Winter Storm Warning 27, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
339 PM AKST MON DEC 21 2015

.SHORT TERM...LOW PRESSURE IS TRACKING FROM THE EASTERN GULF OVER
THE EAST GULF COAST THIS EVENING. THE MODEL TRACK OF THIS WEAKENING
SYSTEM HAS VARIED FROM RUN TO RUN AND MODEL TO MODEL. LATEST
SATELLITE IMAGERY AND NEWEST HIGH RES MODELS NOW HAVE THE LOW
CENTER BIT FURTHER NORTH. WHILE STILL GETTING PRECIP BAND MOVING
OVER PANHANDLE FROM CAPE FAIRWEATHER SOUTH THE LOCATION OF HIGHEST
QPF VALUES COULD SHIFT FROM EXPECTED LOCATION OF CENTRAL PANHANDLE
NORTHWARD. BEHIND THIS CURRENT LOW A WEAK HIGH PRESSURE RIDGE
MOVES ACROSS THE AK GULF WHILE A WEAK LOW DEVELOPING NEAR KODIAK
MOVES INTO THE NORTHERN AK GULF.

SHOWER ACTIVITY WILL PICK UP THIS EVENING AS THE FRONTAL BAND
MOVES OVER. YAKUTAT GOT A BIT MORE PRECIP TODAY AS THE CURRENT LOW
CENTER MOVED FURTHER NORTH. AFTER A LULL PRECIP THERE WILL PICK UP
AGAIN AS THE KODIAK LOW MOVES IN. SHOWER ACTIVITY WILL DIMINISH
THROUGH TUESDAY AS THE FRONTAL BANDS EXIT TO THE EAST. BREAKS
BETWEEN PRECIP BANDS TODAY BROUGHT SOME CLEAR BREAKS AND ALONG
WITH SOUTHERLY FLOW INCREASED TEMPS TO THE MID TO UPPER 30S. THUS
MOST PRECIP SHOULD FALL AS RAIN OVER THE PANHANDLE WITH THE
EXCEPTION OF FAR NORTHERN AREAS WHICH WILL GET MOSTLY SNOW AND
THE YAKUTAT AND JUNEAU AREAS WHERE SNOW MAY MIX LATER TONIGHT.
MODEL HAVE SOME 6 HOUR QPF BULLS EYE  UPWARDS OF 0.25 INCHES BUT
DO NOT HAVE GOOD AGREEMENT ON THE EXACT LOCATION. GFS OVER
GUSTAVUS, NAM FURTHER EAST OVER JUNEAU AND NEW HIGH RES MORE TO
THE NORTH. NOT SO WORRIED ABOUT SNOW ACCUMULATION DUE TO THE
CURRENT WARMER TEMPS BUT COULD SEE ACCUMULATION UP TO AN INCH. NOT
MUCH OF A WARM UP TOMORROW AS FLOW BEGINS TO SHIFT FROM THE SOUTH
BACK NORTH WITH HIGHS IN THE MID 30S.

WINDS OVER THE AK GULF TOPPED OUT AT GALES OUT OF CROSS SOUND
WITH MAX SMALL CRAFT SOUTH OF THE LOW NEAR CAPE DECISION. CENTRAL
INNER CHANNELS SHOULD PICK UP TO SMALL CRAFT AS FRONTAL BAND MOVES
OVER, THEN DIMINISH OVERNIGHT INTO TUESDAY. NORTHERN INNER
CHANNELS WERE MORE INFLUENCED BY PRESSURE GRADIENT STAYING
NORTHERLY THROUGH THE DAY. AS THE FRONT ADVANCES THESE WILL SHIFT
SOUTH BY EARLY TUESDAY THEN FLIP BACK NORTH BY LATE AFTERNOON.
BREEZY OVERLAND WINDS THIS EVENING WILL DROP AS WELL AS FRONT
MOVES ON EAST.

MODELS IN FAIR AGREEMENT ON SYNOPTIC SCALE FEATURES BUT STILL
DIFFERENCES WITH MESO SCALE DETAILS. KEPT WITH A NAM/GEM BLEND
SINCE THEY WERE STILL IN LINE WITH EACH OTHER AND PREVIOUS
FORECAST. GFS/ECMWF HAD BIT DIFFERENT TREND FOR A LOW TRACKING
ACROSS THE SOUTHERN AK GULF TUESDAY, WHICH MAY ONLY IMPACT THE FAR
SOUTHERN PANHANDLE. FORECAST CONFIDENCE IS AVERAGE.

.LONG TERM...HAVE A COOLING TEMPERATURE TREND IN THE EXTENDED
RANGE FORECAST PERIOD THROUGH THE UPCOMING WEEKEND. THIS, IN
COMBINATION WITH A SIGNIFICANT FRONT HEADED OUR WAY FRIDAY NIGHT
INTO SATURDAY, HAS INCREASED FORECASTER CONFIDENCE IS A
SIGNIFICANT SNOW EVENT LATER THIS WEEK. CURRENTLY, MODEL AGREEMENT
BETWEEN ECMWF AND GFS IS BETTER THAN AVERAGE, WITH GFS BEING ABOUT
6 HOURS FASTER WITH THE FRONT. SNOWFALL EXPECTED FOR ALL OF
SOUTHEAST ALASKA EXCEPT CENTRAL AND SOUTHERN OUTER COAST AND THE
SOUTHERN INNER CHANNELS. 12 HOUR SNOW TOTALS FOR FRIDAY NIGHT,
WHEN THE HEAVIEST SNOW IS CURRENTLY FORECAST ARE AT THE MARGINAL
WINTER WEATHER ADVISORY LEVELS OF 4 INCHES. CANNOT SAY WITH
CONFIDENCE YET THAT THIS REPRESENTS THE HIGH END OR THE LOW END OF
WHAT IS POSSIBLE AND THAT RESOLUTION WILL COME OVER THE NEXT
COUPLE DAYS. IF, HOWEVER, THIS EVENT DOES TURN INTO A HIGH END
ADVISORY OR EVEN A WINTER STORM WARNING, IMPACTS WILL BE LIMITED
DUE TO THE FACT THAT IT WILL OCCUR DURING A HOLIDAY WEEKEND AND
WEEKDAY ACTIVITIES, SUCH AS THE MORNING COMMUTE, WILL NOT BE A
FACTOR.

THE OTHER LONG PRIMARY TERM ISSUE WILL OCCUR ON THURSDAY AND
THURSDAY NIGHT. HIGH PRESSURE OVER THE GULF AND OVER WESTERN
YUKON WILL SQUEEZE AN INVERTED TROUGH IN BETWEEN. GOOD POTENTIAL
FOR STRONG OUTFLOW WINDS EAST OF YAKUTAT AND NORTHEASTERLY WIND
DOWN THE KLONDIKE HIGHWAY AS WELL AS INTERIOR PASSES SOUTH TO
ABOUT TRACY ARM. LOOKING AT NORTHERLY GALES OVER NORTHERN LYNN
CANAL FOR THIS TIME AS WELL.

USED ECMWF FOR UPDATES TO PRESSURE AND OFFSHORE WINDS THURSDAY AND
THURSDAY NIGHT. WPC THEREAFTER. POP AND QPF TUESDAY NIGHT AND
WEDNESDAY ADJUSTED BY BLENDING IN GFS22 AND CANADIAN INTO
OFFICIAL. OVERALL FORECAST CONFIDENCE IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ022-043.
         SMALL CRAFT ADVISORY FOR PKZ013-021-031>036-041-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

PRB/FRITSCH

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