Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 220102
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
502 PM AKDT THU MAY 21 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL RIDGE OVER EASTERN ALASKA AND THE YUKON IS
HOLDING FIRM TODAY AND KEEPING THE CLOUDS FROM MAKING IT MUCH
FARTHER EAST THAN THE TALKEETNA MOUNTAINS. THIS RIDGE WILL
ACTUALLY START TO PUSH WESTWARD A LITTLE FRIDAY BEFORE FINALLY
GETTING DISPLACED EASTWARD THROUGH THE COURSE OF THE WEEKEND.

AN UPPER LEVEL DISTURBANCE IS RIDING NORTHWARD OVER SOUTHWEST
MAINLAND ALASKA WHICH WILL KEEP SOME RAIN IN THE REGION. THE MAIN
JET STREAM IS RUNNING FROM JAPAN TO THE CENTRAL ALEUTIANS STEERING
THE REMNANTS OF FORMER TYPHOON DOLPHIN INTO THE WESTERN BERING
SEA.

&&

.MODEL DISCUSSION...
THE BIGGEST MODEL DIFFERENCE OF NOTE OVER SOUTHWEST AND
SOUTHCENTRAL ALASKA IS THE SPEED AT WHICH THE FRONT CURRENTLY OVER
SOUTHWEST ALASKA IS ABLE TO MOVE EASTWARD AND BEGIN TO DISPLACE
THE RIDGE THAT HAS BEEN HOLDING FIRM OVER THE EASTERN PART OF THE
STATE. THE ECMWF AND GFS MODELS SHOW THIS FRONT MOVING INTO COOK
INLET FRIDAY NIGHT AND OVER ANCHORAGE BY SATURDAY AND THEN INTO TO
THE COPPER RIVER BASIN SUNDAY. THE 12Z NAM IS HOLDING THE RIDGE
IN PLACE A LITTLE STRONGER CAUSING THIS FRONT TO BE 12 TO 18 HOURS
SLOWER...HOWEVER THE 18Z NAM IS SPEEDING IT UP TO NEAR THE TIMING
OF THE OTHER MODELS. THE BIGGEST DIFFERENCE THIS WILL MAKE IS THE
BEST CHANCE FOR PRECIPITATION IN NORTHERN KENAI PENINSULA THROUGH
THE SUSITNA VALLEY. THE GFS AND ECMWF BRING IT IN SATURDAY WHILE
THE 12Z NAM HOLDS OFF UNTIL SATURDAY NIGHT OR SUNDAY. SHOULD THE
12Z NAM SOLUTION BE THE BEST THERE WILL ALSO BE INCREASED FIRE
WEATHER CONCERNS FOR THE MATANUSKA VALLEY SATURDAY AS THERE WILL
BE FAIRLY STRONG WINDS BEFORE MUCH MOISTURE MAKES IT INTO THE
AREA. THE GFS AND ECMWF (AND 18Z NAM) WOULD HAVE MOISTURE COMING
IN BEFORE WINDS START TO INCREASE FROM THE SOUTHEAST SATURDAY
WHICH WILL DIMINISH THE FIRE WEATHER CONCERNS. THERE IS A LARGE
SPECTRUM AS TO HOW THIS MAY PLAY OUT IN TERMS OF WINDS AND
HUMIDITY FOR THE MATANUSKA VALLEY ON SATURDAY.

IN THE BERING SEA THE REMNANTS OF FORMER TYPHOON DOLPHIN ARE
BECOMING EXTRA-TROPICAL AND TAKING THE EXPECTED TRACK. THE BIGGEST
DIFFERENCE IS THAT ALL MODES HAVE THE STORM ANALYZED ABOUT 10 MB
WEAKER THAN WHAT THEY WERE SHOWING THE PAST TWO DAYS. THERE ARE
STILL STORM FORCE WINDS AROUND IT BUT IT DOES NOT LOOK TO BE
STRENGTHENING AS MUCH AS EXPECTED AND WATCHING ITS STRUCTURE ON
THE SATELLITE IMAGERY SEEMS TO BEAR THIS OUT AS WELL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
HIGH PRESSURE WILL CONTINUE TO PROMOTE WARM AND DRY CONDITIONS
ACROSS THE AREA THROUGH FRIDAY BENEATH MAINLY CLEAR SKIES WITH THE
EXCEPTION OF A FEW LINGERING HIGH CLOUDS. A FRONT WILL THEN BEGIN
TO MAKE SLOW EASTWARD PROGRESS ACROSS THE GULF LATE FRIDAY INTO
SATURDAY AS THE RIDGE SHIFTS EASTWARD...WITH RAIN SPREADING FROM
KODIAK ISLAND TO THE KENAI PENINSULA BY SATURDAY MORNING AND A
CHANCE OF RAIN RETURNING TO ANCHORAGE AND THE MAT-SU REGION ON
SATURDAY AFTERNOON.

.FIRE WEATHER...
THE MAIN FORECAST CHALLENGE THROUGH SATURDAY WILL CONTINUE TO BE
FIRE WEATHER CONDITIONS OVER THE EASTERN HALF OF THE AREA AS
HUMIDITY REMAINS VERY LOW ACROSS THE COPPER RIVER BASIN...WITH RH
VALUES ONCE AGAIN EXPECTED TO FALL INTO THE TEENS ON FRIDAY
AFTERNOON. RH VALUES WILL IMPROVE SLIGHTLY BY SATURDAY AS THE
FRONT APPROACHES FROM THE WEST...HOWEVER WINDS WILL ALSO BEGIN TO
INCREASE AS THE PRESSURE GRADIENT TIGHTENS. THEREFORE...POTENTIAL
FOR RED FLAG CONDITIONS WILL CONTINUE TO BE CLOSELY MONITORED
THROUGH SATURDAY. MARGINAL RED FLAG POTENTIAL ALSO EXISTS THROUGH
THE MATANUSKA VALLEY ON FRIDAY AFTERNOON AS RH VALUES FALL TO
NEAR 30 PERCENT AND WINDS BEGIN TO INCREASE OUT OF THE KNIK RIVER
VALLEY...HOWEVER WINDS ARE NOT EXPECTED TO BE STRONG ENOUGH TO
MEET CRITERIA AT THIS TIME.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH SATURDAY)...

AFTER A REPRIEVE OF DEEP MOISTURE ACROSS SOUTHWEST ALASKA EARLY
THIS MORNING...WATER VAPOR NOW INDICATES A NICE PLUME OF MOISTURE
FROM THE NORTH PACIFIC/SUBTROPICS IS BEING ADVECTED NORTHWARD. THE
CULPRIT BEHIND THIS MOISTURE IS A WEAK UPPER LEVEL LOW SPINNING IN
THE NORTH PACIFIC SOUTH OF COLD BAY...WHICH HAS A SHORTWAVE
ALREADY MOVING TOWARD SOUTHWEST ALASKA. WHILE MUCH OF SOUTHWEST
ALASKA HAS SEEN RAINFALL TAPER OFF DURING THE AFTERNOON
HOURS...RAIN ACTIVITY IS EXPECTED TO RAMP BACK UP LATE TONIGHT OR
FRIDAY MORNING (DEPENDING ON THE TIMING OF THE SHORTWAVE). MUCH OF
THE RAINFALL WILL FALL OVER THE BRISTOL BAY AREA TOMORROW WITH
RAINFALL SPREADING INTO THE KUSKOKWIM DELTA LATE FRIDAY. A STRONG
UPPER LEVEL TROUGH WILL PUSH ACROSS SOUTHWEST ALASKA LATE FRIDAY
BUT CHANCES FOR RAINFALL LOOK PRETTY BLEAK AS DEEP MOISTURE
APPEARS UNAVAILABLE AND SOUTHEASTERLY WINDS AT MOUNTAIN TOP LEVEL
LOOK TO BE FAVORABLE FOR DOWN-SLOPING ALONG THE ALASKA AND
ALEUTIAN RANGES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH SATURDAY)...

THE STORM FORCE FRONT OVER THE FAR WESTERN BERING SEA HAS VERIFIED
WELL SO FAR TODAY WITH GUSTS IN EXCESS OF 50 KNOTS OBSERVED AT
SHEMYA THROUGHOUT THE AFTERNOON HOURS. THIS FRONT WILL CONTINUE TO
PUSH EASTWARD OVERNIGHT WHILE STEADILY WEAKENING BEFORE IT STALLS
OUT OVER THE CENTRAL BERING SEA. THE STORM FORCE WINDS SHOULD
WEAKEN BY FRIDAY MORNING BUT A SECOND CHANCE OF STRONG WINDS
ACROSS THE WESTERN ALEUTIANS WILL BE LIKELY AGAIN ON FRIDAY NIGHT
AND SATURDAY MORNING AS COLD AIR FROM RUSSIA IS ADVECTED ALONG THE
BACK SIDE OF THE BERING SEA LOW (POST-TROPICAL DOLPHIN). HAVE KEPT
WINDS AT MAX GALE (45 KT) AS THERE IS NO UPPER LEVEL JET STREAK OR
DIFFLUENCE TO REALLY HELP MAXIMIZE THE WIND POTENTIAL. NEEDLESS TO
SAY...ANOTHER VERY WET PERIOD OF WEATHER IS ON TAP ACROSS THE
WESTERN HALF OF THE BERING SEA. HOWEVER...THE EASTERN BERING SEA
WILL BE A BIT A DRIER IN TERMS OF PRECIPITATION IN THE NEAR TERM
BUT DEW POINT VALUES ARE QUITE ELEVATED COMPARED TO NORMAL WHICH
FAVOR THE DEVELOPMENT OF SOME PATCHY TO DENSE FOG...WITH THE
LOWEST VISIBILITIES LIKELY NORTH AND WEST OF NUNIVAK ISLAND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE TENACIOUS RIDGE OVER MUCH OF MAINLAND AK WILL CONTINUE
MIGRATING SOUTHEAST OVER THE WEEKEND. THIS WILL ALLOW  MOIST
ONSHORE FLOW TO BRING RAIN TO THE NORTH GULF COAST THROUGH
MON...WITH SOME SHOWER ACTIVITY CROSSING THE COASTAL MOUNTAINS
INTO SOUTHCENTRAL. BY MIDWEEK HIGH PRESSURE REBUILDS AND ENDS
MOST PRECIPITATION FOR SOUTH CENTRAL...ALTHOUGH RAIN ALONG THE
WESTERN FLANK OF THE HIGH WILL AFFECT KODIAK ISLAND.

A BROAD AREA OF LOW PRESSURE WILL REMAIN OVER THE WESTERN BERING
AND ALEUTIANS FOR SEVERAL DAYS...WITH DECAYING FRONTS REACHING SW
AK. THIS WILL KEEP RAIN AND SHOWERS OVER THE REGION THROUGH NEXT
WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 177.
   GALE WARNING 155 165 170 172 173 174 175 176 178 185.
FIRE WEATHER...RED FLAG WARNING 141.

&&

$$

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


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