Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 021310
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
510 AM AKDT WED SEP 2 2015

.ANALYSIS AND UPPER LEVELS...A CALM AND CLEAR NIGHT IS UNDERWAY
ACROSS MUCH OF SOUTHCENTRAL. AN EXTENSION OF THE NORTH PACIFIC
RIDGE IS HELPING BUILD A SURFACE HIGH OVER THE AREA. THIS SHOULD
LEAD TO OUR COLDEST NIGHT OF THE YEAR SO FAR...SO THE FREEZE
WARNING STILL LOOKS ON TRACK THROUGH 8 AM. BUT THIS HIGH WILL BE
SHORT LIVED AS WARM FRONT IS ALREADY SLIDING ONSHORE ACROSS THE
WEST COAST. GUSTY SOUTH TO SOUTHEAST WINDS AHEAD OF THE FRONT HAVE
ALREADY SKIRTED THE ALASKA PENINSULA AND ARE NOW AFFECTING THE
WESTERN CAPES. OUT OVER THE BERING...THE UPPER LEVEL JET IS
FINALLY STARTING TO BECOME A BIT MORE ACTIVE AND THIS SHOULD LEAD
TO FAIRLY WIDESPREAD CHANGES. A FINGER OF THE POLAR JET AT 100KTS
IS MOVING OFF THE KAMCHATKA PENINSULA AND SHOULD HELP TO FINALLY
MOVE THE UPPER LEVEL LOW THAT HAS BEEN PARKED OVER THE WESTERN
BERING FOR A WEEK. A PIECE OF THE SUBTROPICAL JET IS TRACKING AT
80KTS FROM SOUTHWEST TO NORTHEAST TOWARD THE ALASKA PENINSULA.
THIS WILL HELP TRANSPORT SOME ADDITIONAL MOISTURE ALONG WITH A FEW
PIECES OF ENERGY MAKING FOR A WET FORECAST FOR THE NEXT SEVERAL
DAYS FOR SOUTHWEST AK.

&&

.MODEL DISCUSSION...THINGS ARE IN DECENT SHAPE FOR ABOUT THE FIRST
24 HOURS...THEN ALL BETS ARE OFF. THE SYNOPTIC PATTERN REMAINS
INTACT...RIDGE MOVES OVER THE SOUTHERN MAINLAND TODAY...FRONT
IMPINGES ON WEST COAST...AND ENERGY BLEEDS ACROSS AKPEN AND INTO
GULF. BUT EVEN JUST LOOKING AT WATER VAPOR OVERNIGHT...IT WOULD
SEEM MODELS MIGHT BE UNDER-DOING THE STRENGTH OF THE SHORTWAVE
NEAR 47N 171W. AND THAT SHORTWAVE IS REALLY WHERE THE TROUBLE
BEGINS. AS THE ENERGY ASSOCIATED WITH IT MOVES TOWARD BRISTOL BAY
BY THURSDAY...ALL MODELS PAINT A CLOSED LOW SOMEWHERE IN THAT
VICINITY. BUT THE CANADIAN MODELS DROP IT DOWN ABOUT 4-6MB
STRONGER THAN THE OTHER MODELS. THEN HOW THAT ENERGY TRANSLATES
INTO THE GULF OF AK AND WHERE THE NEW AREA OF LOW PRESSURE SETS UP
AND MOVES THEREAFTER IS ANYONE`S GUESS. THE AMERICAN MODELS ARE
STRONGER AND FASTER MOVING IT EAST...WHILE THE EC AND GEM SHOW IT
DUE SOUTH OF PRINCE WILLIAM SOUND BY 00Z SAT. ALL THAT TO SAY
FORECAST CONFIDENCE IN THE DETAILS IS LOW BEYOND THURSDAY MORNING.

&&

.FIRE WEATHER...BOTTOM LINE IS THAT FIRE WEATHER CONCERNS SHOULD
LESSEN THROUGH THE WEEK. THE GUSTY NORTHERLY WINDS HAVE ALL BUT
DIED OFF EXCEPT FOR THE MOST FAVORABLE OUTFLOW LOCATIONS ALONG THE
COAST (SEWARD...VALDEZ). WHILE THE RIDGE MOVES OVER TODAY...DRY
AND SUNNY CONDITIONS WILL PERSIST FOR MOST AREAS. BUT HUMIDITIES
WILL BE SLIGHTLY HIGHER TODAY WITH CALMER WINDS. BY
THURSDAY...SEVERAL WEAK SYSTEMS WILL WORK IN TANDEM WITH MOIST
SOUTHWEST FLOW TO BRING WETTING RAINS TO MOST AREAS. WIDESPREAD
SHOWERS WILL REMAIN ON FRIDAY. FLOW WILL BECOME SLIGHTLY MORE
ZONAL GOING INTO THE WEEKEND. SO EVEN THOUGH SATURDAY COULD BE
MOSTLY DRY FOR THE MAINLAND...ANOTHER SYSTEM SHOULD BRING MORE
PRECIPITATION BY SUNDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AFTER A CHILLY START TO THE DAY ACROSS MOST OF SOUTHCENTRAL
TEMPERATURES WILL QUICKLY WARM UNDER SUNNY SKIES AS HIGH PRESSURE
MOVES OVERHEAD. THESE CONDITIONS WILL BE SHORT-LIVED THOUGH. AS
THE RIDGE AXIS PASSES DEEP AND BROAD SOUTHWEST FLOW WILL TRANSPORT
TROPICAL MOISTURE (WITH PRECIPITABLE WATER VALUES AROUND 1.5
INCHES) NORTHWARD TOWARD SOUTHCENTRAL.

FORECAST CONFIDENCE IS LOW WITH TRACKING OF PARTICULAR FEATURES
MOVING UP FROM THE NORTH CENTRAL PACIFIC. THIS POSES A CHALLENGE
TO EXACT TIMING OF RAIN MOVING INTO SOUTHCENTRAL ALONG WITH
RAINFALL AMOUNTS...BUT BOTTOM LINE IT IS GOING TO RAIN ACROSS
MOST (IF NOT ALL) OF SOUTHCENTRAL OVER THE NEXT COUPLE DAYS. WITH
GENERALLY WEAK SURFACE FLOW DOWNSLOPE DRYING WILL NOT BE AN
ISSUE...SO EXPECT MUCH OF THE AREA WILL SEE A PERIOD OF MODERATE
RAIN WITH THE INITIAL ARRIVAL OF RAIN SOME TIME TONIGHT OR THURSDAY.
THE ARRIVAL OF CLOUDS AND RAIN WILL MODERATE TEMPERATURES...LEADING
TO NOTABLY WARMER TEMPERATURES AT NIGHT AND COOLER TEMPERATURES
DURING THE DAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
THE FRONTAL SYSTEM PUSHING ONSHORE INTO SOUTHWEST ALASKA THIS
MORNING WILL CONTINUE TO BRING WET WEATHER TO THE REGION FOR THE
NEXT SEVERAL DAYS. A SERIES OF WAVES BOTH RIPPLING UP THE FRONTAL
BOUNDARY FROM THE SOUTH SOUTHWEST AND SWINGING IN FROM THE WEST
OFF OF THE LARGE LOW IN THE BERING WILL KEEP SOUTHWEST ALASKA VERY
WELL SUPPLIED WITH MOISTURE AND ENOUGH LIFT FOR ABUNDANT RAIN
FALL. ONE OF THE MORE ORGANIZED WAVES COMING UP FROM THE SOUTH
WILL CROSS THE ALASKA PENINSULA LATE THIS EVENING AND TRACK INTO
BRISTOL BAY TONIGHT...THEN SLOWLY LIFT NORTH THROUGH SOUTHWEST
ALASKA ON THURSDAY. THE TROUGH SWINGING IN FROM THE WEST THAT
SHOULD FINALLY START THE PUSHING THE FRONTAL SYSTEM EAST AND
CLEAR OF THE AREA WILL ARRIVE THURSDAY NIGHT...HOWEVER ADDITIONAL
TROUGHS FROM THE WEST WILL JUST REPLACE THE WIDESPREAD RAIN WITH
SCATTERED TO NUMEROUS SHOWERS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
THE LARGE UPPER LEVEL LOW IN THE WESTERN BERING WILL GRADUALLY
SHIFT EAST THROUGH THE END OF THE WEEK. TROUGHS ROTATING AROUND
THE SOUTH SIDE OF LOW WILL BRING PERIODS OF SHOWERS TO THE BERING
SEA AND ALEUTIAN ISLANDS.

&&

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

THERE IS STILL A LOT OF DISCREPANCY AMONGST THE GUIDANCE TODAY
STARTING AS EARLY AS THURSDAY EVENING AS A VORT MAX ROTATING
AROUND THE UPPER LOW IN THE BERING SAY EITHER PUSHES INTO
SOUTHWEST ALASKA OR SKIRTS THE ALASKA PENINSULA AND MOVES INTO
THE GULF FRIDAY AFTERNOON. THE MODELS HAVE DEPICTED THE
PROGRESSION OF RAINFALL ALONG THE FRONT MOVING ACROSS SOUTHERN
ALASKA PRETTY WELL. MODELS ARE STARTING TO TREND A TAD DRIER
ACROSS SOUTHCENTRAL ALASKA LATE THURSDAY AND FRIDAY AS THEY TRY TO
CREATE A SURFACE LOW THAT TRANSLATES ACROSS THE NORTHERN GULF
RAPIDLY. THIS WOULD ALLOW SOUTHWEST FLOW TO USHER IN MOISTURE
BEFORE THE LOW SHIFTS SOUTH OF PRINCE WILLIAM SOUND AND THE
MOISTURE THEN BECOMES CONFINED TO THE NORTHERN GULF COAST.
NONETHELESS...THURSDAY AFTERNOON THROUGH FRIDAY MORNING SHOULD BE
PRETTY WET ACROSS SOUTHCENTRAL ALASKA. CHANCES FOR RAINFALL WILL
PERSIST THROUGH THE EXTENDED FOR THE ALASKA MAINLAND AS MODELS ARE
MORE AGGRESSIVE WITH THE UPPER LEVEL RIDGE BEING MORE SHORTWAVE
INDUCED VS A LONGWAVE RIDGE WHICH SHOULD BREAK DOWN THE RIDGE
QUICKER THAN THE MODELS HINTED AT IN PAST DAYS. TEMPERATURES WILL
REMAIN NEAR NORMAL TO SLIGHTLY BELOW NORMAL THROUGH THE MIDDLE OF
NEXT WEEK.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FREEZE WARNING 101 111.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

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


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