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FXAK68 PAFC 241248
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
448 AM AKDT FRI OCT 24 2014

.ANALYSIS AND UPPER LEVELS...
ON THE LARGE SCALE THE PATTERN ALOFT IS CONTROLLED BY A LARGE
SIBERIAN LOW PRESSURE. THE MAIN FRONTAL BOUNDARY/SHORTWAVE TROUGH
ASSOCIATED WITH THE SYSTEM STRETCHES FROM THE CHUKCHI SEA
SOUTHEASTWARD THROUGH THE SOUTHERN MAINLAND...CURRENTLY BETWEEN
THE SOUTHCENTRAL AND SOUTHWEST MAINLAND. THE JET STREAM CURRENTLY
EXHIBITS A SPLIT FLOW PATTERN WITH THE MAIN BRANCH OF SUBTROPICAL
JET SITTING IN THE NORTHWESTERN PACIFIC AND MERGING WITH THE
NORTHERN STREAM JUST SOUTH OF THE ALASKA PENINSULA. 

THE FRONT IS PRODUCING A LARGE AREA OF OVERRUNNING PRECIPITATION
OVER THE LOWER KUSKOKWIM VALLEY AND INTERIOR BRISTOL BAY. ABOVE
FREEZING AIR IN THE SOUTHERLY FLOW AHEAD OF THE FRONT IS LIMITED
TO THE SURFACE AND JUST ABOVE SO FREEZING RAIN IS NOT A CONCERN.
THE WEATHER OVER THE SOUTHCENTRAL IS CURRENTLY BENIGN WITH HIGH
CLOUDS FROM THE FRONT SPREADING OVER MOST AREAS. SHOWERS ARE
BEGINNING TO BLOSSOM OVER THE NORTHERN GULF IN RESPONSE TO
ANTECEDENT INSTABILITY AND WARM AIR ADVECTION DEVELOPING. 

&&

.MODEL DISCUSSION...
GUIDANCE IN DECENT AGREEMENT WITH BOTH THE UPPER LEVELS AND THE
SURFACE IN THE NEAR TERM. OVER THE WEEKEND A STRONG IMPULSE LOOKS
TO ROUND THE BASE OF THE SIBERIAN UPPER LOW AND DEVELOP A STRONG
SYSTEM THAT TRACKS TOWARD THE BERING STRAIT. WHILE THE GUIDANCE
SUITE SHOWS A SIMILAR THEME IN DEVELOPING THIS SYSTEM THERE ARE
DIFFERENCES IN STRENGTH AND TRACK OF BOTH THE SURFACE LOW CENTER
AND FRONTAL BOUNDARY...WHICH WILL AFFECT THE SOUTHWEST MAINLAND BY
THE END OF THE WEEKEND. 

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...TWO DIFFERENT FEATURES WILL AFFECT THE AREA
TODAY...THE FIRST IS A WEAK SPIN-UP IN THE NORTHEASTERN GULF
WILL SPREAD SNOW AND RAIN SHOWERS OVER THE NORTHEAST GULF COAST
AND SNOW SHOWERS OVER THE COPPER RIVER BASIN LATER TODAY. OVER THE
COOK INLET REGION...THE LOW LEVEL FRONTAL BOUNDARY IS LOSING
STRENGTH AS THE ALASKA/ALEUTIAN RANGE. THE UPPER LEVEL SHORTWAVE
TROUGH ASSOCIATED WITH THE FRONT IS ALSO DE-AMPLIFYING AS IT
CROSSES THE RANGE WHILE THE FLOW ALOFT CONTINUES TO SLACKEN. WITH
NO APPRECIABLE THERMAL ADVECTION AND WEAKENING FORCING IT DOES NOT
LOOK LIKE A FAVORABLE SCENARIO FOR PRECIPITATION. INCREASING CLOUD
COVER AND LIGHT NORTHERLY WINDS WILL BE THE NORM TODAY WITH A
CHANCE FOR SOME FLURRIES...THE BEST CHANCES WILL LIE ALONG
ELEVATED TERRAIN IN THE EASTERN COOK INLET REGION. ANOTHER TROUGH
SLIDES THROUGH ON SUNDAY...THIS ONE A BIT STRONGER BUT LOOKS TO
ONLY AFFECT THE NORTHEAST GULF COAST AND SOUTHEASTERN COPPER RIVER
BASIN. 

SOUTHWEST ALASKA...RAIN AND SNOW WILL CONTINUE EARLY THIS MORNING
ALONG THE ALASKA/ALEUTIAN RANGES BEFORE TAPERING OFF BY THE LATE
MORNING. HIGH PRESSURE BUILDING IN AT THE SURFACE AND COLD
ADVECTION ALOFT SHOULD MAKE FOR A MOSTLY CLOUD FREE DAY WITH LIGHT
WINDS ACROSS THE BRISTOL BAY AREA. PRECIPITATION HAS ENDED FOR THE
KUSKOKWIM DELTA BUT LINGERING MOISTURE AND SLACKENING WINDS WILL
MAKE FOR A PERIOD OF FOGGY CONDITIONS THIS MORNING. SOME
DISTURBANCES ALOFT WILL PUSH ACROSS THE DELTA LATE TONIGHT INTO
SATURDAY BRINGING ANOTHER ROUND OF RAIN CHANGING TO SNOW. THAT
WEATHER FRONT WILL PUSH OVER THE REST OF THE SOUTHWEST MAINLAND
LATE SATURDAY INTO SUNDAY.

BERING SEA/ALEUTIANS...A WEAKENING FRONTAL BOUNDARY STRETCHED OVER
THE EASTERN ALEUTIAN AND ALASKA PENINSULA WILL KEEP RAIN SHOWERS
IN THE FORECAST THROUGH THE OVERNIGHT HOURS TONIGHT. ANOTHER FRONT
CROSSES THE BERING LATE TONIGHT BUT SHOULD STAY NORTH OF MOST OF
THE CHAIN. A STRONG LOW PRESSURE WILL DEVELOP OVER THE NORTHWEST
BERING ON SUNDAY AND SEND YET ANOTHER FRONT ACROSS THE BERING
SUNDAY AND MONDAY BRINGING RAIN AND SNOW TO MOST AREAS.

&&

.LONG TERM FORECAST...
MODEL CONSISTENCY...BOTH RUN TO RUN AND BETWEEN MODELS...REMAINS A
PROBLEM. OVERNIGHT OPERATIONAL RUNS RAPIDLY LOST AGREEMENT,
ALTHOUGH THE MORNING RUNS OF THE GFS AND EC WERE MUCH
CLOSER...ESPECIALLY WITH THE LOWS AND FRONTAL SYSTEMS MOVING
ACROSS THE BERING. RELIED HEAVILY ON THE DECISION OF WPC TO BEGIN
WITH A 00Z EC MEAN AS A STARTING POINT. THE GRIDS REPRESENT A
BLEND OF THE WPC GUIDANCE...AND WITH WINDS ENHANCED WITH THE 00Z
EC. THE CONFIDENCE REMAINS FAIRLY LOW...BUT THERE IS SOME HOPE
THAT THE MODELS WILL COME INTO BETTER AGREEMENT IN THE NEXT DAY OR
SO.

THE SOLUTION INVOLVES TWO FRONTAL SYSTEM AFFECTING THE BERING AND
WESTERN AK OVER THE EXTENDED PERIOD. THE INITIAL FRONT...FROM A
BERING STRAIT LOW...MOVES INTO WESTERN AK AND THE EASTERN
ALEUTIANS MON AND DISSIPATES RAPIDLY ON TUE. THE SECOND LOW AND
FRONT AFFECT THE WESTERN BERING TUE NIGHT WITH THE FRONT REACHING
WESTERN AK THU BEFORE DISSIPATING INLAND BY FRI. YET ANOTHER FRONT
MOVES INTO THE WESTERN BERING ON FRI. 

WHILE THIS IS HAPPENING THE REMNANTS OF TROPICAL STORM ANA MOVE
INTO SE AK LATER ON MON AND FORM AN ELONGATED TROUGH ALONG THE
NORTHEASTERN GULF COAST THAT PERSISTS THROUGH WED. HIGH PRESSURE
THEN BUILDS OVER THE GULF ON THU.

SHOWERS WILL PERSIST OVER THE BERING AND ALEUTIANS ON MON..AND
THEN RAIN AND SNOW ARE EXPECTED TUE NIGHT BEFORE CHANGING TO SNOW
SHOWERS WED AND THU. MORE RAIN AND SNOW IS EXPECTED FRI. SOME GALES
WILL ACCOMPANY THE FRONTS AS THEY TRANSIT THE BERING.

SOUTHWEST AK WILL HAVE RAIN AND SNOW SHOWERS MON...DRYING ON
TUE...RAIN AND SNOW WED INTO THU...AND SHOWERS LATER ON THU INTO
FRI.

SOUTHCENTRAL WILL BE GENERALLY DRY INLAND THROUGH FRI WITH
SHOWERS ASSOCIATED WITH THE TROUGH ALONG THE COAST TUE AND WED.

&&

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

$$

MTL/DS OCT 14

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