Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 260046 CCA
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
446 PM AKDT SAT APR 25 2015

.ANALYSIS AND UPPER LEVELS...

THE UPPER LEVEL LOW IS OVER THE ALASKA PENINSULA THIS AFTERNOON
AS IT MAKES ITS WAY INTO THE GULF BY MONDAY. THIS IS LEAVING AN
UPPER LEVEL RIDGE OVER THE CENTRAL BERING SEA WITH ANOTHER UPPER
LEVEL RIDGE OVER THE YUKON...WHICH IS RAPIDLY DECAYING. THE JET
STREAM IS RUNNING OVER THE TOP OF THE ALEUTIANS AND THEN HEADING
SOUTH OF THE UPPER LEVEL LOW BEFORE TURNING BACK TO THE NORTHEAST
AND HEADING TOWARD VANCOUVER ISLAND. IT IS ALONG THE JET STREAM
SOUTH OF THE GULF THAT THE SURFACE LOW IS GATHERING STRENGTH. THIS
LOW IS HEADING INTO THE SOUTHERN GULF TONIGHT AND WILL LOSE ITS
UPPER LEVEL SUPPORT WHEN IT DOES SO...LEAVING IT TO THEN SLOWLY
WEAKEN AND NOT MOVE MUCH THROUGH MONDAY.

&&

.MODEL DISCUSSION...

MODELS ARE IN QUITE GOOD AGREEMENT IN THE GULF OF ALASKA REGION
THROUGH TUESDAY AND ALL KEEP THE LOW FAR ENOUGH SOUTH TO KEEP MOST
OF THE PRECIPITATION FROM IT RELOCATED TO THE COAST. ONE AREA
WHERE THERE IS A LITTLE MORE DIVERGENCE IN THE MODELS IN WITH A
EASTERLY WAVE THAT WILL MOVE INTO THE COPPER RIVER BASIN FROM
CANADA ON SUNDAY NIGHT OR MONDAY AND THE STALL OUT AS IT MOVES
WESTWARD. THE NAM HAS BEEN THE MOST AGGRESSIVE MODEL WITH THIS
FEATURE BRINGING IT INTO THE SUSITNA VALLEY ON TUESDAY. THE GFS IS
NOT AS STRONG AND KEEPS IT MOSTLY IN THE COPPER RIVER BASIN.
IN THE BERING SEA THE MODELS ARE HOLDING TOGETHER WELL THROUGH
MONDAY WHEN THERE IS SOME DIFFERENCE IN HOW A LOW IN THE CENTRAL
BERING SEA IS ABSORBED INTO A SECOND LOW MOVING INTO THE AREA FROM
THE WEST. MODELS ALL SHOW THIS HAPPENING BUT BY TUESDAY AFTERNOON
THE ECMWF HAS THE MAIN LOW CENTER NEARLY 400 MILES FARTHER EAST
THAN THE NAM DOES. THE GFS AND GEM HAVE A MEDIAN POSITION BETWEEN
THE ECMWF AND NAM. THIS WILL MOSTLY IMPACT THE ALEUTIANS AND
BERING SEA AS SOUTHWEST MAINLAND ALASKA REMAINS UNDER HIGH
PRESSURE TUESDAY WITH THE LOW STILL WELL TO THE WEST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE TRACK OF THE SURFACE LOW ACROSS THE FAR SOUTHERN GULF WILL
KEEP THE BULK OF THE IMPACTS CONFINED TO KODIAK ISLAND AND AREAS
ALONG THE COAST THROUGH SUNDAY AS A GALE FORCE FRONT MOVES
NORTHWESTWARD ACROSS THE GULF AND GRADUALLY WEAKENS...BRINGING
RAIN TO KODIAK ISLAND AND THE NORTH GULF COAST. AN EASTERLY WAVE
WILL THEN MOVE OVER THE COPPER RIVER BASIN ON SUNDAY NIGHT AND
SPREAD RAIN SHOWERS OVER THAT AREA THROUGH MONDAY...WITH THE CHANCE
FOR SHOWERS SPREADING TO THE MAT-SU AND COOK INLET REGIONS ON MONDAY
AS THE WAVE PROGRESSES WESTWARD.

FIRE WEATHER CONCERNS ACROSS THE ANCHORAGE BOWL AND MAT-SU WILL
BEGIN TO DIMINISH BY SUNDAY AS DAYTIME MINIMUM RH VALUES UNDERGO A
GRADUAL UPWARD TREND AS MID/HIGH LEVEL CLOUDS INCREASE AHEAD OF
THE EASTERLY WAVE POISED TO MOVE OVERHEAD SUNDAY NIGHT INTO
MONDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SCATTERED SHOWERS WILL CONTINUE TO DEVELOP THIS EVENING ALONG A
WEAK TROUGH AXIS SITUATED ACROSS THE SOUTHWEST MAINLAND. THE AXIS
SHIFTS SOUTH OVERNIGHT WITH PRECIPITATION ENDING BY SUNDAY
MORNING. EASTERLY FLOW ACROSS THE REGION SHIFTS TO THE NORTH ON
SUNDAY AS LOW PRESSURE REMAINS ACROSS THE GULF AND RIDGING SHIFTS
OVER THE EASTERN BERING. RELATIVELY DRIER CONDITIONS PERSIST
THROUGH MONDAY WITH THE LOW PRESSURE REMAINING NEARLY STATIONARY.
PRECIPITATION CHANCES INCREASE MONDAY NIGHT AS A WEAK EASTERLY
WAVE MOVES FROM THE GULF LOW...HOWEVER AMOUNTS WILL BE LIGHT AS
WEAK SURFACE RIDGING WORKS IN FROM THE EASTERN BERING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A FRONT MOVES INTO THE WESTERN BERING TONIGHT BRINGING
PRECIPITATION AND GUSTY WINDS ALONG THE BOUNDARY. THE FRONTAL
BOUNDARY MOVES INTO THE CENTRAL BERING/ALEUTIANS BY LATE SUNDAY
AND THEN REMAINS STATIONARY AS THE LOW CENTER MOVES WEST OF THE
PRIBILOF ISLANDS. PRECIPITATION WILL BE A MIX OF RAIN AND SNOW
THROUGH THIS EVENT AS THE ASSOCIATED SURFACE LOW UNDERCUTS AN
UPPER RIDGE OVER THE BERING AND IS NOT STRONG ENOUGH TO PULL A
WARMER AIR MASS WITH IT. THIS SYSTEM WILL WEAKEN AS IT MOVES INTO
THE NORTHERN BERING ON MONDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A PROGRESSIVE PATTERN WILL DEVELOP EARLY NEXT WEEK AND CONTINUE
THROUGH THE REMAINDER OF THE WEEK WITH VARIOUS LOWS MOVING
THROUGH THE SOUTHERN BERING AND INTO THE GULF. MODEL DIFFERENCES
DEVELOP WITH THE EXACT TRACK OF THESE LOWS BY THE MIDDLE OF NEXT
WEEK AND WITH THE OPERATIONAL MODEL RUNS NOT BEING ABLE TO LOCK
DOWN EXACT LOW PLACEMENT A BLEND OF THE ENSEMBLES WAS USED FOR
THEIR POSITIONS. HOWEVER...THE PROGRESSIVE PATTERN WOULD BE
EXPECTED TO LEAD TO PRECIP FOR THE ALEUTIANS AND AREAS ALONG THE
NORTH GULF COAST AS THESE LOWS PASS. WITH THE INSTABILITY OVER THE
MORE INLAND LOCATIONS SHOWERY ACTIVITY CAN ALSO BE
EXPECTED...ESPECIALLY ALONG THE MOUNTAINS.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 131 132 138 150 177 178.
FIRE WEATHER...RED FLAG WARNING 101 111 145.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...DK


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