Area Forecast Discussion
Issued by NWS Anchorage, AK

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024
FXAK68 PAFC 021239
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
439 AM AKDT MON MAY 2 2016

.ANALYSIS AND UPPER LEVELS...
THE SYNOPTIC PATTERN OVER THE NORTHERN PACIFIC AND ALASKA HAS
BECOME SLIGHTLY MORE ZONAL THAN THIS TIME YESTERDAY WITH THE
MERIDIONAL LONGWAVE TROUGH PREVIOUSLY ALONG 150W STARTING TO
BECOME MORE NEGATIVELY TILTED AND NOW ROUGHLY CENTERED ALONG 140W.
THE HIGH AMPLITUDE RIDGE REMAINS IN PLACE OVER THE WEST NORTH
AMERICAN COAST. FURTHER WEST...THE RIDGE HAS FLATTED OUT SOMEWHAT
AS IT PROGRESSES WEST WITH A RIDGE AXIS ROUGHLY ALONG 170W. OVER
THE WESTERN PACIFIC...A DEEP POSITIVELY TILTED TROUGH IS STARING
TO PROGRESS EASTWARD WITH A CLOSED LOW MOVING INTO THE SOUTHWEST
BERING THIS MORNING. THE POLEWARD LIMB OF THE POLAR JET IS PEAKING
AT ABOUT 100KT THIS MORNING AS IT MOVES INTO SOUTHEASTERN ALASKA.
THE MAIN BRANCH OF THE POLAR JET IS CENTERED SOUTH OF THE ALEUTIAN
CHAIN WITH A 140KT JET STARTING TO ROUND THE TOP OF THE RIDGE
AXIS.

FOR MAINLAND ALASKA...THE DOMINATE WEATHER FEATURE AT THE SURFACE
IS THE STILL WEAKENING 1000 MB LOW NEAR KODIAK ISLAND WITH THE
REMAINS OF THE ASSOCIATED SURFACE FRONT SLOWLY DISSIPATING OVER
SOUTHERN ALASKA THIS MORNING. MULTIPLE WEAK MESO-LOWS CAN BE
IDENTIFIED IN SURFACE OBSERVATIONS OVER SOUTHWEST ALASKA...MAINLY
OVER THE KUSKOKWIM DELTA AND NEAR THE KING SALMON AREA. THE WEAK
SURFACE RIDGE ALONG 165W IS BEING SHUNTED SOUTHEASTWARD OUT OF THE
AREA AS THE FRONT ASSOCIATED WITH THE 994 MB LOW NEAR SHEMYA MOVES
THROUGH THE CENTRAL ALEUTIANS AND INTO THE BERING SEA.

&&

.MODEL DISCUSSION...
THE 00Z RUNS OF THE MAIN GLOBAL MODELS INITIALIZED REASONABLY WELL
WITH FEW SIGNIFICANT ISSUES. MODELS ARE IN GOOD GENERAL AGREEMENT
THROUGH THE SHORT-TERM WITH MOST OF THE SYNOPTIC FEATURES ALOFT.
STARTING TUESDAY MORNING THEY BEGIN TO DEVIATE SOME FROM EACH
OTHER WITH THE PLACEMENT AND STRENGTH OF THE DECAYING LOW NEAR
THE ALASKA PENINSULA AS WELL AS THE DEVELOPMENT OF A NEW LOW
AROUND 43N 173W. THE GFS WAS SELECTED AS THE PRIMARY GUIDANCE FOR
THE WESTERN FORECAST DOMAIN THROUGH THE SHORT TERM WITH THE NAM
BEING USED FOR THE HIGHER RESOLUTION OVER THE EASTERN DOMAIN.

&&

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

A MODERATE-STRENGTH UPPER LEVEL DISTURBANCE OVER THE NORTHERN GULF
WILL MOVE INLAND OVER THE COPPER RIVER BASIN TODAY. DESPITE THE
FACT THAT TEMPERATURES ACROSS THE BASIN DROPPED TO NEAR OR BELOW
FREEZING OVERNIGHT BEFORE CLOUDS INCREASED...ENOUGH WARMING SHOULD
TAKE PLACE TO RESULT IN MAINLY LIGHT RAIN...THOUGH SOME LIGHT SNOW
CAN NOT BE RULED OUT ACROSS PARTS OF THE BASIN TODAY OR
TONIGHT...ESPECIALLY TO THE SOUTH TOWARD THOMPSON PASS.
THUNDERSTORMS ARE NO LONGER EXPECTED IN THE EASTERN BASIN AS
MODELS HAVE DEPICTED A MORE STABLE REGIME TODAY.

THE OTHER AREA OF CONCERN TODAY IS THE RAPIDLY BUILDING RIDGING
EXPECTED ALONG THE NORTH GULF COAST FROM EAST TO WEST THIS
AFTERNOON AND EVENING. THIS WILL ALLOW FOR EAST TO SOUTHEAST GAP
WINDS THROUGH PORTAGE VALLEY AND TURNAGAIN ARM TO INCREASE THIS
AFTERNOON AND PERSIST WELL INTO THE OVERNIGHT TONIGHT.

RAINFALL OVER THE NEXT COUPLE OF DAYS WILL BE HEAVIEST OVER THE
WESTERN PRINCE WILLIAM SOUND REGION WITH PERSISTENT SOUTHEASTERLY
FLOW...AS HAS BEEN THE CASE FOR THE LAST SEVERAL MONTHS. ISOLATED
TO SCATTERED LIGHT RAIN SHOWERS OR SPRINKLES WILL OCCASIONALLY
MAKE IT ACROSS THE CHUGACH RANGE THE NEXT FEW DAYS IN AN
OTHERWISE UNUSUALLY CLOUDY SPRING WEATHER PATTERN...BUT THESE
CLOUDS WILL NOT BRING THE WETTING RAINS WE NEED TO NEGATE THE
INCREASING WILDFIRE RISK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
THE DIURNAL INSTABILITY SHOWERS COMBINED WITH THE THERMAL TROUGH
WILL ENHANCE THE CHANCES FOR ISOLATED THUNDERSTORMS FOR THE
SOUTHWEST REGION THE NEXT SEVERAL AFTERNOON AND EVENINGS. THIS
WILL INCLUDE THE BRISTOL BAY EXTENDING NORTHWARD INTO THE LOWER
KUSKOKWIM VALLEY THROUGH MONDAY BEFORE SPREADING INTO THE
KUSKOKWIM DELTA BY TUESDAY HEADING INTO WEDNESDAY. THIS MOVEMENT
WILL COINCIDE WITH THE THERMAL TROUGH GRADUALLY SHIFTING WESTWARD
INTO THE KUSKOKWIM DELTA BY TUESDAY. BY WEDNESDAY MORNING AN UPPER
LEVEL SHORTWAVE WILL ROTATE THROUGH THE BRISTOL BAY REGION. THIS
WILL RESULT IN INCREASED MOISTURE WITH WIDESPREAD SHOWERS THROUGH
THE REGION. THE OTHER ISSUE WILL BE THE SWATH OF STRATUS AND AREAS
OF FOG ALONG THE SOUTHWEST COASTLINE WITH SOME LOCALIZED AREAS OF
DENSE FOG THIS MORNING BEFORE DISSIPATING BY THE LATE MORNING
HOURS. THIS SAME FOG PATTERN WILL REFORM BY LATE TUESDAY EVENING
THROUGH THE EARLY WEDNESDAY MORNING HOURS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
THE WESTERN ALEUTIANS WILL CONTINUE TO HAVE A WEAK LOW PRESSURE
SYSTEM THIS MORNING THAT WILL TRACK EASTWARD NEAR ADAK BY TUESDAY
AFTERNOON. THIS SYSTEM WILL BECOME ENLONGATED BEFORE PHASING IN
WITH A GALE FORCE NORTH PACIFIC LOW LOCATED FARTHER SOUTH IN THE
NORTH PACIFIC BY WEDNESDAY MORNING. THIS WILL RESULT IN A
NORTHERLY FLOW THROUGH THE BERING/ALEUTIAN CHAIN WITH A SHOWERY
WEATHER REGIME HEADING INTO THE MIDWEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...WED THROUGH SUN)...
THE EXTENDED PORTION HAS HINGED THE PAST FEW DAYS ON HOW STRONG
RIDGING FROM THE NORTH PACIFIC WOULD HOLD AND HOW ENERGY WOULD
EVOLVE SURROUNDING THE UPPER LEVEL LOW NEAR THE ALASKA PENINSULA
WED-THU. MODELS DO SHOW SOME DISPARITY ON HANDLING WHAT HAPPENS
WITH THE REMNANTS OF THE UPPER LEVEL LOW OVER BRISTOL BAY. THE
GFS HOLDS IT TOGETHER BETTER THAN THE OTHER AND THIS SEEMS QUITE
PLAUSIBLE GIVEN THE PATTERN. THUS...WE KEPT POPS RATHER HIGH
THROUGH THE SOUTHWEST INTO THU. BEYOND THAT...FORECAST CONFIDENCE
CONTINUES TO INCREASE...ALBEIT SLOWLY...AS MODELS CONVERGE ON A
SOLUTION. THAT RIDGE DOES BUILD RATHER QUICKLY ALONG THE ALCAN
BORDER WED-THU. THIS SETS THE STAGE FOR THE AKPEN UPPER LEVEL LOW
TO WORK IN TANDEM WITH SOME ENERGY FROM THE NORTH PACIFIC RIDING
UP THE WESTERN PERIPHERY OF THAT RIDGE. THIS WILL RESULT IN SOME
PHASING WITH A TRIPLE POINT LOW TAKING SHAPE OVER THE 45N 170W AND
WORKING ITS WAY TOWARD KODIAK BY EARLY FRI. BUT WHILE THE SYNOPTIC
PATTERN LOOKS SIMILAR FROM MODEL TO MODEL...THERE ARE STILL SOME
SIGNIFICANT DIFFERENCES. BY 06Z FRI MORNING...THE ECMWF MODEL HAS
THE SURFACE LOW JUST SOUTH OF KODIAK AT 995MB WHILE THE GFS PAINTS
IT AT 979MB. THE MODELS THEN AGREE THAT THE LOW WILL TRACK TOWARD
THE NE GULF THROUGH SAT. IT WILL HAVE AN HEALTHY AMOUNT OF
MOISTURE COMING WITH IT. THE QUESTION IS...EXACTLY WHERE DOES THE
LOW TRACK GO AND HOW MUCH CROSS BARRIER FLOW WILL BE PRESENT OVER
SOUTH CENTRAL AK. USING THE PAST FEW WEEKS AS A BASELINE...THE
INCLINATION IS TO THINK THE COAST WILL ONCE AGAIN RECEIVE A FEW
INCHES OF RAIN WHILE AREAS IN THE LEE OF THE MOUNTAINS MIGHT ONLY
SEE A FEW PASSING SHOWERS.

SUN INTO NEXT WEEK...WHILE THERE ARE STILL SOME SIGNS OF
RIDGING...FORECAST CONFIDENCE HAS NOT INCREASED. THE BIGGEST
CHANGE FROM YESTERDAY IS A FAIRLY DEEP LOW THAT QUICKLY MOVES INTO
PLACE OVER THE BERING SEA. IF THIS WERE TO VERIFY...AK COULD
EASILY RETURN TO THE SAME PATTERN WE HAVE BEEN IN THE PAST FEW
WEEKS.

&&


.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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