Blizzard in Alaska, February 29, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST WED FEB 29 2012

.ANALYSIS AND UPPER LEVELS...

UPPER LEVEL TROUGHINESS CONTINUES OVER THE MAINLAND AND THE NORTHERN
AND EASTERN GULF OF ALASKA THIS MORNING. WITHIN THIS TROUGH RESIDES A
SMALL BUT PRONOUNCED UPPER LEVEL LOW OVER THE NORTHERN CHIGMIT
MOUNTAINS THAT WILL BEGIN TO OPEN INTO AN UPPER WAVE AS IT DIGS EAST
ACROSS THE AREA TODAY.

OVER THE BERING REGION...A BROAD UPPER LEVEL RIDGE WITH ITS AXIS
EXTENDING NORTH FROM THE SUBTROPICAL PACIFIC NORTH ACROSS UNALASKA
ISLAND AND THE PRIBILOFS. TO THE WEST...THERE LIES A NEARLY
STATIONARY UPPER LEVEL LOW BETWEEN SHEMYA AND KAMCHATKA. A STRONG
SOUTHERLY JET STREAK BETWEEN THESE TWO IS HELPING TO INITIATE
STRENGTHENING LOW PRESSURE NEAR THE SURFACE SOUTH OF ADAK WHICH WILL
BECOME QUITE STRONG BY LATER TODAY AS IT NEARS ATKA. A STRONG FRONT
EXTENDING FROM THIS LOW WILL MOST LIKELY BRING BLIZZARD CONDITIONS TO
THE PRIBILOFS BEGINNING THIS AFTERNOON AND WILL LIKELY PRODUCE
NEAR-BLIZZARD CONDITIONS ALONG THE ALASKA PENINSULA.

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT OVERALL. USED A BLEND OF MODELS
DEPENDING ON THE PARAMETER IN THE GRIDS...WHICH IS FAIRLY CLOSE TO A
BLEND OF THE GFS...EC AND SREF MODELS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...

SMALL UPPER LEVEL LOW OVER THE CHIGMIT MOUNTAINS WILL SLIDE EAST
ACROSS THE COOK INLET REGION THIS MORNING AND THEN THE PRINCE WILLIAM
SOUND REGION BY THIS EVENING. THERE IS DECENT WARM ADVECTION IN THE
925-700 MB LAYER WHICH WILL PROVIDE ADEQUATE LIFT THIS
MORNING...ALONG WITH MOIST ONSHORE EASTERLY FLOW AT MOUNTAINTOP LEVEL
AND SOUTHEASTERLY FLOW ABOVE THAT. 12Z ANCHORAGE MORNING SOUNDING
TEMPERATURES SHOW THE BEST SATURATION THROUGH THE COLUMN IN THE
TEMPERATURE RANGE OF -8 TO -13 DEGREES CELSIUS...EXCELLENT FOR THE
DEVELOPMENT OF FLUFFY DENDRITES. THE RESULT WILL BE LIGHT SNOW OVER
PARTS OF THE COOK INLET REGION...INCLUDING ANCHORAGE...UNTIL TROUGH
PASSAGE AROUND MIDDAY. SNOW ACCUMULATIONS MAY EXCEED EXPECTATIONS BUT
GENERALLY REMAIN LIGHT...NO MORE THAN A COUPLE OF INCHES MOST LOCALES
BEFORE ENDING AROUND MIDDAY. EXPECT MUCH THE SAME ACROSS PRINCE
WILLIAM SOUND UNTIL TROUGH PASSAGE BY LATE TONIGHT.

A RELATIVE LULL IN THE WEATHER RESULTS FOR TONIGHT BEFORE THE NEXT
SYSTEM MOVES INTO THE REGION FOR THURSDAY. THE APPROACHING FRONT
MOVES INTO THE FAR SOUTHWEST GULF LATE TONIGHT AND WILL BRING SNOW TO
KODIAK...THEN A TRIPLE POINT LOW FORMS AND MOVES NORTH AND EAST TO
ABOUT 50 MILES WEST OF MIDDLETON ISLAND BY LATE THURSDAY NIGHT.
EXPECT THE MAJORITY OF THE SNOW TO REMAIN ACROSS THE KENAI PENINSULA
AND PRINCE WILLIAM SOUND WITH LITTLE TO MINOR ACCUMULATIONS FOR
ANCHORAGE AND POINTS NORTH.

SOUTHWEST...

GENERALLY TRANQUIL WEATHER IN STORE FOR TODAY WITH GENERALLY OFFSHORE
FLOW. EXPECT NORTHEAST WINDS TO INCREASE BY THE EVENING AS A STRONG
WEATHER FRONT BEGINS TO APPROACH THE REGION FROM THE SOUTHWEST
TONIGHT WHICH COMBINED WITH THE COLD AIR COULD PRODUCE MARGINAL
ADVISORY LEVEL WIND CHILLS ALONG THE KUSKOKWIM DELTA. SNOW WILL
DEVELOP OVER THE BRISTOL BAY REGION THURSDAY MORNING AND THEN SNOW
SHOWERS WILL POSSIBLY DEVELOP OVER THE KUSKOKWIM DELTA REGION AS WELL
BY THURSDAY NIGHT.

BERING SEA/ALEUTIANS...

LOW PRESSURE APPROACHING THE CENTRAL ALEUTIANS WILL RAPIDLY INTENSIFY
BY LATE THIS AFTERNOON AND BRING STORM FORCE WINDS AND A FAIRLY TIGHT
CORE OF WINDS AROUND IT. THIS LOW WILL MOVE EAST ALONG OR JUST SOUTH
OF THE ALEUTIANS AND THE ALASKA PENINSULA THROUGH THURSDAY EVENING.
OUT AHEAD OF THIS SYSTEM...A STRONG FRONT WILL BECOME SITUATED JUST
SOUTH OF THE ALASKA PENINSULA AND MAY BRING BLIZZARD CONDITIONS FOR A
SHORT PERIOD OF TIME TO THE REGION. EXPECT MORE DEFINITE BLIZZARD
CONDITIONS TO DEVELOP FOR A LENGTHY DURATION FOR THE PRIBILOFS FROM
THIS AFTERNOON AND LASTING WELL INTO THURSDAY MORNING.

ON THE BACK SIDE OF THIS DEPARTING LOW...EXPECT STRONG NORTHERLY FLOW
AND AREAS OF SNOW SHOWERS.

.LONG TERM FORECAST...

EXPECT LOW PRESSURE TO MOVE INTO THE NORTHERN GULF AND THEN THE
WEATHER PATTERN BECOMES FAIRLY STATIC FOR MOST OF THE LATE WEEK INTO
EARLY NEXT WEEK PERIOD...WITH COLD NORTHERLY FLOW OVER MOST OF THE
BERING AND SNOW AND SNOW SHOWERS ALONG THE NORTHERN GULF COAST AND
SOUTHERN SOUTHCENTRAL MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING...195
MARINE...GALES...120 130 132 160 165 171 175 179 351 352 412 414
         STORMS...150 155 170 172 413
         HVY FRZG SPRY...121 130 132 138 140 141 150 179 411 412 413
                         414
FIRE WEATHER...NONE.

29/CC FEB 12