High Wind in Alaska, September 2 to 3, 2013

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT MON SEP 2 2013

.ANALYSIS AND UPPER LEVELS...
A LARGE 978 MB VERTICALLY STACKED LOW OVER THE EASTERN BERING
CONTINUES TO BE THE BIG WEATHER-MAKER ACROSS THE REGION TODAY. AN
ASSOCIATED WEATHER FRONT BROUGHT HEAVY RAIN TO THE SOUTHWEST MAINLAND
OVERNIGHT...AND IS CURRENTLY CROSSING INTO THE FAR WESTERN GULF.
WINDS THROUGH FAVORED TERRAIN GAPS ACROSS SOUTHERN ALASKA HAVE
INCREASED AS EXPECTED...WITH TURNAGAIN ARM WINDS ALREADY EXCEEDING 60
MPH. A WEAK DISTURBANCE MOVED NORTHWARD THROUGH SOUTHCENTRAL EARLY
THIS MORNING...AND COMBINED WITH UPPER LEVEL DIFLUENCE TO PRODUCE
MODERATE TO HEAVY RAIN SHOWERS AROUND UPPER COOK INLET. THIS FEATURE
HAS NOW WEAKENED AND MOVED AWAY TO THE NORTH...AS THE BERING STORM
MOVES IN FROM THE SOUTHWEST.

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD OVERALL AGREEMENT. THE NAM HAD BEEN TOO
FAST WITH THE FRONTAL PROGRESSION THROUGH SOUTHCENTRAL THIS AFTERNOON
AND EVENING...BUT HAS NOW FLIPPED AND APPEARS TO BE THE SLOWEST OF
THE AVAILABLE MODELS. WITH THE KENAI NEXRAD ALREADY SHOWING STEADY
RAIN MOVING INTO COOK INLET THE GFS/EC FRONTAL TIMING IS VERIFYING
THE BEST. ONCE THE FRONT GOES THROUGH...VIRTUALLY ALL OF SOUTHERN
ALASKA WILL BE IN DEEP SOUTHWEST FLOW WITH EMBEDDED SHORTWAVE TROUGHS
SPINNING AROUND THE ANCHOR LOW IN THE NORTHERN BERING. THE MODELS
OFTEN STRUGGLE WITH THE DETAILS IN THIS TYPE OF PATTERN...SO FORECAST
CONFIDENCE IS LOW IN THE TIMING AND PLACEMENT OF INDIVIDUAL FEATURES
BUT HIGH CONFIDENCE OVERALL THAT MOST PLACES WILL SEE MULTIPLE
PERIODS OF RAIN OVER THE NEXT FEW DAYS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...MOISTURE IS STREAMING BACK INTO COOK INLET AS THE
FRONT MAKES STEADY PROGRESS ACROSS THE ALASKA/ALEUTIAN RANGES INTO
THE REGION. WINDS THROUGH TURNAGAIN ARM HAVE PLATEAUED THIS AFTERNOON
AROUND 60 MPH AND WILL BEGIN TO INCREASE AGAIN THIS AFTERNOON AS THE
GRADIENT CONTINUES TO TIGHTEN IN ADVANCE OF THE FRONT. WITH DEEP
ATMOSPHERIC MOISTURE MOVING IN EXPECT EVEN THE USUAL DOWNSLOPE AREAS
TO SEE RAIN AS THE FRONT GOES THROUGH THIS EVENING...THOUGH HIGHEST
TOTALS WILL DEFINITELY BE LIMITED TO UPSLOPE AREAS IN THE SUSITNA
VALLEY AND AROUND PRINCE WILLIAM SOUND. A SHORTWAVE TROUGH MOVING
NORTHWARD OVERNIGHT ALONG THE FRONT WILL RE-INVIGORATE THE OTHERWISE
SLOWLY DECAYING FRONT AND HELP DEVELOP A DECENT BARRIER JET AND
MULTIPLE-INCH RAINFALL TOTALS THROUGH TOMORROW AROUND VALDEZ. HAVE
ISSUED A FLOOD ADVISORY FOR VALDEZ AREA PRIMARILY FOR SMALL STREAMS
IN THE AREA. MODERATE PRESSURE RISES ARE STILL ON TRACK TOMORROW AS
THE FRONT PUSHES INLAND. AS A RESULT...MOST LOCATIONS FROM COOK INLET
TO PRINCE WILLIAM SOUND SHOULD SEE A BUMP IN WIND SPEEDS OUT OF THE
SOUTH DURING THE DAY TUESDAY.

SOUTHWEST MAINLAND...HEAVY RAIN ALONG THE FRONT IS NOW CONFINED TO
EASTERN SECTIONS OF THE KUSKOKWIM VALLEY AND FAR EASTERN BRISTOL BAY
ZONES. GUSTY WINDS WILL CONTINUE TO BLOW THROUGH THE MOUNTAIN GAPS AS
THE GRADIENT REMAINS TIGHT...BUT SHOULD GRADUALLY DIMINISH AS THE LOW
ITSELF WEAKENS AND THE CIRCULATION OPENS UP TO THE NORTH. AS
MENTIONED ABOVE...BROAD SOUTHWESTERLY ONSHORE FLOW WITH EMBEDDED
SHORTWAVE TROUGHS WILL BRING MULTIPLE PERIODS OF RAIN TO THE REGION
THROUGH THE MIDDLE TO END OF THE WEEK.

BERING SEA AND ALEUTIANS...THE LONGWAVE TROUGH WILL SET UP SHOP OVER
THE EASTERN BERING WHICH WILL ALLOW NORTHERLY FLOW AND A SHOT OF
SEASONABLY COOL AIR TO COME DOWN FROM THE BERING STRAIT AND SLOWLY
MODERATE THROUGH THE END OF THE WEEK.

.LONG TERM FORECAST...
AMPLIFIED LONGWAVE PATTERN LOOKS TO CONTINUE...WITH A GULF RIDGE
INCREASINGLY LIKELY TO SET UP BY NEXT WEEKEND. WHILE THIS WOULD BRING
SOUTHERLY FLOW AND MILD TEMPERATURES TO THE MAINLAND...IT ALSO BRINGS
THE POTENTIAL OF PROLONGED RAINFALL ALONG THE GULF COAST AND
WINDSTORMS TO INTERIOR PARTS OF SOUTHCENTRAL AS LOWS DEVELOP OVER THE
NORTH PACIFIC AND MOVE RAPIDLY NORTHWARD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101
         SMALL STREAM FLOOD ADVISORY 131
MARINE...GALE 120 125 130 172 175 185
FIRE WEATHER...NONE

AMD SEP 13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
700 PM AKDT MON SEP 2 2013

AKZ181-030900

...MINOR ASH FALL POSSIBLE NEAR PORT HEIDEN...

OBSERVED SEISMIC ACTIVITY INDICATES THAT VENIAMINOF VOLCANO CONTINUES
TO ERUPT WITH MINOR ASH EMISSIONS. WINDS ARE EXPECTED TO TRANSPORT
THE ASH TO THE NORTHEAST...WHICH COULD BRING SOME VERY LIGHT ASHFALL
TO AREAS ALONG THE BERING COAST NEAR OR JUST WEST OF PORT HEIDEN
THROUGH THIS EVENING.

THIS STATEMENT WILL BE UPDATED BY 1 AM AKDT TUESDAY OR SOONER IF
CONDITIONS WARRANT.