Area Forecast Discussion
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000
FXAK67 PAJK 292351
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
351 PM AKDT WED OCT 29 2014

.SHORT TERM...BIG CHANGE IN THE SHORT TERM FORECAST WITH A
DEVELOPING SYSTEM NEAR HAIDA GWAII THIS EVENING THAT WILL DEEPEN
TO GALE FORCE TONIGHT AS IT TRACKS NORTHWARD ALONG THE PANHANDLE
COAST. THE REASON FOR THIS CHANGE IS MODELS HAVE BEEN IN SUCH POOR
AGREEMENT AND SHOWING LARGE SHIFTS RUN TO RUN THAT MADE NAILING
DOWN A SOLUTION UNTIL LATE THIS MORNING DIFFICULT AT BEST. THE
12Z MODEL RUNS FINALLY LINED UP BETTER BETWEEN THE GFS/ECMWF/GEM
WITH THE NAM AS THE OUTLIER.

SATELLITE IMAGERY THIS MORNING SHOWING A 995 MB LOW
IN THE SOUTHWESTERN PORTION OF THE AK GULF WITH ASSOCIATED WEAK
FRONT MOVING OVER THE AK PANHANDLE. NOT MUCH FORCING AT UPPER
LEVELS WITH THE CURRENT FRONT WITH AN ELONGATED 500 MB VORT MAX.
RESULT HAS BEEN OVERCAST SKIES WITH PERIODS OF RAIN DIMINISHING
THROUGH THE DAY. COLD POOL OF AIR STILL ALONG HAINES HIGHWAY
CORRIDOR SO SAW SOME SNOW MIX IN WITH RAIN THIS MORNING, BUT NO
ACCUMULATION AT LOW LEVELS. EASTERLY TO SOUTHEASTERLY WINDS AT THE
SURFACE OVER THE SOUTHERN AND CENTRAL PANHANDLE WITH PRESSURE
GRADIENT BETWEEN THE GULF LOW AND WESTERN CANADIAN HIGH. WEAK
NORTHERLIES OVER THE NORTHERN PANHANDLE ALONG THE TILTED PRESSURE
FIELDS.

TEMPERATURE GRADIENT WITH COLDER AIR BEHIND THE FRONT AT 500 MB
WITH A WAVE FORMING AT 850 MB AND THE MODEL SURFACE PRESSURE
GRADIENT ALL FALLING LINE SUPPORTING THE GALE FORCE LOW DEVELOPMENT.
AN UPPER LEVEL WAVE NEAR HAIDA GWAII IS JUST STARTING TO SHOW ON
SATELLITE AND WILL DEEPEN TO 996 MB LATE THIS EVENING AS IT HUGS
THE COAST. SINCE THE LOW WILL MOVE RAPIDLY WINDS WILL INCREASE
THEN DROP OFF JUST AS RAPIDLY. LOW LEVEL 850 MB SOUTHEASTERLY JET OF 50
KT OVER THE COAST WILL PUSH NORTHWARD THROUGH THE EVENING.
EXPECTING GALES ALONG THE COASTAL WATERS AND WESTERN INNER
CHANNELS. THIS EVENING WITH SMALL CRAFT WINDS ELSEWHERE. STRONG
WINDS WILL DEVELOP ALONG THE PANHANDLE COASTAL AREAS THIS EVENING
FOR ZONE 27 THEN 23, BUT DROP OFF LATE TONIGHT INTO THURSDAY
MORNING. AS THE LOW MOVES NORTHWARD THE NORTH-SOUTH GRADIENT WILL
INCREASE WITH GALE FORCE WINDS DEVELOPING OVER NORTHERN LYNN CANAL

PRECIPITATION FROM THE CURRENT WEAK FRONT HAS BEEN DIMINISHING
THROUGH THE DAY OVER THE PANHANDLE BUT STILL HUGS THE COAST. NEXT BAND
ALONG THE DEVELOPING LOW WILL MOVE INLAND THROUGH THE EVENING
SOUTH TO NORTH. NOT SEEING A SIGNIFICANT MOISTURE FEED IN THE THE
CURRENT LOW BUT STILL SOME CONNECTION IN WATER VAPOR IMAGERY DOWN
TO 40 N. HEAVIEST PRECIP SHOULD STAY OFFSHORE WITH 6 HOUR QPF
VALUES IN THE UPWARDS OF ONE QUARTER OF AN INCH WITH HEAVIEST
BANDS OVER THE SOUTHERN PANHANDLE. SURFACE TEMPS STILL UNCERTAIN SINCE THE
LOW IS PULLING UP 850 MB TEMPS ABOVE 0 C TONIGHT BUT 500 MB TEMPS
IN THE -32 TO 36 C RANGE MOVE UP AS WELL. OVERALL NOT
MUCH CHANGE IN LOWS FROM PREVIOUS NIGHT, EXPECT FOR SOME SLIGHTLY
WARMER TEMPS OVER THE NORTHERN REGIONS. THUS NOT EXPECTING SNOW AT
THE SURFACE BUT 1 TO 2 INCHES AT HIGHER ELEVATIONS.

ALL MODELS HAD SHIFTED FROM PREVIOUS RUNS SO THE OPTION WAS TO
LEAVE INHERITED FORECAST AS IS OR HAVE A MAJOR CHANGE. SINCE THE
12Z GFS/ECMWF/GEM FINALLY FELL MORE IN LINE WITH STRENGTH AND
POSITION OF THE LOW WENT WITH THE BIG UPDATE. USED A 50/25/25
BLEND GFS/ECMWF/GEM FOR NEXT 24 HOURS, COUNTED NAM AS AN OUTLIER.
FORECAST CONFIDENCE IS STILL BELOW AVERAGE DUE TO THE MODEL
UNCERTAINTY.

.LONG TERM...CONFIDENCE IMPROVES A BIT EARLY ON IN THE EXTENDED
RANGE FORECAST PERIOD AS THE VERY POORLY MODELED LOW IN THE SHORT
TERM PERIOD WEAKENS OVER THE FAR NORTHERN GULF OR POSSIBLY GETS
ABSORBED BY A VERY LARGE LOW AND ASSOCIATED FRONT APPROACHING FROM
THE WEST. NAM, GFS, AND GEM CURRENTLY EXHIBITING GOOD AGREEMENT ON
THE STRENGTH AND TRACK OF THIS LOW...ACROSS THE PENINSULA AND INTO
THE WESTERN GULF SATURDAY MORNING. ECMWF IS MUCH FARTHER TO THE
WEST WITH THE PARENT LOW, BUT DOES SPIN UP A TRIPLE POINT FEATURE
IN THE SAME GENERAL LOCATION AS THE OTHER THREE, OVER THE NORTHERN
GULF BETWEEN THE KENAI AND SOUTH OF CAPE SUCKLING. WELL ORGANIZED
FRONT EMANATING FROM THE TRIPLE POINT EAST WILL IMPACT SOUTHEAST
ALASKA BY EARLY SATURDAY MORNING WITH POST FRONTAL SHORT WAVE
ACTIVITY KEEPING SHOWERS OVER THE PANHANDLE THROUGH THE WEEKEND.
VERY COLD AIR ALOFT AND PLENTY OF MID LEVEL VORTICITY TO WORK
WITH, SO SHOWERS MAY BE HEAVY AT TIMES THROUGH THE WEEKEND.

AS THIS FRONT FADES AND THE LOW WEAKENS OVER THE NORTHWEST GULF,
A DEVELOPING WAVE ON THE OLD COLD FRONTAL BOUNDARY WILL APPROACH
THE PANHANDLE FROM THE SOUTHWEST LATE SUNDAY NIGHT OR EARLY MONDAY
MORNING RIDING ALONG A 65KT UPPER LEVEL JET IN THE LEFT EXIT
REGION. VERY STRONG AND WELL DEVELOPED FRONTAL SIGNATURE. FAIR
AGREEMENT BETWEEN GFS, ECMWF, AND WPC ON THE STRENGTH AND TRACK
WITH GEM KEEPING THE LOW MUCH FARTHER SOUTH AND SENDING INTO
SOUTHWESTERN BRITISH COLUMBIA. THE FRONT IS CURRENTLY LOOKING
STRONG ENOUGH THAT IT MAY MAKE IT ACROSS THE PANHANDLE AND THE
EXPERIENCE SOME SECONDARY DEVELOPMENT OVER NORTHERN BRITISH
COLUMBIA.

USED A BLEND OF THE 12Z GFS, GEM, AND ECMWF FOR PRESSURE AND WIND THROUGH
SATURDAY NIGHT, THEN TRANSITIONED TO WPC. POP AND QPF FROM GEM AND
ECMWF, ALSO THROUGH SATURDAY NIGHT WITH NO CHANGES BEYOND THEN.
OVERALL FORECAST CONFIDENCE IS BELOW AVERAGE DUE TO RECENT POOR
MODEL CONSISTENCY AND AGREEMENT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 7 PM THIS EVENING TO 1 AM AKDT THURSDAY FOR
     AKZ027.
         STRONG WIND FROM 10 PM AKDT THIS EVENING THROUGH LATE TONIGHT
     FOR AKZ023.
MARINE...GALE WARNING FOR PKZ012-022-033-036-041>043.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-031-032-034-035-051-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

$$

PRB/FRITSCH

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