Blizzard and High Wind in Alaska, February 23, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST WED FEB 23 2011

.MODEL DISCUSSION...00Z MODELS IN GOOD AGREEMENT WITH KEY FEATURES.
NAMELY...STRENGTH AND MOVEMENT OF DEEPENING LOW THAT WILL MOVE N OVER
THE WRN ALEUTIANS TODAY...AND STRONG SURFACE HIGH OVER THE INTERIOR
THAT IS EXPANDING S OVER THE GULF OF AK TODAY AND TONIGHT. THERE IS
EVEN DECENT AGREEMENT INTO THE LONG TERM BETWEEN THE GFS AND ECMWF
AND HENCE...MODERATE FORECAST CONFIDENCE OUT INTO DAYS 3-5. SHORT
TERM FORECASTS WERE MADE USING MAINLY NAM12 FOR RESOLUTION...AND GFS
FOR THE EXTENDED GRIDS.

.ANALYSIS AND UPPER LEVELS...UPPER RIDGING OVER ERN BERING AND SW AK
HAS STRONG CONSOLIDATED SSWRLY JET AHEAD OF IT. THE DEEPENING LOW
S OF PASY WILL RAPIDLY MOVE N TODAY INTO WRN BERING...AND BY TONIGHT
WILL BE AT 60N WELL W OF SAINT MATTHEW ISLAND. BY THU AFTERNOON THE
LOW WILL BE OVER THE FAR ERN TIP OF SIBERIA. THE ASSOCIATED OCCLUDED
FRONT WILL BE SLOW TO MOVE E...SINCE THE PARENT LOW IS MOVING N...AND
IT WILL WEAKEN AND SPLIT AS IT DOES SO...SINCE IT IS MOVING INTO STRONG
UPPER RIDGING. IT WON'T REACH ERN ALEUTIANS UNTIL LATE THU...AND AK
PEN FRI. THE PARENT UPPER LOW...WHILE WEAKENING...IS EXPECTED TO FLATTEN
THE STRONG UPPER RIDGE THU NIGHT AND FRI. A STRONG SHORT-WAVE TROUGH
PASSAGE WILL THEN OCCUR OVER SW AND S-CENTRAL AK FRI WITH THE REMAINS
OF THE FRONTAL SYSTEM. UPPER RIDGING WILL REBOUND BEHIND THIS BACK TO
THE W OVER THE ERN BERING LATE FRI THROUGH THE WEEKEND...LEAVING MAIN-
LAND AK UNDER A STRONG CONSOLIDATED NRLY UPPER FLOW WITH SIGNIFICANT
COLD AIR ADVECTION. WITH A STRONG SURFACE HIGH FORECAST TO BUILD IN
OVER THE INTERIOR AGAIN LATE SAT/SUN...A TROUGH S OF THE ERN GULF
COAST...AND NRLY MID-LEVEL FLOW...ANOTHER ROUND OF STRONG OUTFLOW
WINDS EXPECTED THROUGH COASTAL GAPS/PASSES THEN.

.SHORT TERM FORECAST...
ALEUTIANS: VERY STRONG WINDS EXPECTED ON BACK SIDE OF 975 MB OR SO LOW
MOVING N TODAY SO HIGH WIND WATCH WAS UPGRADED TO WARNING FOR ZONE 191.
STORMS FORCE WINDS TODAY WILL OCCUR OVER WRN ALEUTIANS N TO SAINT
MATTHEW ISLAND WATERS...WITH GALES AS FAR W AS WRN HALF OF THE AK PEN
TONIGHT/THU. SNOW FOR WRN ALEUTIANS TODAY KISKA W...MIXED PRECIP. FOR
CENTRAL ALEUTIANS WITH FRONT. RAIN/SNOW WILL SPREAD E TO ERN ALEUTIANS
THU AND AK PEN THU NIGHT/FRI.

SW AK: WINDS INCREASING TODAY ON OUTER COAST N OF CAPE NEWENHAM AS
PRESSURE GRADIENT TIGHTENS UP. RAIN/SNOW NOT REACHING BERING COAST
UNTIL THU MORNING...THEN SPREADING INLAND THU NIGHT/FRI. SIGNIFICANT
WARMER AIR AHEAD OF FRONT...SO FREEZING RAIN COULD OCCUR IN SW INTERIOR
AND PLACES LIKE DILLINGHAM AND KING SALMON THU NIGHT. PRECIP. WILL
QUICKLY CHANGE TO ALL SNOW WITH FRONTAL PASSAGE EARLY FRI.

S AND E OF AK RANGE: SURFACE HIGH SLIPPING S INTO GULF OF AK TODAY AS
UPPER RIDGING EXPANDS FURTHER E. THUS STRONG OUTFLOW WINDS THROUGH
COASTAL GAPS WILL RAPIDLY DIMINISH TODAY. CLEAR AND DRY WEATHER WITH
WARMING ALOFT UNDER HIGH PRESSURE RIDGING WILL STRENGTHEN VALLEY
INVERSIONS TONIGHT THROUGH THU NIGHT. SHORT-WAVE TROUGH/FRONTAL PASSAGE
FRI WILL BRING QUICK SHOT OF PRECIP. MOST AREAS. MODELS CURRENTLY KEEP
ENOUGH COLD AIR IN OVER SUSITNA VALLEY AND ANCHORAGE BOWL FOR ALL SNOW
WITH MIXED PRECIP. ALONG COAST. WITH FAIRLY STRONG CONSOLIDATED SWRLY
FLOW AND DECENT DYNAMICS...COULD SEE 2-4" SNOW ANC BOWL FRI...AND AT
LEAST THAT MUCH OR MORE SUSITNA VALLEY FROM PARKS HIGHWAY E. COPPER
RIVER BASIN SHOULD BE ABLE TO PICK UP A FEW INCHES LATE FRI AS WELL
UNDER CURRENT MODEL DEPICTIONS.

.LONG TERM FORECAST...UPPER RIDGING BUILDS N OVER CENTRAL/ERN ALEUTIANS
SAT AND CLOSED UPPER HIGH FORMS OVER NRN BERING SUN/MON. MAINLAND AK
AND AK PEN WILL BE UNDER STRONG CONSOLIDATED NRLY FLOW AHEAD OF THIS.
BELOW-AVERAGE TEMPERATURES WITH DRY WEATHER AND STRONG OUTFLOW WINDS
COASTAL GAPS WILL RETURN TO S-CENTRAL AK AND GULF COAST THEN. SLIGHTLY
WARMER BUT VERY WINDY FOR SW AK AND AK PEN. DRY ERN ALEUTIANS...BUT
ANOTHER LOW WILL LIFT N OVER WRN AND CENTRAL ALEUTIANS SAT/SUN WITH
AT LEAST GALE FORCE WINDS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING TODAY ZONE 191/WRN ALEUTIANS
MARINE...STORMS:  176 185 411 412 413
         GALES:  155 160 165 170 171 172 179 180 414
         HEAVY FREEZING SPRAY:  121 129 140 185

MAR FEB 11