Heavy Freezing Spray Warning 129, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST THU MAR 8 2012

.ANALYSIS AND UPPER LEVELS...
TWO LARGE AND FAST MOVING SYSTEMS ARE IMPACTING SOUTHEAST AND WESTERN
ALASKA TODAY. THESE TWO SYSTEMS ARE ROTATING AROUND A BROAD TROUGH
LOCATED OVER THE INTERIOR OF THE STATE. UNDER THIS TROUGH...A MIXTURE
OF SUN AND STRATUS CAN BE FOUND WITH BELOW AVERAGE TEMPERATURES
PREVAILING. THE FIRST OF THE LARGE LOW PRESSURE SYSTEMS HAS FULLY
OCCLUDED AND IS RAPIDLY APPROACHING SOUTHEAST ALASKA. OVERRUNNING
MOISTURE IS SPREADING SNOW NORTHWARD OVER EASTERN PRINCE WILLIAM
SOUND AND THE EASTERN COPPER RIVER BASIN. OUT WEST...A FAST MOVING
LOW IS CROSSING THE EASTERN ALEUTIANS AND WILL CONTINUE TO MARCH EAST
TONIGHT. THE FRONT ASSOCIATED WITH THIS SYSTEM IS BRINGING BLIZZARD
CONDITIONS TO THE PRIBILOFS AS WELL AS REDUCING VISIBILITY IN BLOWING
SNOW AROUND THE ALASKA PENINSULA.

.MODEL DISCUSSION...
OVERALL THE MODELS ARE IN EXCELLENT AGREEMENT ON ALL OF THE MAJOR
FEATURES. SOME MINOR DIFFERENCES IN THE 12Z SOLUTIONS ARE LEADING TO
SOME TWEAKS TO THE FORECAST THIS AFTERNOON. IN THE EAST...IT APPEARS
THAT THE ECMWF INITIALIZES BEST ON THE MAIN CIRCULATION AND THE
DEVELOPING TRIPLE POINT LOW. LIKEWISE OUT WEST THE 12Z RUN OF THE
ECMWF AND GFS HAVE A BETTER HANDLE ON THE LOW AS IT APPROACHES THE
EASTERN ALEUTIANS. DESPITE THE SUBTLE DIFFERENCES IN THE
INITIALIZATION...BEYOND 24 HOURS THE MODELS ARE ALL PAINTING A VERY
SIMILAR PICTURE THROUGH ABOUT 60 HOURS. AFTER THAT...A FEW
DIFFERENCES ARISE IN THE NEXT DEVELOPING SYSTEM OUT WEST. THE ZONAL
FLOW ALOFT WOULD LEND ITSELF MORE TO A SOUTHERN TRACK AND WEAKER LOW
THAT BOTH THE ECMWF AND GFS ARE DEPICTING. THE MID TO LONG RANGE
FORECAST WILL BE NUDGED TOWARD THIS SOLUTION.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...FORECAST ON TRACK EARLY THIS AFTERNOON WITH FOG
DISSIPATING AROUND COOK INLET AND MOISTURE STREAMING NORTH TOWARD
EASTERN PRINCE WILLIAM SOUND. SNOW IS FALLING IN CORDOVA AND THE
EASTERN PORTIONS OF THE COPPER RIVER BASIN. DEPENDING ON THE EXACT
TRACK OF THE TRIPLE POINT LOW...SNOWFALL TOTALS IN CORDOVA COULD BE A
BIT HEFTIER THAN OUR CURRENT FORECAST. HAVE TRENDED HIGHER AMOUNTS
AND WILL CONTINUE TO CLOSELY WATCH THE DEVELOPING TRIPLE POINT AS IT
APPROACHES THE NORTHEAST COAST LATER TONIGHT.

LIKEWISE IN THE COPPER RIVER BASIN...NO ADVISORY IS EXPECTED IN THE
SPARSELY POPULATED REGION OF THE COPPER RIVER BASIN BUT WILL CONTINUE
TO MONITOR TO SEE IF THE LOW DENSITY SNOW BEGINS TO PILE UP MORE THAN
ANTICIPATED.

CLEAR SKIES FROM COOK INLET UP TO THE SUSITNA VALLEY PREVAILING UNDER
AN AREA OF SUBSIDENCE AHEAD OF THE GULF LOW. THE CHALLENGE FOR
TONIGHTS FORECAST WILL BE THE POSSIBILITY OF FOG RETURNING. CURRENT
THINKING IS THAT A SCATTERED TO BROKEN MID LEVEL CLOUD DECK WILL
LIKELY DRIFT OVER THE CHUGACH RANGE TOWARD PALMER AND ANCHORAGE LATE
THIS EVENING. THESE CLOUDS WOULD INHIBIT ANY FOG FROM DEVELOPING
ALTHOUGH CLOUDS WILL NOT QUITE REACH KENAI SO FOG IS A POSSIBILITY
FURTHER DOWN THE INLET.

THROUGH THE WEEKEND...THE BROAD TROUGH STAYS IN PLACE WHILE A SERIES
OF WEAK LOWS ROTATE AROUND THE NORTHERN GULF. CAN NOT RULE OUT THE
POSSIBILITY OF LIGHT SNOW WITH THAT SET UP BUT AT THE MOMENT THERE
ARE NO CLEAR INDICATIONS OF A PARTICULAR UPPER LEVEL OR SURFACE
FEATURE THAT WOULD CREATE THE NECESSARY LIFT. SO FOR THE TIME
BEING...EXPECTING PARTLY TO MOSTLY CLOUDY SKIES WITH BELOW NORMAL
TEMPERATURES WITH SNOW MAINLY CONFINED TO THE COPPER RIVER BASIN AND
COASTAL AREAS...JUST AN OUTSIDE CHANCE OF LIGHT SNOW OVER ANCHORAGE
AND PALMER.

SOUTHWEST ALASKA...
STRATUS AND FLURRIES HANGING TOUGH OVER MUCH OF THE SOUTHWESTERN
PORTION OF THE STATE. A DRYING TREND SHOULD BE IN PLACE BUT THE
SOUTHWEST SOUNDINGS DEPICT A LOT OF LOW LEVEL MOISTURE TRAPPED BELOW
A STRONG INVERSION SO ANY CLEARING THAT OCCURS DURING THE AFTERNOON
HEATING WILL LIKELY FILL BACK IN WITH CLOUDS AND FOG OVERNIGHT. WEAK
COLD AIR ADVECTION UNDER THE BROAD TROUGH WILL CONTINUE THROUGH THE
WEEKEND SO PERSISTENCE IS THE BEST FORECAST AT THIS TIME.

BERING SEA AND ALEUTIANS...THE MOST EXCITING WEATHER IS HAPPENING OUT
WEST WITH THE RAPIDLY MOVING SYSTEM APPROACHING THE EASTERN
ALEUTIANS. BLIZZARD CONDITIONS WILL DIMINISH QUICKLY THIS EVENING AS
THE FLOW BECOMES MORE NORTHEASTERLY OFF OF THE ICE EDGE. STEADY SNOW
AROUND THE ALASKA PENINSULA WILL GIVE WAY TO SNOW SHOWERS OVERNIGHT
UNDER THE COLD NORTHWESTERLY FLOW. HIGH PRESSURE BUILDS OVER THE
CENTRAL BERING SEA WITH A FEW WEAK IMPULSES BRINGING THE EASTERN
PORTION OF THE CHAIN ENHANCED SHOWERS AND BLUSTERY CONDITIONS THROUGH
TOMORROW. AS MENTIONED IN THE MODEL DISCUSSION...THE NEXT LOW
PRESSURE SYSTEM DEVELOPS SOUTHWEST OF THE CHAIN AND WILL FOLLOW AN
EASTERLY TRACK AS IT JUST SKIRTS THE CENTRAL AND WESTERN ALEUTIANS
LATER THIS WEEKEND. ANOTHER SYSTEM EARLY NEXT WEEK WILL MOVE OVER THE
WESTERN ALEUTIANS WITH THE POTENTIAL FOR STRONG GALES ASSOCIATED WITH
IT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195
         WINTER WEATHER ADVISORY 131 181
MARINE...HEAVY FREEZING SPRAY 155 165 179 411 412 414
         GALE 130 132 150 155 160 165 170 172 413
FIRE WEATHER...NONE

AB MAR 12