Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 182157
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
157 PM AKDT MON AUG 18 2014

.ANALYSIS AND UPPER LEVELS...

AN LONG WAVE UPPER LEVEL LOW IS BEGINNING TO TAKE SHAPE IN THE
WESTERN BERING SEA TODAY. THIS FEATURE TO BECOME THE MAJOR PLAYER FOR
WEATHER THIS WEEK. IN THE MEANTIME...A SHORTWAVE TROUGH WITH A
SMALLER CLOSED LOW IS DEVELOPING SOUTH OF ADAK. WITH THE JET
SITUATED FROM THE BASE OF THE LONG WAVE TROUGH IN THE WESTERN
BERING/NORTH PACIFIC TO SOUTH OF THE GULF OF ALASKA...THIS UPPER
LOW WILL TRACK SOUTH OF THE GULF OF ALASKA. ANOTHER SHORT WAVE
TROUGH IS CURRENTLY TRACKING ACROSS THE MAINLAND. THIS HAS ACTED
TO ADD ISOLATED TO SCATTERED THUNDERSTORMS TO THE FORECAST AND
AREAS OF RAIN ACROSS SOUTHWEST ALASKA AND NORTH SUSITNA VALLEY. IN
ADDITION...A SHORT WAVE RIDGE WILL PUSH ACROSS SOUTHWEST ALASKA
TONIGHT AND ACROSS SOUTH CENTRAL ALASKA TUESDAY. THIS WILL
EFFECTIVELY CUT OFF MOST THUNDERSTORM ACTIVITY.

&&

.MODEL DISCUSSION...

MODELS ARE IN DECENT AGREEMENT THROUGH THURSDAY. AN UPPER LEVEL
DISTURBANCE IS LIFTING ACROSS WESTERN ALASKA THIS AFTERNOON WITH
SHOWERS FROM THE WEST COAST TO THE SUSITNA VALLEY. THIS WAVE WILL
CONTINUE TO MOVE THROUGH CENTRAL ALASKA TONIGHT AND TOMORROW. A
SHORT WAVE RIDGE WILL MOVE OVER THE INTERIOR TOMORROW WITH THE
LONG WAVE TROUGH DEVELOPING A CLOSED LOW OVER THE WESTERN ALEUTIAN
CHAIN. MEANWHILE A WEAKER CLOSED LOW WILL MOVE THROUGH THE GULF OF
ALASKA TUESDAY AND WEDNESDAY. THE CLOSED LOW CONTINUES TO DEVELOP
OVER THE BERING WITH AN ASSOCIATED SURFACE LOW INTO WEDNESDAY. THE
GULF LOW WILL EXIT TO THE PANHANDLE WEDNESDAY WITH HIGH PRESSURE
MOVING OVER THE INTERIOR WEDNESDAY INTO THURSDAY.

THE DIVERGENCE AMONG THE FORECAST MODELS STARTS ON FRIDAY WITH HOW
A WAVE ROTATING AROUND THE UPPER LOW THAT HAS MOVED TO SOUTH OF
ADAK BY THIS TIME.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
AN UPPER LEVEL DISTURBANCE TO PASS OVER THE AREA TONIGHT AND OUT
OF THE AREA LATER TOMORROW. THIS WILL CREATE ENOUGH INSTABILITY
FOR SHOWERS AND ISOLATED MOUNTAIN THUNDERSTORMS. THE HEAVIER
ACTIVITY WILL BE OVER THE SUSITNA VALLEY AND ALASKA RANGE OF THE
COPPER BASIN. DUE TO THE WESTERLY FLOW WITH THE WAVE...ANCHORAGE
BOWL AND VICINITY WILL LIKELY SEE ISOLATED ACTIVITY ONLY. AS THE
WAVE PASSES...A WESTERLY PRESSURE GRADIENT DEVELOPS TOMORROW
AFTERNOON/EVENING. WE SHOULD EXPECT SOME INCREASED WINDS THROUGH
THE WHITTIER AREA. TONIGHT...THE BARREN ISLANDS AND KODIAK ISLAND
AND SOUTHERN COOK INLET AREAS SHOULD SEE SOME MODERATE WIND SPEEDS.
THE GRADIENT WILL INCREASE A BIT INTO WEDNESDAY OVER THE PRINCE
WILLIAM SOUND AREA AS HIGH PRESSURE BUILDS IN WESTERN ALASKA. DUE
TO HIGH PRESSURE ALOFT AND BUILDING AT THE SURFACE TUESDAY THROUGH
THURSDAY...ISOLATED SHOWERS WILL BE MAINLY OVER THE MOUNTAINS.

SOUTHWEST ALASKA...

GOOD ONSHORE FLOW OVER WESTERN ALASKA BEHIND THE UPPER LEVEL
DISTURBANCE OVER THE KUSKOKWIM VALLEY CURRENTLY. SHOWERS EXTEND
FROM THE COAST TO THE ALASKA RANGE. A LOT OF STRATUS WITH THE
ONSHORE FLOW AND SHOWER ACTIVITY LAST NIGHT. THIS HAS HAMPERED
BREAKS IN CLOUDS TO POSSIBLY TRIGGER THUNDERSTORMS. ONLY EXPECT
ISOLATED THUNDERSTORMS ALONG THE ALASKA RANGE TONIGHT. WE EXPECT
MORE BREAKS IN THE CLOUDS TOMORROW FOR ISOLATED TO SCATTERED
THUNDERSTORM ACTIVITY. HIGH PRESSURE MOVES IN WEDNESDAY AND
REMAINS INTO THURSDAY FOR ISOLATED SHOWERS OVER THE MOUNTAINS
MAINLY. WITH THE ONSHORE FLOW CONTINUING WE CAN EXPECT STRATUS OFF
AND ON FOR THE NEXT FEW DAYS ALONG THE COAST.

BERING SEA/ALEUTIANS...

HIGH PRESSURE OVER THE EASTERN BERING WITH STRATUS PREVAILING. THE
HIGH PRESSURE WILL SLOWLY MOVE INLAND OVER THE NEXT FEW DAYS WITH
STRATUS REMAINING OVER THE EASTERN BERING. A SURFACE LOW WILL MOVE
INTO THE WESTERN ALEUTIANS TUESDAY AND REMAIN ROUGHLY IN THE SAME
POSITION FOR THE NEXT COUPLE DAYS. BY THURSDAY...THE LOW WILL
BEGIN TO WEAKEN AND A STRONGER LOW WILL TAKE OVER IN THE NORTH
PACIFIC CLOSER TO THE SUPPORT OF THE JET STREAM.


&&

.LONG TERM FORECAST...
THE EXTENDED FORECAST REVOLVES AROUND THE LONG-WAVE TROUGH
CURRENTLY PROPAGATING EASTWARD NEAR THE KAMCHATKA PENINSULA. THE
MAIN UPPER LOW PRESSURE CENTER WITHIN THE TROUGH WILL SLOWLY MOVE
EASTWARD ACROSS THE ALEUTIANS OVER THE WEEKEND. MODEL GUIDANCE IS
IN A BIT BETTER AGREEMENT THAN PREVIOUS DAYS CONCERNING THE
DETAILS BUT THERE ARE STILL LARGE DISAGREEMENTS CONCERNING
STRENGTH AND TIMING. THE MAINLAND WILL SEE A DECENT START TO THE
WEEKEND WITH THE CHANCE FOR SHOWERS MAINLY ALONG HIGHER TERRAIN
AND SEASONABLE TEMPERATURES. A FRONTAL BOUNDARY WILL PUSH UP INTO
THE GULF ON SUNDAY RETURNING SOME AMOUNT OF CLOUDS AND MOISTURE
BUT STRENGTH IS YET TO BE DETERMINED. INTO EARLY NEXT WEEK THAT
TROUGH LOOKS TO BRING UNSETTLED WEATHER TO MOST OF THE SOUTHERN
MAINLAND.


&&

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

$$

JN/MTL AUG 14



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