Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 031323
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
523 AM AKDT SUN MAY 3 2015

.ANALYSIS AND UPPER LEVELS...

SATELLITE IMAGERY THIS MORNING SHOWS QUITE THE ACTIVE WEATHER
PATTERN WITH MULTIPLE SYNOPTIC SCALE SYSTEMS AS WELL AS MESOSCALE
SYSTEMS. STARTING WITH THE SYNOPTIC SCALE SYSTEMS...AN AREA OF LOW
PRESSURE OVER THE FAR WESTERN BERING SEA HAS DRIVEN A RAPIDLY
OCCLUDING FRONT TOWARD THE CENTRAL ALEUTIANS...WHICH HAS BROUGHT
RAIN DURING THE OVERNIGHT HOURS AS FAR EAST AS NIKOLSKI. WHILE
THIS FRONT IS NOT EXPECTED TO MAKE MUCH EASTWARD PROGRESS...A
SECOND AREA OF LOW PRESSURE IS NOW BEGINNING TO SPIN UP APPROX 300
MILES SOUTH OF ADAK. WATER VAPOR SATELLITE SHOWS THAT THE
SHORTWAVE THAT AIDED IN THE DEVELOPMENT OF A WEAK SURFACE LOW IN
THE NORTHERN PACIFIC LAST NIGHT HAS BEGUN TO PHASE WITH THE UPPER
LEVEL LOW ASSOCIATED WITH THE LOW OVER THE WESTERN ALEUTIANS. AT
THE SAME TIME...A STRENGTHENING JET STREAK AND SHORTWAVE RAPIDLY
TRANSITING SOUTHWARD ON THE WESTERN PERIPHERY OF THE TROUGH OVER
THE BERING SEA HAS BEGUN TO INTERACT WITH THIS DEVELOPING LOW. THE
CULMINATION OF ALL THESE FEATURES IS ALLOWING A VERY COMPACT LOW
TO RAPIDLY DEVELOP OVERNIGHT AND DURING THE EARLY MORNING HOURS
THAT WILL PUSH A STORM FORCE FRONT ACROSS THE CENTRAL ALEUTIANS
(ADAK AND ATKA PRIMARILY) DURING THE DAY TODAY.

OVER SOUTHWEST ALASKA...A WEAK UPPER LEVEL LOW CONTINUES TO GET
CUT OFF FROM THE MEAN FLOW AND HAS BEGUN TO PARK ITSELF OVER
SOUTHWEST ALASKA. RAIN SHOWERS WERE OBSERVED OVERNIGHT AND EARLY
THIS MORNING AND ARE LIKELY TO CONTINUE AS THE UPPER LOW PROVIDES
ENOUGH FORCING TO KEEP SHOWERS POSSIBLE. WATER VAPOR IMAGERY HAS
BEEN A HUGE ASSET FOR DETERMINING THE LOCATION OF WHERE SHOWERS
WILL LIKELY DEVELOP AS THE COASTAL REGIONS OF SOUTHWEST ALASKA
HAVE BEEN DRY-SLOTTED (LITTLE MID TO UPPER LEVEL MOISTURE) WHICH
WILL LIMIT PRECIPITATION MAINLY (IF NOT ENTIRELY) TO INLAND AREAS.

LAST AND CERTAINLY NOT LEAST...AN UPPER LEVEL LOW PUSHING EASTWARD
ACROSS THE NORTHERN PACIFIC HAS A WEAK FRONT DRAPED ACROSS THE
SOUTHERN GULF OF ALASKA WHICH HAS BROUGHT SOME 20 TO 25 KT WINDS
BASED ON SCATTEROMETER DATA OVERNIGHT. THIS FRONT HAS BEGUN TO
WEAKEN AND SHIFT EASTWARD OVERNIGHT AND WILL NOT HAVE MUCH IMPACT
ON THE GOING FORECAST.

&&

.MODEL DISCUSSION...

MODELS ARE ONCE AGAIN IN VERY GOOD AGREEMENT IN THE SHORT TERM.
MODELS CONTINUE TO HANDLE THE MULTIPLE PHASING OF UPPER LEVEL
FEATURES OVER THE WESTERN BERING SEA VERY WELL AND ALL DEPICT A
VERY SIMILAR OUTCOME. THE GEM GLOBAL AND GEM REGIONAL STRUGGLED TO
INITIALIZE THE DEVELOPING LOW IN THE NORTH PACIFIC AS WELL AS THE
THE SYNOPTIC OTHER MODELS...SO DECIDED TO LEAN AWAY FROM THOSE TWO
FOR THIS FORECAST PACKAGE. IN ADDITION...THE UPPER LEVEL LOW
SITUATING ITSELF OVER SOUTHWEST ALASKA IS HANDLED VERY WELL BY THE
GUIDANCE. THE NAM BEGINS TO STRUGGLE EARLY NEXT WEEK AS THIS UPPER
LOW LOOKS TO PHASE WITH A VERY BROAD AND ELONGATED TROUGH
ENCOMPASSING NEARLY THE ENTIRE BERING SEA. THE NAM TRIES TO SLIDE
THE UPPER LEVEL ENERGY FURTHER EAST ACROSS THE ALASKA RANGE WHICH
IN TURN BRINGS COOLER 850 AND 500 MB TEMPS TO SOUTHCENTRAL
ALASKA. WITH COLDER TEMPERATURES AT THE MID-LEVELS THE NAM DEPICTS
WIDESPREAD CONVECTIVE SHOWERS DEVELOPING MONDAY AFTERNOON AND
EVENING WHILE THE GFS/ECMWF HOLDS THE MAJORITY OF THE
PRECIPITATION OFF UNTIL THE SURFACE FRONT PUSHES INTO THE GULF AND
IS ACCOMPANIED BY SOME UPPER LEVEL SUPPORT. THUS THE GFS AND ECMWF
WERE UTILIZED IN THE MORNING FORECAST PACKAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (SUNDAY AND MONDAY)...

THE GENERAL WEATHER PATTERN WILL REMAIN UNDER THE INFLUENCE OF A
CLOSED UPPER HIGH SITTING DIRECTLY OVERHEAD UPPER COOK INLET THIS
MORNING. THIS MEANS MORE SUNSHINE AND LIGHT WINDS ARE ON TAP FOR
THE VAST MAJORITY OF SOUTHCENTRAL ALASKA FOR THE NEXT 2 DAYS.
TEMPERATURES WILL SOAR TO AROUND 60 AT INTERIOR LOCATIONS AS
DIURNAL SHOWER ACTIVITY IS HELD IN CHECK BY A STRENGTHENING
"CAPPING" INVERSION AS EVIDENCED BY THE 12 UTC ANCHORAGE RAOB.
GARDEN-VARIETY SEA BREEZES SHOULD AGAIN DEVELOP TODAY...AND WILL
LIKELY BE A LITTLE STRONGER ON MONDAY AS SURFACE HIGH PRESSURE
TRIES TO BUILD IN MORE SUBSTANTIALLY FROM THE SOUTH MONDAY
AFTERNOON.

KODIAK ISLAND WILL REMAIN UNDER MOSTLY CLOUDY CONDITIONS AS A
STRONG AND STATIONARY DEFORMATION BAND BRINGS STEADY RAIN TODAY TO
WESTERN PORTIONS OF THE SOUTHWESTERN ISLAND AND THE ALASKA
PENINSULA...THOUGH THE NORTHERN 2/3 OF THE ISLAND WILL STAY MOSTLY
DRY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
RAIN WILL CONTINUE OVER THE KUSKOKWIM VALLEY AND BRISTOL BAY
REGIONS...WITH MORE SHOWERY CONDITIONS FOR INLAND PORTIONS OF THE
KUSKOKWIM DELTA REGION THROUGH THE NEXT COUPLE OF DAYS AS UPPER
LEVEL LOW PRESSURE MEANDERS OVER THE SOUTHWEST MAINLAND. BY LATE
MONDAY NIGHT RAIN BECOMES MORE FOCUSED TOWARDS SOUTHERN BRISTOL
BAY AS A FRONT ASSOCIATED WITH THE LOW APPROACHING THE CENTRAL
ALEUTIANS MOVES NORTH INTO THE AREA.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
NO CHANGE TO CURRENT THINKING WITH THE LOW PRESSURE SYSTEM
CURRENTLY RAPIDLY INTENSIFYING AND SPREADING A STORM FORCE FRONT
OVER THE CENTRAL CHAIN TODAY. THIS FRONT WILL BRING ESPECIALLY
GUSTY WINDS TO ADAK AND ATKA TODAY AS THE THERMAL PROFILE
ASSOCIATED WITH A DEVELOPING BENT-BACK OCCLUSION SHOULD ALLOW FOR
MIXING DOWN OF WINDS UP TO 70 MPH FROM ALOFT. THE FRONT WILL STALL
OVER THE SOUTHERN BERING AND WEAKEN THROUGH EARLY THIS WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MOSTLY SUNNY SKIES WILL PREVAIL ACROSS SOUTHCENTRAL ALASKA
THROUGH THE BEGINNING OF THE WEEK BEFORE GIVING WAY TO A WETTER
PATTERN LATE TUESDAY INTO WEDNESDAY AS RIDGING OVER THE EASTERN
MAINLAND IS REPLACED BY DEEP SOUTHERLY FLOW AND A FRONT
APPROACHING THE GULF COAST. THIS WILL BE FOLLOWED BY A NORTH
PACIFIC LOW THAT LOOKS TO APPROACH THE WESTERN GULF BY
FRIDAY...KEEPING A CHANCE OF RAIN IN THE FORECAST THROUGH THE END
OF THE WEEK. THE BULK OF THE PRECIPITATION WILL BE ALONG THE GULF
COAST...WITH A MORE SHOWERY REGIME SETTING UP FARTHER INLAND. OUT
WEST...WINDY AND RAINY CONDITIONS WILL GRADUALLY IMPROVE FROM WEST
TO EAST ACROSS THE ALEUTIAN CHAIN AS THE NORTH PACIFIC LOW PASSES
TO THE SOUTH AND MOVES TOWARDS THE WESTERN GULF. THIS WILL BE
REPLACED BY WEAK HIGH PRESSURE WHICH WILL YIELD BENIGN CONDITIONS
DOMINATED BY FOG AND STRATUS THROUGH THE END OF NEXT WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORMS...175 176 177.
         GALES...172 173 174 178.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MC
SOUTHCENTRAL ALASKA...AMD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...CB


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