Gale Warning 317, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
339 PM AKST THU NOV 6 2014

.SHORT TERM...A LOW IN THE FAR SW GULF OF ALASKA HAS A LARGE
OCCLUDED FRONT WRAPPING AROUND IT AND EXTENDING SOUTH TO THE
TROPICS. THIS FRONT WILL MOVE INTO THE EASTERN GULF THROUGH THE
EVENING THEN INTO THE PANHANDLE COAST OVERNIGHT WHILE
STRENGTHENING. WINDS WILL INCREASE TO GALE FORCE 40-45KT OVER THE
OUTSIDE WATERS AND INTO THE OCEAN ENTRANCES THROUGH THE EARLY
MORNING. NORTHERN CLARENCE STRAIT WILL SEE THE STRONGEST WINDS
WHERE A STORM WARNING WITH 50 KT WINDS IS IN EFFECT. THE ADJACENT
LAND AREAS WILL SEE GUST OF 40-55 MPH...JUST UNDER HIGH WIND
WARNING CRITERIA. OPTED TO GO BELOW THIS LEVEL BECAUSE MODELS HAVE
ONLY 45-55KT (50-65MPH) AT 925MB WHEN THE FRONT IS OVER WATER AND
SLIGHTLY LESS AS IT MOVES OVER LAND. THE SOUTHERN ZONES NEAR DIXON
ENTRANCE AND HECATE STRAIT CAN EXPECT THE STRONGEST GUSTS.

SCATTERED SHOWERS OVER THE NORTHERN PANHANDLE WILL DIMINISH THIS
EVENING THEN RAIN ASSOC WITH THE FRONT WILL MOVE INTO THE GULF
COAST LATE TONIGHT. INLAND AREAS LIKE JUNEAU WILL NOT SEE RAIN
FROM THE FRONT UNTIL THE EARLY MORNING HOURS. BREAKS IN THE CLOUDS
THIS EVENING WILL ALLOW FOR RADIATIONAL COOLING. NORTHERN BORDER
AREAS WILL LIKELY FALL BELOW FREEZING AND CAUSE THE PRECIP TO
START OFF AS SNOW THEN CHANGE OVER TO RAIN. HAVE LESS THAN AN INCH
OF ACCUMULATION WEST OF KLUKWAN NEAR HAINES AND DYEA NEAR SKAGWAY.

RAIN WILL BECOME CONVECTIVE AND SHOWERY BEHIND THE FRONT THROUGH
FRIDAY AFTERNOON. MODEL BASED CAPE VALUES OF AROUND 300J/KG OVER
THE GULF HAVE PROMPTED ME TO ADD A CHANCE OF THUNDERSTORMS TO THE
OFFSHORE AREA ALL DAY FRIDAY. THIS CHANCE COULD EASILY SPREAD INTO
THE OTHER OUTSIDE WATERS IN THE AFTERNOON/EVENING.

THE NAM WAS THE STRONGEST WITH THE FRONT AND ITS INFLUENCE WAS
USED TO KEEP THE STRONGER WINDS IN THE FORECAST. OTHERWISE A BLEND
WAS USED WITH ADDED LOCAL EFFECTS.

.LONG TERM...UPPER TROUGH LOCATED OVER THE ALEUTIANS/NRN PAC THU
AFTERNOON WILL BEGIN TO EJECT EWD ACROSS THE GULF BY FRI
NIGHT...ENTERING THE ERN GULF SAT AFTERNOON...AND THEN MOVING
ACROSS THE PANHANDLE SAT NIGHT. MIDLEVEL TEMPERATURES AROUND -30C
COMBINED WITH INCREASING ASCENT AHEAD OF THE APPROACHING TROUGH
WILL FAVOR WIDESPREAD SHOWERS OVER THE REGION ON SAT...WHICH WILL
THEN DISSIPATE BEHIND THE TROUGH ON SUN. NON-ZERO THREAT FOR AN
ISOLATED THUNDERSTORM WILL ALSO EXIST OVER THE GULF WATERS SAT.
HOWEVER...PROBABILITY APPEARS TO BE TOO LOW ATTM TO INCLUDE IN THE
LATEST LONG TERM FORECAST DUE TO A LACK OF OBVIOUS/FOCUSED
FORCING FOR INITIATION.

MODEL GUIDANCE IS IN GOOD AGREEMENT SHOWING AN UPPER RIDGE
BUILDING OVER THE PANHANDLE BY EARLY NEXT WEEK...AND PERSISTING
INTO THE MIDDLE TO LATER PORTIONS OF THE WEEK. WARM 850 MB
TEMPERATURES ON THE ORDER OF 2-6C ARE FORECAST TO SPREAD NWD INTO
THE AREA BY TUE...SIGNALING THE POTENTIAL FOR MODERATING
HIGHS/LOWS. THE PRIMARY FORECAST UNCERTAINTY IS PRECIPITATION. THE
12Z GFS WAS A MUCH WETTER SOLUTION COMPARED TO THE 12Z ECMWF.
HOWEVER...THE 18Z RUN OF THE GFS IS COMING IN LINE WITH THE
ECMWF...SHOWING A DEEP-LAYER OF DRY AIR DEVELOPING OVER THE
PANHANDLE ON WED AND THU. CURRENT POP FORECAST WAS COMPOSED OF WPC
GUIDANCE DURING THIS TIME FRAME...WHICH LEANED TOWARD A WETTER
SCENARIO. HOWEVER...FUTURE FORECASTS MAY NEED TO BACK OFF FROM
THESE HIGHER POP/S IF MODELS CONTINUE TO TREND TOWARDS THE DRIER
ECMWF.

PRESSURE GRIDS WERE LEFT UNCHANGED FRI NIGHT THROUGH SAT. THEN
BLENDED IN THE 12Z ECMWF/GEM BEGINNING 00Z SUN...WITH A TRANSITION
TO WPC 12Z MON. POP/S WERE UPDATED WITH A GFS/ECMWF BLEND THROUGH
00Z TUE...WITH WPC USED THEREAFTER. FORECAST CONFIDENCE IS
AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 3 AM AKST FRIDAY THROUGH FRIDAY MORNING FOR
     AKZ022-026-027.
         STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH FRIDAY MORNING
     FOR AKZ023.
         STRONG WIND FROM 3 AM AKST FRIDAY THROUGH FRIDAY MORNING FOR
     AKZ028.
         STRONG WIND FRIDAY MORNING FOR AKZ029.
MARINE...STORM WARNING FOR PKZ036.
         GALE WARNING FOR PKZ021-022-033-035-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-031-032-034-053.

&&

FERRIN/GARNER

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU