Storm Warning 172, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1240 PM AKDT FRI OCT 29 2010

.ANALYSIS AND UPPER LEVELS...THE MAJOR LOW WHICH BROUGHT WIDESPREAD
IMPACTS TO ALASKA THE LAST COUPLE DAYS IS NOW SLOWLY WEAKENING AS
IT SITS NEARLY STATIONARY OVER THE NORTHERN BERING SEA. THE REMNANTS
OF THE OCCLUDED FRONT ARE NOW OVER EASTERN PORTIONS OF THE COPPER
RIVER BASIN. AN UPPER LEVEL SHORT-WAVE NOW OVERHEAD FROM ANCHORAGE
TO PRINCE WILLIAM SOUND IS VERY SLOW TO LIFT NORTHWARD.
THEREFORE...AREAS OF SNOW CONTINUE FROM THE COPPER RIVER BASIN
TO THE NORTHEASTERN SUSITNA VALLEY. SKIES HAVE CLEARED OUT NICELY
BEHIND THIS TROUGH. THERE IS THEN ANOTHER UPPER LEVEL SHORT-WAVE
OVER THE EASTERN BERING TRACKING EASTWARD AND BRINGING ANOTHER
ROUND OF RAIN AND SNOW SHOWERS TO SOUTHWEST ALASKA. THE BIG STORY
FOR TODAY IS THE DEVELOPMENT OF WHAT WILL BECOME A MAJOR NORTH
PACIFIC STORM. THERE IS A 200 KT JET WHICH HEADS STRAIGHT OUT OF
ASIA AND ACROSS THE NORTH CENTRAL PACIFIC. THERE IS A WEAK SURFACE
LOW RIGHT UNDERNEATH THIS JET AT AROUND 44N 170E. MEANWHILE A
SHORT-WAVE TROUGH IS DROPPING OUT OF RUSSIA WITH ARCTIC AIR
BEGINNING TO ADVECT SOUTHWARD TOWARD THE WEAK SURFACE LOW. ALL
OF THIS WILL LEAD TO RAPID DEEPENING OF THIS LOW OVER THE NEXT
24 TO 36 HOURS. THE BRUNT OF THIS STORM WILL INITIALLY BE FELT
ALONG AND TO THE SOUTH OF THE ALEUTIAN CHAIN AND ALASKA PENINSULA
WITH A EAST TO EAST-NORTHEAST TRACK.

.MODEL DISCUSSION...ALL MODELS ARE IN AGREEMENT EARLY ON IN BOMBING
OF THE NORTH PACIFIC LOW WITH AN EXPECTED DEEPENING OF AROUND 55 MB
OVER THE NEXT 24 HOURS BOTTOMING OUT AROUND 940 MB. THERE ARE THEN
DIFFERENCES IN SPEED AS THE LOW HEADS TO THE GULF SUNDAY AND MONDAY.
THE GFS IS THE OUTLIER WITH ITS SLOWER TRACK AND ENSEMBLES (INCLUDING
GFS) SUPPORT THE FASTER TRACK. WITH GOOD AGREEMENT IN A VERY DEEP
LOW WILL UP WIND FORECASTS OUT WEST AS THE LOW TRACKS TO THE SOUTH.
WILL THEN TREND HEAVILY TOWARD THE FASTER ECMWF SOLUTION AS THE LOW
HEADS TO THE GULF.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WITH CLEAR SKIES AND NEGATIVE VORTICITY
ADVECTION SUPPLYING SOME DOWNWARD MOTION ALOFT BETWEEN EXITING
SHORT-WAVE AND ONE APPROACHING FROM SOUTHWEST ALASKA...CONDITIONS
ARE FAVORABLE FOR FOG TO FORM TONIGHT. THE NEXT SHORT-WAVE WILL
THEN LIFT NORTHWARD ACROSS SOUTHCENTRAL SATURDAY INTO SUNDAY
BRINGING A FEW SHOWERS...PRIMARILY TO COASTAL AREAS. THE MEGA LOW
OVER THE NORTH PACIFIC WILL BEGIN TO IMPACT THE GULF EARLY SUNDAY
WITH CONDITIONS HEADING DOWNHILL OVER SOUTHCENTRAL BY SUNDAY NIGHT.
THERE IS LOW CONFIDENCE IN THE TRACK OF THIS LOW ONCE IT GETS INTO
THE GULF SO IT IS DIFFICULT TO PINPOINT THE IMPACTS ON SOUTHCENTRAL.

SOUTHWEST ALASKA...SHOWERS WILL CONTINUE OVERNIGHT ACROSS SOUTHWEST
ALASKA AS UPPER LEVEL SHORT-WAVE MOVES THROUGH. WITH WEAK ONSHORE
FLOW WOULD EXPECT AREAS OF FOG AS WELL. CONDITIONS WILL THEN DRY OUT
OVER SOUTHWEST ALASKA THIS WEEKEND AND INTO EARLY NEXT WEEK AS MAJOR
PACIFIC STORM PASSES TO THE SOUTH AND MEAN FLOW SHIFTS TO NORTHERLY.

BERING SEA/ALEUTIANS...WITH STORM EXPECTED TO BOMB JUST SOUTH OF THE
CHAIN WINDS WILL RAPIDLY STRENGTHEN TONIGHT INTO SATURDAY. WIDESPREAD
GALE TO STORM FORCE WINDS ARE EXPECTED ALONG THE ALEUTIANS AND
SOUTHERN ALASKA PENINSULA. THERE MAY EVEN BE SOME SMALL AREAS OF
HURRICANE FORCE WINDS SOUTH OF THE CHAIN...BUT WOULD LIKE TO SEE
CONSISTENCY IN THIS WITH NEXT MODEL RUN BEFORE GOING THAT STRONG.
THE STORM WILL TRACK QUICKLY TO THE EAST SO WINDS WILL BEGIN TO
DIMINISH BY SATURDAY NIGHT. COLD ADVECTION ACROSS THE BERING SEA ON
THE BACK SIDE OF THE SYSTEM ALONG WITH A SHORT-WAVE TROUGHS EMBEDDED
WITHIN THE NORTHERLY FLOW ALOFT WILL SET UP A SHOWERY REGIME FOR
THE REST OF THE WEEKEND AND INTO EARLY NEXT WEEK.

.LONG TERM FORECAST...A HIGH AMPLITUDE TROUGH WILL PERSIST OVER
MAINLAND ALASKA AND THE GULF THROUGH THE END OF NEXT WEEK WHICH
WILL ALLOW ARCTIC AIR TO BECOME FAIRLY ENTRENCHED ACROSS THE REGION.
AFTER THE GULF STORM DISSIPATES EARLY NEXT WEEK STORM TRACK WILL B
E FOCUSED OVER SOUTHERN TIER OF FORECAST AREA...ALONG THE ALEUTIAN
CHAIN AND OVER TO SOUTHEAST ALASKA. WILL HAVE TO WAIT AND SEE
WHETHER ANY OF THESE STORMS INTERACT WITH THE MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...155 170 172 175 176.
         GALE WARNING...150 165 171.
FIRE WEATHER...NONE.

SEB OCT 10