Blizzard and High Wind in Alaska, March 12 to 13, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT MON MAR 12 2012

.MODEL DISCUSSION...

MODELS IN GOOD AGREEMENT ESPECIALLY THROUGH THE SHORT TERM. PREFERRED
THE NAM IN THE FIRST 36 HOURS FOR DETAIL. TOOK THE MIDDLE GROUND
BETWEEN THE GFS AND EC FOR THE REMAINDER OF THE PACKAGE.

.ANALYSIS AND SHORT TERM FORECAST...

COMPLEX LOW PRESSURE WILL PERSIST IN THE GULF OF ALASKA THROUGH AT
LEAST MIDWEEK. PRIMARY CENTER THIS MORNING IS A 992 MB JUST SOUTH OF
MIDDLETON ISLAND. THIS CENTER IS EXPECTED TO DISSIPATE BY LATE THIS
AFTERNOON. AS IT DOES SO...THE PRESSURE GRADIENT ALONG THE GULF COAST
WILL GRADUALLY RELAX AND THE GUSTY NORTHEAST TO NORTHWEST WINDS THAT
ARE CONTINUE TO BLOW THROUGH CHANNELED AREAS OF THE CHUGACH AND
ALASKA RANGES WILL FINALLY ABATE. THIS INCLUDES AREAS SUCH AS
THOMPSON PASS...RESURRECTION BAY...AND KAMISHAK BAY WHICH ARE
PRESENTLY GUSTING 30 TO 45 MPH. NORTHEAST WINDS 10 TO 25 MPH OVER
SOUTHWEST ALASKA ARE COMBINING WITH SOME VERY COLD MORNING LOWS TO
PRODUCE WIND CHILLS OF 25 TO 35 BELOW. WIND CHILLS ARE EXPECTED TO
MODERATE LATER TODAY BUT THEN REDEVELOP OVERNIGHT.

LOW PRESSURE IN GULF REINTENSIFIES LATE TONIGHT WITH ASSISTANCE FROM
A DEVELOPING LOW ALOFT. WEAK SHORT WAVES EMBEDDED IN THE UPPER LEVEL
CYCLONIC FLOW SHOULD TRIGGER SCATTERED SNOW SHOWERS ACROSS MUCH OF
SOUTHCENTRAL ALASKA LATE TONIGHT AND EARLY TOMORROW. INCREASED CLOUD
COVER OVER SOUTHWEST ALASKA MAY HELP TO TEMPER OVERNIGHT LOWS IN THE
KUSKOKWIM VALLEY.

THE 964 MB LOW NEAR SHEMYA IS CURRENTLY AT ITS PEAK INTENSITY BUT
WILL BEGIN TO WEAKEN SLIGHTLY AS IT MEANDERS INTO THE SOUTHERN BERING
BY LATE THIS EVENING. LOW SHOULD STILL HAVE A CENTRAL PRESSURE OF
ABOUT 976 MB AS IT PASSES JUST SOUTH OF THE PRIBILOFS EARLY TUESDAY
MORNING BUT THEN RAPIDLY FILL TO 983 MB AS IT CROSSES OVER THE ALASKA
PENINSULA LATE TUESDAY AFTERNOON.

THE ASSOCIATED OCCLUDED FRONT IS QUICKLY APPROACHING THE PRIBILOF
ISLANDS...WHERE IT IS EXPECTED TO BRING BLIZZARD CONDITIONS LATER
THIS MORNING. A TRAILING COLD FRONT EXTENDS THROUGH THE EASTERN
ALEUTIANS. FRONTAL SYSTEM IS EXPECTED TO BOTH TRANSLATE EASTWARD AND
SHIFT SOUTHWARD. BY TUESDAY MORNING FRONT WILL EXTEND FROM SAINT
GEORGE TO SAND POINT. BY TUESDAY EVENING...FRONTAL DYNAMICS WILL HAVE
BROKEN DOWN AND ALL THAT WILL REMAIN WILL BE A RESIDUAL TROUGH OF LOW
PRESSURE EXTENDING ACROSS THE SOUTHERN BERING SEA AND EASTERN
ALEUTIANS.

A NARROW BAND OF STORM FORCE EASTERLIES PRECEDES THE FRONTAL ZONE
THIS MORNING...BUT A MUCH BROADER BAND OF STORM FORCE WESTERLIES IS
EXPECTED TO DEVELOP ACROSS THE SOUTHWESTERN BERING AND ALEUTIAN CHAIN
BY LATE MORNING. BY LATE AFTERNOON...WRAP AROUND COLD AIR ADVECTION
COMBINED WITH RAPID HEIGHT RISES BEHIND THE FAST MOVING LOW ARE
EXPECTED TO BRIEFLY GENERATE HURRICANE FORCE WINDS ACROSS THE CENTRAL
AND WESTERN ALEUTIANS TODAY.

THE MAIN BAND OF PRECIPITATION IS EXPECTED TO REMAIN JUST NORTH OF
THE ALEUTIANS OVER THE SOUTHERN BERING SEA...BUT PORTIONS OF THE
CHAIN COULD NEVERTHELESS SEE PERIODS OF REDUCED VISIBILITIES IN SNOW
AND BLOWING SNOW BOTH TODAY AND TONIGHT. STRONG WINDS OVER THE
ALEUTIANS AND BERING SEA WILL BEGIN TO DROP BELOW GALE FORCE LATE
TONIGHT...BUT SNOW AND RAIN SHOWERS SHOULD LINGER ACROSS THE
ALEUTIANS AND SOUTHERN BERING THROUGH AT LEAST MIDWEEK.

.UPPER LEVELS AND LONG TERM FORECAST...

LONG WAVE TROUGH EXTENDS FROM THE HIGH ARCTIC ACROSS MAINLAND ALASKA
AND THE GULF INTO THE NORTHEAST PACIFIC. CLOSED UPPER CENTER TO THE
WEST OF BRITISH COLUMBIA DISSIPATES OVER THE SOUTHEAST PANHANDLE BY
TUESDAY MORNING WHILE A NEW CLOSED CENTER FORMS OVER SOUTHWEST ALASKA
DURING THE SAME TIME FRAME. UPPER LEVEL RIDGING OVER THE BERING SEA
BREAKS DOWN TODAY AS THE UPPER LOW NEAR CENTER SHEMYA PRESSES
EASTWARD.

BY TUESDAY NIGHT...UPPER LEVEL PATTERN WILL BE TRANSFORMED. CLOSED
CENTER OVER SOUTHWEST ALASKA WILL DOMINATE THE MAP WHILE NEARLY ZONAL
FLOW WILL BE ESTABLISHED ACROSS THE WHOLE OF THE NORTH PACIFIC. THIS
PATTERN IS CONDUCIVE TO CONTINUED COLD WEATHER FOR BOTH SOUTHCENTRAL
AND SOUTHWESTERN ALASKA. MILD SHOWERY CONDITIONS CAN BE EXPECTED
ACROSS THE ALEUTIANS AND SOUTHERN BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195. HIGH WIND WARNING 191.
MARINE...GALE...130 170 179 413 414
         STORM...172 411 412
         HURRICANE FORCE...175 176
         HEAVY SPRAY...121 129 130 132 138 140 150 165 170
                       411 412 413 414
FIRE WEATHER...NONE.

ASB MAR 12