Area Forecast Discussion
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FXAK67 PAJK 280125
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
425 PM AKST TUE JAN 27 2015

.SHORT TERM...A 982 MB LOW IN THE WESTERN GULF IS NEAR MAXIMUM
INTENSITY. AN OCCLUDED FRONT EXTENDS EAST FROM THE LOW TO A TRIPLE
POINT THE EAST-CENTRAL GULF, THEN SOUTH-SOUTHWEST AS A COLD FRONT INTO
THE NORTH PACIFIC. THE ENTIRE FRONTAL BOUNDARY IS GENERALLY
EXPANDING TO THE NORTH AND EAST, WITH THE OCCLUDED PORTION OVER
THE GULF BEGINNING TO SHEAR APART. THE FRONT SHOULD MAKE LANDFALL
OVER THE CENTRAL OUTER COAST LATE TONIGHT OR EARLY TOMORROW
MORNING WITH PRECIP BEGINNING AS RAIN FOR LOCATIONS SOUTH OF
ANGOON. EXCEPTION IS PETERSBURG WHERE UP TO AROUND 2 INCHES OF
SNOW IS FORECAST FROM LATE TONIGHT THROUGH NOON TOMORROW. FARTHER
NORTH, SNOW IS FORECAST TO START EARLY IN THE MORNING AND IS
EXPECTED TO PRODUCE 2 TO 3 INCHES THROUGH THE DAY FROM TENAKEE
SPRINGS NORTH, AND FROM THE OUTER COAST EAST TO THE COAST
MOUNTAINS. HEAVIEST SNOWFALL LOOKS LIKE IT WILL BE IN THE AREA
AROUND GUSTAVUS AND JUNEAU. FARTHER NORTH, THE OCCLUDED FRONT WILL
BE WEAKENING AS IT SHEARS APART. FARTHER SOUTH, RAIN WILL BE
MIXING IN WITH THE SNOW, LOWERING THE SNOW TO LIQUID RATIO. ITS
NOT A LOT, BUT BETTER THAN NOTHING.

AS THE FRONT SWEEPS NORTHWARD, THE NORTHEASTERLY PRESSURE GRADIENT
WILL INCREASE SHARPLY. HAVE A GALE WARNING OUT FOR NORTHERN LYNN
AS A RESULT AND WINDY CONDITIONS IN SKAGWAY. CONSIDERED PUTTING IN
A STRONG WIND HEADLINE AND I THINK AN OCCASIONAL 40 MPH GUST IS
PROBABLE, BUT THE MAJORITY OF THE WIND GUSTS SHOULD BE 35 MPH OR
SO. ELSEWHERE, ALSO HAVE A GALE WARNING OUT FOR EASTERLIES OUT OF CROSS
SOUND, MOST OF THE COASTAL MARINE ZONES, AND CLARENCE STRAIT.

USED A BLEND OF NAM AND GFS FOR UPDATES TO PRESSURE AND WIND
TODAY. POP AND QPF FROM AN EVEN BLEND OF GFS, GEM, AND ECMWF.
ADJUSTMENTS TO TEMPS PER GFS40. OVERALL FORECAST CONFIDENCE IS
AVERAGE TO SLIGHTLY ABOVE AVERAGE.

.LONG TERM...LOW PRESSURE WAVE WILL MOVE N INTO THE ERN GULF WED
NIGHT. LOOKS LIKE IT WILL DISSIPATE AS IT COMES ONSHORE OVER THE
NRN AREA THU MORNING. MODELS DIFFER ON TRACK SOMEWHAT FOR THU
THOUGH...SO CONFIDENCE IS FAIRLY LOW ON ITS TRACK. HIGH PRESSURE
WILL BUILD OVER MUCH OF INTERIOR AK AND NW CANADA FOR FRI INTO THE
WEEKEND. THIS WILL INCREASE NLY FLOW...AND GENERALLY DRY THINGS
OUT. USED BLEND OF THE 12Z GFS/18Z NAM FOR WED NIGHT/THU...THEN
TRANSITIONED TO A 12Z ECMWF/GEM BLEND BY LATE THU NIGHT AND FRI.
DID USE MORE WEIGHT TO THE ECMWF THOUGH DUE TO THE GEM OVERDOING
THE SFC HIGH. FOR FRI NIGHT ONWARD...BASICALLY USED WPC.

FOR WED NIGHT AND THU...PRECIP WILL INCREASE OVER THE MAIN PART OF
THE PANHANDLE AS LOW PRESSURE WAVE RIDES NWD. THE BIGGEST CONCERN
IS PTYPE FROM PAJN NWD. THE FURTHER W THE LOW MOVES...THE MORE
LIKELY LOW LEVEL FLOW WILL TURN SELY AND WARM LOW LEVEL TEMPS. IF
THE 12Z GFS/18Z NAM WORK OUT...MAY END UP WITH MORE SNOW FROM PAJN
NWD THAN CURRENTLY FORECAST. AT THIS POINT...UNTIL LOW TRACK IS
MORE CERTAIN...DECIDED TO USE RAIN AND SNOW FOR THE PAJN AREA.
AREAS TO THE N SHOULD BE MOSTLY SNOW. COULD SEE SEVERAL INCHES OF
SNOW FROM THIS ESPECIALLY OVER THE FAR N...AND LATER SHIFTS MAY
NEED TO ISSUE AT LEAST A WINTER WX ADVY. EVENTUALLY...SHOULD SEE
WARMER AIR MOVE IN THU...SO EVEN THE FAR NRN AREAS MAY GET SOME
RAIN TO MIX IN.

FOR THU NIGHT AND FRI...PRECIP OVER THE AREA WILL DIMINISH AS
OFFSHORE FLOW DEVELOPS. THIS MAY TAKE THE LONGEST OVER THE NRN
AREA THOUGH AS REMNANT OF FRONT SLOWLY DISSIPATES THERE. THINK IT
WILL BE MOSTLY DRY BY LATE IN THE DAY FRI OVER THE N. THE S SHOULD
DRY OUT SOONER...PROBABLY BY EARLY FRI MORNING.

FOR THE WEEKEND...DID LOWER POPS AND TEMPS. COLDER AIR SHOULD
FILTER INTO THE AREA ESPECIALLY OVER THE NRN HALF AS HIGH PRESSURE
BUILDS TO THE N. THINK MOST OTHER SYSTEMS WILL BE FORCED TO STAY
SW OF THE AREA DURING THE WEEKEND DUE TO THIS HIGH...ALTHOUGH A
FRONT MAY THREATEN THE FAR SRN AREAS SUN. MODEL DIFFERENCES GET
RATHER LARGE THOUGH HANDLING INDIVIDUAL SYSTEMS EMBEDDED IN THE
LARGER SCALE LOW TO THE S OF THE GULF...SO NOT OVERLY CONFIDENT ON
THIS ASPECT OF THE FORECAST. MAY SEE INCREASING THREAT FOR PRECIP
EARLY NEXT WEEK AS SOME SRN STREAM ENERGY TRIES TO MOVE IN. ALL IN
ALL...FORECAST CONFIDENCE IS BELOW AVERAGE.

&&

.AVIATION...FORECAST 850MB WINDS SUGGESTING THAT THERE WILL BE
WIDESPREAD LIGHT TO MODERATE TURBULENCE SOUTH OF THE ICY STRAIT
CORRIDOR THROUGH THE SHORT TERM PERIOD. LOCALIZED REDUCTIONS IN
VISIBILITIES IN HEAVIER SNOW WILL PRODUCE IMC CONDITIONS BELOW
CLOUD BASES, WHICH ARE EXPECTED TO BE IN THE 1500 FOOT RANGE OR
HIGHER. SEE THE AAWU AIRMETS SIERRA, AND TANGO FOR ADDITIONAL
DETAILS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ022-036-041>043-051.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-031>035-052-053.

&&

$$

FRITSCH/RWT

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