Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 060015
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
415 PM AKDT SUN JUL 5 2015

.ANALYSIS AND UPPER LEVELS...

A NORTHWESTWARD MOVING 984 MB SURFACE LOW CENTERED JUST SOUTHWEST
OF DUTCH HARBOR HAS INTENSIFIED OVERNIGHT IN THE LEFT EXIT REGION
OF A 100 KT JET STREAK. THE MOISTURE FEED INTO THE LOW FROM THE
TROPICS IS CONFINED TO A VERY NARROW STREAM LOCATED EAST TO
NORTHEAST OF THE LOW. WITH MOST OF THE FORCING ASSOCIATED WITH THE
OCCLUDED FRONT AND THE TROPICAL MOISTURE FEED SHIFTING WESTWARD
INTO THE BERING WITH THE LOW...PRECIPITATION OVER MAINLAND
SOUTHWEST ALASKA IS MAINLY IN THE FORM OF A FEW SCATTERED SHOWERS.
OVER SOUTHCENTRAL...A STOUT RIDGE EXTENDING NORTHWARD FROM THE
GULF IS KEEPING THE AREA DRY. ALL OF THE SCATTERED CLOUDINESS OVER
SOUTHCENTRAL IS ASSOCIATED WITH WEAK UPPER LEVEL DIFFLUENCE
BRINGING SOME RESIDUAL MOISTURE FROM THE LOW OVER THE ALEUTIANS.

&&

.MODEL DISCUSSION...

THE MODELS ALL GENERALLY REMAIN IN EXCELLENT AGREEMENT REGARDING
OVERALL PLACEMENT OF THE SIGNIFICANT WEATHER SYSTEMS. A FEW
DIFFERENCES ARISE IN THEIR DEPICTIONS OF THE NEXT FRONT AND UPPER
LEVEL SHORTWAVE MOVING INTO SOUTHERN ALASKA ON MONDAY NIGHT. THE
GEM GLOBAL AND EC KEEP THE FORCING FURTHEST WEST OVER SOUTHWEST
ALASKA...WHILE THE 12Z NAM IS THE FURTHEST EAST... BRINGING THE
STRONGEST FORCING AS FAR EAST AS COOK INLET. THE GFS IS THE
SLOWEST MODEL IN TERMS OF TIMING... AND RIGHT IN THE MIDDLE FOR
LONGITUDINAL PLACEMENT OF THE SHORTWAVE...TRACKING IT ALONG THE
ALEUTIAN AND ALASKA RANGES. THESE DISCREPANCIES HAVE SIGNIFICANT
BEARING ON THE AMOUNT OF RAIN EXPECTED...WITH THE WESTWARD-MOST
SOLUTIONS FAVORING RAIN IN SOUTHWEST ALASKA AND VERY LITTLE IN
SOUTHCENTRAL...WHILE THE NAM`S EASTERNMOST SOLUTION WOULD BRING
WETTING RAINS TO SOUTHCENTRAL. REGARDLESS OF THE SHORTWAVE`S
EVENTUAL TRACK...ALL MODELS AGREE THAT IT AND THE NORTHEASTWARD
MOVEMENT OF AN UPPER LEVEL JET STREAK CURRENTLY BARRELING ACROSS
THE NORTH CENTRAL PACIFIC WILL ALLOW SOME EASTWARD PROGRESSION OF
THE DEEPENING BERING SEA UPPER LEVEL TROUGH AT THE EXPENSE OF THE
RIDGE OVER THE NORTHEAST PACIFIC. THIS WOULD ENSURE A
CONTINUATION OF MILD...SEASONABLE WEATHER ACROSS MUCH OF ALASKA.

&&

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

RAIN WILL SPREAD ACROSS THE NORTH GULF COAST LATER TONIGHT INTO
MONDAY. STRONG WIND THROUGH CHANNELED TERRAIN WILL AFFECT
TURNAGAIN ARM AND THE KNIK RIVER VALLEY ON MONDAY AS SOUTHEAST
FLOW INCREASES AHEAD OF THE FRONT. DOWNSLOPING FROM THE SOUTHEAST
FLOW ALOFT WILL PREVENT PRECIPITATION FROM CROSSING THE KENAI AND
CHUGACH MOUNTAINS UNTIL LATER ON MONDAY. AT THAT TIME UPPER FLOW
WILL SHIFT TO THE SOUTH AND RAIN AND SHOWERS WILL MOVE INLAND AND
PERSIST THROUGH TUESDAY. BEFORE THE CLOUDS AND PRECIPITATION REACH
THE COPPER BASIN HOWEVER...EXTREMELY WARM TEMPERATURES AND GUSTY
WINDS WILL AFFECT THE COPPER RIVER MON AFTERNOON AND EVENING.
THESE WILL COMBINE TO PRODUCE RED FLAG CONDITIONS DURING THAT
PERIOD. THOSE CONDITIONS WILL END MONDAY NIGHT AS SHOWERS SPREAD
ACROSS THE COPPER RIVER BASIN AND THEN CONTINUE THROUGH TUESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH TUE AFTERNOON)...

IT APPEARS AS IF ANOTHER WET PERIOD IS IN STORE FOR SOUTHWEST
ALASKA AS AN AREA OF LOW PRESSURE SOUTH OF THE ALASKA PENINSULA
MOVES NORTH INTO THE BERING SEA TONIGHT AND PUSHES A FRONT ACROSS
THE AREA. LOCATIONS ON THE LEE SIDE OF THE ALASKA RANGE...THE
ALEUTIAN RANGE AND KILBUCK MOUNTAINS WILL BE INITIALLY DOWNSLOPED
AS A MAJORITY OF THE FORCING REMAINS FAR WEST IN THE BERING SEA
AND CROSS BARRIER FLOW SHOULD CREATE A DRY SURFACE LAYER.
PRECIPITATION HAS BEEN ONGOING ACROSS THE ALASKA PENINSULA DURING
THE DAY AND WILL SHIFT EASTWARD DURING THE EVENING AND OVERNIGHT
HOURS WITH THE PASSAGE OF THE FRONT. BY MONDAY MORNING...A SERIES
OF SHORTWAVES WILL PUSH ACROSS SOUTHWEST ALASKA AND BRING A MUCH
BETTER CHANCE OF PRECIPITATION TO THE LOCATIONS THAT WERE
PREVIOUSLY DOWNSLOPED. RAINFALL WILL TAPER OFF FROM SOUTH TO NORTH
ON TUESDAY AS THE BULK OF THE SHORTWAVE ENERGY SHIFTS NORTHWARD
INTO THE INTERIOR OF ALASKA. A LARGE SWATCH OF SUBTROPICAL
MOISTURE IS BEING ADVECTED NORTHWARD AND WILL CONTINUE TO UPSLOPE
ALONG THE ALASKA PENINSULA...BRINGING STEADY RAIN EVEN AS THE
FRONT PUSHES INLAND. ALSO...THIS MOISTURE WILL ALSO UPSLOPE ALONG
THE AHKLUN MOUNTAINS NORTH OF DILLINGHAM WHICH WILL BRING SOME
LOCALLY HEAVY RAINFALL TO THE AREAS NEARBY THESE MOUNTAINS.
SCATTERED RAIN SHOWERS WILL CONTINUE BEHIND THE FRONTAL PASSAGE ON
TUESDAY AS BROAD CYCLONIC (ONSHORE FLOW) WILL PERSIST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH TUE AFTERNOON)...

AN AREA OF LOW PRESSURE IS CURRENTLY TRANSITIONING FROM THE NORTH
PACIFIC INTO THE BERING SEA AS SCATTEROMETER DATA HAS IT JUST
EAST OF SEGUAM ISLAND. THIS LOW LOOKS TO BRING GALE FORCE WINDS TO
THE EASTERN BERING SEA TONIGHT AND EARLY TOMORROW BEFORE IT
STARTS TO WEAKEN AND MOVES OVER THE CENTRAL AND WESTERN BERING
SEA. THIS LOW WILL ENCOMPASS A VAST MAJORITY OF THE BERING OVER
THE NEXT SEVERAL DAYS AND WILL KEEP RAIN CHANCES ACROSS MUCH OF
THE BERING SEA THROUGH AT LEAST TUESDAY. THE POSITION OF THE LOW
WILL PUT AREAS NEAR DUTCH HARBOR ON THE FAVORABLE SIDE TO SEE
GUSTS UP TO 45 MPH TONIGHT BUT WILL QUICKLY DIMINISH BY EARLY
TOMORROW MORNING AS THE LOW SLIDES NORTHWARD AND THE PRESSURE
GRADIENT RELAXES.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A PERSISTENT LARGE AREA OF LOW PRESSURE WILL REMAIN CENTERED OVER
THE BERING THROUGH AT LEAST NEXT WEEKEND WHILE THE UPPER LEVEL
RIDGE OVER MAINLAND ALASKA SHIFTS EAST INTO CANADA AND FLATTENS.
THE NET RESULT WILL PUT THE AREA INTO A PERSISTENT COOLER AND
MORE MOIST PATTERN...WITH A SURFACE RIDGE ALONG THE EASTERN GULF
AND NORTH GULF COAST SUPPORTING LOW LEVEL ONSHORE FLOW. SHORTWAVE
TROUGHS WILL PERIODICALLY ROTATE UP FROM THE WESTERN GULF AND
EASTERN BERING KEEPING SKIES MOSTLY CLOUDY AND BRINGING SCATTERED
SHOWERS...PERIODS OF RAIN AND MILD TEMPERATURES TO MUCH OF
SOUTHWEST AND SOUTH CENTRAL ALASKA.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 155 160 165 170 172 179 180.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...CC


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