Area Forecast Discussion
Issued by NWS Anchorage, AK

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747
FXAK68 PAFC 031232
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
432 AM AKDT TUE MAY 3 2016

.ANALYSIS AND UPPER LEVELS...
THE GENERAL SYNOPTIC PATTERN REMAINS SIMILAR TO THIS TIME
YESTERDAY WITH A VERY BROAD TROUGH OVER THE NORTH PACIFIC AND
ALASKA WITH A HIGH AMPLITUDE RIDGE TO THE EAST WITH ITS AXIS ALONG
THE ROCKIES. WITHIN THE BROAD TROUGH...TWO FAIRLY DEEP SHORTWAVE
TROUGHS ARE CONTINUING TO PROGRESS EASTWARD IN THE WESTERLY FLOW.
THE EASTERN WAVE IS NEGATIVELY TILTED WITH AN AXIS ALONG 135W AND
IS PROGRESSING SLOWLY TO THE EAST AS THE STOUT RIDGE IS INHIBITING
MUCH EASTWARD MOTION. THE SECOND WAVE IS A POSITIVELY TILTED
TROUGH ROUGHLY ALONG 170E. EMBEDDED AT THE POLEWARD END OF THIS
TROUGH IS AN UPPER CLOSED LOW LOCATED OVER THE CENTRAL ALEUTIAN
ISLANDS. BETWEEN THESE TROUGHS IS A BROAD AND FLAT RIDGE ALONG
165W THAT IS MOSTLY SOUTH OF THE ALEUTIAN CHAIN...ALTHOUGH A WEAK
NORTHWARD EXTENSION OF THIS RIDGE IS PUSHING EASTWARD THROUGH THE
EASTERN ALEUTIANS THIS MORNING. A WEAK UPPER LOW IS VISIBLE ON
SATELLITE THIS MORNING OVER THE NORTHERN GULF OF ALASKA.

THE POLAR JET REMAINS MOSTLY SOUTH OF THE FORECAST AREA WITH A
150KT JET MAX LOCATED ON THE EASTERN SIDE OF THE WESTERN TROUGH
AROUND 40-45N AND CENTERED AROUND 180. THE POLEWARD LIMB OF THE
POLAR JET IS LOCATED OVER SOUTHEASTERN ALASKA WITH A MAX SPEED OF
ABOUT 100KTS.

A WEAKENING 996 MB LOW IS LOCATED NEAR ADAK THIS MORNING WITH A
WEAK FRONTAL BOUNDARY ASSOCIATED WITH THIS LOW STRETCHING
EASTWARD OVER THE PRIBILOF ISLAND AND THROUGH THE EASTERN
ALEUTIANS/ALASKA PENINSULA. A DECAYING 1006 MB LOW REMAINS NEAR
KODIAK ISLAND AND IS CONTINUING TO DRIFT NORTHEASTWARD. A BROAD
AREA OF LOW PRESSURE /ABOUT 1004MB/ IS CENTERED OVER THE LOWER
YUKON VALLEY.

&&

.MODEL DISCUSSION...
THE MAIN QUARTET OF MODELS INITIALIZED ACCEPTABLY AT 00Z WITH ONLY
MINOR DIFFERENCES. THROUGH WEDNESDAY AFTERNOON...MODELS ARE IN
GOOD GENERAL AGREEMENT ON THE MAJOR FEATURES WITH THE MAIN
DIFFERENCES LYING IN THE DEVELOPMENT OF A APPROXIMATELY 987MB LOW
AROUND 50N 165W. THE EC TENDS TO DEVELOP THIS LOW SLIGHTLY DEEPER
THAN THE OTHER MODELS...WITH THE NAM DEVELOPING THE LOW A BIT
FURTHER TO THE EAST AND PROGRESSING THE FRONT A BIT FASTER INTO
THE NORTHERN GULF OF ALASKA BY THE END OF DAY 2. FOR THIS PACKAGE
IN THE SHORT TERM...THE NAM WAS USED FOR GUIDANCE ON THE WESTERN
DOMAIN WITH A BLEND OF THE EC/GFS/GEM-REGIONAL IN THE SHORT TERM
ON THE EASTERN DOMAIN. THE GEM-REGIONAL WAS USED FOR DETAILS OF
THE BARRIER JET EXPECTED TO FORM IN THE NORTHERN GULF COAST AND
INTO PRINCE WILLIAM SOUND.

&&

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

STACKED LOW PRESSURE OVER THE NORTHWEST GULF OF ALASKA WILL MOVE
OVER THE KENAI PENINSULA AND THROUGH THE UPPER COOK INLET REGION
THROUGH TONIGHT BEFORE THE DISTURBANCE DISSIPATES OVER THE ALASKA
RANGE. WITH PERSISTENT SOUTHEAST FLOW AND A LOW-STABILITY
ENVIRONMENT IN PLACE ACROSS THE ENTIRE REGION...SHOWER ACTIVITY
WILL CONTINUE TO BE MOST WIDESPREAD ALONG THE WESTERN PRINCE
WILLIAM SOUND REGION...WHILE SOUTHEAST GAP WINDS AND ISOLATED
SHOWERS THE MAIN IMPACT ON THE WESTERN SLOPES OF THE CHUGACH FROM
THE MATANUSKA VALLEY TO ANCHORAGE.

ANOTHER DISTURBANCE WITH A SURFACE FRONT MOVES NORTH THROUGH THE
GULF OF ALASKA THROUGH TONIGHT AND REACHES THE NORTH GULF COAST
WEDNESDAY. THIS WILL ONCE AGAIN RESULT IN ENHANCED PRECIPITATION
ALONG THE NORTH GULF COAST...PARTICULARLY WESTERN PRINCE WILLIAM
SOUND AGAIN...AND CONTINUED SOUTHEAST GAP WINDS THROUGH THE
CHUGACH RANGE AND COPPER RIVER BASIN.

A MUCH STRONGER SYSTEM MOVES TOWARD THE SOUTHWEST GULF LATE
WEDNESDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
THE SOUTHWEST ALASKA REGION WILL CONTINUE TO HAVE DIURNALLY
ENHANCED RAIN SHOWERS THROUGH WEDNESDAY WITH ISOLATED LATE
AFTERNOON AND EVENING THUNDERSTORMS. THE KEY SYNOPTIC FEATURE
WILL BE THE LINGERING THERMAL TROUGH POSITIONED OVER THE LOWER
KUSKOKWIM VALLEY INTO THE KUSKOKWIM DELTA THROUGH THE MIDWEEK.
THE OTHER FEATURE WILL BE AN UPPER LEVEL SHORTWAVE THAT WILL
MOVE ENTERING THE BRISTOL BAY REGION BY WEDNESDAY AFTERNOON
BEFORE ENTERING THE KUSKOKWIM DELTA AREA HEADING INTO THURSDAY.
THIS SYNOPTIC FEATURE WILL BRING A SWATH OF MOISTURE AND EAST
TO NORTHEASTERLY WINDS. THE SOUTHWEST COASTLINE WILL CONTINUE
TO HAVE LOW STRATUS AND FOG DURING THE EARLY MORNING HOURS
THROUGH WEDNESDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
THE CLOSED UPPER LEVEL LOW POSITIONED OVER THE CENTRAL ALEUTIANS
WILL CONTINUE TO MOVE EASTWARD INTO THE BRISTOL BAY REGION BY
WEDNESDAY. THIS SYSTEM WILL WEAKEN AND DISSIPATE HEADING INTO
THURSDAY. THE BERING SEA/ALEUTIANS WILL BE UNDER THE INFLUENCE OF
NORTHERLY TO NORTHEASTERLY WINDS THROUGH THE MIDWEEK. THIS WILL
RESULT IN A SHOWERY WEATHER REGIME THROUGH THURSDAY. BY THURSDAY
AFTERNOON THE WESTERN ALEUTIANS WILL HAVE A WEATHER FRONT MOVING
INTO THE CHAIN. THIS WILL PRODUCE GALE FORCE SOUTHWESTERLY WINDS
THROUGH THE WESTERN ALEUTIANS AS THE ASSOCIATED LOW PRESSURE
SYSTEM MOVES INTO THE ANADYR GULF REGION.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...THU THROUGH MON)...
BIG PICTURE MOVING FORWARD IS THAT THE PATTERN WILL BE MORE
DYNAMIC THAN WE HAVE SEEN IT OVER THE PAST SEVERAL WEEKS. THE LOW
CURRENTLY TRACKING ALONG THE ALEUTIANS WILL SET UP SHOP NEAR
BRISTOL BAY ON THU. IT WILL STALL OUT THERE AND WEAKEN IN PLACE.
BUT IT WILL SET THE STAGE FOR ANOTHER...STRONGER LOW TO DEVELOP
OVER THE NORTHERN PACIFIC AND TRACK TOWARD KODIAK ISLAND ON FRI.
THIS SYSTEM WILL PUSH A WARM FRONT INTO THE GULF OF AK ON THU AND
INTO SOUTH CENTRAL ON FRI. THE LOW THEN QUICKLY EXITS THE AREA
OVER THE WEEKEND LEAVING SOME RIDGING IN PLACE. ANOTHER LOW
QUICKLY MOVES IN TO THE BERING SEA OVER THE WEEKEND WHILE SOME
RIDGING BUILDS FROM THE NORTH PACIFIC OVER THE MAINLAND.

MODELS HAVE ALL BEEN STRUGGLING IN HANDLING THE EVOLUTION OF THE
ENERGY FROM BRISTOL BAY INTO THE DEVELOPING SYSTEM OVER THE NORTH
PACIFIC ON THU. AS IT WEAKENS...IT DOES SEND AN UPPER LEVEL WAVE
THROUGH SOUTH CENTRAL ALASKA WED EVE INTO THU MORNING. WE HAVE
BUMPED SHOWERS UP TO SCATTERED WITH THIS FEATURE AS CROSS-BARRIER
FLOW SHOULD WEAKEN AS IT MOVES THROUGH. MODELS ARE IN MUCH BETTER
AGREEMENT IN HANDLING THE DEVELOPING NORTH PACIFIC LOW SO
CONFIDENCE HAS INCREASED THERE. IT WILL PULL UP A HEALTHY AMOUNT
OF SUB-TROPICAL MOISTURE INTO THE GULF AND BRING MODERATE RAIN TO
THE COASTLINE THROUGH FRI. WINDS WILL ALSO INCREASE TO GALE-FORCE
ACROSS PORTIONS OF THE GULF...ESPECIALLY THE BARRIER JET REGION.
HOW MUCH PRECIPITATION CAN MAKE IT INLAND IS STILL SOMEWHAT IN
QUESTION...BUT IT DOES LOOK LIKE ANOTHER DOWN-SLOPING SCENARIO
WILL KEEP MOST OF THE RAIN CONFINED TO THE COAST.

INTO THE WEEKEND...CONFIDENCE IS GROWING THAT THIS LOW WILL BE
EXITING TO THE NORTHEAST QUICKLY ON SAT. THIS SHOULD SPELL A
RAPIDLY CLEARING DAY ACROSS THE MAINLAND WITH DRY OFFSHORE FLOW.
THIS COULD RESULT IN MORE ABUNDANT SUNSHINE THAN MANY PLACES HAVE
SEEN FOR SOMETIME. BEYOND THIS...CONFIDENCE DROPS MARKEDLY. MODELS
ARE SORTING OUT HOW FAR EAST THE BERING LOW CAN TRACK VS HOW
STRONG RIDGING OVER SOUTH CENTRAL WILL BE VS IF A NORTH PACIFIC
LOW BRINGS IN MORE CLOUD COVER FROM THE SOUTH. IF RIDGING WERE TO
WIN OUT...WHICH SOME OF THE MEMBERS ARE SHOWING...WE WOULD NEED TO
DRY THE FORECAST OUT CONSIDERABLY FOR MUCH OF THE SOUTHERN HALF OF
THE STATE.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RLF
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...MO



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