Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 200002
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
402 PM AKDT TUE MAY 19 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL RIDGE OVER THE YUKON IS MOVING EASTWARD AS A
SECOND RIDGE OVER THE NORTH PACIFIC IS AMPLIFYING OVER THE
WESTERN GULF OF ALASKA. THE TROUGH IN THE BERING SEA IS DIGGING
SOUTHWARD AS WELL WHICH IS STEERING THE JET STREAM INTO SOUTHWEST
MAINLAND ALASKA. THIS WILL BRING ANOTHER ROUND OF RAIN TO THAT
REGION. THE SURFACE LOW ASSOCIATED WITH THE UPPER LEVEL TROUGH IS
SOUTHWEST OF DUTCH HARBOR AND WILL SPLIT INTO TWO CENTERS AS IT
MOVES EASTWARD. IT WILL NOT BE ABLE TO MAKE IT VERY FAR EASTWARD
DUE TO THE RIDGE IN THE GULF OF ALASKA AND THIS IS A BIG PART OF
THE REASON IT IS ELONGATING AND THEN SPLITTING INTO TWO DISTINCT
CENTERS.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD AGREEMENT WITH KEY FEATURES. A BIG CHANGE FROM
THE PREVIOUS DAYS OCCURS LATE IN THE WEEK WITH THE REMNANTS OF
FORMER TYPHOON DOLPHIN WHICH WILL MOVE INTO THE WESTERN BERING
SEA. MODELS ARE ALL SPEEDING UP THE FORWARD MOVEMENT OF THIS
SYSTEM AS WELL AS SIGNIFICANTLY DROPPING THE CENTRAL PRESSURE FOR
THIS LOW INTO THE UPPER 950S TO MID 960S RANGE BY THURSDAY NIGHT.
THIS IS AROUND A 10 MB DROP IN FORECAST PRESSURE FROM YESTERDAYS
RUNS. THE FAR WEST TRACK OF THIS SYSTEM WILL KEEP THE MAJORITY OF
THE IMPACTS CONFINED TO THE ALEUTIAN ISLANDS AND BERING SEA.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
HIGH PRESSURE CONTINUES TO DOMINATE THE SOUTHCENTRAL BUT THE
APPROACHING FRONT FROM THE SOUTHWEST IS BRINGING CLOUD COVER OVER
THE WESTERN PORTIONS OF THE SOUTHCENTRAL. HOWEVER...THE FRONT WILL
STALL OVER KODIAK ISLAND AND THE HIGH WILL REMAIN THE DOMINATE
FEATURE FOR THE NEXT COUPLE DAYS. THIS WILL KEEP DIURNAL TRENDS
GOING FOR WINDS WITH SEA BREEZES ALONG COASTAL AREAS. TEMPERATURES
WILL ALSO STAY WARM...ESPECIALLY FOR PLACES IN THE COPPER RIVER
BASIN.

&&

.FIRE WEATHER...
AREAS OF CONCERN ARE EXPANDING THROUGHOUT THE SOUTHCENTRAL AS
AFTERNOON AND EVENING WINDS INCREASE. THE TWO AREAS THAT WILL BE
THE CLOSEST TO CRITICAL LEVELS ARE THE COPPER RIVER BASIN AND THE
KNIK RIVER VALLEY. UNDER THE EFFECTS OF THE PERSIST HIGH PRESSURE
THE COPPER RIVER BASIN WILL HAVE RH VALUES DROP BELOW 15 PERCENT
IN THE AFTERNOON AND EVENING HOURS THROUGH WEDNESDAY. ON TOP OF
THAT AFTERNOON AND EVENING WINDS WILL GUST UP TO 25 MPH ALONG THE
COPPER RIVER THROUGH WEDNESDAY. FOR THE KNIK RIVER VALLEY RH
VALUES WILL DROP TO AROUND 30 PERCENT LIKE MUCH OF THE
SOUTHCENTRAL IN THE AFTERNOON AND EVENING HOURS BUT THEY WILL ALSO
HAVE WINDS GETTING UP TO AROUND 20 MPH OUT OF THE VALLEY.

&&

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

A FRONTAL OCCLUSION ASSOCIATED WITH AN AREA OF LOW PRESSURE OVER
THE CENTRAL ALEUTIANS CONTINUES TO PUSH ACROSS THE ALASKA
PENINSULA TOWARD SOUTHWEST ALASKA. WIDESPREAD RAINFALL AND GUSTY
WINDS HAVE BEEN OBSERVED AT MULTIPLE LOCATIONS ACROSS ALASKA
PENINSULA...WITH WINDS GUSTING BETWEEN 40 TO 50 MPH AT TIMES. IN
THE MEANTIME...RAINFALL HAS CONTINUED ACROSS ACROSS THE KUSKOKWIM
DELTA AND PARTS OF THE LOWER KUSKOKWIM VALLEY AS A SHORTWAVE
TROUGH TRAVERSES THE REGION. THIS SHORTWAVE TROUGH IS EXPECTED TO
SLIDE NORTHWARD AND EASTWARD AND DISSIPATE TONIGHT AND BRING A
POSSIBLE SHORT BREAK IN PRECIPITATION TO THE DELTA. THE FRONT
CURRENTLY OVER THE ALASKA PENINSULA WILL PUSH ACROSS BRISTOL BAY
AND MOVE INLAND BEFORE STALLING WEST OF A LINE FROM ILIAMNA TO
SLEETMUTE TO GRAYLING.

YESTERDAY...THE ORIENTATION OF THE FRONT LOOKED FAVORABLE FOR
DOWNSLOPE CONDITIONS TO DEVELOP ON THE LEE SIDE OF THE ALASKA
RANGE AND KEEP KING SALMON AND ILIAMNA ON THE DRY SIDE.
HOWEVER...SATELLITE ANALYSIS WITH A TOUCH OF MODEL DATA HAS SHOWN
A VERY DEEP SUBTROPICAL PLUME OF MOISTURE BEING ADVECTED NORTHWARD
AHEAD OF THE FRONT. THIS DEEP MOISTURE WILL WEAKEN THE DOWNSLOPE
COMPONENT OF THE FRONT BUT NOT COMPLETELY ELIMINATE IT. THIS WILL
LEAVE THE LEE SIDE LOCATIONS WITH MORE SCATTERED TO NUMEROUS
SHOWERS INSTEAD OF STEADY RAINFALL. GUSTY WINDS THROUGH GAPS IN
THE ALASKA AND ALEUTIAN RANGES WILL BE SEEN WITH THE FAVORABLE
FRONTAL ORIENTATIONS WITH GUSTS UP TO 45 MPH POSSIBLE. THE FRONT
WILL REMAINED STALLED OVER THE SOUTHWEST MAINLAND THROUGH THURSDAY
AS IT GRADUALLY WEAKENS. THE STEADY RAINFALL OBSERVED TONIGHT AND
WEDNESDAY WILL GRADUALLY TAPER OFF AND BECOME MORE SHOWERY LATE
THURSDAY AS THE FRONT DISSIPATES.

&&

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

A BROAD AREA OF LOW PRESSURE OVER THE CENTRAL ALEUTIANS WILL SLIDE
EASTWARD OVERNIGHT PRIOR TO SPLITTING INTO TWO SEPARATE LOWS. ONE
OF THESE LOWS WILL DEVELOP NEAR THE PRIBILOF ISLANDS AND MOVE
NORTHWARD INTO EASTERN RUSSIA WHILE THE SOUTHERN LOW SOUTH OF THE
ALEUTIAN CHAIN QUICKLY DISSIPATES. THIS WILL HELP SPREAD RAINFALL
(POSSIBLY MIXED WITH SNOW IN THE NORTHERN BERING SEA) NORTHWARD
WHILE A RIDGE OF HIGH PRESSURE WILL BE QUICK TO REPLACE THE LOW
PRESSURE SYSTEMS. THIS HIGH PRESSURE SYSTEM WILL BRING A REPRIEVE
OF RAINFALL TO THE WESTERN HALF OF THE BERING SEA ON WEDNESDAY
WHILE THE EASTERN HALF CONTINUES TO SEE RAINFALL ASSOCIATED WITH
THE FRONTAL BOUNDARY STALLED OUT OVER SOUTHWEST ALASKA.

THE PATTERN TAKE A BIG SHIFT LATE THURSDAY INTO FRIDAY AS THE
REMNANTS OF TYPHOON DOLPHIN PUSH INTO THE FAR WESTERN BERING SEA.
WHILE THERE IS LITTLE UPPER LEVEL SUPPORT INITIALLY...A STRONG JET
STREAK WILL ENHANCE UPPER LEVEL DIFFLUENCE IN AID IN SOME PRETTY
SIGNIFICANT STRENGTHENING OF THE LOW OVER THE WESTERN BERING SEA.
WHILE THE WINDS AT 2KFT ARE APPROACHING 75 KT...A VERY POTENT
SUBTROPICAL AIR MASS IS BEING ADVECTED NORTHWARD AND SHOULD
PREVENT MUCH OF THE STRONGER WINDS FROM MIXING DOWN DUE TO A
STABLE LAYER DEVELOPING OFF THE SURFACE. THIS DOES NOT MEAN THAT
STRONG WINDS WILL NOT IMPACT THE BERING SEA AS MAX GALE FORCE
WINDS WILL LIKELY BE OBSERVED AND A SMALL CORRIDOR OF STORM FORCE
WINDS MAY DEVELOP OVER THE OPEN WATERS OF THE WESTERN BERING SEA.
ONE INTERESTING POINT OF NOTE IS THAT THIS HAS THE POTENTIAL TO BE
ONE OF THE STRONGEST STORMS IN TERMS OF CENTRAL PRESSURE TO IMPACT
THE BERING SEA IN THE MONTH OF MAY.

&&

.LONG TERM FORECAST (FRIDAY THROUGH TUESDAY)...

BEGINNING THE EXTENDED FORECAST ON FRIDAY...THE STRONG NORTH
EAST PACIFIC RIDGE EXTENDING INTO NORTHERN ALASKA WILL REMAIN IN
PLACE...WITH THE STRONG REMNANTS OF FORMER TYPHOON DOLPHIN OVER
THE FAR WESTERN BERING. THIS WILL MEAN WARM AND DRY WEATHER ACROSS
SOUTHCENTRAL ALASKA...WITH A REMNANT WEAK FRONTAL ZONE OVER
SOUTHWEST AND THE EASTERN BERING KEEPING CLOUDS AND PRECIPITATION
OVER THAT REGION. EVENTUALLY...THE LARGE UPPER LOW OVER THE
WESTERN BERING WILL BEGIN TO MAKE EASTWARD PROGRESS AS NUMEROUS
LOBES OF ENERGY ROTATE AROUND THE LOW. THIS WILL SPREAD CLOUDS AND
PRECIPITATION INTO SOUTHCENTRAL ALASKA SATURDAY AND SUNDAY. BY
NEXT WEEK...THERE IS SOME DISCREPANCY WITH SMALLER SCALE
DETAILS...BUT THERE ARE SIGNS THAT THE STRONG NORTH EAST PACIFIC
RIDGE REBUILDS INTO ALASKA MONDAY AND TUESDAY...BRINGING MORE
WARMER AND DRIER WEATHER TO ALASKA...KEEPING THE STORM TRACK OVER
THE BERING SEA.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...RED FLAG WARNING 141 FOR STRONG WIND AND LOW
  HUMIDITY.

&&

$$

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



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