Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 280123
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
423 PM AKST THU NOV 27 2014

.ANALYSIS AND UPPER LEVELS...
THE VERTICALLY STACKED LOW MOVING NORTHWARD THROUGH THE BERING SEA CONTINUES
TO STEADILY WEAKEN WITH A CENTRAL PRESSURE NOW ESTIMATED NEAR 987
MB. STRONG WINDS AROUND THE STORM ARE ALSO WEAKENING WITH GALE FORCE
WINDS NOW LARGELY CONFINED TO THE NORTHEAST QUADRANT. AN
ASSOCIATED FRONT IS MAKING LANDFALL ACROSS THE KUSKOKWIM DELTA
WITH SNOW NOW FALLING AS FAR INLAND AS BETHEL. MEANWHILE COLD AIR
WRAPPING AROUND THE BERING LOW IS GENERATING WIDESPREAD
INSTABILITY SHOWERS ACROSS THE WESTERN 2/3 OF THE BERING SEA WITH
MULTIPLE UPPER LEVEL TROUGHS HELPING TO FOCUS SHOWER ACTIVITY OVER
THE CENTRAL AND WESTERN ALEUTIANS.

TO THE EAST OF THE ALASKA RANGE MID AND UPPER-LEVEL RIDGING IS PRODUCING
ANOTHER NICE DAY WITH CLEAR SKIES ACROSS MUCH OF THE REGION. THE EXCEPTION
IS OVER UPPER COOK INLET INCLUDING ANCHORAGE AND THE MATANUSKA VALLEY
WHERE LOW-LEVEL MOISTURE TRAPPED BENEATH A STEEP TEMPERATURE INVERSION
CONTINUES TO PRODUCE LOW CLOUDINESS AND AREAS OF LOCALLY DENSE FOG.
GUSTY OFFSHORE WINDS ACROSS PRINCE WILLIAM SOUND AND THE GULF COAST
CONTINUE ON A DOWNWARD TREND. A PROCESS WHICH IS BEING PROLONGED BY
A WEAK JET STREAK OVER THE AREA REINFORCING NORTHWESTERLY WINDS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN ABOVE-AVERAGE AGREEMENT THROUGHOUT THE SHORT TERM
FORECAST PERIOD WITH BOTH MAJOR WEATHER FEATURES AS WELL AS MANY PERTINENT
SMALLER FEATURES. AS A RESULT THE HIGH-RESOLUTION MODELS WERE UTILIZED
IN FORECAST GENERATION TODAY TO TAKE ADVANTAGE OF SUPERIOR HANDLING
OF WINDS IN COMPLEX TERRAIN.

&&

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

AREAS OF FOG AND LOW CLOUDS HAVE PERSISTED ACROSS THE KNIK ARM
AND INTO THE MATANUSKA VALLEY. WEBCAMS AND SATELLITE IMAGERY
CONTINUE TO SHOW A NARROW CORRIDOR OF FOG EXTENDING FROM NORTH
ANCHORAGE NORTHWARD TOWARD EAGLE RIVER AND EVENTUALLY TO THE
PALMER AND WASILLA AREA. CONDITIONS HAVE BEGUN TO IMPROVE DURING
THE AFTERNOON HOURS AS SOME MIXING HAS OCCURRED BUT THE LOW LEVEL
INVERSION REMAINS TOO STRONG FOR THE BULK OF THE FOG TO MIX OUT.
FOG WILL LIKELY RE-DEVELOP THIS EVENING WITH THE LOW LEVEL
INVERSION REMAINING IN PLACE. AS THE PRESSURE GRADIENT TIGHTENS
WITH AN EASTWARD SHIFT OF THE RIDGE AXIS SOME LIGHT NORTHERLY
FLOW COULD POSSIBLY PUSH SOME OF THIS FOG INTO THE ANCHORAGE BOWL.
CONFIDENCE IS RELATIVELY LOW AS MULTIPLE FACTORS MUST ACT IN
UNISON TO PUSH THE FOG INTO ANCHORAGE. FOG SHOULD BEGIN TO LIFT ON
FRIDAY AS CLOUD COVER BEGINS TO OVERSPREAD THE AREA AS THE RIDGE
AXIS CONTINUES TO SHIFT EASTWARD.

CONFIDENCE IN ACCUMULATING SNOW LATE FRIDAY NIGHT INTO SATURDAY
CONTINUES TO GROW. A DIFFUSE UPPER LEVEL TROUGH WILL PUSH ACROSS
SOUTHCENTRAL ALASKA AND BRING A ROUND OF SNOWFALL (EXCEPT RAIN
ACROSS KODIAK ISLAND AND NORTHERN GULF COAST) TO MUCH OF THE
REGION. SNOW AMOUNTS OF 1 TO 3 INCHES WILL BE COMMON FROM THE MAT-
SU VALLEY INTO ANCHORAGE AND KENAI PENINSULA. WITH WEAK OMEGA
VALUES AND WEAK UPPER LEVEL SUPPORT THE POSSIBILITY FOR SNOWFALL
EXCEEDING 3 INCHES WILL BE DIFFICULT. SNOW WILL BEGIN TO TAPER OFF
SATURDAY NIGHT FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER
LEVEL TROUGH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A FRONTAL BOUNDARY WILL MOVE FURTHER INLAND TONIGHT AND SLOWLY
WEAKEN TOMORROW. STEADY SNOW OVER THE KUSKOKWIM DELTA WILL
DIMINISH FROM SOUTH TO NORTH IN THE EVENING AND BECOME SHOWERS. A
QUICK ADDITIONAL INCH OF ACCUMULATION IS POSSIBLE MAINLY FROM
BETHEL NORTHEAST. THE FRONT WILL STALL OUT FROM THE LOWER
KUSKOKWIM VALLEY THROUGH INTERIOR BRISTOL BAY. AREAS OF SNOW IN
THESE AREAS WILL DIMINISH TO AN EXTENT BEFORE AN APPROACHING
DISTURBANCE FROM THE SOUTH WILL BEGIN TO SPREAD RAIN FROM THE
ALASKA PENINSULA NORTHWARD ON FRIDAY CHANGING TO SNOW NORTH OF
KING SALMON. THERE WILL LIKELY BE A SHARP WEST TO EAST GRADIENT
ASSOCIATED WITH THIS PRECIPITATION MAINLY FALLING EAST OF DILLINGHAM.
AN UPPER RIDGE BUILDS IN OVER THE WEEKEND BEGINNING A DRYING
TREND. TEMPERATURES WILL REMAIN ABOVE NORMAL WITH GENERALLY LIGHT
WINDS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE BERING SEA IS BETWEEN SYSTEMS AT THE MOMENT. GENERALLY
CYCLONIC FLOW REMAINS OVERHEAD KEEPING SCATTERED SNOW AND RAIN
SHOWERS OVER A GOOD CHUNK OF THE AREA. SHOWERS WILL GRADUALLY
DIMINISH FROM WEST TO EAST TODAY AND TOMORROW. A NEW FRONTAL
BOUNDARY BEGINS TO HIT THE WESTERN AND CENTRAL ALEUTIANS ON
SATURDAY BRINGING SNOW CHANGING TO RAIN AND GUSTY SOUTHERLY WINDS.
THE EASTERN BERING SEA WILL REMAIN UNDER GENERALLY LIGHT FLOW AND
DECREASING CHANCES FOR PRECIPITATION.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...SUNDAY THROUGH
THURSDAY)...MODELS HAVE COME INTO BETTER AGREEMENT DURING THIS
TIME AND THUS THERE IS INCREASED CONFIDENCE IN THIS PORTION OF
THE FORECAST AT LEAST THROUGH TUESDAY. THE UPPER LEVEL TROUGH THAT
WILL BRING A QUICK SHOT OF SNOW TO MUCH OF SOUTH CENTRAL ALASKA TO
START THE WEEKEND WILL QUICKLY PUSH TOWARDS THE ALCAN BORDER ON
SUNDAY. IT WILL BE REPLACED BY A SHORT WAVE RIDGE THAT SHOULD
BRING DRY CONDITIONS AND CLEARING SKIES TO END THE HOLIDAY
WEEKEND. THE FOCUS WILL SHIFT TO A BROAD AND FAIRLY STRONG AREA
OF LOW PRESSURE THAT WILL COVER ALMOST THE ENTIRE BERING SEA. AS
THE LOW CENTER ITSELF PIVOTS OVER THE EXTREME WESTERN BERING
SUNDAY INTO MONDAY IT SWINGS AN ELONGATED WARM FRONT TOWARDS THE
WEST COAST. THIS FRONT GETS RE-ENERGIZED BY THE UPPER LEVEL
REMNANTS OF A NORTH PACIFIC SYSTEM. WITH ORIGINS NEAR 40N THIS
SYSTEM SHOULD BRING A HEALTHY AMOUNT OF MOISTURE WITH IT. WE DID
INCREASE THE TIMING OF THE PRECIPITATION INTO THE WEST COAST WITH
THIS PACKAGE AND NOW EXPECT TO SEE IT MOVE IN LATE SUNDAY. WITH
COLD AIR IN PLACE PRECIPITATION WILL LIKELY START AS SNOW. BUT AS
THE WARM ADVECTION BEGINS THERE IS A GOOD CHANCE THAT WE WILL SEE
MIXED PRECIPITATION EARLY MONDAY MORNING STRETCHING FROM BRISTOL
BAY THROUGH THE KUSKOKWIM DELTA. THIS FRONT THEN SLOWLY WEAKENS AS
IT TRACKS INLAND TOWARD SOUTH CENTRAL ALASKA. IT SHOULD BRING
ANOTHER ROUND OF SNOW TO THE ANCHORAGE AREA. RIGHT NOW IT LOOKS
LIKE THE WARM AIR DOES NOT CARRY OVER THE ALASKA RANGE. IF IT
SHOULD WE COULD SEE SOME MIXED PRECIPITATION IMPACT LARGER POPULATION
CENTERS EARLY TUESDAY.

MEANWHILE THE PARENT LOW OVER THE BERING WILL PULL DOWN SOME COLD
AIR ON ITS WESTERN FLANK. THIS WILL SERVE TO TIGHTEN THE GRADIENT
AND WE HAVE INTRODUCED STORMS INTO SOME OF THE MARINE AREAS ON
MONDAY. THE PARENT LOW THEN TRACKS ALONG THE ALEUTIAN CHAIN
THROUGH THE MIDDLE OF THE WEEK. THE GFS REMAINED SLOWER AND MUCH
FURTHER NORTH THAN THE EC OR GEM SO IT WAS DISREGARDED FOR THIS
FORECAST PACKAGE. THE LOW POSITION JUST SOUTH OF THE CHAIN WEDNESDAY
INTO THURSDAY WILL KEEP MOIST WARM FLOW MOVING TOWARDS THE MAINLAND
WITH COLD SHOWERS WRAPPING AROUND THE BERING TOWARDS THE ALEUTIANS.

&&


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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AD/SAM
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...MO



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