Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 232148
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
148 PM AKDT TUE SEP 23 2014

.ANALYSIS AND UPPER LEVELS...
A STRONG UPPER LEVEL WAVE HAS FLATTENED THE UPPER LEVEL RIDGE OVER
THE STATE AS IT PASSES THROUGH FROM WEST TO EAST TODAY THROUGH
TONIGHT. THE STRONGEST DYNAMICS WITH THIS WAVE ARE IN THE INTERIOR
AND NORTHERN ALASKA BUT IT IS STRONG ENOUGH TO BRING SOME CLOUDS
TO SOUTHERN ALASKA AS WELL.
THE UPPER LEVEL RIDGE IS STILL OVER THE WESTERN GULF OF ALASKA AND
WILL AMPLIFY AGAIN AS THE AFOREMENTIONED UPPER LEVEL WAVE MOVES
THOUGH THE REGION.
THERE IS ALSO AN UPPER LEVEL LOW IN THE BERING SEA AS WELL ANOTHER
LOW SOUTHEAST OF THE GULF OF ALASKA. THE 250 MB JET STREAM IS
RUNNING JUST SOUTH OF THE BERING SEA LOW AND OVER THE CENTRAL
ALEUTIANS BEFORE TURNING SOUTHEAST AND AROUND THE LOW SOUTHEAST OF
THE GULF.
AT THE SURFACE THERE IS NOT MUCH GRADIENT OVER SOUTHERN ALASKA AT
ALL WITH A LOW IN THE WESTERN BERING SEA AND A MUCH STRONGER LOW
WELL SOUTH OF THE GULF OF ALASKA. GENERALLY HIGH SURFACE PRESSURE
IS OVER SOUTHERN ALASKA WITH A WEAK TROUGH OVER THE NORTH GULF
COAST. THIS TROUGH WILL STRENGTHEN OVERNIGHT AND INCREASE THE
PRESSURE GRADIENT TOMORROW.

&&

.MODEL DISCUSSION...
MODELS ARE IN MUCH BETTER AGREEMENT THAN THEY WERE YESTERDAY OR
OVERNIGHT. THE 12Z RUNS ON THE GFS NAM AND ECMWF HAVE COALESCED
INTO A COMMON SOLUTION FOR BOTH THE LOW THAT WILL BE MOVING INTO THE
BERING SEA THU AND THE ONE SOUTH OF THE GULF OF ALASKA. WHILE
THERE IS STILL SOME DIFFERENCES IN THE BERING SEAS FROM THURSDAY
THROUGH FRIDAY THEY ARE CLOSE ENOUGH TO SHOW THEY ARE LOCKING IN
ON HOW THESE LOWS WILL MERGE AND THEN MOVE AFTER THAT.
THIS HIGHER CONFIDENCE IN THE LOW TRACK EXTENDS INTO THE LONGER
RANGE FORECASTS STRETCHING THROUGH THE WEEKEND.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THERE IS SOME CLOUDINESS IN THE AREA IN ADVANCE OF THE UPPER LEVEL
TROUGH PASSING THROUGH THE REGION TONIGHT. SINCE MOST OF THE
ENERGY ASSOCIATED WITH THIS TROUGH IS TO THE NORTH IT IS NOT
EXPECTED TO BRING IN ANY PRECIPITATION. SKIES WILL CLEAR OUT AGAIN
AND NORTHERLY WINDS WILL INCREASE AGAIN AFTER THE UPPER LEVEL TROUGH
PASSES THROUGH AND THE SURFACE TROUGH ALONG THE NORTH GULF COAST
STRENGTHENS TOMORROW.

SOUTHWEST ALASKA...
SOME CLOUDS AND ISOLATED RAIN SHOWERS WILL MOVE THROUGH THE
NORTHERN PORTIONS OF THE FORECAST AREA TONIGHT IN CONJUNCTION WITH
THE UPPER LEVEL TROUGH.
A WEAK SHORT WAVE IN THE NORTHERN BERING SEA WILL KEEP SOME CLOUDS
IN THE KUSKOKWIM DELTA AREA THROUGH TOMORROW.

BERING SEA/ALEUTIANS...
THE LOW IN THE CENTRAL BERING SEA WILL BE SLOW TO MOVE ANYWHERE
BUT THERE IS SOME INSTABILITY ASSOCIATED WITH IT. THE SHOWERS
UNDERNEATH IT APPEAR TO HAVE RATHER HIGH TOPS ON IR SATELLITE AND
IT IS COLD ENOUGH ALOFT THAT THERE IS A CHANCE FOR A THUNDERSTORM
OR TWO THROUGH THE EVENING WITH THESE HEAVY SHOWERS.

&&

.LONG TERM FORECAST...
MODELS HAVE COME INTO BETTER AGREEMENT TODAY ON A VERY
PROGRESSIVE PATTERN THAT WILL TAKE SHAPE DURING THE NEXT WEEK AS
THE UPPER LOW CURRENTLY OVER THE WESTERN BERING TRACKS QUICKLY
EASTWARD THROUGH THE GULF THIS WEEKEND. THIS WILL BRING ANOTHER
PERIOD OF RAIN TO SOUTHCENTRAL AK...PARTICULARLY FOR AREAS ALONG
THE GULF COAST. HOWEVER...THE RAIN WILL BE RELATIVELY SHORT LIVED
AS UPPER RIDGING THEN BUILDS OVER THE AREA BY EARLY NEXT
WEEK...YIELDING SEVERAL DAYS OF DRIER AND SUNNIER CONDITIONS
AHEAD OF THE NEXT SYSTEM TRAVERSING THE BERING. THIS NEXT LOW
LOOKS TO TRACK ALONG THE ALEUTIAN CHAIN THIS WEEKEND INTO EARLY
NEXT WEEK...RESULTING IN MORE RAIN AND GUSTY WINDS ACROSS THE
SOUTHERN BERING IN THAT TIME FRAME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY 141.
MARINE...NONE.
FIRE WEATHER...NONE.
&&

$$

SEP 14


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