Gale Warning 349, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
120 PM AKDT WED APR 8 2009

.ANALYSIS AND UPPER LEVELS...FAIRLY LOW AMPLITUDE PROGRESSIVE UPPER
FLOW CONTINUES. HOWEVER...THERE IS CERTAINLY ENOUGH AMPLITUDE IN
THE WAVES TO DEVELOP A MAJOR STORM FORCE LOW OUT ALONG THE WESTERN
ALEUTIANS. NEAR BLIZZARD CONDITIONS ARE BEING OBSERVED IN SHEMYA
ALONG THE BENT-BACK OCCLUSION. THE LOW HAS BECOME NEARLY STATIONARY
AS IT BOTTOMS OUT AND BECOMES VERTICALLY STACKED...BUT THE FRONTAL
SYSTEM IS PUSHING QUICKLY OFF TO THE EAST ALONG THE ALEUTIANS DUE
TO STRONG WESTERLY FLOW BEHIND IT SUPPORTED BY COLD AIR FEEDING
INTO THE SYSTEM. THE ONLY OTHER FEATURE OF ANY SIGNIFICANCE ACROSS
THE FORECAST AREA IS A DISSIPATING LOW JUST WEST OF NORTON SOUND.
A WEAK TROUGH EXTENDS FROM THIS LOW SOUTHEASTWARD ACROSS SOUTHWEST
ALASKA. THERE IS VERY LITTLE SNOW ASSOCIATED WITH THIS TROUGH...WITH
JUST SOME LIGHT SNOW ALONG THE ALASKA AND ALEUTIAN RANGES. SATELLITE
IMAGERY SHOWS CLOUDS DISSIPATING AS THEY CROSS THE MOUNTAINS INTO
COOK INLET. THIS LOOKS TO BE AN AREA OF UPPER LEVEL DIFFLUENCE.
THUS...SOUTHCENTRAL IS EXPERIENCING ANOTHER DAY OF MOSTLY SUNNY
SKIES.

.MODEL DISCUSSION...MODELS REMAIN IN GOOD AGREEMENT WITH TRACK OF
ALEUTIAN LOW THROUGH THURSDAY NIGHT. SOME DIFFERENCES DEVELOP AS
THE LOW MOVES INTO THE GULF. WILL STICK CLOSE TO CURRENT FORECAST
WHICH MATCHES UP WELL WITH THE 12Z GFS SOLUTION. WITH NEXT SYSTEM
MOVING TO THE WESTERN ALEUTIANS ON SATURDAY THE GFS SHOWS GOOD
RUN-TO-RUN CONSISTENCY SO WILL STICK WITH IT FOR NOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...WITH TROUGH OVER SOUTHWEST ALASKA PRODUCING
VERY LITTLE IN THE WAY OF PRECIPITATION OR CLOUDS OUT AHEAD OF IT
EXPECT SOUTHCENTRAL WILL REMAIN MOSTLY DRY AS IT MOVES ACROSS THE
REGION TONIGHT. THEREFORE...WILL LOWER POPS TO ZERO IN MANY PLACES
INCLUDING ANCHORAGE AND MAINTAIN CHANCE POPS ONLY ALONG MOUNTAINS
AND ALONG NORTHERN TIER OF SOUTHCENTRAL. THE ALEUTIAN STORM SYSTEM
WILL BEGIN TO AFFECT SOUTHCENTRAL THURSDAY AS STRONG OCCLUDED FRONT
MOVES INTO GULF. UPPER LEVEL SOUTHERLY FLOW WILL QUICKLY PUSH THIS
FRONT TO THE NORTH GULF COAST THURSDAY NIGHT...WITH A BARRIER JET
SETTING UP...AND THEN INLAND FRIDAY WHERE IT WILL RAPIDLY FALL APART.
WILL BE FINE-TUNING WINDS ALONG THIS FRONT...INCLUDING MAINTAINING
BARRIER JET WINDS A LITTLE LONGER THAN CURRENTLY FORECAST.
ORIENTATION OF FRONT AND OF ISOBARS FAVORS A STRONGER PORTAGE VALLEY
AND EASTERN TURNAGAIN ARM WIND THAN WESTERN TURNAGAIN ARM...SO WILL
MAKE THIS ADJUSTMENT. GUSTY WINDS ARE ALSO EXPECTED THROUGH THE
KNIK RIVER VALLEY INTO PALMER THURSDAY AFTERNOON AND EVENING AS THE
SURFACE RIDGE ALONG THE NORTH GULF COAST IS PUSHED INLAND BY THE
APPROACHING FRONT. THE BULK OF PRECIPITATION WILL FALL ALONG THE
COAST DUE TO THE USUAL DOWN-SLOPING AFFECT FOR MANY INLAND
LOCATIONS...BUT THERE IS ENOUGH VERTICAL MOTION ALOFT TO HELP
COUNTER THIS AND PRODUCE AT LEAST A CHANCE OF PRECIP IN ALL AREAS.
SHOWERS WILL PERSIST THROUGH SATURDAY ALONG COASTAL AREAS AS THE
ALEUTIAN LOW MOVES ACROSS THE GULF.

SOUTHWEST ALASKA...SNOW SHOWERS/AREAS OF LIGHT SNOW ASSOCIATED WITH
NORTON SOUND LOW AND UPPER TROUGH WILL TAPER OFF THIS EVENING AS
THE TROUGH EXITS TO SOUTHCENTRAL AND REMNANTS OF LOW DRIFT NORTHWARD.

HOWEVER...PRECIPITATION WILL ONCE AGAIN SPREAD ACROSS THE REGION
THURSDAY AS THE OCCLUDED FRONT FROM ALEUTIAN LOW MOVES INTO BRISTOL
BAY ON THURSDAY. PRECIPITATION TYPE WILL BE MAINLY IN THE FORM OF
SNOW WITH THE EXCEPTION OF THE ALASKA PENINSULA WHERE RAIN IS LIKELY
TO MIX IN. WITH COLD AIR STILL FIRMLY ENTRENCHED OVER THE KUSKOKWIM
DELTA BLOWING SNOW IS ONCE AGAIN LIKELY. AT THIS POINT IT DOESNT
LOOK LIKE WINDS WILL BE STRONG ENOUGH TO PRODUCE A BLIZZARD...BUT
THE KUSKOKWIM DELTA COAST WILL BE RIGHT ON THE EDGE OF COLD AIR
ADVECTING SOUTHWARD ACROSS THE BERING. WINDS COULD BE ENHANCED
ENOUGH BY THIS TO PRODUCE BLIZZARD...SO IT BEARS KEEPING AN EYE ON.
PRECIP WILL TAPER OFF FOR MOST INLAND LOCATIONS FRIDAY NIGHT AND
SATURDAY AS LOW MOVES INTO THE GULF...BUT SHOWERS WILL PERSIST
ALONG COASTAL AREAS DUE TO COLD ADVECTION AND SHORT-WAVES DROPPING
INTO BACK SIDE OF UPPER TROUGH.

BERING SEA/ALEUTIANS...THE STORM SYSTEM WILL MAINTAIN STRENGTH
TONIGHT AND THURSDAY AS IT TRACKS EASTWARD ALONG THE ALEUTIANS
AND THEN BEGIN TO WEAKEN AFTER THAT. THEREFORE...EXPECT WIDESPREAD
GALES ALONG THE FRONT AND AREAS OF STORM FORCE WINDS NEAR THE LOW
CENTER. A BLIZZARD WARNING HAS BEEN ISSUED FOR THE PRIBILOF ISLANDS
FOR TONIGHT THROUGH EARLY THURSDAY MORNING. PRESENCE OF ICE PACK
WILL HELP MAINTAIN SUB-ZERO AIR TEMPERATURES SO THAT SNOW ASSOCIATED
WITH FRONT WILL EASILY BLOW AROUND AND CAUSE NEAR WHITE-OUT
CONDITIONS AT TIMES. A SHORT-WAVE TROUGH WILL DROP DOWN BEHIND THE
STORM SYSTEM...BRINGING A SURGE OF ARCTIC AIR. THIS WILL OF COURSE
PRODUCE THE USUAL GUSTY NORTHERLIES AND SNOW SHOWERS ACROSS THE
REGION. THERE WONT BE MUCH OF A BREAK AS THE PROGRESSIVE UPPER
LEVELS BRING ANOTHER STORM TO THE WESTERN ALEUTIANS BY SATURDAY.

.LONG TERM FORECAST...THE LOW IN THE GULF AT WEEKS END WILL EXIT
TO THE EAST BY THE BEGINNING OF NEXT WEEK HELPING TO DRY OUT
MAINLAND ALASKA. MODELS THEN INDICATE FORMATION OF A HIGH AMPLITUDE
RIDGE AHEAD OF ALEUTIAN/NORTH PACIFIC SYSTEMS WHICH WILL SERVE TO
BLOCK THESE STORMS FROM REACHING MAINLAND ALASKA NEXT WEEK. INSTEAD
STORM TRACK WILL LIKELY BE ALTERED WITH STORMS TRACKING ALONG THE
ALEUTIANS AND THEN SOUTHEASTWARD INTO THE EAST PACIFIC.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195.
MARINE...STORM WARNING...175 176.
         GALE WARNING...120 125 130 132 138 140 150 155 165 170 171
                        172 179.
FIRE WEATHER...NONE.

SEB APR 09