Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 172145
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT WED SEP 17 2014

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL PATTERN HAS A LONG WAVE TROUGH THAT EXTENDS OUT OF
THE ARCTIC AND DOWN THE WESTERN COAST OF ALASKA AND INTO THE
EASTERN BERING SEA. WEST OF THIS TROUGH THERE IS A LARGE UPPER
LEVEL RIDGE THAT IS BUILDING OVER THE KAMCHATKA PENINSULA. THIS
RIDGE WILL MOVE EASTWARD OVER THE NEXT FEW DAYS.
SOUTHCENTRAL ALASKA IS UNDER THE SOUTHWEST FLOW ALOFT AHEAD OF THE
LONGWAVE TROUGH.
THE JET STREAM IS CURRENTLY RUNNING SOUTH OF THE ALEUTIAN ISLANDS
AROUND 45N LATITUDE.
AT THE SURFACE THERE ARE TWO DISTINCT LOWS THAT WILL BE OF NOTE
FOR SOUTHERN ALASKA. THE FIRST IS SITUATED ALONG THE COAST OF EASTERN
BRISTOL BAY. THE SECOND IS SOUTH OF THE ALASKA PENINSULA AND
MOVING TO THE NORTHEAST. THIS SECOND LOW WILL ABSORB THE LOW IN
BRISTOL BAY AND STRENGTHEN AS IT MOVES INTO THE GULF OF ALASKA
TOMORROW.
&&

.MODEL DISCUSSION...
MODELS ARE IN VERY GOOD SYNOPTIC AGREEMENT THROUGH THE REST OF
THE WEEK. THE BIGGEST PROBLEM TO RESOLVE WITH THE MODELS IS THE
BEHAVIOR OF THE LOW THAT IS STRENGTHENING AS IT MOVES INTO THE
GULF OF ALASKA TOMORROW. THE NAM AND EC SHOW A COMPLEX LOW WITH
TWO DISTINCT CENTERS WITH THE GFS CONSOLIDATING THE ENERGY INTO A
SINGLE CENTER. THE MOST LIKELY SCENARIO IS THAT THERE WILL BE TWO
CENTERS BUT THIS ALSO WILL MAKE THE LOWS TRACK AFTER THAT A LITTLE
LESS CERTAIN AS THE MODELS USUALLY HAVE AN EASIER TIME WITH A
SINGLE CENTER LOW.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...
THE FRONT ASSOCIATED WITH THE LOW IN BRISTOL BAY IS MAKING IT WAY
THROUGH SOUTHCENTRAL ALASKA THIS AFTERNOON AND EVENING. THIS IS
BRINGING MORE WIDESPREAD RAIN...ESPECIALLY IN COASTAL AREAS.
THE TYPICAL DOWNSLOPE AREAS SUCH AS ANCHORAGE AND THE COPPER RIVER
BASIN HAVE SEEN LIMITED RAINFALL DUE TO THE DOWNSLOPE PROCESS.
HOWEVER THIS WILL DECREASE THIS EVENING AND STEADY RAINFALL WILL
DEVELOP OVERNIGHT IN THESE AREAS AS WELL.

SOUTHWEST ALASKA...
THE LOW IN EASTERN BRISTOL BAY HAS MADE THE ATMOSPHERE VERY
UNSTABLE IN THAT REGION WITH HEAVY SHOWERS ROTATING AROUND THIS
LOW. THESE SHOWERS WILL DIMINISH IN COVERAGE AND INTENSITY
OVERNIGHT AS THE LOW WEAKENS AND IS ABSORBED INTO THE LOW MOVING
INTO THE GULF OF ALASKA.
FOG MAY BECOME AN ISSUE OVERNIGHT INTO TOMORROW MORNING ACROSS THE
BRISTOL BAY REGION AS THE RAINFALL HAS SATURATED THE AIR ACROSS
THE ARE AND THE LONGER NIGHTS MAY BE ENOUGH TO PRODUCE AREA OF
FOG.
THESE MAY BE SOME FOG IN THE KUSKOKWIM DELTA AREA TONIGHT BUT THIS
IS LESS LIKELY THAN IN BRISTOL BAY AS THE AMOUNT OF FOG OVER THE
NORTHEAST BERING SEA IS LIMITED. THIS IS THE TYPE OF SITUATION
WHERE THE FOG WILL NEED TO FORM OVER THE BERING SEA AND THEN MOVE
ON SHORE OVER THE AREA FROM THERE.

BERING SEA/ALEUTIANS...
THE BERING SEA HAS A BIT OF SHOWERS OVER IT WHICH IS ALLOWING SOME
BREAKS IN THE CLOUDS...ESPECIALLY TO THE WEST. THE ALASKA
PENINSULA AND ALEUTIANS ARE IN THE NORTHWEST WINDS AROUND THE LOW
AND THIS IS BRINGING QUITE A BIT OF SHOWER ACTIVITY AS WELL AS
GUSTY WINDS. WHILE THE SHOWERS WILL SLOWLY DIMINISH OVER THE
COURSE OF THE NIGHT AND INTO TOMORROW THE BREEZY CONDITIONS WILL
PERSIST.

&&

.LONG TERM FORECAST...
BEGINNING THE EXTENDED PERIOD ON SUNDAY...THE UPPER AIR PATTERN
WILL CONSIST OF A BLOCKING HIGH OVER THE BERING AND A SPLIT TROUGH
OVER ALASKA AND THE GULF OF ALASKA. A SHARP NORTH AMERICAN RIDGE
WILL TRACK A SUBTROPICAL FRONT NORTHWARD INTO THE GULF LATE SUNDAY
INTO MONDAY. THE EXACT TRACK REMAINS UNCERTAIN...WITH MORE BULLISH
SCENARIOS FROM THE ECMWF AND CANADIAN GDPS FAVORING DEEP AND
STRONG LOW LIFTING INTO THE NORTHERN GULF COAST...WHILE THE GFS
FAVORS AN EASTWARD TRACK ALONG THE ALASKA/CANADA BORDER. THE
CURRENT FORECAST FAVORS A LESS AGGRESSIVE GFS/WPC APPROACH GIVEN
LARGE TRACK AND STRENGTH VARIABILITY AMONG THE DETERMINISTIC AND
ENSEMBLE GUIDANCE. WITH THAT SAID...PRECIPITATION CHANCES WILL
REMAIN THROUGH WEDNESDAY AS ALASKA REMAINS IN BETWEEN TWO LARGE
HIGH PRESSURE CENTERS ACROSS THE BERING AND WESTERN NORTH AMERICA.
NO SIGNIFICANT WET OR COLD PATTERNS ARE EXPECTED THROUGH THE
EXTENDED PERIOD.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 125.
FIRE WEATHER...NONE.
&&

$$

SEP 14


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