000
FXAK68 PAFC 192128
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
130 PM AKDT SUN MAY 19 2013
.ANALYSIS AND UPPER LEVELS...THE UPPER LOW WHICH FORMED OVER THE
GULF ON SATURDAY HAS NOW MOVED TO THE YUKON. A WAVE ROTATING AROUND
THE BACK SIDE OF THE LOW CENTER IS JUST CLIPPING THE NORTHEAST
COPPER RIVER BASIN PRODUCING SOME SNOW SHOWERS ALONG THE WRANGELL
MOUNTAINS. OTHERWISE SUNNY SKIES DOMINATE THE REST OF SOUTHCENTRAL
ALASKA...THE WESTERN GULF...AND MUCH OF SOUTHWEST ALASKA THANKS TO
A HIGH AMPLITUDE RIDGE BUILDING IN FROM THE BERING SEA. UPSTREAM OF
THE RIDGE A VERTICALLY STACKED CLOSED LOW SOUTH OF THE WESTERN
ALEUTIANS IS TRACKING TO THE EAST-NORTHEAST WITH THE OCCLUDED FRONT
SPREADING NORTH AND EASTWARD INTO THE BERING SEA. THIS IS BRINGING
WIDESPREAD RAIN AND FOG TO THE ALEUTIANS AND CENTRAL BERING.
.MODEL DISCUSSION...THERE ARE MINOR DIFFERENCES IN HOW QUICKLY THE
UPPER RIDGE MOVES THROUGH SOUTHWEST ALASKA WHICH RESULTS IN TIMING
IN THE EASTWARD PROGRESSION OF PRECIPITATION. PREFER THE NAM WHICH
IS A MIDDLE GROUND BETWEEN THE FASTER ECMWF AND SLOWER GFS. OTHER
THAN THAT MODELS ARE IN GOOD AGREEMENT WITH MAJOR FEATURES OVER THE
NEXT FEW DAYS.
.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...THE UPPER RIDGE WILL BUILD OVER SOUTHCENTRAL
TONIGHT AND MONDAY...BUT WILL THEN QUICKLY WEAKEN AS A PIECE SPLITS
OFF AND HEADS TO NORTHWEST CANADA TUESDAY. UNTIL THEN EXPECT DRY
AND CLEAR CONDITIONS. THERE WILL BE ONE MORE NIGHT OF WIDESPREAD
SUB-FREEZING TEMPERATURES BEFORE TEMPERATURES RETURN TO NEAR NORMAL
TUESDAY AND TUESDAY NIGHT. AS THE RIDGE WEAKENS ON TUESDAY THE
REMNANTS OF THE OCCLUDED FRONT CROSSING THE BERING WILL MOVE TO
THE WESTERN GULF TUESDAY AND WEDNESDAY. MOST OF THE DYNAMICS WITH
THIS SYSTEM WILL HEAD TO THE NORTHERN BERING...SO EXPECT THE MAIN
IMPACT TO BE CLOUDS MOVING INTO WESTERN PORTIONS OF SOUTHCENTRAL...
WITH JUST A CHANCE OF RAIN. OTHERWISE...TEMPERATURES WILL CONTINUE
TO MODERATE AS WE HEAD THROUGH THE WEEK.
SOUTHWEST ALASKA...THE UPPER RIDGE WILL SLIDE PAST SOUTHWEST ALASKA
RELATIVELY QUICK WITH CLOUDS AND PRECIP ARRIVING ALONG THE COAST BY
LATE MONDAY AND THEN SPREADING INLAND TUESDAY AND WEDNESDAY. WITH
MUCH OF THE ENERGY BEING PULLED NORTHWARD UP THE WEST SIDE OF THE
RIDGE THE OCCLUDED FRONT WILL STRETCH APART OVER SOUTHWEST ALASKA.
STRONG SOUTHEAST FLOW WILL ALSO PRODUCE DOWNSLOPE DRYING FOR MANY
INLAND LOCATIONS. THUS...EXPECT THE BULK OF RAIN TO FALL ALONG THE
COAST WITH JUST A CHANCE INLAND. THERE MAY BE A BIT OF SNOW AS
PRECIP FIRST ARRIVE IN THE KUSKOKWIM DELTA. OTHERWISE TEMPERATURES
WILL MODERATE QUICKLY ACROSS THE SOUTHWEST ALASKA SO THAT ANY
PRECIP THAT DOES FALL WILL BE IN THE FORM OF RAIN.
BERING SEA/ALEUTIANS...THE LOW SOUTH OF THE ALEUTIANS WILL TRACK
RIGHT ACROSS THE HEART OF THE BERING SEA ADVECTING LOTS OF WARM
AIR AND MOISTURE NORTHWARD RESULTING IN WIDESPREAD RAIN AND FOG.
THE SYSTEM WILL EXIT TO THE NORTH MID WEEK...ALTHOUGH CONDITIONS
WILL REMAIN FAVORABLE FOR FOG AND STRATUS.
.LONG TERM FORECAST...MODELS SHOW POOR RUN-TO-RUN CONSISTENCY
IN THE DAY 4 THROUGH 7 TIME PERIOD AND SOLUTIONS VARY SIGNIFICANTLY
AMONG THE VARIOUS MEDIUM RANGE MODELS. INDICATIONS ARE THAT ANOTHER
LARGE PACIFIC SYSTEM WILL AFFECT THE ALEUTIANS AND BERING...BUT
EXACTLY WHERE THIS SYSTEM TRACKS IS HIGHLY UNCERTAIN. THE REST OF
THE FORECAST AREA WILL LIKELY REMAIN UNDER THE INFLUENCE OF WEAKER
FEATURES. FORECAST CONFIDENCE IS BELOW NORMAL.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...155 160 165 170 171 172 179 180.
FIRE WEATHER...NONE.
SEB MAY 13
000
FXAK68 PAFC 191319
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
519 AM AKDT SUN MAY 19 2013
.ANALYSIS AND UPPER LEVELS...
THE REMNANTS OF THE SYSTEM THAT BROUGHT A LATE SEASON SNOWFALL TO
MUCH OF SOUTHCENTRAL ALASKA ON FRIDAY AND SATURDAY HAS BECOME A
VERTICALLY STACKED LOW NEAR MIDDELTON ISLAND. THIS LOW WILL SLOWLY
SLIDE TO THE EAST AS IT DISSIPATES TODAY. THE NEXT ALEUTIAN LOW IS
CURRENTLY LOCATED 500 MILES SOUTHWEST OF SHEMYA...AND IS PROGRESSING
OFF TO THE NORTHEAST. THE ASSOCIATED FRONT FROM THIS LOW CURRENTLY
OVER THE WESTERN ALEUTIANS WILL MOVE TO THE EASTERN BERING BY MONDAY.
AN UPPER LEVEL ARCTIC LOW IS ALSO CLIPPING THE EXTREME NORTHWESTERN
EDGE OF THE STATE...AND WILL REMAIN WELL OUT OF THE AOR AS THE
ALEUTIAN LOW PUSHES IT TOWARDS THE NORTH POLE.
.MODEL DISCUSSION...
THE MODELS HAVE NOW ALL COME INTO VERY GOOD AGREEMENT WITH BOTH THE
TRACK AND INTENSITY OF THE ALEUTIAN LOW THROUGH MID WEEK...WITH GOOD
RUN TO RUN CONSISTENCY IN THE NAM AND EC. PREVIOUS RUNS OF THE GFS
WERE SLIGHTLY SLOWER THAN THE NAM/EC SOLUTIONS...HOWEVER LATER GFS
RUNS HAVE SINCE COME INTO LINE WITH THE REST.
.SHORT TERM FORECAST...
SOUTHCENTRAL...CLOUDS WILL CONTINUE TO DECREASE THROUGHOUT MUCH OF
SOUTHCENTRAL AS THE GULF LOW CONTINUES TO WEAKEN. THIS WILL LEAD TO A
WARMER AFTERNOON UNDER CLEAR SKIES FOR MOST AREAS WITH THE EXCEPTION
OF THE COPPER RIVER BASIN...ALTHOUGH TEMPERATURES WILL REMAIN BELOW
NORMAL FOR AT LEAST ANOTHER DAY. THE ONLY CHANCE OF PRECIP IN THE
AREA TODAY WILL BE ALONG THE WRANGELL MOUNTAINS OF THE COPPER RIVER
BASIN. THE GUSTY WESTERLY WINDS NEAR KODIAK ISLAND...BARREN
ISLANDS...AND WHITTIER WILL DIMINISH THIS MORNING AS THE GULF LOW
CONTINUES TO WEAKEN AND MOVE EAST.
SOUTHWEST/AKPENN...THE MOST SIGNIFICANT WEATHER TO NOTE FOR THE
SOUTHWEST MAINLAND IS A BAND OF ISOLATED SNOW SHOWERS CURRENTLY
MOVING THROUGH THE KUSKOKWIM DELTA. THIS BAND WILL BRING A QUICK SHOT
OF SNOW TO THE BETHEL AREA THIS MORNING...THEN INTO THE WESTERN
KUSKOKWIM DELTA THIS AFTERNOON BEFORE DISSIPATING OVER THE KUSKOKWIM
MOUNTAINS. OTHERWISE THE WEATHER WILL REMAIN MOSTLY CLEAR WITH BELOW
NORMAL TEMPERATURES UNTIL MONDAY WHEN THE FRONT AHEAD OF THE ALEUTIAN
LOW WILL BEGIN AFFECTING THE SOUTHWEST COAST.
BERING SEA/ALEUTIANS...MOST OF ACTIVE WEATHER TODAY WILL BE CENTERED
HERE AS THE ALEUTIAN LOW PROGRESSES THROUGH THE AREA. THIS SYSTEM
WILL BRING A ROUND OF RAIN AND STRONG WINDS THROUGHOUT THE ALEUTIAN
AND PRIBILOF ISLANDS THROUGH MONDAY EVENING.
.LONG TERM FORECAST...
THE MODELS REMAIN IN GOOD AGREEMENT IN DEVELOPING RIDGING OVER THE
GULF OF ALASKA MID WEEK...WHICH WILL KEEP SYSTEMS MOVING THROUGH THE
ALEUTIANS ON MORE NORTHERLY TRACKS INTO NEXT WEEKEND. WHILE THERE IS
CONSIDERABLE DISAGREEMENT AS TO EXACTLY WHERE THESE NEXT ALEUTIAN
LOWS WILL BE LOCATED...THIS SETUP WILL NOT ONLY KEEP MOST OF THE
ACTIVE WEATHER WEST OF MAINLAND ALASKA...BUT WILL ALSO BRING NEAR TO
EVEN ABOVE NORMAL TEMPERATURES INTO THE AREA.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...155 160 165 170 171 172 175 179 180
FIRE WEATHER...NONE
DEK MAY 13
000
FXAK68 PAFC 182107
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
105 PM AKDT SAT MAY 18 2013
.ANALYSIS AND UPPER LEVELS...A NEGATIVELY TILTED HIGH AMPLITUDE
UPPER LEVEL TROUGH EXTENDS FROM AN ANCHOR LOW OVER THE CHUKCHI
SEA SOUTHEASTWARD TO SOUTHCENTRAL ALASKA AND THE GULF OF ALASKA.
A STRONG VORT-MAX MOVING INTO THE BOTTOM OF THE TROUGH IS LEADING
TO FORMATION OF AN UPPER LOW CENTER OVER THE NORTHWEST GULF. THIS
IN TURN HAS SLOWED DOWN THE NORTHEASTWARD PROGRESSION OF THE TROUGH.
A WAVE MOVING UP THE FRONT SIDE OF THE TROUGH IS PRODUCING THE BULK
OF THE VERTICAL MOTION AS INDICATED BY THE COLD CLOUD TOPS JUST OUT
AHEAD OF IT. THIS CORRESPONDS WITH THE AREA OF HEAVIEST PRECIPITATION
WHICH IS NOW OVER THE COPPER RIVER BASIN. THERE IS STILL SOME WEAK
LIFT BEHIND THIS WAVE...PRIMARILY LOW LEVEL LIFT INDUCED BY COLD
ADVECTION. THIS IS CAUSING AREAS OF LIGHT SNOW TO LINGER FROM THE
WESTERN KENAI TO ANCHORAGE AND THE MAT-SU. STRONG GUSTY WINDS ARE
BEING OBSERVED BEHIND THE ARCTIC FRONT PRIMARILY ALONG THE ALASKA
PENINSULA AND THE WESTERN GULF (INCLUDING KODIAK ISLAND).
LOOKING UPSTREAM...A LARGE MATURE LOW OVER THE NORTHWEST PACIFIC
IS TRACKING SLOWLY TOWARD THE ALEUTIANS WITH A RIDGE BEGINNING TO
BUILD OUT AHEAD OF IT.
.MODEL DISCUSSION...MODELS ARE ALL IN GENERAL AGREEMENT WITH
EVOLUTION OF MAJOR FEATURES THROUGH THE NEXT THREE DAYS.
.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...THE UPPER WAVE MOVING THROUGH THE COPPER RIVER
BASIN WILL QUICKLY EXIT TO THE NORTH LATER THIS AFTERNOON BRINGING
AN END TO THE HEAVIEST PRECIPITATION. THE FORMATION OF AN UPPER LOW
OVER THE NORTHWEST GULF IS CAUSING UPPER LEVEL VERTICAL MOTION TO
BECOME WEAK AND DIFFUSE ACROSS THE REST OF SOUTHCENTRAL. EXPECT THIS
TO CONTINUE AS THE LOW BECOMES MORE DEFINED THIS AFTERNOON AND EXITS
TO THE EAST-NORTHEAST. THE MAIN TROUGH AXIS WHICH IS LAGGING BACK
ALONG THE ALASKA RANGE WILL FINALLY BE ABLE TO CROSS THE REGION
OVERNIGHT THROUGH SUNDAY MORNING...HELPING TO KICK ANY REMAINING
PRECIP EASTWARD AND CLEAR OUT SKIES ACROSS MOST OF THE REGION.
WITH AN ANOMALOUSLY COLD AIR MASS IN PLACE RECORD OR NEAR RECORD
TEMPERATURES ARE POSSIBLE TONIGHT...ESPECIALLY ACROSS WESTERN
PORTIONS OF SOUTHCENTRAL WHERE SKIES WILL LIKELY CLEAR OUT DURING
THE EVENING. TEMPERATURES ON SUNDAY AND SUNDAY NIGHT WILL REMAIN ON
THE COOL SIDE AS THE AIR MASS VERY SLOWLY MODERATES. HIGH PRESSURE
WILL BUILD OVER THE REGION SUNDAY AND THEN HOLD IN PLACE THROUGH
THE EARLY PART OF NEXT WEEK. NOT ONLY WILL THIS PROVIDE A PERIOD
OF DRY WEATHER...BUT TEMPERATURES WILL MODERATE TO NEAR NORMAL.
SOUTHWEST ALASKA...THE KUSKOKWIM DELTA WILL REMAIN MOSTLY CLOUDY
WITH SCATTERED SNOW SHOWERS THROUGH SUNDAY MORNING AS WEAK UPPER
WAVES MOVING OVER TOP OF THE BUILDING BERING SEA RIDGE PASSES
THROUGH. THE REST OF SOUTHWEST ALASKA WILL REMAIN DRY AND COLD
THROUGH THE REMAINDER OF THE WEEKEND. THE UPPER RIDGE WILL BUILD
OVERHEAD SUNDAY AND THEN SLIDE EASTWARD MONDAY. THIS WILL LEAD TO
A SIGNIFICANT PATTERN CHANGE DURING THE EARLY TO MIDDLE OF NEXT
WEEK AS SOUTHERLY FLOW BRINGS MUCH WARMER TEMPERATURES AND RAIN
TO MOST OF THE REGION.
BERING SEA/ALEUTIANS...THE BERING SEA AND ALEUTIANS ARE QUIET UNDER
THE INFLUENCE OF HIGH PRESSURE. THAT WILL CHANGE TONIGHT THROUGH
SUNDAY AS A VERY LARGE LOW OVER THE NORTHWEST PACIFIC HEADS FOR
THE BERING SEA. EXPECT MODERATING TEMPERATURES AND PERIODS OF RAIN
AS THIS SYSTEM MOVES IN.
.LONG TERM FORECAST...WITH A HIGH AMPLITUDE RIDGE SETTING UP OVER
MAINLAND ALASKA EARLY NEXT WEEK THE SYSTEM OVER THE BERING WILL
BE FORCED NORTHWARD...KEEPING RAIN CONFINED TO THE BERING SEA AND
SOUTHWEST ALASKA. SOUTHCENTRAL WILL STEADILY GET WARMER UNDERNEATH
THE RIDGE...WITH TEMPERATURES POSSIBLY MOVING TO ABOVE NORMAL BY
THE END OF THE WEEK. MODELS INDICATE ANOTHER SYSTEM MOVING UP FROM
THE PACIFIC INTO THE BERING BY NEXT WEEKEND...BUT THERE IS A PRETTY
LARGE SPREAD IN THE TRACK OF THIS SYSTEM SO CONFIDENCE IS VERY LOW.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING 130 170 171 172 175 176 179.
FIRE WEATHER...NONE.
SEB MAY 13
000
FXAK68 PAFC 181239
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT SAT MAY 18 2013
.ANALYSIS AND UPPER LEVELS...
NEGATIVE TILTED UPPER LEVEL TROUGH CONTINUES TO HANG FROM FROM
NORTHWEST ALASKA SOUTHEASTWARD THROUGH THE WESTERN GULF OF ALASKA.
THE FIRST VORTICITY MAXIMUM IN THE TROUGH IS PUSHING INLAND OVER THE
NORTH GULF COAST EARLY THIS MORNING WHILE THE SECOND IS DIGGING INTO
THE GULF. THE EDGE OF HIGHER MOISTURE VALUES AHEAD OF THE FIRST
DISTURBANCE IS EVIDENT ON WATER VAPOR IMAGERY...WHICH SIGNALS THE
DECLINE OF DYNAMIC LIFT FROM SOUTHWEST TO NORTHEAST OVER THE
SOUTHCENTRAL. THE REMAINING SNOWFALL WEST OF THE CHUGACH WILL
PRIMARILY BE DRIVEN BY COLD ADVECTION FROM THE WEST/NORTHWEST. THE
SOUTHWEST MAINLAND IS ENTRENCHED IN THE GUSTY NORTHWESTERLY FLOW
BEHIND THE ARCTIC FRONT WITH ISOLATED SHOWERS AND BELOW NORMAL
TEMPERATURES.
.MODEL DISCUSSION...
GUIDANCE REMAINING IN GREAT AGREEMENT WITH THIS LATE SEASON SNOW
EVENT AND COLD OUTBREAK. VERY SIMILAR TIMING AND PROGRESSION OF THE
UPPER TROUGH BRIEFLY CLOSING OFF THEN SHIFTING TO THE EAST AS A RIDGE
BUILDS OVER THE SOUTHWEST MAINLAND AND SOUTHCENTRAL. SOME SLIGHT
DIFFERENCES CONCERNING A WEAK SURFACE LOW IN THE GULF BUT SHOULD NOT
HAVE ANY IMPLICATIONS ON THE CURRENT FORECAST. THE NAM WAS PREFERRED
IN THE SHORT TERM.
.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...LIGHT SNOWFALL WILL CONTINUE FROM THE SUSITNA
VALLEY SOUTHWARD TO THE ANCHORAGE BOWL THROUGH THE MORNING
HOURS...GRADUALLY TAPERING OFF BY AFTERNOON. SNOWFALL WILL LINGER
LONGEST AT HIGHER ELEVATIONS OF THE CHUGACH AND TALKEETNA MOUNTAINS.
UNSEASONABLE COLD TEMPERATURE WILL PERSIST TODAY WITH BRISK
NORTHWESTERLY WINDS CONTINUING THROUGHOUT THE DAY. THE NEXT FORECAST
CONCERN IS HOW LOW TEMPERATURES FALL TONIGHT INTO SUNDAY MORNING.
WITH DECREASING CLOUDS THROUGHOUT THE DAY AND A VERY COLD AIR MASS
ALOFT LOW TEMPERATURES ARE EXPECTED TO DROP RAPIDLY INTO THE 20S
EARLY SUNDAY MORNING...FLIRTING WITH RECORD LOWS. RIDGING OVERHEAD
INTO EARLY NEXT WEEK WILL KEEP DRY CONDITIONS WITH MODERATE
TEMPERATURES BACK TO MORE REASONABLE LEVELS BUT STILL SLIGHTLY BELOW
NORMAL.
SOUTHWEST ALASKA...NORTHWESTERLY FLOW WILL BEGIN TO SLACKEN TODAY
OVER THE KUSKOKWIM DELTA AS RIDGING BUILDS IN FROM THE BERING SEA
BRINGING SOUTHERLY WINDS AND MODERATING TEMPERATURES. THE BRISTOL BAY
REGION WILL SEE CONTINUED GUSTY NORTHWESTERLY FLOW SLOWLY LIGHTENING
THROUGH THE DAY WITH PARTLY SUNNY SKIES. A BERING SEA FRONT WILL
RETURN RAIN AND SNOW TO THE KUSKOKWIM DELTA ON MONDAY WHILE DRY
CONDITIONS WILL PERSIST FOR THE BRISTOL BAY AREA.
BERING SEA AND ALEUTIANS...HIGH PRESSURE OVER THE EASTERN BERING WILL
KEEP PARTLY SUNNY SKIES AND DRY CONDITIONS ON HAND WITH SOME
LINGERING SNOW SHOWERS ALONG THE ALASKA PENINSULA. A NORTH PACIFIC
LOW WILL SEND A WARM FRONT OVER THE WESTERN ALEUTIANS ALONG WITH
STRONG SOUTHEASTERLY WINDS AND RAIN. THE FRONT WILL PROGRESS TO THE
EASTERN BERING BY MONDAY RETURNING WARMER TEMPERATURES...RAIN AND
STRONG SOUTHERLY WINDS TO MOST OF THE CHAIN.
.LONG TERM FORECAST...
A STRONG NORTH PACIFIC SYSTEM MOVING INTO THE BERING SEA WILL PROMOTE
RIDGING OVER THE SOUTHERN MAINLAND. DRY CONDITIONS WILL PERSIST WITH
NEAR NORMAL TEMPERATURES EAST OF THE ALASKA RANGE WITH WETTER
CONDITIONS WEST OF THE ALASKA RANGE.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY 111 145
MARINE...
FIRE WEATHER...NONE
MTL MAY 13
000
FXAK68 PAFC 172136
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
130 PM AKDT FRI MAY 17 2013
.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL TROUGH ACCOMPANIED BY MUCH-ADVERTISED UNSEASONABLY
COLD AIR IS MOVING THROUGH SOUTHERN ALASKA THIS AFTERNOON. A WEAK LOW
PRESSURE SYSTEM IN THE GULF HAS SPREAD WIDESPREAD PRECIPITATION
ACROSS ALL OF SOUTHCENTRAL ALASKA...WHICH IS FALLING GENERALLY IN THE
FORM OF RAIN AT LOWER ELEVATIONS AND SNOW AT HIGHER ELEVATIONS.
SATELLITE IMAGERY SHOWS THE UPPER TROUGH BECOMING INCREASINGLY
NEGATIVELY TILTED...WITH AN UPPER LEVEL LOW NEAR THE BERING STRAIT
DROPPING INTO THE BASE OF THE TROUGH. FURTHER WEST...THE COLD FRONT
HAS PASSED THROUGH MOST OF THE SOUTHWEST MAINLAND...CLEARING SKIES
AND ALLOWING TEMPERATURES TO DROP INTO THE TEENS EARLIER THIS MORNING
FROM THE KUSKOKWIM DELTA TO THE WESTERN KUSKOKWIM VALLEY. HIGH
TEMPERATURES THIS AFTERNOON WILL STRUGGLE TO REACH THE UPPER 20S IN
PARTS OF THE DELTA...WHERE THE AVERAGE HIGH THIS TIME OF YEAR SHOULD
BE UPWARDS OF 50 DEGREES. WAY OUT WEST...HIGH PRESSURE REMAINS IN
COMMAND OF THE BERING SEA REGION...THOUGH HIGH CLOUDS IN ADVANCE OF A
NORTH PACIFIC LOW ARE APPROACHING THE FAR WESTERN ALEUTIANS.
.MODEL DISCUSSION...
MODEL AGREEMENT HAS CONTINUED TO IMPROVE TODAY WITH THE NAM JOINING
THE OTHER SOLUTIONS IN THE TIMING AND EVOLUTION OF THE UPPER LEVEL
TROUGH OVER THE MAINLAND TODAY (NAM HAD BEEN FASTER WITH SPEED OF THE
UPPER TROUGH IN PREVIOUS DAYS). THUS CONFIDENCE HAS CONTINUED TO
INCREASE THAT AN UNUSUAL LATE-SEASON SNOWFALL EVENT WILL BE UNFOLDING
ACROSS SOUTHCENTRAL ALASKA TONIGHT AND CONTINUING THROUGH SATURDAY
MORNING. THE NAM WAS THE PRIMARY MODEL USED TODAY...THOUGH NO STRONG
PREFERENCES WERE NOTED AND NO MODELS WERE UNUSABLE.
.SHORT TERM FORECAST...
EAST OF THE ALASKA RANGE...COLD AIR IS SLOWLY BLEEDING INTO THE AREA
BUT THIS TREND WILL ACCELERATE DRAMATICALLY BY LATE THIS AFTERNOON.
AS THE ATMOSPHERIC COLUMN COOLS THE RAIN/SNOW MIX WILL TURN TO ALL
SNOW EVEN AT LOWER ELEVATIONS. HIGHER ELEVATIONS WILL SEE THE MOST
SNOWFALL...LIKELY APPROACHING 6 INCHES IN SOME LOCATIONS...WITH LOWER
ELEVATIONS SIGNIFICANTLY LESS. AS SKIES CLEAR ON SATURDAY AFTERNOON
TEMPERATURES SHOULD DROP SIGNIFICANTLY OVERNIGHT INTO SUNDAY MORNING.
RECORD LOW TEMPERATURES IN ANCHORAGE ARE IN THE MID 20S...AND THESE
RECORDS MAY BE THREATENED IF WINDS DIMINISH ENOUGH TO ALLOW
SIGNIFICANT OVERNIGHT COOLING. EVEN IF THE RECORD LOWS ARE NOT
REACHED...A WIDESPREAD HARD FREEZE IS EXPECTED ACROSS MUCH OF THE
REGION FROM THE INLAND KENAI PENINSULA NORTHWARD. TEMPERATURES WILL
START TO SLOWLY REBOUND ON SUNDAY AS HIGH PRESSURE MOVES IN FROM THE
WEST.
WEST OF THE ALASKA RANGE...BEHIND THE COLD FRONT TEMPERATURES DROPPED
WELL BELOW FREEZING THIS MORNING AT MANY INLAND LOCATIONS OVER THE
MAINLAND. MOSTLY CLEAR SKIES WILL ALLOW TEMPERATURES TO DROP AGAIN
TONIGHT INTO THE LOWER TEENS...BEFORE A STEADY WARMING TREND ENSUES
FOR THE LATTER HALF OF THE WEEKEND. HIGH PRESSURE CURRENTLY OVER THE
BERING SEA WILL DRIFT EASTWARD...CONTINUING BENIGN CONDITIONS AND
MOSTLY SUNNY SKIES. MARINE FOG/STRATUS OVER THE BERING AND ALEUTIANS
WILL START TO SLOWLY DISSIPATE SATURDAY AS A GALE-FORCE FRONT
APPROACHES THE WESTERN ALEUTIANS. THIS WEATHER FRONT AND ASSOCIATED
RAIN SHIELD WILL MOVE TO THE EASTERN BERING BY LATE SUNDAY.
.LONG TERM FORECAST...
A MORE PROGRESSIVE WEATHER PATTERN WILL MOVE INTO THE REGION STARTING
SUNDAY. THIS WILL SEE MOST AREAS RETURN TO NEAR-NORMAL TEMPERATURES
BY THE MIDDLE OF NEXT WEEK...WITH RAIN MOVING INTO THE SOUTHWEST
MAINLAND BUT SOUTHCENTRAL REMAINING MOSTLY DRY.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...SNOW ADVISORY 101 111 145
MARINE...GALE 130 132 150 172 175 176
FIRE WEATHER...NONE
DIXON MAY 13
000
FXAK68 PAFC 171245
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT FRI MAY 17 2013
.ANALYSIS AND UPPER LEVELS...
A LARGE LONG-WAVE TROUGH/CLOSED UPPER LEVEL LOW LIES CENTERED ABOVE
THE CHUKCHI SEA EXTENDING WELL SOUTH INTO THE MID-LATITUDES. A
SHORTWAVE TROUGH EMBEDDED IN THE FLOW IS DIGGING OVER THE SOUTHWEST
MAINLAND PULLING A COLD FRONT ALONG FOR THE RIDE...STRETCHING FROM
THE ALASKA RANGE SOUTHWEST THROUGH THE ALEUTIANS BRINGING VERY
UNSEASONABLE ARCTIC AIR BEHIND IT. MOIST SOUTHERLY FLOW IS EVIDENT ON
THE FRONT SIDE OF THE TROUGH AS WARM ADVECTION HAS OVERSPREAD RAIN
OVER MOST OF SOUTHCENTRAL ALASKA. MORE SOUTHERLY FLOW ALOFT RATHER
THAN SOUTHEASTERLY ALONG WITH THE CORE OF THE STRONGEST WINDS
REMAINING ABOVE THE CHUGACH/KENAI MOUNTAINS HAVE MADE DOWN-SLOPE
DRYING A NON-ISSUE FOR MOST OF THE AREA SAVE THE MATANUSKA VALLEY.
EXTENSIVE CLOUD COVER AND RAIN HAVE KEPT TEMPERATURES WELL BELOW
NORMAL FOR MOST OF THE AREA. MOIST ONSHORE FLOW ACROSS THE NORTHERN
GULF COAST HAS KEPT THE AREA IN STEADY HEAVY PRECIPITATION AS WELL AS
PROMOTED STRONG WINDS THROUGH TURNAGAIN ARM.
.MODEL DISCUSSION...
GUIDANCE REMAINING IN GREAT SYNOPTIC AGREEMENT WITH THE MAJOR PLAYERS
OF THE FORECAST. CONCERNING THE UPPER TROUGH...THE MODELS ARE
CONSISTENT WITH SHOWING THE INITIAL TROUGH SHEARING JUST TO THE WEST
OF THE SOUTHCENTRAL WITH THE JET DIGGING DOWN THE BACKSIDE OF THE
TROUGH PROMOTING A CLOSED LOW DEVELOPMENT IN THE NORTHERN GULF
KEEPING THE TROUGH AXIS FROM THE ALASKA/ALEUTIAN RANGE THROUGH THE
WESTERN GULF THROUGH SATURDAY AFTERNOON. A LITTLE MORE SPREAD EXISTS
WITH THE ARRIVAL OF THE COLD AIR THIS AFTERNOON. THE NAM CONTINUES TO
BE THE MOST AGGRESSIVE WITH THE COLD AIR MOVING EASTWARD OWING TO THE
LEADING TROUGH STAYING A LITTLE MORE POSITIVE TILT. GENERALLY ALL
GUIDANCE PUSHES THE RAIN/SNOW LINE EAST OF TALKEETNA-ANCHORAGE-KENAI
BY MID-AFTERNOON.
.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...PRECIPITATION WILL INCREASE IN INTENSITY THIS
MORNING AS THE SURFACE LOW MOVES CLOSER TOWARD THE EASTERN KENAI
PENINSULA...CUTTING OFF ANY REMAINING CROSS-BARRIER FLOW AND
DOWNSLOPE. COLD AIR ADVECTION WILL INCREASE IN INTENSITY FROM THE
WEST TODAY FACILITATING A CHANGE FROM RAIN TO SNOW DURING THE
AFTERNOON HOURS AND WILL BE THE MAIN DRIVER OF PRECIPITATION THROUGH
THE OVERNIGHT HOURS. THE GREATEST ACCUMULATIONS WILL BE AT HIGHER
ELEVATIONS THOUGH MOST LOCATIONS FROM THE SUSITNA VALLEY THROUGH THE
NORTHERN KENAI PENINSULA WILL SEE AT LEAST SOME ACCUMULATION OF SNOW
AT SEA LEVEL. SNOW WILL LINGER THROUGH SATURDAY MORNING AND TAPER OFF
BY AFTERNOON.
SOUTHWEST ALASKA...THE DIGGING UPPER TROUGH IS PRODUCING LIGHT SNOW
ACROSS THE BRISTOL BAY AREA WITH THE COLD FRONT RIGHT ON ITS HEELS.
LIGHT SNOW WILL CONTINUE EARLY THIS MORNING AND SLOWLY TAPER OFF BY
AFTERNOON...LINGERING THE LONGEST OVER THE ALASKA PENINSULA. BEHIND
THE COLD FRONT GUSTY NORTHWESTERLY WINDS WILL REMAIN WITH SCATTERED
SNOW SHOWERS ACROSS THE REGION. HIGH PRESSURE WILL BUILD INTO THE
AREA ON SATURDAY WITH LIGHTER WINDS AND RECOVERING TEMPERATURES.
BERING SEA AND ALEUTIANS...BRISK NORTHERLY FLOW OVER THE CENTRAL AND
EASTERN BERING WILL KEEP SCATTERED SNOW SHOWERS ACROSS THE AREA. THE
WESTERN BERING WILL REMAIN UNDER HIGH PRESSURE AND LIGHT WESTERLY
WINDS. HIGH PRESSURE WILL BUILD OVER THE EASTERN BERING OVER THE
WEEKEND WHILE A NORTH PACIFIC LOW WILL APPROACH THE WESTERN ALEUTIANS
BRINGING RAIN AND STRONG SOUTHEASTERLY WINDS.
.LONG TERM FORECAST...
A DISSIPATING UPPER LOW WILL MIGRATE INTO THE BERING EARLY NEXT WEEK
BUILDING AN UPPER RIDGE AHEAD TO THE EAST...WHICH WILL BRING MOST OF
THE MAINLAND BACK TO REASONABLE CLIMATOLOGICAL TEMPERATURES WITH
DRIER WEATHER.
.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER WEATHER ADVISORY 101 111 145
MARINE...HEAVY FREEZING SPRAY 180
GALE 120 130 132 150 175 176
FIRE WEATHER...NONE
MTL MAY 13
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