Gale Warning 264, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AKDT SUN MAR 14 2010

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE PATTERN IS IN PLACE
WITH TROUGHS CENTERED OVER EASTERN RUSSIA/FAR WESTERN BERING AND
MAINLAND ALASKA/GULF OF ALASKA...AND RIDGES OVER THE CENTRAL BERING
AND CANADIAN ROCKIES. BOTH OF THESE RIDGES ARE AMPLIFYING AS THE
TROUGHS DIG SOUTHEASTWARD AND THIS IS SLOWING DOWN THE EASTWARD
PROGRESSION OF THESE TROUGHS AND RIDGES. THE MAJOR ALEUTIAN LOW
FROM THE PAST FEW DAYS HAS NOW EVOLVED INTO A COMPLEX LOW...WITH
TWO MAIN CENTERS OVER THE SOUTHERN GULF AND ANOTHER FURTHER SOUTH.
THE OCCLUDED FRONT HAS MOVED TO SOUTHCENTRAL BRINGING SNOW PRIMARILY
TO PRINCE WILLIAM SOUND AND THE COOK INLET REGION. OFFSHORE FLOW
HAS LIMITED SNOWFALL IN MANY PLACES SUCH AS ANCHORAGE...THE
MATANUSKA VALLEY...AND VALDEZ BY MAINTAINING VERY DRY LOW LEVEL
AIR MASS RESULTING IN A LOT OF VIRGA. THIS FLOW HAS WEAKENED AND
LOW LEVELS HAVE MOISTENED A BIT...SO EXPECT TO SEE A LITTLE MORE
SNOW REACHING THE GROUND THIS AFTERNOON AS BANDS OF SNOW CONTINUE
TO MOVE ACROSS THE AREA. STRONG NORTHERLY WINDS ARE PRODUCING THE
USUAL BLIZZARD THROUGH THOMPSON PASS...BUT CONDITIONS WILL IMPROVE
LATER THIS AFTERNOON AS WINDS DIMINISH.

COLD ADVECTION ON THE BACK SIDE OF THE SYSTEM CONTINUE TO PRODUCE
SNOW SHOWERS...BLOWING SNOW...AND FRIGID TEMPERATURES ACROSS THE
EASTERN BERING REGION. BLIZZARD CONDITIONS...WHICH BEGAN
APPROXIMATELY 30 HOURS AGO...PERSIST ACROSS THE SOUTHERN ALASKA
PENINSULA. WITH THE BERING SEA ICE PACK NOT TOO FAR NORTH OF COLD
BAY (APPROXIMATELY 20 MILES) THE SOUTHERN PENINSULA IS OBSERVING
CONTINENTAL LIKE WEATHER WITH TEMPERATURES IN THE SINGLE DIGITS.
AN UPPER SHORT-WAVE TROUGH IS MOVING ACROSS THE PENINSULA NOW
WITH UPPER RIDGE RIGHT BEHIND IT...SO CONDITIONS ARE IMPROVING
FROM WEST TO EAST ACROSS THE EASTERN BERING.

.MODEL DISCUSSION...SOLUTIONS CONTINUE TO VARY WITH WAVES FORMING
ALONG THE BERING FRONT TONIGHT THROUGH MONDAY NIGHT. THE 12Z ECMWF
IS THE MOST AGGRESSIVE IN DEVELOPING ONE OF THESE LOWS AS IT MOVES
UP THE FRONT MONDAY NIGHT AND TUESDAY. SINCE NONE OF THE MODELS
HAVE VERY GOOD RUN-TO-RUN CONSISTENCY WITH THIS WILL GO WITH THE
MAJORITY SOLUTION OF WEAK FRONTAL WAVES WITHOUT FURTHER DEVELOPMENT.
OTHERWISE...MODELS ARE IN FAIR AGREEMENT WITH MAJOR FEATURES IN
THE SHORT-TERM.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE OCCLUDED FRONT WILL DISSIPATE THIS
AFTERNOON. HOWEVER...UPPER WAVES ROTATING AROUND THE GULF LOW
WILL CONTINUE TO PRODUCE SHOWERS THROUGH MONDAY NIGHT...ESPECIALLY
ALONG THE COAST. THE BERING RIDGE WILL THEN BUILD OVER MAINLAND
ALASKA TUESDAY AND WEDNESDAY WHICH WILL PUSH THE GULF LOW OFF
TO THE SOUTH AND SET UP DRY WEATHER ACROSS SOUTHCENTRAL. THERE
MAY BE A WEAK NORTHERLY WIND EVENT IN THE USUAL PLACES TUESDAY
NIGHT AND WEDNESDAY AS THE PRESSURE GRADIENT TIGHTENS AND COLDER
AIR MOVES DOWN THE EAST SIDE OF THE RIDGE.

SOUTHWEST ALASKA/EASTERN BERING...SNOW SHOWERS AND STRONG WINDS
WILL FINALLY COME TO AN END TONIGHT INTO MONDAY AS THE RIDGE
MOVES TO THE EASTERN BERING AND WESTERN ALASKA. THIS RIDGE WILL
STRENGTHEN AND BECOME CUT-OFF OVER WESTERN ALASKA TUESDAY...ENSURING
A PERIOD OF DRY AND CALM WEATHER ACROSS THE REGION.

BERING SEA/ALEUTIANS...THE STRENGTHENING RIDGE WILL SERVE TO BLOCK
STORMS OUT WEST FROM PROGRESSING BEYOND THE CENTRAL BERING. IN
FACT...MAJOR STORMS WILL REMAIN WEST OF THE FORECAST AREAS THE
NEXT FEW DAYS...ROTATING AROUND A LARGE LOW OVER EASTERN RUSSIA.
FRONTS EXTENDING FROM THESE LOWS WILL MOVE ACROSS THE WESTERN
BERING AND ALEUTIANS AND THEN STALL AND WEAKEN OVER THE CENTRAL
BERING.

.LONG TERM FORECAST...MEDIUM RANGE MODELS HAVE NOW COME INTO GOOD
AGREEMENT IN EVOLUTION OF THE BLOCKING RIDGE THE END OF NEXT WEEK.
IT WILL MOVE OVER THE NORTHERN MAINLAND MID WEEK AND THEN PHASE
WITH RIDGE ALONG WESTERN NORTH AMERICA COAST AT THE END OF THE WEEK.
THIS WILL ALLOW LONG-WAVE TROUGH TO SET UP FROM THE SOUTHERN
MAINLAND WESTWARD ACROSS THE BERING. SO...DRY WEATHER WILL PERSIST
THROUGH MID WEEK OVER THE MAINLAND WITH STORMS CONFINED TO THE
BERING AND ALEUTIANS. WEATHER WILL THEN BECOME MORE ACTIVE AT THE
END OF THE WEEK AS STORMS MOVE UP THE WESTERN SIDE OF THE RIDGE
TO MAINLAND ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 131 181.
MARINE...GALE WARNING...130 132 150 155 160 170 172 175 176 179 185.
         HEAVY FREEZING SPRAY WARNING...130 132 138 140 141 150 155
                                        165 170.
FIRE WEATHER...NONE.

SEB MAR 10