Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 261331
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
531 AM AKDT SUN APR 26 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN ACTIVE FEATURE ON WATER VAPOR IMAGERY THIS MORNING
CONTINUES TO BE THE UPPER LEVEL LOW PRESSURE FORMERLY OF THE
BERING SEA...NOW SETTING UP SHOP IN THE SOUTHERN GULF/NORTHEAST
PACIFIC. A STRONG SHORTWAVE TROUGH IS VYING TO BECOME THE NEW
CENTER OF CIRCULATION ALOFT AS THE SURFACE CIRCULATION WITH SAID
SYSTEM ENCOMPASSES MUCH OF THE NORTHEAST PACIFIC/GULF OF ALASKA.
THE VERY WRAPPED UP SYSTEM LOOKS TO BE AT PEAK MATURITY WITH A
GALE FORCE FRONT IN THE CENTRAL GULF. A NARROW RIDGE SITS OVER THE
CENTRAL BERING SEA AHEAD OF A SHORTWAVE TROUGH/FRONT IN THE
WESTERN BERING. THE MAINLAND IS MOSTLY CLOUD FREE AT THE MOMENT
WHILE MOISTURE FROM THE GULF SYSTEM IS ON THE DOORSTEP. WINDS ARE
GENERALLY LIGHT ACROSS MOST OF THE MAINLAND WHILE TEMPERATURES
ARE SLIGHTLY ABOVE NORMAL FOR LATE APRIL.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN GREAT AGREEMENT AS FAR AS POSITION AND STRENGTH OF
THE GULF SYSTEM AND CONTINUE TO BE IN LOCKSTEP FOR THE NEXT COUPLE
DAYS. HOWEVER...THE EXCELLENT AGREEMENT OF THE LAST COUPLE WEEKS
IS ABOUT TO GO DOWN THE TUBES BY MID-WEEK AS MODELS STRUGGLE TO
GRASP THE EVOLUTION OF A SPLIT FLOW PATTERN ALOFT EARLY IN THE
WEEK TO A MORE PROGRESSIVE ZONAL FLOW LATER IN THE WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

DRY NORTHERLY WINDS ARE CURRENTLY INCREASING AHEAD OF A WEAK
FRONT THAT WILL MOVE EAST TO WEST ACROSS SOUTHCENTRAL ALASKA
TODAY...REACHING THE COOK INLET AND SOUTHERN SUSITNA VALLEY BY
LATE THIS AFTERNOON OR EARLY THIS EVENING. THE FRONTAL BOUNDARY
WILL END CRITICAL FIRE WEATHER CONDITIONS GRADUALLY FROM EAST TO
WEST STARTING THIS AFTERNOON THROUGH LATE THIS EVENING.

VERY MEAGER HUMIDITY RECOVERIES OVER PARTS OF THE MATANUSKA VALLEY...
ALONG WITH A LATER-THAN-EXPECTED ARRIVAL OF A MARGINALLY SUFFICIENT
WIND OUT OF THE MATANUSKA RIVER VALLEY WILL SIGNAL ONE MORE DAY
OF CRITICAL FIRE WEATHER CONDITIONS IS IN STORE BEFORE THE FRONT
MOVES ACROSS THE AREA THIS AFTERNOON.

FOR THE WESTERN KENAI PENINSULA AND SUSITNA VALLEY...WINDS WILL
INCREASE THROUGH THIS MORNING...BEFORE GRADUALLY DIMINISHING THROUGH
THE AFTERNOON OVER THE WESTERN KENAI PENINSULA. WINDS WILL BE SLOWER
TO DIMINISH OVER NORTHERN AND WESTERN SUSITNA VALLEY AS THE FRONT
WILL STALL OVER THE SOUTHERN SUSITNA VALLEY LATE THIS AFTERNOON THROUGH
TONIGHT.

SYNOPTICALLY...THE STATIONARY LOW PRESSURE SYSTEM OVER THE FAR
SOUTHERN GULF WILL KEEP THE BULK OF THE RAIN AND WIND IMPACTS
CONFINED TO KODIAK ISLAND AND AREAS ALONG THE COAST THROUGH
TONIGHT. A SERIES OF EASTERLY WAVES WITH VARYING STRENGTH WILL
BEGIN TO MOVE ACROSS SOUTHCENTRAL ALASKA BEGINNING TODAY...WITH
THE LEADING SYSTEM BRINGING AN END TO THE RUN OF CRITICAL FIRE
WEATHER DAYS OVER THE UPPER COOK INLET REGION. A STRONGER
DISTURBANCE MOVES OVER THE COPPER RIVER BASIN TONIGHT INTO MONDAY
AND SPREAD RAIN AND SNOW SHOWERS OVER THAT AREA THROUGH
MONDAY...WITH THE CHANCE FOR SHOWERS SPREADING TO THE MAT-SU AND
COOK INLET REGIONS ON MONDAY AS THE WAVE PROGRESSES WESTWARD.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TODAY AND MONDAY)...

THE OFFSHORE FLOW REGIME HAS BEEN ESTABLISHED ACROSS SOUTHWEST
ALASKA AND IS EXPECTED TO CONTINUE THROUGH MONDAY. WHILE AN
OVERALL DRYING TREND IS EXPECTED AS DRIER AIR IS ADVECTED FROM THE
ALASKAN INTERIOR...A FEW RAIN SHOWERS CANNOT BE RULED OUT OVER THE
COMING DAYS. MONDAY LOOKS TO BE THE MORE FAVORABLE DAY TO SEE SOME
RAIN SHOWERS DEVELOP OVER THE MIDDLE KUSKOKWIM VALLEY AND WESTERN
ALASKA RANGE AS A WEAK SHORTWAVE CROSSES THE ALASKA RANGE FROM THE
EAST. WITH RELATIVE HUMIDITY VALUES TO RANGE FROM THE UPPER TEENS
TO LOWER 30S...IT IS POSSIBLE MUCH OF THE PRECIPITATION WILL
EVAPORATE PRIOR TO REACHING THE SURFACE (VIRGA). THE ENHANCED LIFT
MONDAY AFTERNOON WOULD HELP SOME OF THE RAIN SHOWERS TO OVERCOME A
DEEP DRY LAYER BUT WIDESPREAD SHOWER ACTIVITY IS NOT LIKELY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TODAY AND MONDAY)...

AN AREA OF LOW PRESSURE WELL TREK ACROSS THE WESTERN BERING SEA
TODAY BEFORE STALLING OUT WELL WEST OF THE PRIBILOF ISLANDS ON
MONDAY. A SECOND AREA OF LOW PRESSURE PUSHING OFF THE KOREAN
PENINSULA THIS AFTERNOON WILL QUICKLY CATCH UP TO THE STALLING LOW
IN THE BERING SEA LATE MONDAY AND ABSORB THE DECAYING LOW PRESSURE
SYSTEM. THE FIRST LOW WILL DRIVE A POTENT FRONT ACROSS THE BERING
SEA TODAY WITH RAINFALL EXPECTED FROM SHEMYA TO DUTCH HARBOR
TONIGHT. THE OVERALL PRESSURE FIELD AND 500 MB HEIGHT FIELDS OVER
THE PAST SEVERAL DAYS HAVE BEEN LOWER THAN AVERAGE SO EVEN THOUGH
THESE LOWS WILL BE STRENGTHENING OVER THE BERING SEA...ONLY A VERY
NARROW BAND OF GALE FORCE WINDS IS EXPECTED OVER THE FAR WESTERN
BERING SEA. PRECIPITATION WILL END QUICKLY BEHIND THIS FRONT BUT
ANOTHER ROUND OF RAIN WILL BE OBSERVED WHEN THE SECOND LOW MOVES
INTO THE WESTERN BERING SEA LATE MONDAY.

&&

.LONG TERM FORECAST (MONDAY NIGHT THROUGH SUNDAY)...
A PROGRESSIVE PATTERN WILL DEVELOP EARLY NEXT WEEK AND CONTINUE
THROUGH THE REMAINDER OF THE WEEK WITH VARIOUS LOWS MOVING THROUGH
THE SOUTHERN BERING AND INTO THE GULF. THERE IS GOOD AGREEMENT
HOWEVER THAT THESE LOWS WILL STAY MAINLY SOUTH OF THE
MAINLAND...WHICH WILL ALLOW FOR GENERALLY OFFSHORE FLOW AND RAIN
CHANCES LIMITED TO CONVECTIVE SHOWERS THROUGH EARLY NEXT WEEK. BY
THE MIDDLE OF NEXT WEEK...MODEL DIFFERENCES DEVELOP WITH THE EXACT
TRACK OF THESE LOWS AND THE OPERATIONAL MODEL RUNS HAVE NOT BEEN
ABLE TO LOCK DOWN EXACT LOW PLACEMENT. THEREFORE A BLEND OF THE
ENSEMBLES WAS USED FOR THEIR POSITIONS. HOWEVER...THE PROGRESSIVE
PATTERN WOULD BE EXPECTED TO LEAD TO PRECIP FOR THE ALEUTIANS AND
AREAS ALONG THE NORTH GULF COAST AS THESE LOWS PASS. WITH THE
INSTABILITY OVER THE MORE INLAND LOCATIONS SHOWERY ACTIVITY CAN
ALSO BE EXPECTED...ESPECIALLY ALONG THE MOUNTAINS.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 131 132 177 178.
FIRE WEATHER...RED FLAG WARNING 111 121 145.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DK/DEK



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