFECT WILL BE ON THE LOW
LEVEL WIND FIELD AS TROUGHING SETTING UP ALONG THE COAST WILL
INDUCE SOME VERY WINTER-LIKE OUTFLOW WINDS ALONG THE GULF COAST.
BOTH DOMAINS PREFERRED THE ECMWF WITH THE CURRENT FORECAST
PACKAGE.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WHILE THE TROUGH ALOFT HAS WEAKENED
SIGNIFICANTLY...A POOL OF COLD AIR ALOFT AND A DISTURBANCE
SKIRTING THE ALASKA RANGE WILL KEEP AT LEAST SOME SHOWERY ACTIVITY
ACROSS THE AREA. A FRONT ALOFT ASSOCIATED WITH A TROUGH OVER THE
BROOKS RANGE WILL BRING MORE STABLE AIR ALOFT WHICH WILL SUPRESSCONVECTION.
THE QUESTION IS HOW MUCH CLEARING WILL THERE BE AHEAD OF THE FRONT
TO ENCOURAGE SURFACE HEATING? THE BEST WINDOW WILL BE IN THE MID
TO LATE AFTERNOON DURING PEAK SURFACE HEATING JUST AS THE TAIL OF
THE UPPER TROUGH SWINGS THROUGH. THE 00Z SOUNDING OVER ANCHORAGE
YIELDED 600 J/KG OF INSTABILITY WITH A CONVECTIVE TEMPERATURE OF
62F. THE ENVIRONMENT TODAY SHOULD BE JUST AS CONDUCIVE AS WE WILL
NOT HAVE SOUTHEAST WINDS OFF THE SURFACE AND LESS CLOUD COVER.

EXPECT AFTERNOON SHOWERS FROM THE WESTERN KENAI THROUGH THE
SUSITNA VALLEY...ESPECIALLY EAST. WINDS WILL REMAIN LIGHT BEFORE
SWITCHING TO THE NORTHWEST WITH SOME GUSTS. THE NEXT COUPLE DAYS
WILL BE COOLER AND DRIER AS RIDGING ALOFT BUILDS OVER THE AREA.

SOUTHWEST ALASKA...DRY CONDITIONS AND DECREASING CLOUDS CAN BE
EXPECTED TODAY. SOME GUSTY NORTHERLY WINDS WILL DEVELOP IN THE
AFTERNOON FOR INTERIOR BRISTOL BAY BEFORE DIMINISHING ON MONDAY.

BERING SEA/ALEUTIANS...A FRONTAL BOUNDARY WILL WASH OUT OVER THE
CENTRAL ALEUTIANS TODAY BRINGING SOME SPOTTY SHOWERS. AN UPPER LOW
PRESSURE DRIFTS EASTWARD THROUGH THE WEEK KEEPING SCATTERED
SHOWERS IN THE FORECAST.


&&

.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON WEDNESDAY...THE REGION WILL BE
UNDER THE INFLUENCE OF A SPLIT JET STREAM REGIME...WITH A DISTINCT
POLAR JET TO OUR NORTH...AND A MUCH STRONGER AND ACTIVE
SUBTROPICAL JET STREAM ACROSS THE NORTH PACIFIC. THIS WILL BE A
SOMEWHAT LARGE SHIFT FROM THE PREVIOUS TWO WEEKS WHERE THE
SUBTROPICAL JET STREAM WAS IN PHASE WITH THE POLAR JET...HELPING
TO PROMOTE A VERY ACTIVE PATTERN FOR ALASKA. THIS SPLIT JET STREAM
PATTERN WILL LINGER THROUGH FRIDAY...WITH UPPER LEVEL DISTURBANCES
TRACKING THROUGH NORTHERN AND CENTRAL ALASKA. THE NET EFFECT WILL
BE COOLER AND DRY AIR OCCASIONALLY DRIVING SOUTHWARD INTO THE GULF
OF ALASKA. OTHERWISE...THIS WILL LIKELY REPRESENT THE DRIEST AND
OVERALL MOST PLEASANT STRETCH OF WEATHER IN SEPTEMBER OVER THE
PAST THREE YEARS. OUTFLOW GAP WINDS INTO THE GULF OF ALASKA WILL
PEAK WEDNESDAY AND THEN POSSIBLY AGAIN ON SATURDAY. EXPECT THE
COLDEST TEMPERATURES OF THE YEAR ACROSS MANY LOCATIONS AS
OVERNIGHT TEMPERATURES PLUMMET WITH FAVORABLE RADIATIONAL COOLING.
BY FRIDAY...THE ECMWF IS HINTING AT A NORTH PACIFIC LOW TRACKING
INTO SOUTHWEST AND EVENTUALLY SOUTHCENTRAL...BUT CURRENTLY THAT IS
A LOW PROBABILITY SOLUTION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

MTL/JA SEP 14





000
FXAK68 PAFC 202136
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
136 PM AKDT SAT SEP 20 2014

.ANALYSIS AND UPPER LEVELS...

A BAGGY YET HIGHLY AMPLIFIED TROUGH PERSISTS OVER THE MAINLAND OF
ALASKA EXTENDING SOUTH INTO THE MID-LATITUDES OF THE PACIFIC OCEAN
ALONG 150W. NUMEROUS STRONG CONVECTIVE SHOWERS WITH ISOLATED
LIGHTNING STRIKES ARE OCCURRING OVER THE NORTHERN GULF AND PRINCE
WILLIAM SOUND GIVEN IMPRESSIVE INSTABILITY IN THIS REGION. HIGH
PRESSURE OVER THE CENTRAL BERING HAS MOVED INTO THE EASTERN BERING
TODAY...WITH A SECOND TROUGH ON THE NORTHEAST SIDE OF THE RIDGE
CURRENTLY DIGGING INTO NORTHERN AND CENTRAL ALASKA TOWARD THE
BASE OF THE LONGWAVE TROUGH OVER THE MAINLAND. OUT WEST...A
KAMCHATKA LOW IS MOVING TOWARD THE FAR WESTERN ALEUTIANS AND
WESTERN BERING.

&&

.MODEL DISCUSSION...

MODELS HAD BEEN STRUGGLING WITH A SURFACE LOW THAT FORMS IN THE
MID-LATITUDES THIS AFTERNOON AND THEN RACES NORTH AND STRENGTHENS
AS IT ENTERS THE GULF SUNDAY MORNING AND THEN MOVES INLAND
SOMEWHERE OVER THE NORTH-CENTRAL OR NORTHEAST GULF. MODEL TRENDS
OVER THE LAST 24 HOURS HAVE MOVED FROM A STRONGER LOW MOVING INLAND
WEST OF YAKUTAT TO A WEAKER LOW MOVING INLAND NEAR OR EAST OF
YAKUTAT...THOUGH THERE ARE STILL NOTABLE OUTLIER SOLUTIONS. FOR
THIS TIME PERIOD DEFERRED TO NWS JUNEAU OFFICE WHICH PREFERRED THE
EUROPEAN (EC) MODEL...WHICH IN THE PAST HAS BEEN THE SUPERIOR
MODEL IN THIS TYPE OF SITUATION. OTHERWISE...MODELS ARE IN GOOD
AGREEMENT THROUGH THE REST OF THE SHORT TERM OTHERWISE.


&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

WITH IMPRESSIVE INSTABILITY EVEN FOR THIS TIME OF THE YEAR OVER
THE NORTHERN GULF WILL KEEP ISOLATED THUNDERSTORM WORDING IN THE
FORECAST FROM EASTERN PRINCE WILLIAM SOUND INTO THE NORTHERN
GULF THROUGH SUNSET THIS EVENING. LIKEWISE...CONVECTIVE SHOWERS
ARE EXPECTED INLAND AS WELL TO LOCATIONS SUCH AS THE MATANUSKA
VALLEY AND ANCHORAGE THIS AFTERNOON AND EVENING UNDER THIS UPPER
LEVEL LOW.

AS LOW PRESSURE MOVES NORTH OVER THE EASTERN GULF
SUNDAY...NORTH TO WEST OFFSHORE WINDS SHOULD DEVELOP BY THE
AFTERNOON SUNDAY...AND COULD BE LOCALLY GUSTY WHERE THOSE WINDS
ARE CHANNELED THROUGH MOUNTAIN GAPS SUCH AS THOMPSON PASS AND NEAR
WHITTIER. IN ADDITION...THE DIGGING DISTURBANCE INTO THE BASE OF
THE LONGWAVE TROUGH OVER SOUTHCENTRAL WILL ALLOW FOR AN AREA OF
RAIN TO DEVELOP MAINLY OVER THE SUSITNA VALLEY TONIGHT INTO
SUNDAY...BUT THIS RAIN WILL BEGIN TO DISSIPATE THROUGH SUNDAY AS
DRIER AIR BEGINS TO MOVE INTO THE REGION AS A NORTH AND WESTERLY
OFFSHORE PRESSURE GRADIENT BEGINS TO DEVELOP. THIS OFFSHORE FLOW
WILL HELP INCREASE NORTHWEST WINDS INTO TURNAGAIN ARM AND EVEN
ALONG THE HILLSIDE...WHERE GUSTS 25 TO 30 MPH ARE POSSIBLE SUNDAY
AFTERNOON INTO THE OVERNIGHT HOURS.

THE CLEARING AND DRYING TREND CONTINUES THROUGH THE EARLY PART OF
THE WEEK EXCEPT AROUND THE PRINCE WILLIAM SOUND REGION WHERE A
CHANCE OF SHOWERS WILL PERSIST. THIS WILL RESULT IN DRAMATICALLY
COOLER NIGHTTIME AND MORNING TEMPERATURES ACROSS THE
AREA...WITH LOWS INTO THE UPPER 20S TO UPPER 30S INLAND BY TUESDAY
MORNING.


SOUTHWEST ALASKA...

CONVECTIVE SHOWERS ARE EXPECTED THIS AFTERNOON AND EVENING ALONG
AND JUST WEST OF THE ALASKA AND ALEUTIAN RANGES...BUT HIGH
PRESSURE BUILDS IN LATE TONIGHT INTO THE EARLY PART OF THE WEEK
AND WILL BRING MAINLY TRANQUIL WEATHER AND LIGHT WINDS...EXCEPT A
BIT GUSTIER WINDS OVER INTERIOR BRISTOL BAY AREAS NEAR OUTFLOW
CHANNELS TOWARD THE GULF SUNDAY INTO MONDAY. THIS CLEARING TREND
WILL ALLOW FOR A NOTABLE COOLING TREND IN TEMPERATURES OVER THE
SOUTHWEST MAINLAND FOR THE NEXT SEVERAL NIGHTS.


BERING SEA/ALEUTIANS...

HIGH PRESSURE BUILDING EASTWARD CONTINUES TO TAPER THE NORTHWEST
FLOW AND SHOWERS OVER THE EASTERN BERING AND ALASKA PENINSULA
THROUGH THIS EVENING. A WEAKENING FRONT AND LOW PRESSURE SYSTEM
OVER THE WESTERN ALEUTIANS WILL LINGER THROUGH THE WEEKEND.
OTHERWISE RELATIVELY TRANQUIL CONDITIONS WILL PERSIST OVER THIS
REGION THROUGH EARLY NEXT WEEK.

&&

.LONG TERM FORECAST (WED SEPT 24 - SAT SEPT 27)...

BEGINNING THE EXTENDED PERIOD ON WEDNESDAY...THE REGION WILL BE
UNDER THE INFLUENCE OF A SPLIT JET STREAM REGIME...WITH A DISTINCT
POLAR JET TO OUR NORTH...AND A MUCH STRONGER AND ACTIVE
SUBTROPICAL JET STREAM ACROSS THE NORTH PACIFIC. THIS WILL BE A
SOMEWHAT LARGE SHIFT FROM THE PREVIOUS TWO WEEKS WHERE THE
SUBTROPICAL JET STREAM WAS IN PHASE WITH THE POLAR JET...HELPING
TO PROMOTE A VERY ACTIVE PATTERN FOR ALASKA. THIS SPLIT JET STREAM
PATTERN WILL LINGER THROUGH FRIDAY...WITH UPPER LEVEL DISTURBANCES
TRACKING THROUGH NORTHERN AND CENTRAL ALASKA. THE NET EFFECT WILL
BE COOLER AND DRY AIR OCCASIONALLY DRIVING SOUTHWARD INTO THE GULF
OF ALASKA. OTHERWISE...THIS WILL LIKELY REPRESENT THE DRIEST AND
OVERALL MOST PLEASANT STRETCH OF WEATHER IN SEPTEMBER OVER THE
PAST THREE YEARS. OUTFLOW GAP WINDS INTO THE GULF OF ALASKA WILL
PEAK WEDNESDAY AND THEN POSSIBLY AGAIN ON SATURDAY. EXPECT THE
COLDEST TEMPERATURES OF THE YEAR ACROSS MANY LOCATIONS AS
OVERNIGHT TEMPERATURES PLUMMET WITH FAVORABLE RADIATIONAL COOLING.
BY FRIDAY...THE ECMWF IS HINTING AT A NORTH PACIFIC LOW TRACKING
INTO SOUTHWEST AND EVENTUALLY SOUTHCENTRAL...BUT CURRENTLY THAT IS
A LOW PROBABILITY SOLUTION.


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

CC/JA SEP 14





000
FXAK68 PAFC 202136
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
136 PM AKDT SAT SEP 20 2014

.ANALYSIS AND UPPER LEVELS...

A BAGGY YET HIGHLY AMPLIFIED TROUGH PERSISTS OVER THE MAINLAND OF
ALASKA EXTENDING SOUTH INTO THE MID-LATITUDES OF THE PACIFIC OCEAN
ALONG 150W. NUMEROUS STRONG CONVECTIVE SHOWERS WITH ISOLATED
LIGHTNING STRIKES ARE OCCURRING OVER THE NORTHERN GULF AND PRINCE
WILLIAM SOUND GIVEN IMPRESSIVE INSTABILITY IN THIS REGION. HIGH
PRESSURE OVER THE CENTRAL BERING HAS MOVED INTO THE EASTERN BERING
TODAY...WITH A SECOND TROUGH ON THE NORTHEAST SIDE OF THE RIDGE
CURRENTLY DIGGING INTO NORTHERN AND CENTRAL ALASKA TOWARD THE
BASE OF THE LONGWAVE TROUGH OVER THE MAINLAND. OUT WEST...A
KAMCHATKA LOW IS MOVING TOWARD THE FAR WESTERN ALEUTIANS AND
WESTERN BERING.

&&

.MODEL DISCUSSION...

MODELS HAD BEEN STRUGGLING WITH A SURFACE LOW THAT FORMS IN THE
MID-LATITUDES THIS AFTERNOON AND THEN RACES NORTH AND STRENGTHENS
AS IT ENTERS THE GULF SUNDAY MORNING AND THEN MOVES INLAND
SOMEWHERE OVER THE NORTH-CENTRAL OR NORTHEAST GULF. MODEL TRENDS
OVER THE LAST 24 HOURS HAVE MOVED FROM A STRONGER LOW MOVING INLAND
WEST OF YAKUTAT TO A WEAKER LOW MOVING INLAND NEAR OR EAST OF
YAKUTAT...THOUGH THERE ARE STILL NOTABLE OUTLIER SOLUTIONS. FOR
THIS TIME PERIOD DEFERRED TO NWS JUNEAU OFFICE WHICH PREFERRED THE
EUROPEAN (EC) MODEL...WHICH IN THE PAST HAS BEEN THE SUPERIOR
MODEL IN THIS TYPE OF SITUATION. OTHERWISE...MODELS ARE IN GOOD
AGREEMENT THROUGH THE REST OF THE SHORT TERM OTHERWISE.


&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

WITH IMPRESSIVE INSTABILITY EVEN FOR THIS TIME OF THE YEAR OVER
THE NORTHERN GULF WILL KEEP ISOLATED THUNDERSTORM WORDING IN THE
FORECAST FROM EASTERN PRINCE WILLIAM SOUND INTO THE NORTHERN
GULF THROUGH SUNSET THIS EVENING. LIKEWISE...CONVECTIVE SHOWERS
ARE EXPECTED INLAND AS WELL TO LOCATIONS SUCH AS THE MATANUSKA
VALLEY AND ANCHORAGE THIS AFTERNOON AND EVENING UNDER THIS UPPER
LEVEL LOW.

AS LOW PRESSURE MOVES NORTH OVER THE EASTERN GULF
SUNDAY...NORTH TO WEST OFFSHORE WINDS SHOULD DEVELOP BY THE
AFTERNOON SUNDAY...AND COULD BE LOCALLY GUSTY WHERE THOSE WINDS
ARE CHANNELED THROUGH MOUNTAIN GAPS SUCH AS THOMPSON PASS AND NEAR
WHITTIER. IN ADDITION...THE DIGGING DISTURBANCE INTO THE BASE OF
THE LONGWAVE TROUGH OVER SOUTHCENTRAL WILL ALLOW FOR AN AREA OF
RAIN TO DEVELOP MAINLY OVER THE SUSITNA VALLEY TONIGHT INTO
SUNDAY...BUT THIS RAIN WILL BEGIN TO DISSIPATE THROUGH SUNDAY AS
DRIER AIR BEGINS TO MOVE INTO THE REGION AS A NORTH AND WESTERLY
OFFSHORE PRESSURE GRADIENT BEGINS TO DEVELOP. THIS OFFSHORE FLOW
WILL HELP INCREASE NORTHWEST WINDS INTO TURNAGAIN ARM AND EVEN
ALONG THE HILLSIDE...WHERE GUSTS 25 TO 30 MPH ARE POSSIBLE SUNDAY
AFTERNOON INTO THE OVERNIGHT HOURS.

THE CLEARING AND DRYING TREND CONTINUES THROUGH THE EARLY PART OF
THE WEEK EXCEPT AROUND THE PRINCE WILLIAM SOUND REGION WHERE A
CHANCE OF SHOWERS WILL PERSIST. THIS WILL RESULT IN DRAMATICALLY
COOLER NIGHTTIME AND MORNING TEMPERATURES ACROSS THE
AREA...WITH LOWS INTO THE UPPER 20S TO UPPER 30S INLAND BY TUESDAY
MORNING.


SOUTHWEST ALASKA...

CONVECTIVE SHOWERS ARE EXPECTED THIS AFTERNOON AND EVENING ALONG
AND JUST WEST OF THE ALASKA AND ALEUTIAN RANGES...BUT HIGH
PRESSURE BUILDS IN LATE TONIGHT INTO THE EARLY PART OF THE WEEK
AND WILL BRING MAINLY TRANQUIL WEATHER AND LIGHT WINDS...EXCEPT A
BIT GUSTIER WINDS OVER INTERIOR BRISTOL BAY AREAS NEAR OUTFLOW
CHANNELS TOWARD THE GULF SUNDAY INTO MONDAY. THIS CLEARING TREND
WILL ALLOW FOR A NOTABLE COOLING TREND IN TEMPERATURES OVER THE
SOUTHWEST MAINLAND FOR THE NEXT SEVERAL NIGHTS.


BERING SEA/ALEUTIANS...

HIGH PRESSURE BUILDING EASTWARD CONTINUES TO TAPER THE NORTHWEST
FLOW AND SHOWERS OVER THE EASTERN BERING AND ALASKA PENINSULA
THROUGH THIS EVENING. A WEAKENING FRONT AND LOW PRESSURE SYSTEM
OVER THE WESTERN ALEUTIANS WILL LINGER THROUGH THE WEEKEND.
OTHERWISE RELATIVELY TRANQUIL CONDITIONS WILL PERSIST OVER THIS
REGION THROUGH EARLY NEXT WEEK.

&&

.LONG TERM FORECAST (WED SEPT 24 - SAT SEPT 27)...

BEGINNING THE EXTENDED PERIOD ON WEDNESDAY...THE REGION WILL BE
UNDER THE INFLUENCE OF A SPLIT JET STREAM REGIME...WITH A DISTINCT
POLAR JET TO OUR NORTH...AND A MUCH STRONGER AND ACTIVE
SUBTROPICAL JET STREAM ACROSS THE NORTH PACIFIC. THIS WILL BE A
SOMEWHAT LARGE SHIFT FROM THE PREVIOUS TWO WEEKS WHERE THE
SUBTROPICAL JET STREAM WAS IN PHASE WITH THE POLAR JET...HELPING
TO PROMOTE A VERY ACTIVE PATTERN FOR ALASKA. THIS SPLIT JET STREAM
PATTERN WILL LINGER THROUGH FRIDAY...WITH UPPER LEVEL DISTURBANCES
TRACKING THROUGH NORTHERN AND CENTRAL ALASKA. THE NET EFFECT WILL
BE COOLER AND DRY AIR OCCASIONALLY DRIVING SOUTHWARD INTO THE GULF
OF ALASKA. OTHERWISE...THIS WILL LIKELY REPRESENT THE DRIEST AND
OVERALL MOST PLEASANT STRETCH OF WEATHER IN SEPTEMBER OVER THE
PAST THREE YEARS. OUTFLOW GAP WINDS INTO THE GULF OF ALASKA WILL
PEAK WEDNESDAY AND THEN POSSIBLY AGAIN ON SATURDAY. EXPECT THE
COLDEST TEMPERATURES OF THE YEAR ACROSS MANY LOCATIONS AS
OVERNIGHT TEMPERATURES PLUMMET WITH FAVORABLE RADIATIONAL COOLING.
BY FRIDAY...THE ECMWF IS HINTING AT A NORTH PACIFIC LOW TRACKING
INTO SOUTHWEST AND EVENTUALLY SOUTHCENTRAL...BUT CURRENTLY THAT IS
A LOW PROBABILITY SOLUTION.


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

CC/JA SEP 14




000
FXAK68 PAFC 201246
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
446 AM AKDT SAT SEP 20 2014

.ANALYSIS AND UPPER LEVELS...
THE HIGH AMPLITUDE LONGWAVE TROUGH CONTINUES TO SIT CENTERED BETWEEN
THE SOUTHWEST AND SOUTHCENTRAL MAINLAND. IMPRESSIVELY THE TROUGH
STRETCHES FROM THE BROOKS RANGE WELL INTO THE SUB-TROPICS WITH
SOME CYCLONIC CURVATURE TO THE WIND FIELD ALOFT JUST EAST OF THE
HAWAIIAN ISLANDS AROUND 20N LATITUDE. ON THE DOWNSTREAM SIDE OF
SAID LONGWAVE SEVERAL BAROCLINIC LEAF STRUCTURES ARE APPARENT ON
WATER VAPOR IMAGERY...A TELLTALE SIGN OF DEVELOPING LOW PRESSURE.
ONE IS JUST WEST OF THE PANHANDLE...THE OTHER DOWN IN THE MID-
LATITUDES. CLOSER TO HOME...THE PREVIOUS CLOSED LOW CENTER ALOFT
IN THE GULF IS QUICKLY MOVING INLAND AND DEAMPLIFYING AS AN OPEN
WAVE. THE STEADY RAIN ASSOCIATED WITH IT IS NOW DISSIPATING WHILE
A MORE SHOWERY REGIME IS SETTING UP IN THE NORTHERN GULF. PRESSURE
RISES BEHIND THE DEPARTING SYSTEM HAVE BROUGHT A WAVE OF STRONGER
SOUTHERLY WINDS ACROSS THE NORTH GULF COAST AND THROUGH THE GAPS
IN THE CHUGACH AS WELL. FURTHER OUT WEST...AN UPPER RIDGE IS
TRANSLATING EASTWARD ACROSS THE BERING SEA AHEAD OF A STRONG
KAMCHATKA LOW PRESSURE SYSTEM.

&&

.MODEL DISCUSSION...
IN THE UPPER LEVELS...GUIDANCE IS IN GREAT AGREEMENT THROUGH THE
SHORT TERM FORECAST. THE TWO DEVELOPING SYSTEMS IN THE EASTERN
GULF WILL EFFECTIVELY REFOCUS THE UPPER TROUGH TO THE EAST WHILE
BOTH THE KAMCHATKA LOW AND UPPER RIDGE IN THE BERING SEA CONTINUE
TO SLIDE EASTWARD. AT THE SURFACE THERE IS A LITTLE MORE
VARIABILITY...MAINLY WITH THE STRONG LOW DEVELOPING IN THE EASTERN
GULF...BUT IN GENERAL ALL GUIDANCE HAS A STRONG COMPACT SYSTEM
MOVING WEST OF THE PANHANDLE THROUGH THE WEEKEND BEFORE WEAKENING
IN THE NORTHERN GULF.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...MOSTLY CLOUDY CONDITIONS A MORE SHOWERY
PATTERN IS IN THE WORKS TODAY. THE BEST CHANCES WILL REMAIN ALONG
THE NORTH GULF COAST AND OVER PRINCE WILLIAM SOUND. DIURNAL
SHOWERS MOVING OFF THE TERRAIN WILL BE IN STORE FOR THE AFTERNOON
AND EVENING HOURS FOR THE CHUGACH. AFTER TODAY A STRONG SYSTEM
MOVING UP TOWARD THE PANHANDLE WILL BEGIN TO SWITCH THE FLOW
AROUND ALOFT IN CONJUNCTION WITH RIDGING BUILDING OVER THE
SOUTHWEST MAINLAND. THIS FLOW REVERSAL WILL BRING SOME COLDER AIR
ACROSS THE ALASKA RANGE OVER THE REGION. COMBINED WITH A WEAK
SURFACE PRESSURE PATTERN AND DECREASING CLOUD COVER...SOME OF THE
COLDEST OVERNIGHT TEMPERATURES OF THE SEASON CAN BE EXPECTED INTO
EARLY NEXT WEEK.

SOUTHWEST ALASKA...THE UPPER LEVEL IS FINALLY STARTING TO EXIT THE
AREA BUT IT WILL KEEP SOME "PARTING" SHOWERS IN THE FORECAST
THROUGH TODAY. LATER TONIGHT AND INTO SUNDAY...RIDGING FROM THE
BERING WILL NUDGE INTO THE MAINLAND AND FINALLY SHOVE THE LOW INTO
THE LONGWAVE TROUGH OVER THE GULF. THIS WILL BRING A DRYING
OFFSHORE FLOW TO MOST OF THE MAINLAND. OVER THE ALASKA
PENINSULA...IT WILL BRING STOUT NORTHERLY FLOW WHICH RESULTS IN A CHANCE
OF SHOWERS....MAINLY ON THE BERING SIDE... THROUGH THE WEEKEND.
THE OFFSHORE FLOW OVER THE MAINLAND WILL INCREASE THROUGH THE DAY
SUNDAY AND SHOULD HELP TO LIMIT FOG DEVELOPMENT. HOWEVER IT COULD
MAKE FOR GUSTY CONDITIONS...ESPECIALLY IN THE AFTERNOONS WITH
BOUNTIFUL SUNSHINE AND A WELL MIXED ATMOSPHERE. THE OFFSHORE FLOW
WILL ALSO BRING COOLING CONDITIONS. MANY SPOTS ARE LIKELY TO
APPROACH THE FREEZING MARK BY MONDAY MORNING. THE FLOW WILL RELAX
MONDAY AND TUESDAY AS THE RIDGE AXIS MOVES OVERHEAD. CLOUDS WON`T
START TO INCREASE AGAIN UNTIL LATE TUESDAY.

BERING SEA/ALEUTIANS...HIGH PRESSURE BUILDING EASTWARD WILL BEGIN
TO TAPER THE NORTHWEST FLOW AND SHOWERS OVER THE EASTERN BERING
AND ALASKA PENINSULA TODAY. A WEAKENING FRONT AND LOW PRESSURE
SYSTEM OVER THE WESTERN ALEUTIANS WILL LINGER THROUGH THE WEEKEND.


&&

.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON TUESDAY...A TROUGH OF LOW
PRESSURE WILL EXIST ACROSS THE WESTERN BERING...WITH A WEAKENING
UPPER LOW IN THE VICINITY OF THE COPPER BASIN STRETCHING SOUTHWARD TO
THE CENTRAL GULF OF ALASKA. HIGH PRESSURE ALOFT WILL BE CENTERED
OVER THE EASTERN BERING AND SOUTHWEST ALASKA. LINGERING CLOUDS AND
SHOWERS OVER THE COPPER BASIN AND ALONG THE CHUGACH MOUNTAINS WILL
RAPIDLY DIMINISH AS OFFSHORE FLOW DEVELOPS THROUGH MIDWEEK. THIS
WILL SET THE STAGE FOR A SOMEWHAT UNUSUAL EXTENDED PERIOD OF DRY
WEATHER...AND COOLING TEMPERATURES...ESPECIALLY DURING THE NIGHT
TIME PERIODS. THE DRY AND PLEASANT WEATHER WILL LIKELY PERSIST
INTO AND POSSIBLY THROUGH NEXT WEEKEND AS THE MAIN STORM TRACK
REMAINS ACROSS THE NORTH PACIFIC.


&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

MTL/MO/JA SEP 14





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