Gale Warning 360, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
350 PM AKST SUN NOV 29 2015

.SHORT TERM...STALLED FRONT LIES N-S ACROSS THE FAR ERN GULF AND
WILL DRIFT EWD INTO THE NRN AND CENTRAL PANHANDLE BY LATE TONIGHT.
THIS FRONT WILL WEAKEN BUT DRIFT BACK TO THE NW MON AS ANOTHER
FRONT APPROACHES THE SRN GULF FROM THE SW. USED BLEND OF THE 12Z
GFS AND ECMWF AS THEY APPEARED TO HAVE BEST HANDLE ON THE MAIN
FEATURES.

MAIN FORECAST CONCERNS ARE HOW FAST AND FAR E PRECIP WITH FRONT
MOVES IN...HOW MUCH PRECIP MAY DEVELOP OVER THE SRN AREA
TONIGHT...HOW MUCH SNOW FALLS OVER THE FAR N...AND WINDS. RIGHT
NOW...THE PRECIP BAND IS MAINLY W OF A PAJN-PASI LINE. THIS WILL
DRIFT EWD AND ENCOMPASS MOST OF THE NRN AND CENTRAL PANHANDLE BY
LATE EVENING...REACHING THE PAPG/PAWG AREAS LATE TONIGHT. AT THE
SAME TIME...DEEP LAYER LIFTING BY UPPER TROF LIFTING TO THE NE
WILL INCREASE BOUNDARY LAYER DEPTH AND MOISTURE OVER THE SRN
PANHANDLE...WHICH WILL ALLOW SOME SHOWERS TO FORM ONCE THE
BOUNDARY LAYER IS SUFFICIENTLY DEEP BY LATE TONIGHT. THE SHOWERS
AND RAIN AREA WITH FRONT WILL MERGE MON MORNING. FOR
SIMPLICITY...WENT WITH STRATIFORM TERMINOLOGY TO HANDLE ALL THE
PRECIP AT THIS POINT. APPROACH OF NEXT FRONT AND THE FRONT OVER
THE PANHANDLE DRIFTING BACK TO THE NW WILL INCREASE PRECIP OVER
THE AREA AGAIN MON AFTERNOON. THE NE GULF COAST WILL SEE PRECIP
DIMINISH TONIGHT AS DRIER AIR MOVES INTO THE NE GULF TONIGHT AND
WILL REMAIN MOSTLY DRY MON ALTHOUGH THERE COULD BE A FEW
SPRINKLES OR SHOWERS IN THE AREA MON MORNING.

LOOKS LIKE THE FAR NRN AREA AT HIGHER ELEVATIONS WILL KEEP SNOWING
AT A DECENT CLIP THIS EVENING...BUT SHOULD DIMINISH LATER TONIGHT
ONCE FRONT PASSES THRU THEM. DECIDED TO EXTEND THE WINTER STORM
WARNINGS FOR ZONES 18 AND 19 AT HIGHER ELEVATIONS UNTIL MIDNIGHT
TONIGHT FOR AN ADDITIONAL 4 TO 8 INCHES OF ACCUMULATION...WITH THE
HIGHER AMOUNTS EXPECTED CLOSEST TO THE CANADIAN BORDER.

WINDS WILL PICK UP SOME AS FRONT GETS CLOSER TO THE COAST THIS
EVENING. LOOKS LIKE A BAND OF GALES FOR THE FAR ERN GULF WILL
SLOWLY GET PUSHED SEWD...WITH ONLY THE FAR SE GULF EXPECTED TO
STILL BE IN GALES BY LATE TONIGHT. ADJACENT INNER CHANNELS WILL
SEE SCA TO GALE FORCE WINDS...WITH CLARENCE STRAIT AND STEPHENS
PASSAGE TO SW OF DOUGLAS ISLAND SEEING THE HIGHEST WINDS OVER THE
INNER CHANNELS. THE NRN END OF THIS AREA WILL SEE WINDS DROP OFF
LATE TONIGHT. THEN AS FRONT MOVES BACK TO THE NW MON...SOME
INCREASE IN WINDS WILL OCCUR OVER THE E-CENTRAL GULF AND N-CENTRAL
INNER CHANNELS ESPECIALLY BY THE AFTERNOON. WILL MAINTAIN STRONG
WIND HEADLINES FOR ZONES 22..23..25..AND 27 FOR AT LEAST PART OF
TONIGHT.

.LONG TERM...A LARGE UPPER WILL BE LOW LOCATED OVER THE WESTERN
GULF AT THE START OF THE EXTENDED RANGE FORECAST PERIOD. THIS LOW
WILL ROTATE AT LEAST TWO UPPER LEVEL SHORT WAVES UP OVER THE
EASTERN GULF AND SOUTHEAST ALASKA BEFORE BECOME ABSORBED BY A
STRONGER UPPER LOW THAT MOVES INTO THE CENTRAL GULF FROM THE
SOUTH ON WEDNESDAY NIGHT. MODEL AGREEMENT ON THE SYNOPTIC SCALE IS
GOOD THROUGH THIS POINT, BUT DETERIORATES RAPIDLY THEREAFTER. LOW
LEVEL SOUTHERLY OR SOUTHWESTERLY FETCH WILL ENSURE AN UNBROKEN
SUPPLY OF WARM, WET AIR, SO SNOW LEVELS WILL REMAIN SUFFICIENTLY
HIGH ENOUGH THAT ANY SNOW ACCUMULATIONS SHOULD BE LIMITED TO THE
HAINES AND KLONDIKE HIGHWAYS. EXCEPTION TO THIS WILL BE YAKUTAT
MONDAY NIGHT, AND THEN AGAIN LATE WEEK. AT THIS POINT, WEATHER AND
SNOW GRIDS SPAN 12 HOURS AND DIURNAL TEMPERATURE VARIABILITY ABOVE
AND BELOW THE FREEZING MARK IS LOST IN THESE LOWER RESOLUTION
GRIDS. OPTED TO GO WITH CHARACTERIZING WEATHER THERE DURING THIS
TIME AS RAIN RATHER THAN SNOW, SINCE WINDS ARE EXPECTED TO BE
SOUTH OF EAST AND IT IS DIFFICULT TO GET SNOW IN THESE SITUATIONS.
CAVEAT TO THIS GENERALIZATION WOULD BE THE POSSIBILITY OF MIXED
PRECIPITATION DURING THE COLDEST OVERNIGHT HOURS DURING THE LATTER
HALF OF THE UPCOMING WEEK.

AT THE SURFACE, THE STATIONARY FRONT THAT HAS NEARLY BECOME A
PERMANENT FIXTURE OVER THE PANHANDLE THIS PAST WEEK WILL STILL BE
LOCATED OVER THE PANHANDLE ON MONDAY EVENING. A WEAK FRONT
ASSOCIATED WITH ONE OF THE AFOREMENTIONED UPPER SHORTWAVES WILL
PUSH EAST MONDAY NIGHT AND FINALLY DISPLACE THE STATIONARY FRONTAL
BOUNDARY OUT OF THE AREA. NO BREAK FROM THE PRECIPITATION,
HOWEVER, UNTIL LATE TUESDAY NIGHT WHEN THE NORTHERN HALF OF
SOUTHEAST ALASKA MAY GET A BREAK. MEANWHILE, LOCATIONS SOUTH OF
TAKU INLET AND EAST OF SITKA WILL REMAIN IN CATEGORICAL UNTIL AT
LEAST THURSDAY MORNING. ANOTHER FRONT WILL APPROACH THE PANHANDLE
FROM THE SOUTHWEST ON WEDNESDAY NIGHT. PRECIPITATION WILL BE
HEAVY AT TIMES THROUGH WEDNESDAY NIGHT AND WILL LIKELY CONTINUE TO
BE SO INTO THE NEXT WEEKEND.

NO REMARKABLE CHANGES TO THE EXTENDED RANGE FORECAST. UPDATES TO
PRESSURE LIMITED TO MONDAY NIGHT USING ECMWF WITH CHANGES TO WIND
BASED ON GFS. TWEAKS TO POP AND QPF USING GFS, CANADIAN NH, AND
ECMWF THROUGH WEDNESDAY NIGHT WITH NEGLIGIBLE CHANGE. USED WPC
FROM THURSDAY ONWARD DUE TO CONTINUED MODEL SPREAD AND
UNCERTAINTY. OVERALL FORECAST CONFIDENCE IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH MONDAY AFTERNOON FOR AKZ027.
         STRONG WIND UNTIL MIDNIGHT AKST TONIGHT FOR AKZ025.
         STRONG WIND UNTIL 9 PM AKST THIS EVENING FOR AKZ023.
         WINTER STORM WARNING UNTIL MIDNIGHT AKST TONIGHT FOR AKZ018-019.
MARINE...GALE WARNING FOR PKZ013-031-033>036-041>043.
         SMALL CRAFT ADVISORY FOR PKZ011-012-021-022-032-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

RWT/FRITSCH

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