Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 301259
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
459 AM AKDT SAT APR 30 2016

.ANALYSIS AND UPPER LEVELS...
THE NORTH PACIFIC AND ALASKA REMAIN UNDER THE INFLUENCE OF A BROAD
AND DEEPENING LONGWAVE TROUGH CENTERED ALONG 160W WITH SLIGHTLY
LOWER AMPLITUDE RIDGES ALONG THE NORTHEASTERN PACIFIC COAST AND
OVER THE NORTHWEST PACIFIC ALONG 175E. A CLOSED UPPER LOW REMAINS
EMBEDDED WITHIN THE LONGWAVE TROUGH CENTERED OVER THE ALASKA
PENINSULA. THE POLAR JET HAS BECOME SIGNIFICANTLY MORE MERIDIONAL
THAN THIS TIME YESTERDAY DUE TO THE AMPLIFICATION OF THE
TROUGH/RIDGE PATTERN...WITH A 130KT JET MAX ALONG THE EASTERN SIDE
OF THE TROUGH /ROUGHLY BETWEEN 40-50N AND ALONG 148W/ AND A
STRONGER 150KT MAX ON THE ON THE WESTERN SIDE OF THE RIDGE ALONG
165E.

AT THE SURFACE...WEATHER FOR MOST OF ALASKA IS DOMINATED BY A
983MB LOW LOCATED ABOUT 600 MILES SOUTH OF KODIAK ISLAND THIS
MORNING. THIS LOW HAS EXCELLENT SUPPORT FROM THE 130KT JET MAX
MENTIONED ABOVE. THE ASSOCIATED SURFACE FRONT IS MOVING NORTHWARD
THROUGH THE GULF OF ALASKA THIS MORNING...PRODUCING STORM FORCE
WINDS OVER THE NORTHERN GULF. THE AMPLITUDE OF THE TROUGH IS DEEP
ENOUGH THAT MOISTURE IS STREAMING NORTHWARD INTO THE SURFACE
SYSTEM FROM ABOUT 30N...ALTHOUGH MOST OF THIS MOISTURE IS BEING
SHUNTED TOWARDS SOUTHEASTERN ALASKA. OUT WEST...A LARGE 966 MB LOW
SOUTH OF THE KAMCHATKA PENINSULA IS PUSHING ITS ASSOCIATED FRONT
INTO THE WESTERN ALEUTIANS. FINALLY...A WEAK 1002 MB LOW OVER THE
KUSKOKWIM DELTA IS MOVING OFF SHORE AND DISSIPATING.

&&

.MODEL DISCUSSION...
MODEL GUIDANCE FROM THE MAJOR MODELS ALL INITIALIZED WITH FEW
ERRORS AND THE FORECAST GUIDANCE THROUGH 84 HOURS ARE ALL IN
REASONABLY GOOD AGREEMENT THROUGH THE DAY 3 PERIOD. IN THE SHORT
TERM...THE GFS IS KEEPING WINDS AT STORM FORCE WITH THE FRONT
PUSHING THROUGH THE NORTHERN GULF OF ALASKA THIS MORNING WHEREAS
THE OTHER MODELS ARE KEEPING WINDS IN THE GALE FORCE RANGE. FOR
THIS PACKAGE...THE GFS WAS GENERALLY USED FOR GUIDANCE THROUGH
DAY 3.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE MAIN FORECAST CHALLENGE THIS WEEKEND IS THE FRONT ALONG THE
GULF THAT WILL BRING INCREASED RAIN CHANCES AND GUSTY WINDS
THROUGH SUNDAY. THE FRONTAL BOUNDARY MOVES QUICKLY TO THE
NORTHERN COAST THIS MORNING BRINGING GUSTY WINDS AND A BAND OF
RAIN...FROM THE CENTRAL GULF AND ACROSS THE EASTERN KENAI...TO
THE COAST. GUSTY GALE TO STORM FORCE WINDS ACROSS THE GULF
CONTINUE THROUGH THE AFTERNOON EXCEPT FOR DIMINISHING CONDITIONS
ALONG THE SOUTHERN GULF DURING THE AFTERNOON. STRONG WINDS ACROSS
KODIAK ISLAND WILL END QUICKLY DURING THE AFTERNOON BEHIND THE
FRONT. THIS SYSTEM WEAKENS ALONG THE COAST THIS EVENING WITH
WINDS TAPERING DOWN THROUGH THE NIGHT.

WINDS BECOME GUSTY ON SUNDAY ACROSS GAP LOCATIONS...INCLUDING THE
COPPER RIVER VALLEY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN THE
SURFACE LOW SOUTH OF KODIAK ISLAND AND A BUILDING RIDGE ALONG
THE NORTHEAST COAST. BY EARLY MONDAY MORNING...DRIER CONDITIONS
AND QUIETER WINDS SETTLE IN AS THE SURFACE LOW WEAKENS ALONG THE
WESTERN GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SAT AND SUN)...
A LOW MOVING INTO THE GULF TODAY WILL PROVIDE SHOWERS ACROSS
MAINLY THE ALASKA AND ALEUTIAN RANGES AS WELL AS THE BRISTOL BAY
AREA. FURTHER WEST...NORTHEASTERLY FLOW WILL KEEP MUCH OF THE
KUSKOKWIM VALLEY AND DELTA DRY ALTHOUGH DAYTIME HEATING MAY PROVIDE
ENOUGH INSTABILITY FOR A FEW SHOWERS TO DEVELOP AND DRIFT INTO THE
KUSKOKWIM DELTA THIS AFTERNOON. BY SUNDAY...THE NEXT LOW WILL BE
MOVING IN PROVIDING SHOWERS FOR INTERIOR LOCATIONS. THERE COULD
BE ENOUGH INSTABILITY FOR A FEW THUNDERSTORMS IN THE AFTERNOON AND
EVENING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SAT AND
SUN)...

A GALE FORCE LOW MOVING INTO THE GULF OF ALASKA WILL WEAKEN AND
MOVE NORTHEAST...WITH THE ASSOCIATED GALE FORCE FRONT OVER THE FAR
EASTERN ALEUTIANS MOVING INTO THE GULF...LEAVING BROAD NORTHERLY
FLOW IN ITS WAKE OVER THE REMAINDER OF THE BERING/ALEUTIANS. A
WEAKENING OCCLUDED FRONT WILL MOVE INTO THE WESTERN BERING TONIGHT
AND SUNDAY...THEN SLOWLY MOVE EASTWARD AS FAR AS THE CENTRAL
ALEUTIANS BY MONDAY...BRINGING A PERIOD OF RAIN AND SWITCHING
WINDS AROUND TO THE SOUTHEAST/SOUTHWEST. OTHERWISE....RATHER
QUIESCENT WEATHER WILL ABOUND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...MON THROUGH FRI)...
NOT A LOT OF CHANGE EXPECTED IN THE LONG TERM. ONE UPPER-LEVEL
WILL SLOWLY FILL AND WEAKEN OVER THE GULF EARLY IN THE WEEK.
ANOTHER NEW LOW WILL DEVELOP OVER THE CENTRAL ALEUTIANS AND TRACK
SLOWLY EAST. THIS WILL ALLOW A RIDGE TO BUILD IN FRONT OF THE
SECOND LOW OVER SOUTHERN ALASKA ON TUE AND WED. THIS WILL BRING A
BRIEF BREAK TO THE CONTINUOUS SOUTHEAST FLOW AND ASSOCIATED
FRONTS IMPACTING THE GULF COAST. IT COULD ALSO BRING THE BEST
CHANCE FOR SOME WIDESPREAD SUNSHINE ACROSS MUCH OF THE SOUTHERN
MAINLAND. BY THE MIDDLE OF THE WEEK THOUGH...MODELS BEGIN TO
DIVERGE ON TWO SIGNIFICANT ISSUES. THE FIRST IS HOW MUCH ENERGY
PUSHES INTO THE RIDGE OVER SE ALASKA AND THE SECOND IS WHAT
STRUCTURE THE LOW APPROACHING FROM THE ALEUTIANS TAKES ON. IF
ENOUGH ENERGY PUSHES INTO THE RIDGE...IT WILL SIMPLY GIVE WAY AND
MOVE EAST. BUT IF SOME WARM AIR ADVECTED INTO IT CAUSING IT TO
BUILD...THE ENERGY MIGHT JUST RIDE UP ITS WESTERN FLANK STRAIGHT
INTO SOUTHERN AK. THE STRUCTURE OF THE LOW VARIES FROM THE GFS
DEPICTION OF A VERTICALLY STACKED LOW TRACKING SLOWLY EAST TO THE
EC SHOWING IT MORE PROGRESSIVE WITH A NEW TRIPLE-POINT LOW FORMING
OVER THE SOUTHERN GULF BY NEXT WEEKEND. THIS FORECAST PACKAGE
LEANED TOWARDS KEEPING THE HIGHEST POPS ALONG COASTAL LOCATIONS AT
THIS TIME. TEMPERATURES LOOK TO REMAINS NORMAL TO ABOVE NORMAL AS
WE START MAY. THIS COULD LEAD TO SOME WEAK INSTABILITY...SO WE
WILL BE WATCHING CHANCES FOR CONVECTION.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 119 120 130 131
         GALE 125 132 137 138 139 140 141 150 351 352

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RLF
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...LIW/JA
LONG TERM...MO



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