Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 011258
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
458 AM AKDT SUN MAY 1 2016

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH REMAINS OVER MAINLAND ALASKA WITH AN AXIS ALONG
150W THIS MORNING WITH A HIGH AMPLITUDE RIDGE TO THE EAST OVER
THE WESTERN NORTH AMERICA COAST. TO THE WEST OF THE TROUGH...A
MUCH LOWER AMPLITUDE RIDGE ALONG 175W IS BEING ERODED BY A LARGE
UPPER LOW WITHIN A BROAD TROUGH NEAR THE KAMCHATKA PENINSULA THAT
IS PUSHING EASTWARD INTO THE SOUTHWEST BERING SEA. A CLOSED UPPER
LOW REMAINS EMBEDDED WITHIN THE MAIN LONGWAVE TROUGH AND IS MOVING
INTO SOUTHWEST ALASKA. THE POLAR JET REMAINS STOUT WITH A 155 KT
JET MAX IN THE POLEWARD LIMB ALONG THE EASTERN SIDE OF THE
LONGWAVE TROUGH AND A BROAD AREA OF 130+ KT WINDS SOUTH OF THE
KAMCHATKA LOW.

A 994 MB LOW NEAR KODIAK ISLAND IS THE DOMINATE SURFACE FEATURE
OVER ALASKA THIS MORNING WITH THE ASSOCIATED SURFACE FRONT PUSHING
ONSHORE OVER THE NORTH GULF COAST...PRODUCING WIDESPREAD SHOWERS
AND RAIN OVER THE COAST AND PORTIONS OF COOK INLET AND THE SUSITNA
VALLEY. ENERGY ROTATING AROUND THE LOW AND AHEAD OF THE FRONT IS
PRODUCING SHOWERS OVER MUCH OF SOUTHWEST ALASKA THIS MORNING. OVER
THE CENTRAL ALEUTIANS...A WEAKENING RIDGE IS MOVING EASTWARD
AHEAD OF A BROAD AND WEAKENING 986 MB LOW AND ITS ASSOCIATED FRONT
LOCATED NEAR KAMCHATKA.

&&

.MODEL DISCUSSION...
GLOBAL MODELS ALL INITIALIZED ACCEPTABLY FOR THE 00Z RUN WITH FEW
SIGNIFICANT DIFFERENCES. THROUGH 48 HOURS...MODELS ARE IN
REASONABLE AGREEMENT WITH THEIR HANDING OF FEATURES WITH ONLY
MINOR DIFFERENCES. FOR THIS PACKAGE...THE GFS WAS USED ON BOTH
EAST AND WEST FORECAST DOMAINS WITH THE NAM USED OVER LAND AREAS
IN SOUTHWEST ALASKA.

&&

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

THE MAIN CONCERN IN THE FORECAST THROUGH MONDAY SURROUNDS GUSTY
WINDS THAT DEVELOP IN RESPONSE TO A BUILDING RIDGE ALONG THE
NORTHEAST GULF COAST. SUNDAY MORNING STARTS OFF WITH LOW PRESSURE
SOUTH OF KODIAK ISLAND PUSHING A WEAK FRONT OVER THE NORTHERN GULF TO
THE SUSITNA AND COPPER RIVER VALLEYS. RAIN WILL LARGELY BE
CONFINED TO THE GULF AND COASTAL AREAS WITH SCATTERED SHOWERS
INLAND. THE DRIVING MECHANISM FOR THE BUILDING RIDGE TODAY IS FROM
THE AMPLIFICATION OF THE NORTH AMERICAN RIDGE TO THE COPPER
RIVER. A LOW LEVEL JET ACCELERATES TO 30 TO 45 MPH AS THE PRESSURE
GRADIENT TIGHTENS ALONG THE NORTHERN COAST THIS MORNING. WINDS MIX
DOWN TO THE SURFACE WITH DOWNWARD FORCING BEHIND THE FRONT. THERE
CONTINUES TO BE SOME UNCERTAINTY IN THE TIMING AND STRENGTH FOR
SURFACE WINDS AS MODELS STRUGGLE TO CAPTURE THE ORIENTATION OF THE
PRESSURE GRADIENT. FORECAST WINDS ACROSS EAST TO WEST GAPS AND
ALONG THE COPPER RIVER WERE INCREASED THIS AFTERNOON TO FOLLOW
TRENDS OF THE HIRES MODELS. A PERSISTENT PATTERN CONTINUES INTO
MONDAY WITH SHOWERS ACROSS THE GULF AND AFTERNOON GUSTS DEVELOPING
AS ANOTHER SHORTWAVE MOVES UP FROM THE SOUTHERN GULF.

&&

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

REMNANTS OF A TROUGH MOVING THROUGH THE BRISTOL BAY AREA IS
BRINGING SOME SHOWERS THIS MORNING. ELSEWHERE...A WEAK SURFACE LOW
WILL BE DEVELOPING LATER TODAY ACROSS THE WESTERN INTERIOR.
COMBINED WITH DAYTIME HEATING...SOME INSTABILITY IS EXPECTED TO
RETURN ALLOWING FOR DIURNAL SHOWERS AND THUNDERSTORMS. THIS LOW
WILL REMAIN IN PLACE FOR MONDAY AND EXPECT MUCH OF THE SAME WITH
DIURNAL SHOWERS AND THUNDERSTORMS.

&&

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

A SHORTWAVE RIDGE AXIS IS BUILDING INTO THE BERING SEA AHEAD OF A
ONCE STRONG LOW WHICH PEAKED IN STRENGTH SOUTH OF THE KAMCHATKA
PENINSULA. THE ASSOCIATED OCCLUDED FRONT WILL MAKE EASTWARD
PROGRESS AND REACH THE EASTERN ALEUTIANS BY TUESDAY. AS THE
REMNANTS OF THE CLOSED UPPER LOW MOVE EAST IN CONJUNCTION...SHOWERS
BEHIND THE FRONT WILL FILL IN ACROSS MOST OF THE BERING SEA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...TUE THROUGH SAT)...
THE LONG RANGE PATTERN WILL PRESENT SOME INTERESTING CHALLENGES
AND A POSSIBLE CHANGE IN THE LONGWAVE REGIME. THIS TIME FRAME
STARTS WITH ONE LOW FILLING AND MOVING INLAND OVER THE GULF OF AK.
MEANWHILE...OVER THE CENTRAL ALEUTIANS...THE NEXT UPPER LEVEL LOW
IS ALREADY TAKING A VERY FAMILIAR TRACK TOWARDS THE GULF. AS THE
FIRST LOW WEAKENS AND MOVES INLAND...THIS SHOULD ALLOW THE
GRADIENT TO RELAX. THIS WILL FINALLY BRING AN END TO THE GUSTY
SOUTHEAST WINDS THAT HAVE BEEN BLOWING THROUGH FAVORED
LOCATIONS SUCH AS THE TURNAGAIN ARM AND THE KNIK RIVER VALLEY.
RATHER MOIST ONSHORE FLOW WILL CONTINUE TO MAKE FOR SOME STEADY
RAIN FOR IMMEDIATE COASTAL AREAS. BUT PRECIPITATION INLAND SHOULD
BE LIMITED TO SHOWERS...MAINLY DRIVEN BY WEAK AFTERNOON
INSTABILITY WITH A COLD POCKET OF RELATIVELY COLD AIR AT 500MB.

BY LATE WED...THE LOW FROM THE CENTRAL ALEUTIANS WILL MAKE ITS WAY
TO THE ALASKA PENINSULA. IT WILL PUSH A WARM OCCLUSION IN FRONT OF
IT. THIS WILL BRING RAIN BACK INTO KODIAK WITH CLOUDS STARTING TO
OVERSPREAD SOUTH CENTRAL. BUT IT IS AT THIS POINT WHEN MODELS
DIVERGE DRAMATICALLY. THE BIGGEST QUESTION IS WHERE THE UPPER
LEVEL LOW SETS UP RESIDENCE. SOME OF THIS DEPENDS ON HOW EFFECTIVE
ENERGY TRACKING THROUGH THE GULF IS AT PUSHING THE NORTH AMERICAN
RIDGE OFF TO THE EAST. THE EC HOLDS THE LOW CENTER THE FURTHEST
NORTH AND WEST...WHILE THE GFS ALLOWS IT TO MIGRATE ALL THE WAY
INTO THE CENTRAL GULF. EARLIER RUNS WILL SHOWING SOME PHASING
OCCURRING WITH THIS LOW AND SOME ENERGY TRACKING ALONG THE JET IN
THE NORTH PACIFIC. THEY WERE SHOWING THE POTENTIAL FOR A TRIPLE-
POINT LOW TO FORM AND TRACK QUICKLY INTO SOUTH CENTRAL. SOLUTIONS
HAVE BACKED OFF THIS IDEA AND NOW MORE SETTLED ON JUST ANOTHER
UPPER LEVEL LOW SITTING OVER THE CENTRAL GULF BY NEXT SAT.

BY LATE NEXT WEEKEND INTO THE WEEK OF 9-13 MAY...THERE SEEMS TO BE
FAIR TO GOOD MODEL AGREEMENT IN SOME FORM OF RIDGE BUILDING OVER
THE EASTERN INTERIOR PORTION OF AK. MODELS HAVE VARIOUS SOLUTIONS
OF HOW THE RIDGE GETS THERE (SOME FROM THE NORTH PAC...SOME FROM
NW CONUS) BUT THEY ALL SHOW SIGNS OF IT. CLIMATOLOGICALLY THIS
MAKES SENSE AS WELL AS WE USUALLY SEE A WARMER STRETCH TOWARD THE
MIDDLE TO END OF MAY.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

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



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