Heavy Freezing Spray Warning 68, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
150 PM AKST SUN FEB 19 2012

.ANALYSIS AND UPPER LEVELS...
THE OVERALL PATTERN REMAINS RELATIVELY UNCHANGED WITH A BROAD UPPER
LEVEL TROF ANCHORED OVER THE BERING SEA AND A WEAK RIDGE OVER THE
ALASKA PANHANDLE. A LARGE PLUME OF MOISTURE IS EVIDENT ON THE 21Z
SATELLITE IMAGERY DEPICTING DIVERGENT FLOW ALOFT...POINTED DIRECTLY
AT THE PANHANDLE. ALSO EVIDENT ON THE SATELLITE IMAGERY IS A
SHORTWAVE STRETCHING FROM NEAR THE PRIBILOF ISLANDS BACK ACROSS THE
ALASKA PENINSULA AND SOUTHEAST THROUGH THE SOUTHERN GULF OF ALASKA.
THIS UPPER LEVEL WAVE IS MAKING PROGRESS TO THE NORTHEAST BRINGING
LIGHT PRECIPITATION NEAR BRISTOL BAY AND THE NORTHERN GULF.

AT THE SURFACE...A WEAK AREA OF LOW PRESSURE IS SITUATED JUST NORTH
OF KODIAK ISLAND AND DRIFTING WEST TOWARD THE MAINLAND. A DEVELOPING
LOW ASSOCIATED WITH THE JET STREAM SOUTH OF OUR DOMAIN IS MOVING
TOWARD THE ALASKA PENINSULA. THIS LOW WILL BE THE MAIN WEATHER MAKER
ACROSS SOUTHCENTRAL ALASKA INTO THE MIDDLE OF THIS WEEK. OUT WEST...A
VERTICALLY STACKED LOW WEST OF THE PRIBILOFS CONTINUES TO DRIFT EAST
AS IT WEAKENS.

.MODEL DISCUSSION...
ALL MODELS INITIALIZE WELL COMPARED TO THE 18Z AND 21Z SATELLITE
IMAGERY. VERY FEW CHANGES WILL BE MADE TO THE FORECAST AS MODELS ARE
VERY CONSISTENT OVER THE FIRST 60 HOURS WITH THE PREVIOUS SOLUTIONS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...
THE DEVELOPING LOW SOUTH OF THE ALASKA PENINSULA IS APPROXIMATELY 970
MB AND WILL CONTINUE TO STRENGTHEN TO 960 MB AS IT APPROACHES KODIAK
ISLAND TONIGHT. A SHORTWAVE EMBEDDED IN THE SOUTHWEST FLOW ALOFT WILL
USHER MOST OF THE ENERGY AND SUBSEQUENTLY THE MOISTURE TOWARD THE
SOUTHEAST. THE LOW OCCLUDES AND BEGINS TO WEAKEN BY TOMORROW MORNING
AS IT ENTERS THE GULF. KODIAK ISLAND WILL SEE ABUNDANT RAIN OUT OF
THIS SYSTEM AS WILL MOST OF PRINCE WILLIAM SOUND. SINCE MOST OF THE
ENERGY SHOOTS OFF TOWARD SOUTHEAST ALASKA...ONLY LIGHT PRECIP IS
EXPECTED WITH THIS SYSTEM OVER THE INTERIOR AND THAT WILL NOT HAPPEN
UNTIL LATE MONDAY NIGHT AND EARLY TUESDAY WHEN THE SURFACE LOW MOVES
INTO WESTERN PRINCE WILLIAM SOUND. THE SURFACE GRADIENT BECOMES VERY
WEAK ALLOWING FOR CEILINGS TO DROP UP COOK INLET AND LIGHT SNOW TO
FALL OVER MUCH OF THE INTERIOR THROUGH TUESDAY NIGHT. WEAK COLD AIR
ADVECTION ACROSS THE ALASKA PENINSULA WILL HELP SUSTAIN A SURFACE LOW
IN THE VICINITY OF PRINCE WILLIAM SOUND THROUGH MID WEEK...ALSO
MAINTAINING THE CHANCE OF LIGHT SNOW FOR MANY AREAS.

SOUTHWEST...
VERY LIGHT SNOW IS FALLING OVER PORTIONS OF SOUTHWEST ALASKA AS A
RESULT OF THE FIRST SHORTWAVE MOVING OVERHEAD. THIS AREA OF LIFT WILL
SUBSIDE THIS EVENING AS THE WAVE MOVES INLAND AND THE DEVELOPING LOW
SOUTH OF THE AKPEN TAKES OVER. MOISTURE ASSOCIATED WITH THIS SYSTEM
WILL AGAIN SPREAD ACROSS THE BRISTOL BAY ZONE LATE TONIGHT...COUPLED
WITH A STRENGTHENING PRESSURE GRADIENT WILL LIKELY RESULT IN AREAS OF
BLOWING SNOW. AGAIN...THE MAIN ENERGY WITH THIS SYSTEM WILL MISS OUR
DOMAIN SO NOT EXPECTING MUCH ACCUMULATION...SO NO ADVISORIES OR
WARNING ANTICIPATED FOR SOUTHWEST ALASKA EITHER.

WEAK HIGH PRESSURE BUILDS OVER THE REGION THROUGH MID WEEK WITH LIGHT
ONSHORE FLOW. THIS WILL LIKELY RESULT IN LOW CEILINGS...FOG...OR
FLURRIES FOR MUCH OF THE COASTAL AREAS. THIS PATTERN OF INTERIOR SUN
AND COASTAL CLOUDS/PRECIP WILL PERSIST THROUGH AT LEAST WEDNESDAY
INTO THURSDAY.

BERING SEA/ALEUTIANS...
THE BERING SEA REMAINS RELATIVELY TAME FOR THIS TIME OF YEAR. THE LOW
WILL SKIRT THE ALASKA PENINSULA BRINGING RAIN AND SNOW TO THAT
REGION...BEFORE TRANSITIONING BACK TO ALL SNOW LATE TONIGHT. WINDS
ARE NOT EXPECTED TO BE TOO STRONG ON THE BACKSIDE OF THE LOW BUT
COULD SEE BRIEF WHITE OUT CONDITIONS IN THE HEAVIER SNOW SHOWERS AND
BLOWING SNOW ON THE NORTH SIDE OF THE PENINSULA. THROUGH MID
WEEK...EXPECT THE WEAKENING VERTICALLY STACKED LOW TO DRIFT
EAST...BRINGING LIGHT PRECIPITATION AND LOW CEILINGS TO MUCH OF THE
BERING SEA. COLD ADVECTION SNOW SHOWERS WILL PERSIST ON THE BACKSIDE
OF THIS LOW UNTIL HIGH PRESSURE BUILDS IN OVER THE WESTERN BERING
LATE TUESDAY NIGHT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM...120 130 138 140 352
         GALE...132 141 150 155 351
FIRE WEATHER...NONE

AB FEB 12