000
FXAK68 PAFC 280100
AFDAFC
SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST MON DEC 27 2010
.ANALYSIS...
A LARGE BROAD TROUGH CONTINUES TO DOMINATE THE UPPER LEVELS ACROSS
MOST OF THE STATE. MULTIPLE SHORT WAVES ARE ROTATING AROUND THE BASE
OF THE BROAD CYCLONIC CIRCULATION. THE MOST POTENT IS CURRENTLY
NEARING KODIAK ISLAND OVER THE NORTHWESTERN GULF. THIS CLOSED LOW
DEVELOPED SUNDAY AND HAS BECOME THE MAIN CIRCULATION FOR THE REGION
OVERNIGHT. A SECOND UPPER LEVEL CIRCULATION IS OVER BRISTOL BAY. THIS
AREA OF CIRCULATION WILL WEAKEN INTO AN OPEN WAVE OVER THE NEXT 24
HOURS. TOWARD THE BERING SEA...A COL PERSISTS OVER THE CENTRAL
ALEUTIANS WHILE A NORTH PACIFIC LOW RAPIDLY DEEPENS SOUTH OF THE
WESTERN ALEUTIANS.
.MODEL DISCUSSION...
THE MODELS CONTINUE TO STRUGGLE ON THE LOCATION AND STRENGTH OF THE
LOWS IN THE GULF OF ALASKA. BASED ON SATELLITE IMAGES...THE NAM AND
GFS ARE OFF ON THEIR INITIALIZATION WHILE THE ECMWF HAS THE LOCATION
SPOT ON. THE GFS IS ALSO ABOUT 10 MB TOO WEAK WITH THE LOW WHILE THE
NAM AND ECMWF PUT THE LOW AT ABOUT 980 MB EARLY THIS AFTERNOON. BASED
ON THE INITIALIZATION...DECIDED TO BASE THE SHORT TERM FORECAST ON
THE ECMWF. OUT WEST...THE CURRENT FORECAST HAS A GOOD HANDLE ON
POSITION AND EVOLUTION OF A DEVELOPING LOW AND FRONTAL BOUNDARY SO
MINIMAL CHANGES WERE REQUIRED.
.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...THE CURRENT LOW IN THE WESTERN GULF HAS
MINIMAL IMPACTS ON THE INTERIOR. SCATTERED SNOW SHOWERS ARE
OCCASIONALLY SWEEPING ACROSS THE KENAI PENINSULA AND KODIAK
ISLAND...OTHERWISE ANOTHER PARTLY CLOUDY DAY WITH BELOW NORMAL
TEMPERATURES. TUESDAY PROMISES TO BE VERY SIMILAR AS THE LOW BEGINS
TO FILL AND DRIFT TO THE EAST. THIS IS IN RESPONSE TO AN OPEN WAVE
CROSSING THE ALASKA PENINSULA AND PUSHING THE LOW TOWARD THE
PANHANDLE...AND INITIATING A PATTERN CHANGE FOR THE ALASKA MAINLAND.
THE OPEN SHORTWAVE WILL MOVE INTO SOUTHCENTRAL ALASKA TUESDAY
EVENING. ISENTROPIC ANALYSIS IS INDICATING GOOD VERTICAL MOTION IN A
COLUMN THAT WILL BE RAPIDLY ADDING MOISTURE. THE RESULT WILL BE LIGHT
SNOW LIKELY FROM THE WESTERN KENAI PENINSULA UP TO THE SUSITNA
VALLEY...INCLUDING ANCHORAGE AND THE MATSU VALLEY. THIS IS A SETUP
THAT THE MODELS HAVE A DIFFICULT TIME NAILING DOWN THE ONSET OF
PRECIPITATION SO THIS FORECAST WILL BE FINE TUNED...BUT AT THE MOMENT
EXPECTED LIGHT SNOW TO DEVELOP FROM SOUTH TO NORTH TUESDAY NIGHT
THROUGH WEDNESDAY MORNING.
BROAD SOUTHWESTERLY FLOW ALOFT WILL SPREAD ACROSS THE REGION BEHIND
THE SHORTWAVE. THIS WILL USHER ABUNDANT MOISTURE TO OUR FORECAST
DOMAIN WHILE OCCLUSIONS DEVELOPING ALONG THE SOUTHWESTERLY JET
PROVIDES ADDITIONAL LIFT...RESULTING IN WIDESPREAD SNOW.
AT THIS TIME FOR THE ANCHORAGE BOWL THE BEST CHANCES OF PRECIPITATION
WILL BE LIGHT SNOW ON TUESDAY NIGHT AND WEDNESDAY MORNING...AGAIN
THURSDAY MORNING...THEN A MORE SIGNIFICANT EVENT LATE THURSDAY NIGHT
INTO FRIDAY. EXTENDED MODELS CONTINUE THIS SURGE OF MOISTURE THROUGH
THE WEEKEND.
.SOUTHWEST MAINLAND...FLURRIES AROUND BRISTOL BAY AND THE KUSKOKWIM
DELTA PERSIST THIS MORNING AND EARLY AFTERNOON. A BRIEF PERIOD OF
QUIET ALBEIT COLD WEATHER WILL LAST THROUGH TUESDAY BEFORE THE
AFOREMENTIONED SHORTWAVE CROSSES THE ALASKA PENINSULA...SPREADING
LIGHT SNOW FROM BRISTOL BAY TO THE UPPER KUSKOKWIM VALLEY. THE COLD
CORE UPPER LOW CENTER WILL RE-ESTABLISH ITSELF NEAR THE DELTA LATER
IN THE WEEK...PROMISING ABUNDANT COLD AIR AND SNOW SHOWERS FOR THE
REGION THROUGH THE WEEKEND.
.BERING SEA AND ALEUTIANS...A PROLONGED PERIOD OF RELATIVELY BENIGN
COLD ADVECTION SNOW SHOWERS ACROSS THE ALEUTIANS WILL CHANGE TOMORROW
AS A STRONG NORTH PACIFIC LOW AND ASSOCIATED FRONTAL BOUNDARY
APPROACHES THE WESTERN ALEUTIANS. POSSIBLY BLIZZARD CONDITIONS WILL
SPREAD EAST WITH STORM FORCE WINDS.
SOME UNCERTAINTY STILL REMAINS WITH THE EXTENT OF THE BLIZZARD
CONDITIONS LATER TONIGHT ALONG THE CENTRAL ALEUTIANS. EASTERLY
SURFACE WINDS IS TYPICALLY NOT A FAVORABLE DIRECTION BECAUSE IT IS
EASIER TO DRAW WARM AIR FROM THE LOWER LATITUDES. PRECIPITATION WILL
BE HEAVY AT TIMES INITIALLY WHICH MAY HELP KEEP TEMPERATURES NEAR
FREEZING SO AT THIS TIME WE ARE ANTICIPATING PERIODS OF NEAR WHITE
OUT CONDITIONS BUT NOT WIDESPREAD ENOUGH TO WARRANT A BLIZZARD
WARNING. THIS COULD CHANGE AS THE LOW DEVELOPS AND APPROACHES THE
CHAIN LATER TONIGHT.
THE BAROCLINIC ZONE SETS UP JUST NORTH OF THE CHAIN BY TUESDAY
AFTERNOON ALLOWING SNOW TO MIX OR CHANGE OVER TO RAIN. THE LOW
MAINTAINS ITS STRENGTH AT APPROX 968 MB AS IT DRIFTS EAST DURING THE
WEEK UNDER THE ALEUTIANS. BY THURSDAY...COLD ARCTIC AIR BEGINS TO
AGAIN FILTER SOUTH ON THE BACK SIDE OF THE LOW ACROSS THE WESTERN
ALEUTIANS.
.AER/ALU...WATCH/WARNING/ADVISORY SUMMARY
PUBLIC...WINTER WEATHER ADVISORY FOR BLOWING SNOW 187
MARINE...STORMS 175 176
GALES...132 170 172 352 411 413 414
HEAVY FREEZING SPRAY...121 129 138 140 141 160 165 179 180
185 412 414
FIRE WEATHER...NONE.
AB DEC 10
