000
FXAK67 PAJK 251424
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
624 AM AKDT SAT MAY 25 2013
.SHORT TERM...SCATTERED SHOWERS ARE EXPECTED THIS AFTERNOON FOR
MANY OF THE ZONES NEAR THE COAST MOUNTAIN RANGE. OTHERWISE THE
STABLE CONDITIONS INCLUDING DIURNAL CYCLES OF SEA STRATUS AND FOG
ARE EXPECTED TO BE PREVALENT. SHOWERS DEVELOPING FROM THE EASTERLY
FLOW FEATURES HAVE BELOW AVERAGE CONFIDENCE. THE REMAINDER OF THE
SHORT RANGE FORECAST PACKAGE HAS AVERAGE CONFIDENCE.
A 500H LOW OVER THE SEATTLE VICINITY, AS WELL AS A SECOND LOW OVER
ALBERTA, ARE SUPPORTING SYNOPTIC-SCALE FLOW THAT INCLUDES E FLOW
ACROSS MOST OF B.C. THE GOES IR LOOP SHOWS SEVERAL SMALL- SCALE
VORTICITY FEATURES MOVING FROM OVER CENTRAL B.C. AND OVER THE
PANHANDLE.
A 500H RIDGE EXTENDS WSW FROM OVER GREAT SLAVE LAKE AND OVER THE
CENTRAL PANHANDLE. WE SOMETIMES CALL A RIDGE ALOFT "DIRTY" IF
SHORT WAVES ARE ABLE TO TRAVEL THROUGH IT, EVEN IF THESE WAVES ARE
WEAKENING. IN THE PRESENT CASE, WE HAVE A DIRTY RIDGE THAT IS
WEAKENING THE SHORT WAVES ENOUGH TO LIMIT PRECIPITATION, BUT THE
ISENTROPIC LIFT SHOULD PREVAIL ENOUGH TO GENERATE THE SCATTERED
SHOWERS DISCUSSED ABOVE. THE ISENTROPIC LIFT IS WEAK AND DIFFICULT
TO IDENTIFY S OF SUMNER STRAIT.
THE MODELS POINT TO A SMALL LOW ALOFT ABOUT 300 NM S OF MIDDLETON
ISLAND, AND THE GOES IR SHOWS A LIMITED AREA OF CLOUD MASS
CONSISTENT TO THIS COLD CORE LOW ALOFT. THIS LOW WILL DRIFT N BUT
HAS ALMOST NO ASSOCIATED FEATURES LOWER THAN THE 700H.
A SURFACE RIDGE OF HIGH PRESSURE EXTENDS N FROM THE N PACIFIC
ALONG TO THE VICINITY OF ICY CAPE. THE RIDGE AXIS WILL TILT IN
RESPONSE TO A 995 MB LOW ABOUT 400 NM S OF KODIAK, AND BY 12Z SUN
THE RESULT WILL BE THE RIDGE EXTENDING NW ALONG A LINE FROM
KETCHIKAN TO SITKA AND NW TO PRINCE WILLIAM SOUND.
THE GOES IR ALSO SHOWS THE CLOUD SHIELD ASSOCIATED WITH AN OCCLUDED
SYSTEM WITH A TRIPLE POINT ABOUT 500 NM S OF KODIAK. THE NAM IS
ACCEPTED WITH A SOLUTION OF 25 KT WINDS IN THE SW SECTION OF THE
OFFSHORE ZONE (PKZ310) BY 12Z SUN. THE SYSTEM DISCUSSED IN THIS
PARAGRAPH IS NOT SIGNIFICANT FOR ANY OTHER ZONE IN OUR AREA OF
RESPONSIBILITY THROUGH 12Z SUN. PLEASE NOTE THE LONG RANGE SECTION
FOR FEATURES MOVING TOWARD OUR AREA FROM THE SW.
MODELS: THE CONVECTION FOR THIS AFTERNOON WILL BE ASSOCIATED WITH
ESE FLOW ACROSS THE COAST MOUNTAIN RANGE. ISENTROPIC UPGLIDE IS
INDICATED FOR THE FLOW MOVING PAST THE UPPER LEVELS OF THE COAST
MOUNTAIN RANGE ON THE TWO MODELS THAT HAD BEST INITIALIZATION: THE
NAM AND THE ECMWF.
.LONG TERM...UPPER HIGH OVER NW CANADA WILL DRIFT WWD INTO SE
INTERIOR AK BY TUE. ELONGATED UPPER LOW WILL DRIFT EWD ACROSS THE
NE PAC THEN STALL OVER THE FAR ERN PART OF THE NE PAC BY TUE
NIGHT. A GENERAL ELY FLOW WILL CONTINUE OVER SE AK THRU MIDWEEK.
MODELS STILL STRUGGLING WITH DETAILS ON SHORTWAVES MOVING WWD THRU
THE AREA...WITH THE MOST CONCERNING SHORTWAVE NOW OVER SRN ALBERTA
PROVINCE. LOOKS LIKE THIS FEATURE WILL DRIFT NW THRU SUN NIGHT
THEN DRIFT WWD ACROSS NRN BC EARLY NEXT WEEK. EVENTUALLY THE UPPER
LOW TO THE SOUTH WILL LIFT NWD THRU THE AREA...LIKELY DURING THE
LATTER HALF OF NEXT WEEK. ENDED UP USING A GFS/NAM BLEND MAINLY
FOR THE WAY THEY HANDLED THE WINDS OVER THE GULF FOR SUN- MON
PERIOD.
FOR SUN INTO MON...SMALL UPPER LOW OVER THE GULF WILL DRIFT NW
ACROSS THE NRN GULF EARLY IN THE PERIOD. THIS FEATURE WILL
INTERACT WITH SOME OF THE MOISTURE BEING ADVECTED IN FROM THE ESE
AND LIKELY CAUSE SOME RAIN OVER THE NE GULF AREA SUN MORNING.
WOULD EXPECT THIS PRECIP TO MOVE OUT SUN AFTERNOON AS UPPER LOW
PULLS AWAY FROM THE AREA AND SHORT WAVE RIDGING MOVES IN. THE
OTHER AREA THAT MIGHT GET SOME PRECIP DURING THIS PERIOD IS THE
FAR SE...WHERE SOME SHORTWAVE ENERGY WILL MOVE ACROSS FROM THE E.
THIS PRECIP LOOKS MORE SHOWERY...AND BY MON AFTERNOON...SOME
MODELS SUGGEST POTENTIAL FOR TSTMS IN THE HYDER AREA. DID NOT PUT
TSTMS IN YET DUE TO MODEL TIMING OF SHORTWAVE FEATURES AND
POSITION OF BEST INSTABILITY AND LOW LEVEL CONVERGENCE CHANGING
WITH EACH MODEL RUN. GFS DID SHOW NEGATIVE SHOWALTER INDEX
VALUES...WHICH WOULD ALLOW CONVECTION MOVING IN FROM THE E TO
SURVIVE LONGER EVEN IF LOWER LEVEL AIRMASS REMAINS ON THE COOL
SIDE.
FOR MON NIGHT INTO MIDWEEK...LOOKS LIKE MORE SHORTWAVE ENERGY
WILL BE MOVING IN FROM THE E DURING THIS TIME. BROUGHT IN MORE
CLOUDS TO MUCH OF THE AREA MON NIGHT AND TUE DUE TO POTENTIAL FOR
MID-LEVEL CLOUDS MOVING IN FROM THE E. ALSO WENT FOR A LARGER AREA
OF CHANCE POPS ESPECIALLY BY LATE TUE NIGHT DUE TO THE UNCERTAINTY
ON EXACT TRACK OF SHORTWAVE FEATURES. BLENDED IN WPC POPS WITH
PREVIOUS FORECAST TO DO THIS.
BETTER CHANCE FOR PRECIP SHOULD ARRIVE FOR THE LATTER HALF OF THE
WEEK AS UPPER LOW LIFTS NWD THRU THE ERN GULF. KEPT IN CHANCE TO
LIKELY POPS FOR MOST OF THE AREA WED NIGHT INTO FRI. ALL IN
ALL...FORECAST CONFIDENCE REMAINS BELOW AVERAGE DUE TO THE UPPER
AIR PATTERN WE ARE IN.
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY UNTIL 8 AM AKDT THIS MORNING FOR AKZ017.
MARINE...NONE.
&&
$$
JBT/RWT
000
FXAK67 PAJK 242357 CCA
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE JUNEAU AK
356 PM AKDT FRI MAY 24 2013
.SHORT TERM...WEATHER IS STILL RATHER QUIET ACROSS THE AREA BUT
THERE IS A BIT MORE TO TALK ABOUT TODAY. THE SUNNY WEATHER OF THE
PAST FEW DAYS HAS GIVEN WAY TO A MOSTLY CLOUDY TO OVERCAST MID TO
HIGH LEVEL DECK AND A FEW SCATTERED RAIN SHOWERS. THE SHOWERS
HAVE MAINLY BEEN CONFINED TO THE SOUTHERN PANHANDLE AND ALONG THE
COAST MOUNTAINS AS KETCHIKAN, JUNEAU, AND STEWART, BRITISH
COLUMBIA HAVE ALL REPORTED SOME VERY LIGHT RAIN SHOWERS TODAY.
THIS IS THE RESULT OF A LOW IN BRITISH COLUMBIA THAT IS SENDING
SOME WEAK UPPER LEVEL WAVES OVER THE COAST MOUNTAINS. HOWEVER LOW
LEVEL OFFSHORE FLOW IS DRYING OUT THE LOWER LAYERS OF THE
ATMOSPHERE CREATING A RATHER SUBSTANTIAL WARM AND DRY LAYER IN
UPPER AIR SOUNDINGS PARTICULARLY IN THE NORTH, AND IS MAKING IT
HARD FOR THE RAIN THAT DOES MAKE IT OVER THE MOUNTAINS TO REACH
THE SURFACE.
THIS HIGH TO MID LEVEL CLOUD LAYER AND THE SHOWERS WILL CONTINUE
INTO TOMORROW AS MORE WEAK UPPER LEVEL WAVES MOVE THROUGH AND TRY
TO OVERCOME THE LOW LEVEL OFFSHORE FLOW. CHANCE TO SLIGHT CHANCE
POPS AND MOSTLY CLOUDY TO CLOUDY SKIES REMAIN IN THE FORECAST FOR
MOST AREAS OF THE PANHANDLE INTO TOMORROW. WITH THE HIGHEST POPS
CONCENTRATED NEAR THE COAST MOUNTAINS OR THE SOUTHERN PANHANDLE.
THE EXCEPTION IS YAKUTAT SINCE IT WILL REMAIN MOSTLY DRY AS IT IS
TOO FAR WEST FOR THE WEAK WAVES TO REACH IT.
MEANWHILE THE OUTER COAST WILL HAVE DRIER CONDITIONS BUT WILL
HAVE TO DEAL WITH THE MARINE LAYER CLOUDS AND FOG AGAIN TONIGHT.
LAST NIGHT SAW THE MARINE LAYER CREEP INTO YAKUTAT, CROSS SOUND,
PELICAN, SITKA, AND KLAWOCK WITH REDUCED VISIBILITIES OBSERVED AT
THE FORMER THREE. I EXPECT A REPEAT PERFORMANCE TONIGHT WITH THE
LOW CLOUDS POSSIBLY GETTING TO GUSTAVUS AND HYDABURG LATE TONIGHT
BEFORE THEY RETREAT AGAIN TOMORROW MORNING.
WITH ALL THE CLOUDS AROUND TEMPERATURES TODAY AND TOMORROW WILL
NOT BE AS WARM AS THEY WERE YESTERDAY. MOST PLACES WILL MOST
LIKELY ONLY MAKE THE UPPER 50 TO LOW 60S TOMORROW. HOWEVER THIS
WILL ALSO RESULT IN WARMER OVERNIGHT LOWS AS THE HIGH OVERCAST
PREVENTS A RAPID COOLING EFFECT FROM RADIATIONAL COOLING. AS A
SECONDARY RESULT, SEA BREEZE CIRCULATIONS WILL NOT BE AS STRONG
OVER THE NEXT 24 HOURS EITHER.
FIRE WEATHER. FUEL CONDITIONS REMAIN DRY OVER THE NORTHERN
PANHANDLE TODAY. WHILE HUMIDITY VALUES MOISTENED UP OVERNIGHT THE
SKAGWAY AND HAINES AREAS ALREADY HAVE HUMIDITY VALUES IN THE
25 TO 35 PERCENT RANGE. SKAGWAY ALSO HAD A BRIEF BURST OF WIND
THIS MORNING SO FOR A SHORT TIME SOME VERY HIGH FIRE DANGER DID
EXIST IN SKAGWAY THIS MORNING. THOSE WINDS HAVE SINCE SLACKENED
OFF A BIT AND WILL CONTINUE TO DECLINE THIS AFTERNOON. PLUS, WITH
THE HIGH CLOUDS MOVING IN THE AIR TEMPERATURE IS NOT EXPECTED TO
REACH MUCH HIGHER THAN IT ALREADY IS. SO EXTREME FIRE WEATHER
CONDITIONS ARE NOT EXPECTED FOR THE REST OF THE DAY BUT WILL BE
WATCHED CLOSELY. DEW POINT TEMPERATURES ARE EXPECTED TO RISE
TOMORROW AS LOW LEVEL FLOW TURNS TO THE SOUTH AND WITH CONTINUED
CLOUD COVER TEMPERATURES WILL REMAIN LOW SO NO EXTREME FIRE
DANGER IS EXPECTED FOR TOMORROW AT THIS POINT.
SHORT RANGE MODELS WERE IN GOOD AGREEMENT ON OVERALL FEATURES.
ALTHOUGH THERE WERE SOME CONSISTENCY ISSUES ON HOW THE MODELS
HANDLED THE PRECIP ONCE IT GOT OVER THE MOUNTAINS. GFS IN A
PREVIOUS RUN WAS A BIT OVERAGGRESSIVE BRINGING THE PRECIP ACROSS
THE SOUTHERN PANHANDLE TODAY. DECIDED ON USING THE NAM WITH A BIT
OF THE ECMWF OR GFS HERE AND THERE. FORECAST CONFIDENCE IS ABOVE
AVERAGE.
&&
.LONG TERM...MODELS REMAIN IN GENERAL AGREEMENT WITH A WEAKENING
RIDGE OF HIGH PRESSURE THROUGH MONDAY ACROSS THE EASTERN GULF AND
THE PANHANDLE FOLLOWED BY A WEAK FRONTAL PASSAGE ASSOCIATED WITH A
LOW IN THE GULF THROUGH THE MIDDLE OF NEXT WEEK. THE LOW WILL
EXPAND ITS AREA TO BECOME A BROAD ACROSS SOUTHEAST ALASKA. BLENDED
THE PRESSURE FIELD WITH THE GFS AND ECMWF FOR THEIR GOOD CONSENSUS
THROUGH LATE WEDNESDAY THEN USED THE NEW WPC OUTPUTS FOR THE
REMAINING PERIODS. USED 50/50 OF THE GFS AND ECMWF FOR POPS AND
QPF VALUES FOR ENTIRE PERIODS.
A DEVELOPING LOW IN THE WESTERN GULF EARLY NEXT WEEK WILL
CONTINUE TO EXPAND OVER THE GULF AND WEAKEN THE RIDGE OF HIGH
PRESSURE TO THE EAST. AS THE RIDGE WEAKENS AND DISSIPATES THE
EXPANDING LOW WILL BECOME A BROAD AREA OF LOW PRESSURE ACROSS
SOUTHEAST ALASKA BY THE MIDDLE OF NEXT WEEK. THE WEAK FRONTAL
PASSAGE WILL BRING LIKELY POPS TO THE CENTRAL AND SOUTHERN
PANHANDLE COASTAL AREAS WEDNESDAY AND WEDNESDAY NIGHT BEFORE
DISSIPATING BY LATE WEDNESDAY NIGHT. AS THE LOW BECOMES A BROAD
AREA ACROSS SOUTHEAST ALASKA...THE EXTENDED FORECAST GOES MOSTLY
CLOUDY SKIES WITH A CHANCE POP AND NO SIGNIFICANT WINDS/SEAS.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
&&
$$
EAL/AHN
000
FXAK67 PAJK 242340
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
340 PM AKDT FRI MAY 24 2013
.SHORT TERM...WEATHER IS STILL RATHER QUIET ACROSS THE AREA BUT
THERE IS A BIT MORE TO TALK ABOUT TODAY. THE SUNNY WEATHER OF THE
PAST FEW DAYS HAS GIVEN WAY TO A MOSTLY CLOUDY TO OVERCAST MID TO
HIGH LEVEL DECK AND A FEW SCATTERED RAIN SHOWERS. THE SHOWERS
HAVE MAINLY BEEN CONFINED TO THE SOUTHERN PANHANDLE AND ALONG THE
COAST MOUNTAINS AS KETCHIKAN, JUNEAU, AND STEWART, BRITISH
COLUMBIA HAVE ALL REPORTED SOME VERY LIGHT RAIN SHOWERS TODAY.
THIS IS THE RESULT OF A LOW IN BRITISH COLUMBIA THAT IS SENDING
SOME WEAK UPPER LEVEL WAVES OVER THE COAST MOUNTAINS. HOWEVER LOW
LEVEL OFFSHORE FLOW IS DRYING OUT THE LOWER LAYERS OF THE
ATMOSPHERE CREATING A RATHER SUBSTANTIAL WARM AND DRY LAYER IN
UPPER AIR SOUNDINGS PARTICULARLY IN THE NORTH, AND IS MAKING IT
HARD FOR THE RAIN THAT DOES MAKE IT OVER THE MOUNTAINS TO REACH
THE SURFACE.
THIS HIGH TO MID LEVEL CLOUD LAYER AND THE SHOWERS WILL CONTINUE
INTO TOMORROW AS MORE WEAK UPPER LEVEL WAVES MOVE THROUGH AND TRY
TO OVERCOME THE LOW LEVEL OFFSHORE FLOW. CHANCE TO SLIGHT CHANCE
POPS AND MOSTLY CLOUDY TO CLOUDY SKIES REMAIN IN THE FORECAST FOR
MOST AREAS OF THE PANHANDLE INTO TOMORROW. WITH THE HIGHEST POPS
CONCENTRATED NEAR THE COAST MOUNTAINS OR THE SOUTHERN PANHANDLE.
THE EXCEPTION IS YAKUTAT SINCE IT WILL REMAIN MOSTLY DRY AS IT IS
TOO FAR WEST FOR THE WEAK WAVES TO REACH IT.
MEANWHILE THE OUTER COAST WILL HAVE DRIER CONDITIONS BUT WILL
HAVE TO DEAL WITH THE MARINE LAYER CLOUDS AND FOG AGAIN TONIGHT.
LAST NIGHT SAW THE MARINE LAYER CREEP INTO YAKUTAT, CROSS SOUND,
PELICAN, SITKA, AND KLAWOCK WITH REDUCED VISIBILITIES OBSERVED AT
THE FORMER THREE. I EXPECT A REPEAT PERFORMANCE TONIGHT WITH THE
LOW CLOUDS POSSIBLY GETTING TO GUSTAVUS AND HYDABURG LATE TONIGHT
BEFORE THEY RETREAT AGAIN TOMORROW MORNING.
WITH ALL THE CLOUDS AROUND TEMPERATURES TODAY AND TOMORROW WILL
NOT BE AS WARM AS THEY WERE YESTERDAY. MOST PLACES WILL MOST
LIKELY ONLY MAKE THE UPPER 50 TO LOW 60S TOMORROW. HOWEVER THIS
WILL ALSO RESULT IN WARMER OVERNIGHT LOWS AS THE HIGH OVERCAST
PREVENTS A RAPID COOLING EFFECT FROM RADIATIONAL COOLING. AS A
SECONDARY RESULT, SEA BREEZE CIRCULATIONS WILL NOT BE AS STRONG
OVER THE NEXT 24 HOURS EITHER.
FIRE WEATHER. FUEL CONDITIONS REMAIN DRY OVER THE NORTHERN
PANHANDLE TODAY. WHILE HUMIDITY VALUES MOISTENED UP OVERNIGHT THE
SKAGWAY AND HAINES AREAS ALREADY HAVE HUMIDITY VALUES IN THE
25 TO 35 PERCENT RANGE. SKAGWAY ALSO HAD A BRIEF BURST OF WIND
THIS MORNING SO FOR A SHORT TIME SOME VERY HIGH FIRE DANGER DID
EXIST IN SKAGWAY THIS MORNING. THOSE WINDS HAVE SINCE SLACKENED
OFF A BIT AND WILL CONTINUE TO DECLINE THIS AFTERNOON. PLUS, WITH
THE HIGH CLOUDS MOVING IN THE AIR TEMPERATURE IS NOT EXPECTED TO
REACH MUCH HIGHER THAN IT ALREADY IS. SO EXTREME FIRE WEATHER
CONDITIONS ARE NOT EXPECTED FOR THE REST OF THE DAY BUT WILL BE
WATCHED CLOSELY. DEW POINT TEMPERATURES ARE EXPECTED TO RISE
TOMORROW AS LOW LEVEL FLOW TURNS TO THE SOUTH AND WITH CONTINUED
CLOUD COVER TEMPERATURES WILL REMAIN LOW SO NO EXTREME FIRE
DANGER IS EXPECTED FOR TOMORROW AT THIS POINT.
SHORT RANGE MODELS WERE IN GOOD AGREEMENT ON OVERALL FEATURES.
ALTHOUGH THERE WERE SOME CONSISTENCY ISSUES ON HOW THE MODELS
HANDLED THE PRECIP ONCE IT GOT OVER THE MOUNTAINS. GFS IN A
PREVIOUS RUN WAS A BIT OVERAGGRESSIVE BRINGING THE PRECIP ACROSS
THE SOUTHERN PANHANDLE TODAY. DECIDED ON USING THE NAM WITH A BIT
OF THE ECMWF OR GFS HERE AND THERE. FORECAST CONFIDENCE IS ABOVE
AVERAGE.
&&
.LONG TERM...MODELS REMAIN IN GENERAL AGREEMENT WITH A WEAKENING
RIDGE OF HIGH PRESSURE THROUGH MONDAY ACROSS THE EASTERN GULF AND
THE PANHANDLE FOLLOWED BY A WEAK FRONTAL PASSAGE ASSOCIATED WITH A
LOW IN THE GULF THROUGH THE MIDDLE OF NEXT WEEK. THE LOW WILL
EXPAND ITS AREA TO BECOME A BROAD ACROSS SOUTHEAST ALASKA. BLENDED
THE PRESSURE FIELD WITH THE GFS AND ECMWF FOR THEIR GOOD CONSENSUS
THROUGH LATE WEDNESDAY THEN USED THE NEW WPC OUTPUTS FOR THE
REMAINING PERIODS. USED 50/50 OF THE GFS AND ECMWF FOR POPS AND
QPF VALUES FOR ENTIRE PERIODS.
A DEVELOPING LOW IN THE NORTHERN GULF EARLY NEXT WEEK WILL
CONTINUE TO EXPAND OVER THE GULF AND WEAKEN THE RIDGE OF HIGH
PRESSURE TO THE EAST. AS THE RIDGE WEAKENS AND DISSIPATES THE
EXPANDING LOW WILL BECOME A BROAD AREA OF LOW PRESSURE ACROSS
SOUTHEAST ALASKA BY THE MIDDLE OF NEXT WEEK. THE WEAK FRONTAL
PASSAGE WILL BRING LIKELY POPS TO THE CENTRAL AND SOUTHERN
PANHANDLE COASTAL AREAS WEDNESDAY AND WEDNESDAY NIGHT BEFORE
DISSIPATING BY LATE WEDNESDAY NIGHT. AS THE LOW BECOMES A BROAD
AREA ACROSS SOUTHEAST ALASKA...THE EXTENDED FORECAST GOES MOSTLY
CLOUDY SKIES WITH A CHANCE POP AND NO SIGNIFICANT WINDS/SEAS.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
&&
$$
EAL/AHN
000
FXAK67 PAJK 241445
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
645 AM AKDT FRI MAY 24 2013
.SHORT TERM...MOSTLY CLOUDY SKIES OVER THE PANHANDLE THIS MORNING,
WITH RAIN DEVELOPING IN MUCH OF SOUTHERN SOUTHEAST ALASKA BY THIS
AFTERNOON. RELATIVELY LIGHT WINDS WILL PERSIST, AND ONLY CROSS
SOUND HAS BEEN GIVEN A SMALL CRAFT ADVISORY. THIS SHORT RANGE
SECTION CONCLUDES WITH AN ANALYSIS OF A WARMING EVENT THAT TOOK
PLACE AT SKAGWAY EARLY THIS MORNING.
THE LARGEST ADJUSTMENTS TO THE SHORT RANGE FORECASTS ARE FOR
RAISING THE CLOUD COVER AMOUNTS FOR MOST OF THE AREA OF
RESPONSIBILITY. NOTE THE CLOUD COVER INCREASES ARE RAISED IN THREE
WAYS: FIRST, THE GOES VI SABLE IMAGERY THIS MORNING REVEALS AN
EXTENSIVE COVERAGE OF SEA STRATUS AND THE ONSHORE THE PANHANDLE.
SECOND, PATCHES OF FOG HAVE BEEN REPORTED AND PATCHY FOG WILL
DEVELOP TONIGHT. THIRD WE HAVE RAISED AMOUNTS OF MID AND UPPER
LEVEL DECK WITH CAUSES THAT ARE DISCUSSED IN THE NEXT PARAGRAPH.
CONFIDENCE IS AVERAGE.
A 500H LOW OVER THE SEATTLE VICINITY HAS A SYNOPTIC-SCALE FLOW
THAT EXTENDS AS FAR AS CENTRAL B.C. THE GOES IR LOOP DEPICTS THE
UPPER LEVEL EAST FLOW REACHING SOUTHERN SOUTHEAST ALASKA WITH
CLOUD COVER FROM THE WEAKENING OF SMALLER-SCALE CYCLONIC FEATURES.
A 500H RIDGE EXTENDS WSW FROM OVER GREAT BEAR LAKE AND OVER THE
CENTRAL PANHANDLE. WE SOMETIMES CALL A RIDGE ALOFT "DIRTY" IF
SHORT WAVES ARE ABLE TO TRAVEL THROUGH IT, EVEN IF THESE WAVES ARE
WEAKENING. IN THE PRESENT CASE, WE HAVE A DIRTY RIDGE THAT IS
WEAKENING THE SHORT WAVES ENOUGH TO LIMIT PRECIPITATION, HOWEVER
THE CLOUD MASS AT MID AND UPPER LEVELS WILL CONTINUE TO BE
CEILINGS.
MODELS: THE GFS MODEL RUN AT 24.00 WAS EASIER TO RECONCILE WITH
OBSERVABLE FEATURES ALOFT, AND THE MODEL HAS HAD A HIGHER POP
FIELD FARTHER WEST ACROSS THE SOUTHERN PANHANDLE. IN THIS WESTERN
EXTENT OF THE RAISED POPS AS WELL AS FOR CLOUD COVER, THE GFS WAS
AN OUTLIER, AND CORRECT.
THE YAKUTAT AND ANNETTE ISLAND RAOBS AT 12Z SHOW STRONG SUBSIDENCE
INVERSIONS. THE YAKUTAT RAOB INVERSION INCLUDES A MEASUREMENT OF
9C AT 900H, AND IF SUCH A VALUE IS ADIABATICALLY SUBSIDED TO NEAR
SEA LEVEL, WOULD BE 18C, OR 64F. A SIMILAR SUBSIDENCE EVENT RAISED
THE TEMPERATURES AT SKAGWAY THIS MORNING. THE SKAGWAY AIRPORT AT
3 AM REPORTED A TEMPERATURE OF 50F WITH CALM WINDS. BY 4 AM THAT
AIRPORT HAD WINDS FROM THE NORTH AT 7KT WITH GUSTS TO 14KT AND A
SURFACE TEMPERATURE OF 60F. DURING THE SAME TWO HOUR PERIOD THE
DEW POINT WENT DOWN FROM 37F TO 30F. THE NORTH WINDS AT SKAGWAY
PROVIDED THE DRY ADIABATIC PROCESS THIS MORNING.
.LONG TERM...AREA WILL REMAIN UNDER A GENERALLY E-SE FLOW ALOFT
OVER THE NEXT 5-7 DAYS...WITH UPPER RIDGE/HIGH REMAINING TO THE NE
OF THE AREA AND UPPER TROF TO THE SW. THIS PATTERN IS OFTEN NOT
HANDLED WELL BY THE MODELS AS FAR AS THE DETAILS GO. WILL PROBABLY
HAVE WEAK SHORTWAVE FEATURES MOVE ACROSS THE AREA FROM THE E
DURING THE PERIOD...BUT THE GFS AND ECMWF DO SUGGEST A SHARPER
LOBE OF THE UPPER RIDGE/HIGH TO THE NE WILL EXTEND INTO THE AREA
AT LEAST SUN-TUE...WHICH WOULD TEND TO WEAKEN THE SHORTWAVES.
ALSO...WILL HAVE A SMALL UPPER LOW LOOP AROUND THE ERN GULF SAT
THRU SUN THEN PULL NW AND OUT OF THE AREA BY EARLY NEXT WEEK.
AFTER COORD WITH WFO PAFC WENT WITH A BLEND OF THE 00Z GFS AND
ECMWF.
FOR SAT...WEAK SHORTWAVE WILL DRIFT NW ACROSS THE AREA WITH BANDS
OF MID-LEVEL CLOUDS AND POSSIBLY A LITTLE PRECIP. BEST CHANCES FOR
PRECIP APPEAR TO BE ALONG THE COAST MTNS WITH A WEAK ONSHORE FLOW
IN LOWER LEVELS AND SOME MID-LEVEL WARM ADVECTION OVER THE TOP.
FOR SAT NIGHT INTO SUN...UPPER LOW WILL DRIFT N THEN NW THRU THE
ERN GULF. THIS WILL INTERACT WITH THE LEFTOVER MOISTURE FROM THE
SAT SHORTWAVE AND MAY ORGANIZE PRECIP OVER THE NE GULF AND
ADJACENT COASTAL AREA. KEPT IN CHANCE POPS THERE TO HANDLE THIS
SYSTEM. FURTHER INLAND AND S...POPS SHOULD LOWER AS THE SHARPER
LOBE OF THE UPPER RIDGE/HIGH BEGINS TO AFFECT THE AREA. HAVE
LOWERED POPS SOME IN THESE AREAS. HAVE KEPT IN MOSTLY CLOUDY SKIES
THOUGH DUE TO WEAK ONSHORE FLOW KEEPING A STRATOCU LAYER IN.
FOR SUN NIGHT INTO TUE...SHARPER RIDGE LOBE SHOULD DOMINATE THE
AREA. THERE MAY BE SOME WEAK SHORTWAVE ENERGY DRIFTING ACROSS THE
FAR SERN AREA THOUGH...SO WILL KEEP IN LOW POPS THERE. OTHERWISE
SHOULD SEE MORE BREAKS IN THE CLOUDS ESPECIALLY MON. IF THE MODELS
MAINTAIN THE STRENGTH OF THE RIDGE LOBE OVER THE AREA...LATER
SHIFTS WILL LIKELY NEED TO DECREASE CLOUD COVER ESPECIALLY OVER
THE NRN AREA.
FROM MIDWEEK ON...LOOKS LIKE UPPER TROF TO THE SW WILL TRY TO
DRIFT CLOSER TO THE AREA AND THE RIDGE LOBE WILL WEAKEN. THIS
WOULD BRING IN A BETTER THREAT FOR PRECIP DUE TO INCREASED ELY
WAVE ACTIVITY. LEFT THE CHANCE POPS IN TO COVER THIS. PRECIP MAY
BE MORE SHOWERY AS WELL AS CONVECTION THAT FIRES OVER BC COULD
DRIFT WWD INTO THE AREA. THIS WILL NEED TO BE WATCHED CLOSELY.
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022.
&&
$$
JBT/RWT
000
FXAK67 PAJK 232332
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
332 PM AKDT THU MAY 23 2013
.SHORT TERM...ANOTHER QUIET AND SUNNY DAY ACROSS THE AREA TODAY
WITH SCATTERED HIGH CLOUDS MOVING THROUGH. THE EXCEPTION WAS IN
THE GULF AND ALONG THE OUTER COAST THIS MORNING AS THE MARINE
LAYER CLOUDS MADE THEIR PRESENCE KNOWN PARTICULARLY IN YAKUTAT
WHICH JUST BROKE OUT OF THE CLOUDS A LITTLE AFTER NOON.
TEMPERATURES ARE WELL ON THEIR WAY TO THE UPPER 50S AND MID 60S
TODAY WITH THE SUNNY WEATHER. WINDS ARE GENERALLY LESS THEN 20 KT
IN MOST PLACES WITH SEA BREEZE CIRCULATIONS BEING THE MAIN
DRIVER. THE EXCEPTION TO THIS IS CROSS SOUND WHICH HAS A NW SMALL
CRAFT THIS AFTERNOON.
FOR TONIGHT INTO TOMORROW, THE NICE WEATHER CONTINUES WITH MOSTLY
CLEAR TO PARTLY CLOUDY SKIES MOST PLACES TONIGHT AND INCREASING
HIGH TO MID LEVEL CLOUDS TOMORROW. THE INCREASING CLOUDS IS DUE TO
THE REMAINS OF A FRONT IN THE UPPER TO MID LEVELS MOVING NW FROM
SOUTHERN BRITISH COLUMBIA. THIS MAY BRING SOME SCATTERED SHOWERS
TO THE SOUTHERN PANHANDLE AND COAST MOUNTAINS TOMORROW. THE REST
OF THE PANHANDLE SHOULD STAY DRY AS LOW LEVEL FLOW IS STILL
OFFSHORE AND DOWNSLOPE. ALONG THE OUTER COAST, THE MARINE LAYER
CLOUDS WILL RETURN TONIGHT BRINGING MORE OVERCAST SKIES BEFORE
THEY BURN OFF AGAIN TOMORROW MORNING.
WITH THE INCREASING CLOUDS TOMORROW, THE HIGHS WILL NOT BE QUITE
AS WARM AS THEY WERE TODAY ESPECIALLY IN THE SOUTH. GOING FOR
UPPER 50S TO LOW 60S DOWN SOUTH WHILE IN THE NORTH, WHERE THE
CLOUDS WILL NOT COME IN UNTIL LATER IN THE DAY, WILL GET INTO THE
LOW TO MID 60S.
FIRE WEATHER. FUEL CONDITIONS HAVE DRIED OUT IN MOST NORTHERN
PANHANDLE LOCATIONS ACCORDING TO AICC. HOWEVER, WIND HAS BEEN LOW
AND HUMIDITY VALUES HAVE NOT DROPPED MUCH LOWER THEN 30 TO 40
PERCENT. THE PLACE THAT HAS THE BEST CHANCE OF EXTREME FIRE DANGER
IS SKAGWAY WHERE THE HUMIDITY HAS FALLEN TO 24 PERCENT SO FAR
TODAY. DO NOT THINK THAT IT WILL REACH RED FLAG CRITERIA TODAY BUT
IT WILL GET CLOSE. TOMORROW AFTERNOON WILL LIKELY HAVE THE SAME
CONDITIONS BUT DEW POINTS MIGHT BE A BIT HIGHER THEN THEY ARE
TODAY SO DON`T ANTICIPATE A RED FLAG WARNING NEEDED TOMORROW
EITHER.
SHORT RANGE MODELS WERE IN GOOD AGREEMENT TODAY. DECIDED ON USING
THE NAM AND ECMWF AGAIN TODAY FOR THE DETAIL THAT THEY PROVIDED.
FORECAST CONFIDENCE IS A LITTLE ABOVE AVERAGE.
&&
.LONG TERM...THE RIDGE OVER THE GULF ALASKA REMAINS ONE OF PRIMARY
FEATURE AFFECTING SOUTHEAST ALASKA. EASTERLY FLOW TRYING TO SPREAD
CLOUDS AND LIGHT RAIN ACROSS THE COAST MOUNTAINS IN THE SOUTHEAST
PORTIONS OF THE PANHANDLE. FURTHER WEST AN OLD PARENT LOW OVER THE
SOUTHERN BERING SEA IS SPREADING A WEAKENING BAND/WEAK LOW ACROSS
THE SOUTHERN GULF. THINK THAT THE LOW WILL HEAD SOUTHEAST AND
THE FRONT WILL BE LIKELY SHEERING OUT OVER THE CENTRAL GULF. THERE
IS A SMALL VORTICITY LOBE THAT WILL BE ROTATING INTO THE NORTHERN
GULF AND THAT MAY TRY AND POP A FEW SMALL SHOWERS OVER THE
NORTHEAST PANHANDLE AREA LATE SATURDAY TO SUNDAY. IT SORT OF
DEPENDS AMOUNT OF MOIST THAT IS STREAMING ACROSS THE PANHANDLE.
HEADED INTO EARLY NEXT WEEK A LOW WILL LIKELY BE ESTABLISHING
ITSELF SOUTH OF KODIAK ISLAND AND THE RIDGE WILL BE LIMITED TO
PANHANDLE AND COAST MOUNTAIN AREA. THROUGH THE MIDDLE PART OF THE
WEEK EXPECT THE PANHANDLE AREA TO BE ABSORBED INTO A BROAD WEAK
AREA OF LOW PRESSURE THE PANHANDLE AREA IN THE CENTER OF THE
REGION. AS RESULT A LARGE PORTION OF THE EXTENDED FORECAST IS
MOSTLY CLOUDY, LIGHT WINDS AND POSSIBLY A CHANCE OF RAIN.
CONFIDENCE IN THE LATER PERIODS IS LOW OTHER THAN THE GENERALITY I
MENTIONED ABOVE, AS TO HOW MUCH IF ANY RAIN WILL FALL AND THEN HOW
MUCH. FOR THE MOST PART INTO THE HOLIDAY WEEKEND THE FORECAST
SEEMS TO BE BEHAVING RATHER WELL WITH AN AVERAGE TO ABOVE AVERAGE
CONFIDENCE FACTOR.
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-033.
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041-042.
&&
$$
EAL/BEZENEK
000
FXAK67 PAJK 231429
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
629 AM AKDT THU MAY 23 2013
.SHORT TERM...THIS WAS A TRICKY FORECAST DEFINED BY RELATIVELY
LIGHT FLOW AND POORLY DEFINED FEATURES IN THE MODELS AND ON OTHER
TOOLS LIKE SATELLITE. LET US START WITH WHAT WE KNOW. WE ARE IN A
WARM PATTERN WITH LOTS OF SOUTHEASTERLY FLOW ALOFT AND
TEMPERATURES WILL ONCE AGAIN WARM WELL INTO THE 60S ACROSS THE
REGION TODAY. A FEW INTERIOR LOCATIONS WILL LIKELY SEE THE 70S
LIKE DEEPER PARTS OF THE MENDENHALL VALLEY. THINK IN THE FAR
NORTH LIKE SKAGWAY AND HAINES, TEMPERATURES WILL RECOVER NOW THAT
CLOUDS HAVE MOVED NORTH. WITH WEAKENING HIGH PRESSURE OVER THE
GULF OF ALASKA AND A THERMAL TROUGH OF LOW PRESSURE EXTENDING
NORTHWEST, MOST WINDS WILL BE NORTHWESTERLY ACROSS THE PANHANDLE.
AS INTERIOR PARTS WARM RAPIDLY THIS AFTERNOON, WE SHOULD SEE
ANOTHER SURGE OF WESTERLIES INTO THE OCEAN ENTRANCES, SIMILAR TO
YESTERDAY AND THUS HAVE BUMPED UP CROSS SOUND AND SOUTHERN
CHATHAM INTO SCA WINDS THIS AFTERNOON, AND EMPHASIZED SOME 25 KT
WINDS IN SUMNER WITHOUT PLACING THEM IN SMALL CRAFT ADVISORY. SEA
BREEZES WILL DEVELOP LATE MORNING INTO THE AFTERNOON BEFORE
SHUTTING OFF IN THE EVENING. WE ALSO HAVE A LOT OF SEA STRATUS
OFFSHORE WITH SOME FOG BEING REPORTED BY MARINERS. THE SEA
STRATUS REACHED YAKUTAT, SITKA, AND CROSS SOUND AROUND MIDNIGHT.
THIS IS SOMETHING WE EXPECTED AND SEE NO REASON WHY THE PATTERN
WILL VARY MUCH TONIGHT. FOG WAS ADDED ACROSS THE OFFSHORE ZONES
USING NAM BOUNDARY LAYER HUMIDITY FIELDS AND THE FACT THAT
CONFIRMATION HAS BEEN REPORTED.
NOW FOR THE TRICKY PART: SKY COVER...A LOT MORE HIGH AND
MID-LEVEL CLOUDS ARRIVED INTO THE SOUTHERN PANHANDLE YESTERDAY
EVENING AND OVERNIGHT THAN PREVIOUSLY THOUGHT. CANNOT SAY THAT
MECHANISMS WEREN`T REVEALED: THERE WAS SOME WEAK VORTICITY
ADVECTION RIDING OVER THE RIDGE ALOFT OVERNIGHT COMING FROM THE
SOUTHWEST. BUT MOST OF THE MODELS DID NOT SUGGEST CLOUD COVER OF
ANY SIGNIFICANCE, WITH THE EXCEPTION OF THE ECMWF...WHICH SEEMED
TO OVERCOMPENSATE FOR THE LACK OF CLOUDS IN THE OTHER MODELS.
WHILE CLOUD COVER ON IR SATELLITE IMAGERY OVERNIGHT SEEMS TO
SUGGEST WEAKENING...CLOUDS LOOKED THICKER THAN THOUGHT ON WEBCAMS
AND WITH COORDINATION FROM ANNETTE WSO, ELECTED TO CALL THINGS
MOSTLY CLOUDY IN THE SOUTH. BUT FEEL AS THOUGH THEY WILL HAVE
SOME SUNSHINE THIS AFTERNOON. THE IMPORTANT THING IS DRY WEATHER
HERE. CLOUD COVER OVER THE CENTRAL PANHANDLE SEEMED THINNER AND
LESS SHADOW INHIBITING, SO CALLED FOR MAINLY SUNNY CONDITIONS
HERE AND TO THE NORTH. FOR THE NORTHEAST GULF COAST, WORRIED THAT
MID TO HIGH LEVEL CLOUDS FROM THE WEST MAY TAMPER WITH SUNSHINE
THIS AFTERNOON AS MARINE LAYER BREAKS UP...SO WENT WITH PARTLY
CLOUDY FOR THIS AFTERNOON FOR YAKUTAT. CLOUD COVER TONIGHT WAS
EQUALLY CHALLENGING. MODELS...ESPECIALLY GFS SHOWING A SURGE OF
MOISTURE MOVING IN FROM THE SOUTHEAST. MOS GUIDANCE CLOUD COVER
HAS BEEN UNHELPFUL AS IT HAS CARED LITTLE ABOUT THE CURRENT
CONDITIONS OVER THE SOUTH. THINK SOME DOWN-SLOPING WILL TEND
TOWARD CLEARER CONDITIONS THAN WHAT MODELS ARE INDICATING, AND SO
HAVE LEFT THINGS MAINLY CLEAR FOR MUCH OF THE INTERIOR PANHANDLE
OVERNIGHT. BUT PARTLY CLOUDY SKIES MAY HAVE BEEN THE SAFER
ALTERNATIVE.
THIS WEAK VORTICITY CENTER OVER THE SOUTHEAST GULF IS FORECAST
TO WEAKEN AND MOVE NORTH AND AS IT DOES IT WILL PUMP MORE WARM
AIR OVER THE REGION FROM THE SOUTHEAST, AND WITH THAT INEVITABLY
COMES MOISTURE AS WELL. THE MOISTURE WILL BEGIN TO WORK THROUGH
THE SOUTHERN COAST MOUNTAINS THIS AFTERNOON THAT MAY BRING THE
THREAT OF AN ISOLATED OR SCATTERED SHOWER NEAR HYDER. THINGS
DISSIPATE QUICKLY OVER THE EVENING, BUT A MORE SIGNIFICANT LOBE
OF MOISTURE ARRIVES LATE THAT WILL SPREAD SCATTERED SHOWERS OVER
HYDER TOWARD THE EARLY FRIDAY MORNING HOURS. FOR MORE ABOUT THIS
ONSET OF SOME WETTER WEATHER FOR THE SOUTHERN PANHANDLE SEE THE
LONG TERM SEGMENT.
ONE FINAL NOTE ABOUT TEMPERATURES, COOLED THEM A LITTLE FOR THIS
AFTERNOON GIVEN OUR THINKING AT THE TIME THAT SKIES WOULD BE A
LITTLE CLOUDIER, SO IT COULD GET WARMER THAN ADVERTISED...ESPECIALLY
OVER THE NORTH. WHITE PASS TEMPERATURES WERE WARMED TONIGHT
THINKING AN INVERSION MAY SET IN BELOW KEEPING TEMPERATURES AT
PASS LEVEL RELATIVELY MILD. RELIED ON NAM 925 MB TEMPS FOR
GUIDANCE.
MODELS WERE HAVING A DIFFICULT TIME WITH SOME OF THE POSITIONING
AND STRENGTH OF THE SURFACE HIGH OFFSHORE, AND ESPECIALLY CLOUDS
OVER THE REGION. SO INSTEAD CHOSE NOT TO CHANGE PRESSURE FIELD
AND CONFINED WIND CHANGES TO LOCAL EFFECTS. RELIED ON SATELLITE
INTERPRETATION FOR CLOUD COVER AND LOCAL KNOWLEDGE OF SEA BREEZES
FOR HELP ON WINDS. FORECAST CONFIDENCE AVERAGE TO GOOD, BUT FALLS
FOR SKY COVER...ESPECIALLY OVER THE SOUTHERN AND EVEN THE CENTRAL
ZONES. LUCKILY, IMPACTS OF MISSED FORECAST WILL BE MINIMAL.
&&
.LONG TERM...THE EXTENDED FORECAST PERIOD LOOKS LIKE IT WILL BE
DOMINATED BY HIGH PRESSURE ALOFT CENTERED OVER WESTERN CANADA AND
EASTERN AK. THE PACIFIC STORM TRACK WILL STAY WELL SOUTH OF THE
PANHANDLE. A COLD UPPER LEVEL LOW CENTER PRODUCING RAIN AND MTN SNOW
IS STUCK OVER THE PAC NW. CLOUDINESS IS CURVING AROUND THIS LOW
AND MOVING NW OVER BRITISH COLUMBIA TOWARD SE AK. THE PANHANDLE WILL
BE UNDER THIS SE FLOW ALOFT THROUGH THE MIDDLE OF NEXT WEEK. THE
MAIN FORECAST CHALLENGE WILL BE DETERMINING IF AND HOW MUCH RAIN
WILL SPILL OVER THE COASTAL MOUNTAINS FROM BRITISH COLUMBIA AND
INTO SE AK. THIS WEATHER PATTERN FAVORS A BIT HIGHER CHANCE OF
RAIN OVER THE SOUTHERN PANHANDLE AND DRIER BUT CLOUDY WEATHER OVER
THE NORTHERN PANHANDLE. THERE IS BETTER AGREEMENT IN NEARLY ALL
MODELS AND NATIONAL WPC GUIDANCE THAT MAINTAIN TEMPS WILL REMAIN
AT OR ABOVE NORMAL THROUGH THE EXTENDED RANGE.
THE GFS ENSEMBLE MEAN WAS USED TO UPDATE THE GRID FORECASTS. THE
DETERMINISTIC HEMISPHERIC MODELS SUCH AS THE GFS EC AND GEM HAD
VARIOUS SOLUTIONS SO THE ENSEMBLE MEAN WAS IS AN EFFECTIVE
COMPROMISE FOR DESCRIBING THE GENERAL LARGE SCALE FEATURES.
FORECAST CONFIDENCE REGARDING THE LOCATION AND TIMING OF
PRECIPITATION IS LOW.
THE FIRST SHOT OF POSSIBLE PRECIPITATION OVER SE AK APPEARS TO
BE DURING THE DAY ON FRI OVER THE SOUTHERN ZONES. DEFORMATION
ALOFT AND AN INCREASINGLY MOIST AIR MASS COULD LEAD TO LIGHT RAIN
ESPECIALLY N AND E OF KETCHIKAN. THIS WILL LIKELY DISSIPATE AND
DRY OUT AS IT MOVES NORTH FRIDAY NIGHT. ANOTHER BATCH OF RAIN
SHOWERS COULD DEVELOP SAT AND SAT NIGHT OVER THE CENTRAL AND
NORTHERN COASTAL MOUNTAINS. RELATED TO THIS I LOWERED DAYTIME MAX
TEMPS A BIT FROM PREVIOUS FCSTS THROUGH THE WEEKEND. THE CHANCE
OF PRECIP DOES APPEAR TO BE HIGHER AND MORE WIDESPREAD BY MON AND
TUES BUT RAIN AMOUNTS ARE NOT SIGNIFICANT...CERTAINLY LESS THAN
THE LAST TWO VERY WET WEEKENDS IN SE AK.
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-033-041-042.
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043.
&&
$$
JWA/TA
000
FXAK67 PAJK 222225
AFDAJK
SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
225 PM AKDT WED MAY 22 2013
.SHORT TERM...RATHER QUIET ALONG THE PANHANDLE TODAY AS MOSTLY
CLEAR SKIES AND DRY WEATHER REMAIN THE NORM. THE EXCEPTIONS TO
THIS RULE TODAY ARE SKAGWAY AND HAINES WHERE A MID LEVEL CLOUD
DECK HAS GIVEN THEM OVERCAST SKIES AND COOLER WEATHER TODAY. THE
CLOUD COVER THERE IS THE RESULT OF A MID LEVEL LOW THAT IS MOVING
NORTH JUST TO THEIR NE. THE LOW IS JUST FAR ENOUGH EAST THAT THE
NORTHERLY MID LEVEL FLOW IS DRAGGING THE CLOUDS OVER HAINES AND
SKAGWAY AND HAS PUSHED THE CLOUDS AS FAR SOUTH AS BERNER`S BAY
AND LENA POINT. AS THIS MID LEVEL LOW MOVES NORTH THIS EVENING
THE MID LEVEL FLOW SHOULD TURN MORE NW THEN W AND EVENTUALLY
CLEAR THE CLOUDS OUT OF THE AREA. THERE ALREADY IS EVIDENCE OF
THIS STARTING TO OCCUR ON RECENT SATELLITE IMAGES.
WINDS ARE BECOMING LESS OF A CONCERN AS THE INVERTED TROUGH OVER
THE PANHANDLE SLOWLY WEAKENS. CURRENTLY THE ONLY PLACES WITH
SMALL CRAFT WINDS ARE LYNN CANAL, STEPHENS PASSAGE, AND THE SE
GULF. THE FORMER TWO ARE ON A SLOW DECREASING TREND AT THE MOMENT
AND SHOULD DROP BELOW SMALL CRAFT BY THIS EVENING.
FOR TONIGHT AND TOMORROW, THE CLOUDS OVER THE EXTREME NORTH WILL
DIMINISH THIS EVENING AS THE MID LEVEL LOW MOVES NORTHWARD. SAME
FOR THE HIGH LEVEL CLOUDS THAT ARE SCATTERED OVER THE SOUTHERN
PANHANDLE. THESE WILL BE REPLACED ALONG THE OUTER COAST AND THE
GULF BY THE RETURN OF THE MARINE LAYER CLOUDS AS THE RIDGE THAT
IS IN THE GULF FLATTENS TONIGHT. SATELLITE IMAGES ALREADY SHOW
SOME MARINE LAYER CLOUDS STARTING TO FORM IN THE EASTERN GULF.
THESE CLOUDS SHOULD SPREAD ACROSS MOST OF THE GULF TONIGHT AND
MAY ENCROACH INTO YAKUTAT, CROSS SOUND, SITKA, AND THE EXTREME
WESTERN PARTS OF PRINCE OF WALES ISLAND. THESE CLOUDS WILL THEN
DO THEIR USUAL RETREAT OUT INTO THE GULF TOMORROW WITH THE DAY
TIME HEATING. OTHERWISE MOST AREAS WILL REMAIN DRY AND MOSTLY
CLEAR.
WINDS WILL NOT BE MUCH OF A CONCERN OVER THE PANHANDLE FOR THE
NEXT 24 HOURS. BESIDES THE USUAL SEA BREEZE PATTERNS MOST AREAS
WILL REMAIN BELOW 20 KT. THE SE GULF IS A DIFFERENT STORY, THE
CONTINUED INTERACTION BETWEEN THE GULF HIGH AND THE BRITISH
COLUMBIA LOW WILL CONTINUE TO CAUSE 25 KT NW WINDS IN THE SE GULF
THROUGH AT LEAST MIDDAY TOMORROW AS THE HIGH SLOWLY WEAKENS.
FIRE WEATHER. CLOUD COVER OVER THE EXTREME NORTHERN PANHANDLE
HAS SO FAR PREVENTED ANY DRASTICALLY LOW HUMIDITIES FROM
OCCURRING IN SKAGWAY TODAY. AIR TEMPERATURES AT SKAGWAY HAVE ONLY
RISEN INTO THE MID 50S AND WITH DEW POINTS HAVING RISEN OVERNIGHT
TO AROUND 30, THE RELATIVE HUMIDITY HAS BEEN HOLDING AROUND
40 PERCENT. WINDS HAVE ALSO BEEN 15 MPH OR LESS TODAY SO NO RED
FLAG WARNING WAS ISSUED. WE WILL CONTINUE TO MONITOR FIRE WEATHER
CONDITIONS IN THE AREA TOMORROW AS WITH CLEARER SKIES THE DAYTIME
TEMPERATURES ARE EXPECTED TO RISE AGAIN AND FUEL CONDITIONS
REMAIN DRY, BUT WITH INCREASING DEW POINT TEMPERATURES AND
CONTINUED LIGHTER WINDS IT IS BECOMING LESS OF A CONCERN THAT RED
FLAG CONDITIONS WILL BE REACHED TOMORROW. FUEL MOISTURE LEVELS
REMAIN TOO MOIST IN OTHER AREAS OF THE PANHANDLE FOR EXTREME FIRE
WEATHER CONDITIONS TO DEVELOP.
SHORT RANGE MODELS WERE IN GOOD AGREEMENT TODAY WITH FEW
DIFFERENCES NOTED. DECIDED ON STICKING WITH THE NAM AND A LITTLE
OF THE ECMWF FOR UPDATES TO GET MORE OF THE DETAILS THAT THOSE
MODELS PROVIDE. FORECAST CONFIDENCE IS ABOVE AVERAGE.
&&
.LONG TERM...HIGH PRESSURE RIDGE OVER THE AK GULF THAT HAS BEEN
PROVIDING SUNNY DRY WEATHER WILL BREAK DOWN THROUGH THE WEEK. LOW
PRESSURE SYSTEM OVER BRITISH COLUMBIA WILL TRACK NORTHWARD WITH
POTENTIAL FOR RAIN MOVING WESTWARD OVER THE COAST MOUNTAINS.
MARINE LAYER OVER THE AK GULF WILL MOVE EASTWARD BUT STILL
UNCERTAIN TO ITS EASTWARD EXTENT OVER THE PANHANDLE. LOW PRESSURE
SYSTEM MOVING ACROSS THE NORTH PACIFIC WILL INTERACT WITH A
BERING SEA LOW AS IT PASSES SOUTH OF THE ALEUTIAN CHAIN.
INTERACTION BETWEEN THESE TOW SYSTEMS ALONG WITH THE BREAK DOWN
OF THE RIDGE LEAD TO HIGH UNCERTAINTY IN EXTENDED FORECAST. BY
THE WEEKEND A SERIES OF RESULTING WEAK LOW PRESSURE SYSTEM WILL
MOVE INTO THE AK GULF. OVERALL THE STRONGER CENTERS LOOK TO NOW
TRACK SOUTHWARD SO OVERALL PRECIP SHOULD BE ALONG THE SOUTHERN
PANHANDLE STARTING ON SUNDAY AND FOR AREAS ALONG THE COAST
MOUNTAINS FROM THE BC LOW. KEEPING INCREASING CLOUD COVER THROUGH
THE WEEKEND WITH THE ADVANCING MARINE LAYER AND LOW PRESSURE
SYSTEMS. NOT MUCH IN THE WAY OF PRESSURE GRADIENTS OR FRONTAL
BOUNDARIES SO WINDS THROUGH THE LONG RANGE SHOULD BE LESS THAN
20 KTS. TEMPERATURES ARE ALSO LOOKING HIGHLY VARIABLE BETWEEN
MODELS. GFS IS BRINGING IN A WARMER AIR MASS WITH POSITIVE
TEMPERATURE ANOMALIES OVER THE REGION WHILE NAM/ECMWF ARE COOLER
BY 4 TO 8 DEGREES F. CLOUD COVER WILL BE ONE OF THE MAIN ISSUE
REGARDING DAY TIME HIGHS WITH THE TRACKING OF MID LEVEL AIR
MASSES ANOTHER.
HAD FAIR AGREEMENT BETWEEN MODELS FOR PRESSURE AND WINDS OVER
THE GULF. MORE VARIATION FOR THE INVERTED TROUGH OVER THE
PANHANDLE. BLENDED IN SOME NAM/GFS WITH INHERITED GRID BUT
OVERALL LITTLE CHANGE THROUGH DAY 4. NEW WPC WAS A BLEND OF
ENSEMBLES AS OPERATIONAL MODELS ARE SHOWING LARGE DISCREPANCIES
WHILE ENSEMBLE SPREAD IS FAIRLY LOW. UPDATED GRIDS THROUGH DAY
8 WITH NEW WPC, ALSO WITH LITTLE OVERALL CHANGE. FORECAST
CONFIDENCE IS LOW AT THIS TIME DUE TO THE LARGE VARIATIONS
BETWEEN MODELS IN POOR RUN TO RUN CONSISTENCY.
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ041-042.
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043.
&&
$$
EAL/PRB
|
