Blizzard in Alaska, February 17 to 18, 2009

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST TUE FEB 17 2009

.ANALYSIS AND UPPER LEVELS...
AT THE SURFACE...A WEAKENING 1002 MB LOW IS LOCATED OVER THE NORTHERN
GULF. MOIST SOUTHERLY FLOW OVER THE ALEUTIANS AND BERING SEA
CONTINUES IN ASSOCIATION WITH A DEEPENING 981 MB LOW SOUTH OF SHEMYA.
THIS LOW AND AN ASSOCIATED FRONTAL BOUNDARY WILL BE THE MAJOR WEATHER
MAKERS OVER THE STATE THROUGH THE NEXT SEVERAL DAYS.

IN THE UPPER LEVELS...A BROAD TROUGH FUELING THE ACTIVE WEATHER
PATTERN OVER THE AREA EXTENDS THROUGH THE WESTERN MAINLAND AND INTO
THE NORTH PACIFIC. VARIOUS SHORTWAVE TROUGHS ARE EMBEDDED WITHIN THE
LARGER WAVE PATTERN. THE MOST SIGNIFICANT OF THESE TROUGHS CURRENTLY
EXTENDS THROUGH THE KUSKOKWIM DELTA AND THE ALASKA PENINSULA.
PROGRESSIVE RIDGING OVER THE CENTRAL BERING SEA IS BUILDING BEHIND
THE TROUGH. ANOTHER STRONG UPPER TROUGH IS TRANSLATING
EASTWARD...CURRENTLY CENTERED OVER THE KAMCHATKA PENINSULA.

.MODEL DISCUSSION...
MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH NO TRULY SIGNIFICANT
DIFFERENCES ARISING UNTIL 12Z THURSDAY. THE MAIN AREA OF CONTENTION
AFTER THIS TIME IS THE EVOLUTION AND POSITIONING OF THE LOW CURRENTLY
WEST OF SHEMYA AFTER IS MOVES INTO THE BERING SEA. OTHER DIFFERENCES
EXIST REGARDING THE WEAK LOW IN THE NORTHERN GULF. THE GFS IS THE
OUTLIER...TAKING THE LOW NORTH INTO PRINCE WILLIAM SOUND. MINOR
CHANGES WERE MADE TO THE EXISTING SHORT TERM FORECAST...WITH A FOCUS
ON THE NAM SOLUTION THROUGH 84 HOURS.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
THE LOW IN THE NORTHERN GULF WILL MOVE EASTWARD TODAY WHILE
DISSIPATING. THE AFOREMENTIONED TROUGH CURRENTLY OVER THE WESTERN
MAINLAND WILL SWING THROUGH THE REGION THIS AFTERNOON AND TONIGHT. AS
A RESULT...RAIN AND SNOW WILL CONTINUE ALONG COASTAL AREAS...WITH
LIGHTER SNOW INLAND. DRYING WILL BE RAPID ALBEIT SHORT LIVED AS THE
TROUGH PUSHES OFF TO THE EAST...WITH FOG BECOMING A CONCERN OVER COOK
INLET AND SUSITNA VALLEY AREAS TONIGHT. WEDNESDAY WILL SEE INCREASING
CLOUDINESS AND CHANCES OF PRECIPITATION AS THE AFOREMENTIONED FRONT
MOVES INTO THE AREA. HAVE INCREASED PRECIP CHANCES ONCE AGAIN WITH
THE MORNING PACKAGE AS CONFIDENCE CONTINUES TO INCREASE. DEEP
SOUTHERLY FLOW AND GOOD ISENTROPIC LIFT WILL LEAD TO WIDESPREAD
PRECIPITATION ACROSS SOUTHCENTRAL BY WEDNESDAY NIGHT...WITH ANOTHER
GOOD UPSLOPE SNOW EVENT SETTING UP FOR THE SUSITNA VALLEY. AT THIS
TIME...EXPECT RAIN AND SNOW ALONG COASTAL LOCATIONS...WITH SNOW
FARTHER INLAND. STRONG WINDS THROUGH CHANNELED TERRAIN AND HIGHER
ELEVATIONS WILL ALSO BECOME AN ISSUE AS THE FRONT MOVES INTO THE
AREA.

.SOUTHWEST...
CLOUDS AND MOISTURE WILL BE ON THE INCREASE THROUGHOUT THE
DAY...ESPECIALLY ALONG THE COAST...AS THE FRONT BEGINS TO PUSH INTO
THE AREA. OVERRUNNING WILL LEAD TO PRECIPITATION ALONG THE COAST
TONIGHT...PUSHING INLAND THROUGHOUT THE DAY ON WEDNESDAY. WINDS WILL
BE INCREASING WELL AHEAD OF THE FRONT...AND WITH PRECIPITATION
EXPECTED TO START OUT AS SNOW...THE POSSIBILITY FOR BLIZZARD
CONDITIONS WILL HAVE TO BE MONITORED ALONG THE WESTERN CAPES AND
KUSKOKWIM DELTA. AS WARMER AIR IS ADVECTED INTO THE REGION
WEDNESDAY...PRECIPITATION WILL BECOME ALL RAIN ACROSS THE ALASKA
PENINSULA AND PARTS OF BRISTOL BAY. DEEP SOUTHERLY FLOW AND AMPLE
MOISTURE WILL SET UP DECENT UPSLOPE SNOW IN THE KUSKOKWIM
VALLEY...WHERE WARM AIR WILL HAVE TROUBLE PENETRATING SO FAR INLAND.
AS THE FRONT PUSHES TO THE EAST...COLD ADVECTION WILL TURN PRECIP
BACK TO ALL SNOW WITH SHOWERS LINGERING INTO THURSDAY.

.BERING SEA AND ALEUTIANS...
MAIN STORY IN THE SHORT TERM WILL BE THE DEEPENING LOW CURRENTLY
SOUTH OF SHEMYA...AND ITS ASSOCIATED FRONT. THE LOW WILL MOVE
NORTHWARD INTO THE BERING SEA BY THIS AFTERNOON...PASSING JUST EAST
OF SHEMYA. THE FRONT ASSOCIATED WITH THE LOW IS ALREADY IMPACTING THE
CENTRAL ISLANDS...AND WILL SPREAD TO THE EASTERN ISLANDS BY
WEDNESDAY. WINDS ALONG THE FRONT WILL STRENGTHEN TO HURRICANE FORCE
OVER THE NORTH CENTRAL BERING SEA BY THIS AFTERNOON...WITH WIDESPREAD
STORM AND GALE FORCE WINDS ELSEWHERE. REMNANT COLD AIR IN PLACE OVER
THE PRIBILOFS WILL RESULT IN POTENTIAL BLIZZARD CONDITIONS AS SNOW
AND HIGH WINDS MOVE INTO THE AREA TONIGHT. AS THE WARM FRONT MOVES
THROUGH...ALL LOCATIONS WILL SEE A RAIN SNOW MIX...WITH SOME AREAS
BECOMING ALL RAIN. BEHIND THE FRONT...GUSTY SOUTHERLY WINDS AND
SCATTERED SHOWERS WILL PERSIST.

.LONG TERM FORECAST...
A PROGRESSIVE PATTERN WILL CONTINUE ACROSS THE AREA THROUGH THE
EXTENDED. MODELS AGREE ON A LARGE AREA OF HIGH PRESSURE BUILDING OVER
THE ALEUTIANS AND SOUTHWEST ALASKA LATE WEEK...SLIDING EASTWARD OVER
THE MAINLAND THROUGH THE WEEKEND. BEHIND THIS HIGH...ANOTHER NORTH
PACIFIC LOW WILL BEGIN TO AFFECT THE WESTERN AND CENTRAL ALEUTIANS AS
WE MOVE INTO THE WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WIND CHILL ADVISORY...155
MARINE...GALE WARNING...155 160 165 170 172 176 179 180 414
         STORM WARNING...175 411 413
         HURRICANE FORCE WIND WARNING...185 412
         HEAVY FREEZING SPRAY WARNING...130 138 150 155 160 165 411
                                        412
FIRE WEATHER...NONE

NRH FEB 09