Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 171337
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
537 AM AKDT FRI APR 17 2015

.ANALYSIS AND UPPER LEVELS...

BROAD TROUGHING CONTINUES TO DOMINATE THE REGIONAL WEATHER PATTERN
THIS MORNING. A WEAKENING NEGATIVE TILT TROUGH IS TRACKING
INLAND...WITH THE REMAINS OF A MODERATED ARCTIC AIR MASS TRACKING
INTO SOUTHCENTRAL BEHIND IT. SHOWERS BEHIND THE TROUGH WILL
CONTINUE TO IMPACT COASTAL LOCATIONS AND HIGHER ELEVATION
MOUNTAINS...BUT WILL DIMINISH INLAND AS THE TROUGH LIFTS NORTHWARD
OUT OF THE REGION. THE MAIN CENTER OF ACTION EXISTS OVER THE NORTH
PACIFIC WHERE A SUBTROPICAL WARM FRONT IS INTERACTING WITH AN
ACTIVE NORTH PACIFIC JET AND A DIGGING ARCTIC TROUGH/JET MAX.
WATER VAPOR IMAGERY DEPICTS THE MERGING OFF THESE VARIOUS SYSTEMS
SOUTH OF THE ALEUTIAN CHAIN. EVENTUALLY...THE CURRENT ELONGATED
FRONTAL ZONE WILL STRENGTHEN INTO A STRONGER SURFACE LOW AS IT
TRACKS INTO EASTERN BRISTOL BAY. THE ASSOCIATED STORM FORCE
FRONT WILL RAPIDLY TRACK THROUGH THE GULF...THEN REMAIN ALONG THE
NORTHERN GULF COAST INTO THE WEEKEND.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN SUPERB AGREEMENT WITH THE LARGE SCALE PATTERN
HEADING INTO THE MIDDLE OF NEXT WEEK...BUT AS USUAL...CONTINUE TO
STRUGGLE WITH VERY IMPORTANT SMALLER SCALE DETAILS. WHILE THE LOW
TRACK IS MUCH MORE CERTAIN THROUGH SATURDAY THAN YESTERDAY...THE
STRENGTH OF THE UPPER LOW AND ITS POSITION REMAINS LESS CERTAIN.
THIS CREATES CHALLENGES WITH RESPECT TO IMPACTS ACROSS THE BERING
SEA AND ALEUTIANS...AND WHICH LOCATIONS SEE THE POTENTIAL FOR
HEAVIER ACCUMULATING SNOW ALONG WITH STRONG NORTHERLY WINDS.
CURRENTLY...THE ECMWF DEPICTS THE STRONGEST AND MOST INTENSE
PRECIPITATION BAND...WHILE ALL OTHER GUIDANCE HAS A NARROWER AND
LESS INTENSE BAND AS THE LOW TRACKS INTO THE EASTERN BERING. THESE
DIFFERENCES ARE SIGNIFICANT ENOUGH TO LEND LESS THAN HIGH
CONFIDENCE TO POTENTIAL BLIZZARD AND/OR BLOWING SNOW THREATS
ACROSS THE AFOREMENTIONED REGIONS. WITH THAT SAID...GIVEN THE
MAGNITUDE OF NORTHERLY WINDS...AND THE COLD AIR ADVECTION
PROCESSES ALONG WITH POTENTIAL ACCUMULATING SNOW...THE THREAT IS
DEFINITELY THERE FOR SELECT LOCATIONS TO SEE IMPACTFUL WINTER
CONDITIONS AS THE LOW MOVES NORTH SATURDAY AND SUNDAY. WITH THESE
DIFFERENCES IN MIND...THE FORECAST WILL GIVE MODERATE WEIGHTING TO
THE ECMWF FOR THE BERING SEA...WITH A NAM FAVORED APPROACH OVER
THE SOUTHCENTRAL AND GULF OF ALASKA REGION OWING TO RESOLUTION AND
BETTER PRECIPITATION DETAILS ASSOCIATED WITH DOWNSLOPE FLOW.

&&

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

THE SYSTEM THAT BROUGHT RAIN AND SNOW TO SOUTHCENTRAL ON THURSDAY
HAS NOW MOVED NORTH OF THE ALASKA RANGE LEAVING A FEW RAIN AND
SNOW SHOWERS OVER THE AREA THIS MORNING. THIS IS THE BREAK BEFORE
THE NEXT SYSTEM MOVES INTO THE AREA WHICH WILL MOVE OVER KODIAK
ISLAND TODAY AND BRING IN SOME STRONG WINDS AND RAIN. THIS SYSTEM
IS A BIT WARMER THAN THE PREVIOUS ONE AND MOST OF THE
PRECIPITATION AT LOWER ELEVATIONS WILL BE ALL RAIN. TEMPERATURES
MAY EVEN REACH INTO THE LOWER 50S IN A NUMBER OF LOCATIONS
SATURDAY...ESPECIALLY IF SUPPORTED BY ADIABATIC WARMING FROM
DOWNSLOPE WINDS. AT THIS TIME IT LOOKS LIKE THE LEEWARD SIDE OF
THE MOUNTAINS WILL REMAIN MOSTLY DRY DUE TO THE DOWNSLOPE EFFECT.
HOWEVER THIS SYSTEM HAS DEEP MOISTURE AND UPPER LEVEL SUPPORT
WHICH MAY HELP TO BRING SOME RAINFALL TO THE LEEWARD SIDES OF THE
MOUNTAINS IS SPITE OF THE DOWNSLOPE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAINLAND FORECAST FOR THE SHORT TERM WILL REVOLVE AROUND A
FRONTAL BOUNDARY PIVOTING NORTHWARD OVER THE MAINLAND. THE WARM
FRONT WILL BRING AREAS OF RAIN TO INTERIOR BRISTOL BAY LATE THIS
AFTERNOON AND EVENING WHILE AREAS CLOSER TO THE WOOD RIVER
MOUNTAINS COULD SEE ACCUMULATING SNOW BEFORE EVENTUALLY TURNING TO
RAIN ON SATURDAY. AREAS ALONG THE ALASKA PENINSULA AND ALEUTIAN
RANGE WILL REMAIN MOSTLY DRY BUT SOME SPOTTY RAIN COULD MAKE IT TO
THE GROUND. GUSTY EASTERLY WINDS WILL ACCOMPANY THE FRONT AS WELL. AS
THE FRONT SWINGS ACROSS THE KUSKOKWIM DELTA ON SATURDAY...STRONG
NORTHERLY WINDS WILL BRING BLOWING SNOW CONCERNS...MAINLY ALONG
THE WESTERN COAST AND NUNIVAK ISLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A LOW PRESSURE SYSTEM AND FRONT OVER THE EASTERN CHAIN WILL
INCREASE EASTERLY THEN NORTHERLY WINDS ACROSS MOST OF THE BERING
SEA. DEPENDING ON WHERE THE HEAVIEST BAND OF PRECIPITATION SETS
UP...SOMEWHERE AROUND UNIMAK PASS...BLIZZARD CONDITIONS COULD BE
PRESENT AS NORTHERLY WINDS WILL INCREASE TO 40 TO 50 MPH. THE
SYSTEM WILL SLOWLY TRANSLATE EASTWARD OVER THE WEEKEND LEAVING
MOST OF THE BERING IN A SNOW SHOWER REGIME WITH GUSTY
NORTHWESTERLY WINDS.

&&

.LONG TERM FORECAST (SUNDAY THROUGH THURSDAY)...

THE AREA OF LOW PRESSURE SOUTH OF THE ALEUTIAN ISLANDS WILL CROSS
THE ALASKA PENINSULA EARLY SUNDAY MORNING. THIS WILL BRING A
PERIOD OF NORTHERLY GALE FORCE WINDS TO THE EASTERN BERING SEA
INCLUDING THE PRIBILOF ISLANDS WHILE SOUTHWEST ALASKA WILL SEE A
PERIOD OF GUSTY SOUTHEASTERLY WINDS. PRECIPITATION WILL OVERSPREAD
MUCH OF SOUTHWEST AND SOUTHCENTRAL ALASKA AS THE LOW CROSSES THE
ALASKA PENINSULA...WITH MAINLY RAIN OBSERVED ACROSS INLAND AREAS
AND A MIX OF RAIN AND SNOW ACROSS THE COASTAL AREAS AS A BRIEF
PERIOD OF SLIGHTLY WARMER TEMPERATURES WILL BE OBSERVED.
SOUTHCENTRAL ALASKA WILL SEE MAINLY RAIN ACROSS MOST LOCATIONS
WHILE HIGHER ELEVATIONS WILL BE MORE PRONE TO SEEING PERIODS OF
SNOWFALL. STRONG WINDS WILL PUSH THROUGH PORTAGE VALLEY AND
TURNAGAIN ARM WITH THE ORIENTATION OF THE FRONT AS IT PUSHES NORTH
TOWARD NUNIVAK ISLAND. ONCE THE LOW REACHES NUNIVAK ISLAND (ABOUT
60N)...THE NORMAL DOWN INLET GRADIENT ACROSS COOK INLET WILL
REVERSE AND BECOME UP INLET WHICH SHOULD BRING SOME GUSTY WINDS
INTO WEST ANCHORAGE ON SUNDAY.

THE OVERALL SYNOPTIC PATTERN DOES NOT APPEAR TO SHIFT MUCH IN THE
EXTENDED PERIOD WITH THE ARCTIC JET STREAM REMAINING IN THE NORTH
PACIFIC. THIS PATTERN IS FAVORABLE FOR LOW PRESSURE SYSTEMS TO
PUSH OFF EITHER JAPAN OR RUSSIA...PASS SOUTH OF THE ALEUTIAN
ISLANDS AND EVENTUALLY TOWARD THE GULF OF ALASKA. MODELS ARE
PRESENTLY HINTING AT THIS SCENARIO BEGINNING TO DEVELOP AGAIN BY
MIDWEEK. OVERALL...THE TYPE OF WEATHER PATTERN OBSERVED OVER THE
PAST 7 TO 10 DAYS WILL LIKELY PERSIST AT LEAST ANOTHER 7 TO 10
DAYS.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WATCH 185
MARINE...
STORMS 119 120 130 131
GALES 125 129 132 136-139 141 150 155 160 165 170-176 179-181 185
HEAVY FREEZING SPRAY 179 180.
FIRE WEATHER...NONE.

&&

$$

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


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