Blizzard Watch 23, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
215 PM AKST FRI MAR 6 2009

.ANALYSIS AND UPPER LEVELS...
ALTHOUGH THERE ARE NOT MANY FEATURES ON THE WEATHER
MAP THIS MORNING...THERE CERTAINLY IS A LOT OF WEATHER TO DISCUSS
ACROSS THE REGION. A NEGATIVELY TILTED TROUGH IS LOCATED FROM NORTH
CENTRAL ALASKA TO THE PANHANDLE AND IS QUICKLY MOVING EAST INTO
CANADA. A HIGHLY AMPLIFIED RIDGE IS BUILDING OVER SOUTHWEST ALASKA
AND THE EASTERN BERING SEA WHILE AN UPPER LEVEL TROF DIGS OVER THE
WESTERN BERING SEA. THE JET IS ALSO VERY AMPLIFIED FLOWING AROUND
THESE FEATURES...MAXING OUT AT 145 KNOTS ACROSS THE ALASKA RANGE
WHICH IS PLAYING A KEY ROLE IN THE STRONG SURFACE WINDS THROUGHOUT
SOUTHCENTRAL.

AT THE SURFACE...A 1004 MB LOW IS MOVING RAPIDLY EAST OF OUR DOMAIN
IN THE NORTHEASTERN GULF WHILE A STRONG AREA OF HIGH PRESSURE BUILDS
OVER SOUTHWEST ALASKA. THE PRESSURE GRADIENT BETWEEN THESE TWO
FEATURES IS RESULTING IN STRONG WINDS ACROSS MOST OF OUR
DOMAIN...COMBINED WITH THE RECENT SNOW FALL AND MANY AREAS ARE
SEEING
BLOWING AND DRIFTING SNOW. OUT WEST...A STRONG VERTICALLY STACKED
LOW
AND ITS ASSOCIATED FRONTAL BOUNDARY WILL MOVE NORTH ACROSS THE
CENTRAL ALEUTIAN ISLANDS LATE TONIGHT.

.MODEL DISCUSSION...
THE GFS CONTINUES TO BE THE MODEL OF CHOICE DUE TO RUN TO RUN
CONSISTENCY. GENERAL MODEL AGREEMENT IS GOOD THROUGH 84
HOURS...BEFORE MODELS BEGIN TO DIVERGE ON THE EVOLUTION OF THE
NUMEROUS SHORT WAVES MOVING ALONG THE SOUTHERN PERIPHERY OF THE
VERTICALLY STACKED LOW IN THE NORTH BERING.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
THE WEATHER MAP LOOKS BENIGN THIS MORNING BUT PLENTY OF WEATHER TO
CONTEND WITH. SNOW IS SLOWLY TAPERING OFF EAST OF THE RICHARDSON
HIGHWAY AS THE UPPER LEVEL TROUGH PUSHES EAST INTO CANADA THIS
AFTERNOON. A WINTER WEATHER ADVISORY FOR SNOW WAS EXTENDED THIS
MORNING TO ACCOUNT FOR THE SLOWER THAN EXPECTED MOVEMENT OF THE
UPPER
FEATURE. BEHIND THE TROUGH ARE SIGNIFICANT WINDS ASSOCIATED WITH THE
AFOREMENTIONED JET MAX FLOWING NW TO SE ACROSS THE REGION. A 1040 MB
AREA OF HIGH PRESSURE IS NOSING NORTHWARD OVER SOUTHWEST ALASKA AND
IS ADDING TO THE STRONG PRESSURE GRADIENT ACROSS THE MOUNTAIN
RANGES.
THE RESULT IS WIDESPREAD GUSTY CONDITIONS WITH MANY AREAS SEEING
BLOWING AND DRIFTING SNOW. CURRENTLY...THOMPSON PASS IS THE ONLY
REGION THAT HAS A BLIZZARD WARNING BUT ALMOST EVERY ZONE HAS LOCAL
AREAS OF BLOWING AND DRIFTING SNOW MENTIONED.

CONDITIONS WILL IMPROVE OVERNIGHT AS HIGH PRESSURE MOVES OVER
CENTRAL
ALASKA SATURDAY BEFORE MOVING EAST OF THE YUKON TERRITORY ON SUNDAY.
OVER THE WEEKEND...ONLY HIGH AND MIDDLE LEVEL CLOUDS WILL AFFECT
SOUTHCENTRAL UNTIL SUNDAY EVENING WHEN A FRONTAL BOUNDARY BRINGS
SOUTHEASTERLY WINDS AND THE CHANCE OF PRECIPITATION BACK TO KODIAK
ISLAND AND OTHER COASTAL AREAS. CLOUDS AND SNOW WILL CREEP BACK INTO
THE FORECAST EARLY NEXT WEEK AS THAT FRONT STALLS OVER THE REGION
AND
A WEAK SURFACE LOW DEVELOPS OVER THE NORTHERN GULF.

.SOUTHWEST...
BLUSTERY CONDITIONS CAN BE FOUND ALL ALONG THE ALASKA RANGE TODAY
INCLUDING THE UPPER KUSKOKWIM VALLEY. WINDS WILL QUICKLY DIMINISH
OVERNIGHT AS HIGH PRESSURE BUILDS OVER THE AREA. THE NEXT FRONTAL
BOUNDARY WILL APPROACH BRISTOL BAY AND KUSKOKWIM DELTA SATURDAY
AFTERNOON AND WILL LIKELY BRING A PERIOD OF BLIZZARD CONDITIONS
AGAIN
TO THE DELTA. THE WARM AIR ALOFT COULD ALSO LEAD TO PERIODS OF
FREEZING RAIN FOR MUCH OF SOUTHWEST ALASKA UNTIL SUNDAY WHEN COLDER
AIR ALOFT ASSOCIATED WITH THE OCCLUSION MOVES INLAND AGAIN.
REGARDLESS...IT WILL BE A MESSY AND ACTIVE FORECAST OUT WEST AS THE
LONG WAVE TROUGH MOVES OVER THE CENTRAL BERING SEA ALLOWING
SOUTHWESTERLY FLOW AND ABUNDANT MOISTURE TO FILTER INLAND.

.BERING SEA AND ALEUTIANS...
THE CENTRAL AND WESTERN ALEUTIANS ARE ALREADY SEEING THE AFFECTS
FROM
THE VERTICALLY STACKED LOW DEVELOPING SOUTH OF THE CHAIN. THERE IS A
SHARP FRONTAL BOUNDARY THAT IS SEPARATING THE WARM SUBTROPICAL AIR
AND THE ARCTIC AIRMASS OVER THE FAR WESTERN ALEUTIANS. THERE IS
ENOUGH COLD AIR AND PLENTY OF WIND TO RESULT IN BLIZZARD CONDITIONS
OVER ATTU AND SHEMYA ISLANDS THIS AFTERNOON. THE THREAT WILL
CONTINUE
OVERNIGHT BEFORE THE STRONGEST WINDS AND COLD AIR ADVECTION MOVES
OVER THE CENTRAL BERING SEA. OVER THE WEEKEND...THIS LOW WILL MOVE
NORTH AND SLOWLY WEAKEN. SHORT WAVES EMBEDDED IN THIS LARGE AREA OF
CYCLONIC CIRCULATION WILL DEVELOP EARLY NEXT WEEK AND WILL BE THE
NEXT FOCAL POINT FOR WEATHER THROUGH THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...131 191
         BLIZZARD WATCH...155
MARINE...GALE WARNING...121 125 130 132 140 155 160 165 170 171 172

           175 179 180 185
         STORM WARNING...120 176
         HEAVY FREEZING SPRAY WARNING...185
FIRE WEATHER...NONE

AB MAR 09