Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 181338
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
538 AM AKDT SAT APR 18 2015

.ANALYSIS AND UPPER LEVELS...A RATHER IMPRESSIVE MID TO UPPER
LEVEL LOW IS MOVING QUICKLY FROM THE SOUTHWEST TO THE NORTHEAST
PORTION OF THE GULF THIS MORNING. THIS DEVELOPED UNDER A 100KT
JET STREAK THAT PUNCHED THROUGH THAT SAME AREA FRIDAY EVENING.
WINDS HAVE RESPONDED AT THE SURFACE HELPING THE FORMER MERE GALE-
FORCE FRONT TO NOW BE BRINGING STORMS FROM THE WESTERN BARRENS TO
THE EASTERN GULF. OVER SOUTHWEST ALASKA...A WARM FRONT IS
CURRENTLY SWEEPING NORTH TOWARD THE INTERIOR PORTION OF THE STATE.
WIDESPREAD SOUTHEAST FLOW IS KEEPING MANY OF THE TYPICAL
AREAS...KING SALMON...BETHEL...AND ILIAMNA...IN THE DOWNSLOPE HOLE
OF THE MOUNTAINS. BUT THERE ARE PLENTY OF GUSTY SOUTHEAST TO
NORTHEAST WINDS ALONG THE FRONT ITSELF. THE PLACE WHERE THE
PRECIPITATION AND WINDS ARE WORKING IN TANDEM IS ALONG THE
KUSKOKWIM DELTA COAST. SOME PLACES HAVE REPORTED BLOWING SNOW WITH
VISIBILITIES REDUCED TO A QUARTER MILE FOR BRIEF PERIODS. SLIGHTLY
FURTHER WEST WE SEE ONE OF THE MORE ACTIVE JET PATTERNS MOVING
OVER THE STATE THAT WE HAVE SEEN IN SOME TIME. THE JET DIVES SOUTH
OFF EASTERN RUSSIA BEFORE TURNING EAST AT 120-130 KTS SOUTH OF THE
ALEUTIANS. IT THEN CLIMBS QUICKLY INTO BRISTOL BAY. THIS IS
PROVIDING THE UPPER LEVEL SUPPORT TO A MID-970`S SURFACE LOW
CURRENTLY JUST SOUTH OF DUTCH HARBOR.

&&

.MODEL DISCUSSION...THE MODELS ARE NEARLY IN LOCK-STEP THROUGH
SUNDAY AFTERNOON. SOME OF THE NOTABLE ITEMS ARE THAT NONE OF THE
MODELS HAD A SURFACE FEATURE OVER THE GULF THIS MORNING AS OF
THE FRIDAY EVENING RUNS. HOWEVER...ALL THE OVERNIGHT/EARLY
MORNING MODELS INITIALIZED WITH A CLOSED LOW SOUTH OF KODIAK WHICH
SEEMS REASONABLE BASED OFF OF SCATTEROMETER DATA. THIS COULD
FACTOR IN A LITTLE OVER SOUTHWEST ALASKA THIS MORNING PERHAPS
ADDING IN A BIT MORE INSTABILITY. OTHERWISE...THE SUBTLE
DIFFERENCES REMAIN IN HOW THE ENERGY WITH THE PRIMARY LOW NEAR
DUTCH HARBOR TRANSLATES UP TO THE WEST COAST TONIGHT. THE HIGH RES
MODELS (NAM/GEM REGIONAL) WERE USED TO HANDLE THIS. BY SUNDAY
AFTERNOON MODELS ARE ALSO SLIGHTLY DIFFERENT WITH THE TIMING OF A
FEW WEAKER TROUGHS AND COLD AIR ROTATING AROUND THE PARENT LOW
LOCATED OVER THE EASTERN BERING. WE WILL BE WATCHING EACH OF THESE
WAVES AS SOME OF THE HIGHER RESOLUTION MODELS ARE NOW SHOWING POTENTIAL
FOR CONVECTION SUNDAY AFTERNOON OVER THE LOWER KUSKOKWIM VALLEY.
BY MONDAY...MODELS ARE IN REMARKABLY GOOD AGREEMENT ON A FAST-
MOVING SHARP COLD FRONT THAT CUTS THROUGH THE COOK INLET. THE
TIMING OF THIS WILL BE CRITICAL TO SEE IF ANY OF THE COLD AIR CAN
TAKE ADVANTAGE OF THE MOISTURE BROUGHT INTO THE AREA UNDER
SOUTHWEST FLOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A STRONG FRONT IN THE NORTHERN GULF IS BRINGING GALE AND STORM
FORCE WINDS TO THE AREA TODAY. THIS FRONT IS ALSO BRINGING HEAVY
RAINFALL TO THE WINDWARD SIDES OF THE MOUNTAINS WHICH IS TURNING
TO SNOW AT HIGHER ELEVATIONS. WHILE LEEWARD SIDES OF THE MOUNTAINS
ARE SEEING STRONG DOWNSLOPE ACTION THE DEEP MOISTURE ASSOCIATED
WITH THE FRONT IS ENOUGH TO ALLOW SOME PRECIPITATION TO SPILL OVER
THE MOUNTAINS AND BRING IN SOME LIGHT RAIN. THE SURFACE PRESSURE
GRADIENT IS STRONGLY DOWN-INLET IN THE COOK INLET AREA THIS
MORNING WHICH IS KEEPING THE STRONG WINDS THROUGH TURNAGAIN ARM
FROM COMING INTO ANCHORAGE. HOWEVER AS THE FRONT MOVES NORTHWARD
THE GRADIENT WILL LESSEN AND ALLOW GUSTY SOUTHEAST WINDS TO MAKE
IT INTO THE CITY THIS AFTERNOON. ANOTHER ROUND OF PRECIPITATION
WILL MOVE INTO SOUTHCENTRAL TONIGHT IN ASSOCIATION WITH AN UPPER
LEVEL DISTURBANCE. TEMPERATURES ALOFT WILL COOL SOME BEHIND THIS
DISTURBANCE WHICH MAY BRING A LARGER AREA OF SNOW FOR THE UPPER
LEVEL WAVE MOVING THOUGH SUNDAY NIGHT INTO MONDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE WARM FRONT ASSOCIATED WITH THE NORTH PACIFIC LOW IS MOVING
THROUGH THE SOUTHWEST ALASKA MAINLAND THIS MORNING PRODUCING
GUSTY WINDS ALONG THE UPPER KUSKOKWIM COAST AND THE ALEUTIAN
RANGE. THE COMBINATION OF STRONG NORTHERLY WINDS AND SNOWFALL
ALONG THE KUSKOKWIM COAST WILL PRODUCE AREAS OF BLOWING SNOW WHICH
WILL REDUCE VISIBILITY TO ONE-HALF MILE AT TIMES. SNOWFALL TOTALS
IN THIS AREA OF 3 TO 6 INCHES ARE EXPECTED THROUGH LATE TONIGHT.
WINDS WILL BEGIN TO DECREASE THIS EVENING AS THE LOW BEGINS TO
CROSS INTO THE BRISTOL BAY REGION AND THE PRESSURE GRADIENT
WEAKENS OVER THE MAINLAND. ELSEWHERE...PRECIPITATION WILL STAY AS
MOSTLY RAIN AS WARM AIR MOVES INTO THE REGION FROM THE SOUTHEAST.

THE NEXT SYSTEM TO IMPACT THE SOUTHWEST MAINLAND WILL BE THE COLD
FRONT ASSOCIATED WITH THE LOW AS IT PUSHES INTO THE REGION ON
SUNDAY MORNING. PRECIPITATION SHOULD BEGIN AS A RAIN/SNOW MIX OVER
THE BRISTOL BAY REGION BEFORE BECOMING ALL SNOW SUNDAY NIGHT AS
THE COLD AIR ADVECTS IN BEHIND THE FRONT SUNDAY NIGHT. EXPECT
PRECIPITATION TO REMAIN ALL SNOW SUNDAY FOR THE KUSKOKWIM COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE LOW THAT HAS BEEN MOVING SOUTH OF THE ALEUTIAN CHAIN THE LAST
SEVERAL DAYS IS EXPECTED TO MOVE NORTH INTO BRISTOL BAY THIS
EVENING. AS THE LOW MOVES THROUGH STRONG WINDS ARE EXPECTED ON THE
WESTERN SIDE OF THE LOW AS THE COLD AIR MOVES SOUTH OVER THE
EASTERN BERING SEA. THIS WILL BRING PERIODS OF RAIN AND SNOW
ALONG WITH STRONG WINDS TO PORTIONS OF THE EASTERN ALEUTIANS AND
THE WESTERN ALASKA PENINSULA. AREAS OF BLOWING SNOW ARE ALSO
POSSIBLE IN THE SAME REGION. FURTHER NORTH IN THE
PRIBILOFS...STRONG WINDS WILL PERSIST THROUGH TOMORROW HOWEVER
THE LACK OF TRANSPORTABLE SNOW ON THE ISLANDS AND LIGHT AMOUNT OF
PRECIPITATION EXPECTED WILL LIMIT IMPACTS FROM THIS SYSTEM THROUGH
SUNDAY.

&&

.LONG TERM FORECAST (MONDAY THROUGH FRIDAY)...

ON MONDAY...THE NORTH PACIFIC JET STREAM AND ASSOCIATED WARM FRONT
WILL BE MOVING EASTWARD TOWARDS THE ALCAN...WITH A BROAD REGION OF
ARCTIC AIR TRACKING OVER THE STATE. THE MARITIME INFLUENCE WILL
MODERATE THE AIR MASS SOME...BUT IT WILL USHER IN COLDER AIR
REGION WIDE...AS WELL AS REGIONS OF RAIN AND SNOW SHOWERS. AS THE
COLD FRONT TRACKS THROUGH SOUTHCENTRAL...IT WILL BE AIDED BY AN
UPPER LEVEL SHORTWAVE TROUGH...AND THIS MAY RESULT IN ENHANCED
SNOW SHOWERS ALONG THE FRONT AS IT TRACKS UP COOK INLET.

-JRA

MODELS LOOK PRETTY SIMILAR TO YESTERDAY IN REGARDS TO THE POSITION
OF THE JET STREAM AND UPPER LEVEL FEATURES. THE TWO MAJOR CHANGES
OBSERVED IN THE MOST RECENT DATA IS THE SEPARATION OF CENTRAL
PACIFIC FLOW (WHICH DELAYS THE LOW PRESSURE SYSTEM THAT HAD BEEN
ANALYZED TO BE SOUTHWEST OF THE PENINSULA ON WEDNESDAY) AND A
FASTER TREND WITH THE KAMCHATKA SYSTEM (AT LEAST WITH THE PARENT
LOW VS THE LEADING FRONT). THE KAMCHATKA LOW IS EXPECTED TO PUSH
OFF THE KAMCHATKA PENINSULA MONDAY AFTERNOON AND DRIVE A FRONT
ACROSS THE BERING SEA/ALEUTIAN ISLANDS DURING THE WEEK WITH
PERIODS OF GALE FORCE WINDS INITIALLY OVER THE WESTERN BERING
SEA. MODEL CONSENSUS NOW SHOWS THE LOW TRACKING ACROSS THE
ALEUTIAN CHAIN BEFORE DIVING SOUTH INTO THE GULF OF ALASKA. THE
GULF OF ALASKA WILL SEE PRECIPITATION TAPER OFF DURING THE
BEGINNING OF THE WEEK AS A FRONT ALONG THE GULF COAST DISSIPATED
AND AN AREA OF LOW PRESSURE OVER SOUTHWEST ALASKA PUSHES INTO THE
BERING STRAIT. ONE THING THAT WILL BE WATCHED IN THE COMING DAYS
IS THE POTENTIAL FOR A BUILDING PACIFIC NORTH AMERICAN RIDGE WHICH
COULD USHER IN A MUCH WARMER AIR MASS WITH PLACES IN SOUTH CENTRAL
ALASKA WARMING INTO THE LOWER TO MID 50S. THIS IS THE FIRST DAY
THE MODELS HAVE HINTED AT THIS BUILDING RIDGE ON FRIDAY SO DID NOT
GO TOO WARM WITH TEMPERATURES JUST YET.

-MC

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY 155.
MARINE...GALE 129 130 132 150 155 165 170 171-174 179 180 181 185.
         STORM 119 125.
         HEAVY FREEZING SPRAY 179 180 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RF
LONG TERM...MC



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