Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 211257
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
457 AM AKDT THU MAY 21 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL AMPLIFIED RIDGE HAS BEGUN TO MOVE EASTWARD AND IS
LOCATED OVER SOUTHEASTERN ALASKA EXTENDING NORTHWESTWARD THROUGH
THE YUKON TERRITORY INTO THE BEAUFORT SEA REGION THIS MORNING.
WHILE...UPSTREAM THERE IS A CLOSED LOW OVER THE EASTERN SIBERIAN
AREA WITH AN ASSOCIATED TROUGH EXTENDING INTO THE NORTHERN BERING
SEA. SOUTH OF THE EASTERN ALEUTIAN CHAIN...AT THE SURFACE THERE IS
A CUT-OFF LOW POSITIONED AT THE BASE OF THE LONGWAVE TROUGH IN THE
NORTHERN PACIFIC. THE SATELLITE IMAGERY IS SHOWING A WEAK LOW
PRESSURE CYCLONIC CIRCULATION JUST SOUTH OF COLD BAY. THE SURFACE
FLOW IS PREDOMINANTLY SOUTHERLY FLOW FROM THE EASTERN ALEUTIANS
EXTENDING INTO THE GULF ACCOMPANIED BY A LARGE SWATH OF MOISTURE
WITH LOW STRATUS AND AREAS OF FOG. THE SATELLITE IMAGERY IS
SHOWING HIGH CIRRUS CLOUDS OVER THE INTERIOR OF THE SOUTHCENTRAL
REGION WITH MAJORITY OF SURFACE OBSERVATIONS REPORTING LIGHT WINDS
THIS MORNING. WHILE ON THE BERING SIDE...THE GOES IFR SATELLITE IS
SHOWING THE EASTERN BERING SEA AND THE BRISTOL BAY REGION WITH LOW
STRATUS AND PATCHY FOG EXCEPT FOR AREAS OF DENSE FOG FORMING ALONG
THE KUSKOKWIM DELTA COASTLINE. IN THE WESTERN BERING SEA THE
PRESSURE GRADIENTS ARE INCREASING WITH THE ARRIVAL OF THE STORM
FORCE LOW APPROACHING FROM THE REMNANTS OF TYPHOON DOLPHIN. THE
ASCAT SCATTEROMETER WINDS IMAGERY WERE SHOWING GALE FORCE WINDS
JUST UPSTREAM FROM THE WESTERN ALEUTIANS THIS MORNING. THIS SYSTEM
IS BEING SUPPORTED BY A VERY STRONG 160 KNOT ZONAL JET STREAK
STRETCHING FROM JAPAN REGION EXTENDING JUST SOUTH OF THE KISKA
REGION.

&&

.MODEL DISCUSSION...
THE MODELS WERE IN GOOD AGREEMENT WITH THE HIGH PRESSURE RIDGE
OVER THE GULF AS IT BUILDS BACK INTO THE AREA BY FRIDAY.
WHILE...THE MODELS WERE DOING BETTER WITH THE STORM FORCE LOW
ENTERING THE WESTERN ALEUTIANS/BERING SEA BY THURSDAY AFTERNOON.
THERE WAS UNCERTAINTY WITH THE STRENGTH AND POSITIONING OF THIS
LOW. THE ECMWF/GFS WERE THE PREFERRED MODELS OF CHOICE THIS
MORNING. THE FORECAST CONFIDENCE REMAINS ABOVE AVERAGE HEADING
INTO THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE AMPLIFIED RIDGE OF HIGH PRESSURE WILL KEEP MAJORITY OF
SOUTHCENTRAL WITH WARMER AND DRIER CONDITIONS AS THE RIDGE MOVES
EASTWARD HEADING INTO THE WEEKEND. BY SATURDAY WITH THE RIDGE
FARTHER EAST...THIS WILL ALLOW MORE MOISTURE TO THE INTERIOR WITH
THE SOUTHERLY FLOW IN THE LOWER LEVELS. THEREFORE...THERE WILL BE
SCATTERED RAIN SHOWERS ALONG THE KENAI PENINSULA COASTAL MARINE
AREAS EXTENDING THROUGH KODIAK ISLAND AS A WEAK FRONTAL BOUNDARY
DISSIPATES THIS MORNING. OTHERWISE...LOOK FOR LIGHT WINDS THIS
MORNING BEFORE THE ONSET OF THE SEABREEZES FOR THE SOUTHCENTRAL
ALASKA REGION.

.FIRE WEATHER...
AREAS OF CONCERN WILL REMAIN WITH THE COPPER RIVER BASIN.
YESTERDAY...EVEN WITH THE HIGH CLOUD COVER THE RH VALUES STILL
DROPPED INTO THE LOWER TEENS. NOW THE WINDS FOR TODAY WILL NOT BE
AS STRONG AS YESTERDAY...BUT THE RH VALUES WILL STILL REDEVELOP FOR
THE AFTERNOON AND EVENING HOURS THROUGH FRIDAY FOR THE COPPER
RIVER BASIN REGION. THEREFORE...THE RED FLAG WARNING FOR ONLY LOW
RH VALUES WILL BE EXTENDED THROUGH FRIDAY FOR THE COPPER RIVER
BASIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE STALLED FRONT STILL SITS OVER THE MAINLAND HOWEVER DEEP LAYER
MOISTURE WILL TAKE A SHORT BREAK TODAY. AREAS OF LIGHT RAIN WILL
DIMINISH THROUGH THE DAY WITH SOME LINGERING SHOWERS DURING THE
AFTERNOON AND EVENING HOURS. AREAS OF DENSE FOG WILL LINGER ALONG
THE KUSKOKWIM DELTA COAST THIS MORNING BEFORE BURNING OFF IN THE
AFTERNOON. THE BREAK IN PRECIPITATION IS BRIEF AS ANOTHER SLUG OF
MOISTURE AND SHORTWAVE TROUGH COME OVER THE MAINLAND FROM THE
PACIFIC TONIGHT. THE BULK OF RAIN WILL FALL OVER THE GREATER
BRISTOL BAY AREA WITH JUST A CHANCE FOR THE KUSKOKWIM VALLEY AND
DELTA. A STRONGER TROUGH MOVES OVER LATE FRIDAY NIGHT BUT MOISTURE
IS LACKING AND SOUTHEASTERLY DOWNSLOPE FLOW INCREASES SO THE BEST
CHANCES FOR RAIN WILL BE ALONG WINDWARD TERRAIN AND ALONG THE
KUSKOKWIM DELTA COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A STORM FORCE FRONT WILL TRANSIT ACROSS THE WESTERN AND CENTRAL
ALEUTAINS TODAY AND TONIGHT BRINGING WIDESPREAD RAIN WITH IT. THIS
FRONT WILL STALL OUT OVER THE CENTRAL BERING SEA ON FRIDAY AND
FRIDAY NIGHT. IN THE EASTERN BERING SEA...AS SOUTHEASTERLY WINDS
PICK UP AHEAD OF THE APPROACHING FRONT LATE TONIGHT...HIGHER
DEWPOINT AIR LEFTOVER FROM THE PREVIOUS MOIST SOUTHERLY FLOW WILL
ADVECT NORTHWESTWARD OVER COOLER SEA SURFACE TEMPERATURES CREATING
A VERY FAVORABLE ENVIRONMENT FOR DENSE FOG THROUGH FRIDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BEGINNING THE EXTENDED FORECAST ON SATURDAY...THE REMNANTS OF
FORMER TYPHOON DOLPHIN WILL BE SPINNING OVER THE FAR WESTERN
BERING...WITH A STRONG NORTH AMERICAN RIDGE CENTERED OVER THE
YUKON. A WEAKENING LOW IN THE NORTH PACIFIC WILL MERGE WITH THE
LARGE LOW OVER THE BERING...EFFECTIVELY ENDING THE LONG PERIOD OF
WARMTH AND DRY WEATHER FOR SOUTHCENTRAL. THAT SAID...THE FRONT
WILL BE FALLING APART AS IT MOVES EAST...WITH THE WETTEST WEATHER
ON SATURDAY AND SUNDAY BEFORE DRYING OUT AND BECOMING MORE SHOWERY
TUESDAY AND WEATHER...WITH TEMPERATURES ONCE AGAIN SLOWLY
REBOUNDING. THE PATTERN BECOMES A LITTLE LESS CERTAIN BY
MIDWEEK...BUT THE GENERAL IDEA IS HIGH PRESSURE ALOFT WILL SLOWLY
BEGIN TO EXERT ITS INFLUENCE OVER MOST OF MAINLAND ALASKA...WITH
THE MAIN STORM TRACK REMAINING OVER THE BERING SEA.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING...177 178.
         GALE WARNING...170 172 173 174 175 176 185.
FIRE WEATHER...RED FLAG WARNING...141.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PLD
SOUTHCENTRAL ALASKA...PLD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...JA


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