Gale Warning 801, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
105 PM AKST THU NOV 14 2013

.ANALYSIS AND UPPER LEVELS...DEEP WARM AND MOIST AIR CONTINUES
TO MOVE OVER TOP OF WHAT IS NOW A FLATTENED NORTH PACIFIC
RIDGE...TRACKING EASTWARD ACROSS THE BERING AND ALEUTIANS TO
BRISTOL BAY AND INTO THE GULF OF ALASKA. A SHORT-WAVE OVER
NORTHWEST ALASKA IS BEGINNING TO DIG SOUTHEASTWARD ACROSS THE
MAINLAND...BRINGING MUCH COLDER AIR WITH IT. AT THE SURFACE A
COLD FRONT IS SLOWLY SINKING SOUTHWARD ACROSS THE SOUTHERN MAINLAND.
ALTHOUGH TEMPERATURES ARE COLD ENOUGH TO SUPPORT ALL SNOW OVER THE
MAT-SU THERE ARE STILL A FEW AREAS OF FREEZING RAIN BEING REPORTED.
A LOOK AT THE 12Z ANCHORAGE SOUNDING SHOWS THE PRIME ZONE FOR SNOW
CRYSTAL GROWTH (-12 TO -18 DEGREES CELSIUS) IS DRY.
THUS...SUPERCOOLED DROPLETS IN THE FIRST FEW THOUSAND FEET ARE
FALLING AS LIGHT RAIN OR DRIZZLE ONTO FROZEN SURFACES. PRECIPITATION
WILL BE ENDING FOR ALL BUT A FEW UPSLOPE AREAS AS COLDER AND DRIER
AIR CONTINUES TO WORK ITS WAY IN FROM THE NORTH. MEANWHILE...SOUTH
OF THE COLD FRONT AREAS OF RAIN AND FOG PERSIST FROM THE ALEUTIANS
TO BRISTOL BAY.

.MODEL DISCUSSION...MODELS STILL REFLECT MINOR DIFFERENCES IN THE
TRACK OF A WEAK LOW NEAR THE WESTERN ALEUTIANS AS IT TRACKS TO THE
KUSKOKWIM DELTA FRIDAY MORNING. THERE IS A NOTABLE TREND TOWARD A
WEAKER LOW WITH WEAKER THERMAL ADVECTION. THIS WOULD SUGGEST THAT
THERE WILL NOT BE A SIGNIFICANT WARM NOSE AND FREEZING RAIN WILL
NOT BE WIDESPREAD. HOWEVER...THERE WILL STILL BE A NARROW TRANSITION
ZONE FROM RAIN TO FREEZING RAIN TO SNOW. FORECAST CONFIDENCE IN
THE LOCATION OF THIS TRANSITION ZONE IS LOW. ANOTHER MODEL TREND
OF NOTE IS TOWARD MORE RAPID DISSIPATION OF THIS SYSTEM SUCH THAT
PRECIP NOW LOOKS UNLIKELY TO MAKE IT INTO SOUTHCENTRAL OR THE GULF.

MUCH LARGER MODEL DIFFERENCES DEVELOP ON THE WEST SIDE OF THE
UPPER RIDGE AS SHORT-WAVE TROUGH APPROACHING FROM THE WEST INDUCES
DEVELOPMENT OF A SURFACE LOW. THIS LOW WAS NOT PRESENT AT ALL IN
MODEL RUNS FROM YESTERDAY MORNING AND THERE IS A FAIRLY LARGE
SPREAD IN THE TRACK OF THIS LOW AS IT APPROACHES THE WESTERN
ALEUTIANS FRIDAY. FOR NOW WILL INTRODUCE THIS LOW AND GO WITH AN
AVERAGE OF THE VARIOUS SOLUTIONS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE UPPER SHORT-WAVE DIGGING SOUTHEASTWARD
ACROSS THE MAINLAND WILL BRING ENOUGH COLD AND DRY AIR WITH IT
TO CLEAR SOUTHCENTRAL OUT OVERNIGHT. GAP WINDS WILL BEGIN IN THE
PRINCE WILLIAM SOUND LATE THIS AFTERNOON AND PEAK TONIGHT INTO
FRIDAY MORNING AS COLD AIR ADVECTS SOUTHWARD INTO THE GULF...AIDED
BY SUBSIDENCE AS UPPER WAVE MOVES THROUGH AND THE PRESENCE OF A
VERY STRONG UPPER LEVEL JET. MODELS INDICATE A LESS AMPLIFIED WAVE
THAN YESTERDAY...SO LOW LEVEL COLD ADVECTION IS WEAKER AND WINDS
DON'T LOOK LIKE THEY WILL BE AS STRONG AN INITIALLY THOUGHT. A HIGH
WIND WARNING REMAINS IN EFFECT FOR WHITTIER THIS EVENING. IT IS NOW
LOOKING LIKE A MARGINAL EVENT...BUT TOO CLOSE TO CANCEL THE WARNING.
THE NEXT SYSTEM CROSS THE BERING LOOKS LIKE IT WILL MOSTLY DISSIPATE
OVER SOUTHWEST ALASKA FRIDAY AFTERNOON...SO IMPACT ON SOUTHCENTRAL
MAY JUST BE SOME PASSING CLOUDS AND FLURRIES. WILL CONTINUE TO BACK
OFF POPS WITH THIS. HEADING THROUGH THE WEEKEND MODELS ARE NOW IN
VERY GOOD AGREEMENT ON DROPPING ANOTHER SHORT-WAVE DOWN FROM THE
NORTH PROVIDING A REINFORCING SHOT OF ARCTIC AIR. THUS...EXPECT
CLEAR AND COLD CONDITIONS TO SETTLE IN.

SOUTHWEST ALASKA...THE COLD FRONT HAS STALLED OUT IN THE BRISTOL BAY
AREA AND WON'T MAKE MUCH MORE PROGRESS SOUTHWARD. AS THE NEXT LOW
ROUNDS THE RIDGE THIS FRONT WILL HEAD BACK NORTHWARD AS A WARM FRONT.
WITH MORE OF A WESTERLY COMPONENT THAN A SOUTHERLY COMPONENT TO THE
LOW LEVEL FLOW THE FRONT WON'T MAKE MUCH PROGRESS INLAND. THE BIGGEST
FORECAST CHALLENGE IS FIGURING OUT WHERE THE TRANSITION ZONE FROM
RAIN TO MIXED PRECIP TO SNOW WILL SET UP. THE MOST SIGNIFICANT QPF
WILL BE OVER THE KUSKOKWIM DELTA...SO EXPECT P-TYPE IMPACTS TO BE
PRIMARILY IN THAT AREA. RIGHT NOW LOOKS LIKE BETHEL MAY END UP RIGHT
IN THAT TRANSITION ZONE WITH WARMER AIR MOVING IN ALOFT AND SURFACE
EASTERLY FLOW HOLDING IN SUB-FREEZING TEMPERATURES. WILL ISSUE A
FREEZING RAIN ADVISORY AND ATTEMPT TO GENERALLY DEPICT WHERE THE
VARIOUS P-TYPES ARE EXPECTED. THIS SYSTEM WILL RAPIDLY DISSIPATE
OVER BRISTOL BAY AND INTERIOR SOUTHWEST ALASKA FRIDAY NIGHT. A
MAJOR SHIFT IN THE PATTERN WILL THEN TAKE PLACE WITH A RIDGE BUILDING
OVER THE FAR WESTERN BERING AND EASTERN ASIA...WHICH WILL ALLOW
ARCTIC AIR TO PLUNGE SOUTHWARD ACROSS MAINLAND ALASKA. CLEAR AND
COLD CONDITIONS WILL SETTLE IN OVER THE WEEKEND AND MAY HOLD THROUGH
ALL OF NEXT WEEK.

BERING SEA/ALEUTIANS...THE NEW LOW INDICATED BY THE MODELS WILL
AFFECT THE WESTERN ALEUTIANS WITH MORE RAIN WIND AND FOG FRIDAY AND
SATURDAY. ALTHOUGH THERE IS DISAGREEMENT IN THE EXACT TRACK OF THE
LOW IT DOES LOOK LIKE IT WILL BE PUSHED BACK SOUTHWARD OVER THE
WEEKEND AS THE RIDGE BUILDS TO THE NORTH AND WEST. BY EARLY NEXT
WEEK EXPECT MUCH COLDER AND DRIER AIR TO PUSH SOUTHWARD ACROSS THE
BERING AND ALEUTIANS. ALTHOUGH NOT ANOMALOUSLY COLD...IT WILL BE
MUCH COLDER THAN THE CURRENT TROPICAL LIKE AIRMASS WHERE TEMPERATURES
ARE REACHING THE MID TO UPPER 40S.

.LONG TERM FORECAST...MEDIUM RANGE MODELS HAVE ALL CONVERGED ON
COLD AND DRY CONDITIONS SETTLING IN ACROSS MAINLAND ALASKA AND THE
EASTERN BERING SEA NEXT WEEK. AS COLD AIR ADVECTS INTO THE GULF OF
ALASKA EXPECT A LOW TO FORM...HOWEVER MOST IF NOT ALL OF THE PRECIP
WILL REMAIN OFFSHORE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 125.
MARINE...GALE WARNING...119 121 127 128 129 130 131 178.
FIRE WEATHER...NONE.

SEB NOV 13