Gale Warning 854, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
556 AM AKST FRI DEC 25 2015

.ANALYSIS AND UPPER LEVELS...

A VERY DYNAMIC AND IMPRESSIVE HIGHLY AMPLIFIED PATTERN IS IN PLACE
ACROSS THE REGION THIS MORNING...HIGHLIGHTED BY A DEEPENING
STORM-FORCE BENT-BACK OCCLUSION JUST SOUTH OF THE WESTERN ALASKA
PENINSULA. A SECONDARY STORM FORCE LOW OVER THE WESTERN BERING IS
IN THE PROCESS OF WEAKENING...BUT IT IS STILL BRINGING HURRICANE
FORCE GUSTS TO THE WESTERN ALEUTIANS AS IT ADVECTS A REGION OF
ARCTIC AIR INTO THAT AREA...ENHANCING VERTICAL TURBULENT MIXING.
THE DEEPENING LOW SOUTH OF THE ALASKA PENINSULA IS TAPPING
SUBTROPICAL MOISTURE FROM 30N...WITH THE ASSOCIATED WARM FRONT
BEING ENHANCED BY STRONG AGEOSTROPHIC VERTICAL MOTIONS IN THE
NORTH TO SOUTH ORIENTED 150 KT PACIFIC JET STREAM. THE MASSIVE
PLUME OF WARM AIR ADVECTION CAN BE SEEN ON SATELLITE IMAGERY WITH
AN EXPANSIVE AREA OF VERY HIGH CIRRUS CLOUD TOPS SPREADING ACROSS
WESTERN AND SOUTHERN ALASKA THIS MORNING...ALSO BEING ENHANCED BY
A VIGOROUS VERTICALLY PROPAGATING MOUNTAIN WAVE ALONG THE ALASKA
PENINSULA. OVER SOUTHCENTRAL...SHORTWAVE RIDGING AHEAD OF THE
BERING/PACIFIC FRONT IS KEEPING RATHER QUIET CONDITIONS
INLAND...WITH WEAK OUTFLOW GAP WINDS ALONG THE COAST.

WITH THE SURFACE LOW SOUTH OF THE ALASKA PENINSULA TIGHTENING AND
MOVING NORTH INTO THE SOUTHERN PORTION OF THE EASTERN BERING...THE
PRESSURE GRADIENT WILL CONTINUE TO DRIVE POWERFUL EAST TO
SOUTHEAST WINDS THROUGH MUCH OF SOUTHWEST ALASKA. WIND GUSTS HAVE
ALREADY REACHED NEAR HURRICANE FORCE ACROSS THE ALASKA PENINSULA
AND ACROSS COASTAL PORTIONS OF BRISTOL BAY.

WITH TIME...THE DEEP LOW WILL RAPIDLY OCCLUDE IN THE SOUTHEAST
BERING SEA...WITH THE ASSOCIATED FRONT MAKING RAPID PROGRESS
EASTWARD THROUGH THE NORTHERN GULF AND KENAI PENINSULA BY FRIDAY.

&&

.MODEL DISCUSSION...

THE SUITE OF DYNAMICAL NUMERICAL GUIDANCES ARE IN VERY GOOD
AGREEMENT AS A WHOLE WITH BOTH THE SYNOPTIC PATTERN THROUGH THE
WEEKEND...AND THE POWERFUL LOW CURRENTLY DEVELOPING SOUTH OF THE
ALASKA PENINSULA. THERE REMAINS SOME SMALL DISCREPANCIES WITH THE
EXACT NORTHWARD TRACK OF THE LOW INTO THE SOUTHEASTERN
BERING...BUT THE IMPACTS ARE RATHER MINIMAL. THE ONE DISCREPANCY
IS WITH RESPECT TO PRECIPITATION ACROSS PARTS OF KACHEMAK
BAY...WITH WETTER MODELS SUCH AS THE GFS AND NAM SUGGESTING THE
POTENTIAL FOR MODERATE TO HEAVIER SNOW NEAR THERE TODAY AND THIS
EVENING AS THE OCCLUDED FRONT MOVES IN. GIVEN THE PATTERN...THERE
IS POTENTIAL FOR AT LEAST A QUICK BURST OF LOCALIZED SNOWFALL SO
THESE MODELS WERE UTILIZED. OTHERWISE...FORECAST CONFIDENCE IS
HIGH ON BOTH THE BERING SIDE AND MAINLAND SIDE WITH THIS DEEP LOW
AND ITS ASSOCIATED FRONT AS IT MOVES INTO THE NORTHERN GULF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE EXTREMELY STRONG UPPER LEVEL JET WITH ASSOCIATED UPWARD
VERTICAL MOTION ALONG WITH A STORM FORCE OCCLUDED FRONT WILL LIFT
NORTHWARD ACROSS THE GULF TODAY BRING SEVERE WEATHER TO THE GULF
COASTAL WATERS...KODIAK ISLAND...PRINCE WILLIAM SOUND...AND PORTIONS
OF THE SOUTHERN AND EASTERN KENAI PENINSULA. BASED ON OBSERVATIONS
OVERNIGHT AND THE VERY IMPRESSIVE NATURE OF THE STORM AS
INDICATED IN SATELLITE IMAGERY...HAVE GENERALLY TRENDED TOWARD
STRONGER WINDS AND HEAVIER PRECIPITATION FOR THESE AREAS. THE
FRONT WILL INITIALLY MOVE FAIRLY QUICKLY NORTHWARD...BUT WILL THEN
RAPIDLY SLOW ITS MOTION AND ELONGATE ALONG THE NORTH GULF COAST
TONIGHT AS UPPER FLOW WEAKENS AND BECOMES PARALLEL TO THE FRONT.
THIS WILL LEAD TO A PROLONGED PERIOD OF HEAVY SNOW FOR INLAND
PORTIONS OF THE WESTERN PRINCE WILLIAM SOUND ZONE...INCLUDING
GIRDWOOD AND MUCH OF THE SEWARD HIGHWAY CORRIDOR. STRONG EASTERLY
WINDS WILL WARM TEMPS UP ALONG THE COAST AND INTO PORTAGE VALLEY
AND THE VERY EASTERN PORTION OF TURNAGAIN ARM...BUT THE INTENSITY
OF THE PRECIP WILL DELAY THE CHANGE-OVER TO RAIN.

MEANWHILE...A SOUTHEASTERLY UPPER LEVEL JET STREAK WILL MOVE RIGHT
ACROSS THE SOUTHERN KENAI PENINSULA. DESPITE THE VERY STRONG CROSS
BARRIER FLOW THE JET DYNAMICS WILL PRODUCE PRECIPITATION...WHICH
WILL START AS SNOW THIS MORNING. EXPECT TEMPS TO WARM UP AND
CHANGE PRECIP TO RAIN...BUT THERE LIKELY WILL BE AT LEAST A BRIEF
PERIOD OF HEAVY SNOW...ESPECIALLY FOR THE HOMER BLUFF AND OTHER
HILLS TO THE NORTH. THEREFORE...HAVE UPPED SNOW AMOUNTS FOR THESE
AREAS.

WITH THE FRONT WEAKENING ALONG THE NORTH GULF COAST/PRINCE WILLIAM
SOUND TONIGHT AND THE LOSS OF THE STRONG UPPER JET DYNAMICS EXPECT
LITTLE PRECIP INLAND. THERE WILL BE SOME AREAS OF LIGHT SNOW OR
FLURRIES BUT LITTLE IN THE WAY OF SNOW ACCUMULATION. A MORE
UNSTABLE AIR MASS WILL MOVE IN BEHIND THE FRONT. A STEADY STREAM
OF UPPER WAVES FOLLOWED BY THE REMNANTS OF THE BERING SEA LOW
WILL PROVIDE NEARLY CONTINUOUS SHOWERS FOR KODIAK AND THE GULF
COAST THROUGH THE WEEKEND. INLAND AREAS WILL REMAIN MOSTLY DRY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE ASSOCIATED WEATHER FRONT WITH THE STRONG LOW CROSSING THE
AKPEN LATER TODAY INTO THE SOUTHERN BERING WILL TRACK A FRONT
INTO THE SOUTHWEST REGION THIS MORNING. THIS WILL PRODUCE HIGH
WINDS ACROSS THE BRISTOL BAY REGION. THE KUSKOKWIM DELTA COASTLINE
NORTH OF KIPNUK WILL HAVE BLOWING SNOW CONDITIONS THIS MORNING
THROUGH THE AFTERNOON...ALONG WITH STRONG WINDS. THEREFORE...A
WINTER WEATHER ADVISORY FOR STRONG WIND AND BLOWING SNOW HAS BEEN
ISSUED TO ACCOUNT FOR THIS. IF VISIBILITY REMAINS SEVERELY
RESTRICTED ALONG THE COAST...THE ADVISORY MAY NEED TO BE UPGRADED
TO A BLIZZARD WARNING LATER THIS MORNING. BY SATURDAY THE
SOUTHWEST WILL REMAIN UNDER WEAKER EASTERLY FLOW WITH A SHOWERY
WEATHER REGIME THROUGH THE WEEKEND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE NORTH PACIFIC LOW WILL CONTINUE TO INTENSIFY AS IT CROSSES THE
EASTERN ALEUTIANS THIS MORNING BRINGING WARMER TEMPERATURES
ACCOMPANIED BY A LARGE SWATH OF MOISTURE SPILLING OVER INTO THE
EASTERN BERING SEA. THIS WILL BRING UPPER END STORM FORCE WINDS
TO BRISTOL BAY EXTENDING INTO THE KUSKOKWIM BAY TODAY. THIS
SYSTEM WILL WEAKEN AS IT BEGINS TO CROSS THE EASTERN ALEUTIANS ON
SATURDAY NEAR PORT MOLLER. HIGH WINDS THAT GUSTED OVER 100 MPH AT
ADAK OVERNIGHT WILL SLOWLY DIMINISH THROUGH THE LATE MORNING
HOURS. THERE WILL BE COOLER TEMPERATURES IN THE CENTRAL/WESTERN
BERING SEA EXTENDING INTO THE WESTERN TO CENTRAL CHAIN DUE TO THE
COLD AIR ADVECTION ON THE BACKSIDE OF THE NORTH PACIFIC LOW. THESE
WINDS WILL WEAKEN BELOW HIGH WIND THRESHOLDS AS THE SYSTEM MOVES
FARTHER EAST AND WEAKENS THROUGHOUT THE DAY TODAY. THE BERING
WILL HAVE A SHOWERY WEATHER REGIME THROUGH THE WEEKEND AS THE
WINDS SHIFT TO MORE NORTHEASTERLY FLOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

AN ACTIVE PATTERN IS EXPECTED TO CONTINUE INTO NEXT WEEK WITH
MULTIPLE LOWS COMING UP FROM THE SOUTH BRINGING WARMER CONDITIONS
TO THE STATE...EXCEPT ON THE BACK SIDE OF THE LOWS IN THE WESTERN
AND CENTRAL ALEUTIANS WHERE TEMPERATURES MAY BE JUST COLD ENOUGH
FOR ACCUMULATING SNOWS AS EARLY AS SATURDAY NIGHT. OVER THE
SOUTHERN MAINLAND AND SOUTHWEST ALASKA TEMPERATURES LOOK TO BE AT
OR ABOVE NORMALS FOR MUCH OF NEXT WEEK. WITH THE MULTIPLE LOWS
MOVING INTO THE AREA THERE IS DISAGREEMENT AMONGST THE MODELS ON
HOW THEY TRACK THROUGH THE AREA AND HOW MUCH SNOW/RAIN THEY WILL
BRING. BECAUSE OF THIS THE ENSEMBLE MEANS WERE USED. THEY ARE MUCH
CLOSER TOGETHER THAN THE OPERATIONAL RUNS WITH THE LOW CENTERS SO
EVEN THOUGH CONFIDENCE IS LOW FOR SOME TIMING ISSUES WITH THE
LOWS...THERE IS HIGHER CONFIDENCE IN THE CONTINUING ACTIVE
PATTERN.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING...125
         HIGH WIND WARNING...161 187
         WINTER WEATHER ADVISORY...155.
MARINE...GALES...125 127 129 140 141 170 171 178 179 185
 STORMS...119 120 130-132 136-139 150 155 160 165 172-177 180 181
 HVY FRZG SPRY...127 140 181 185

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DK/CC