High Wind Watch 20, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SAT OCT 26 2013

.ANALYSIS AND UPPER LEVELS...
THE RAPID AMPLIFICATION OF THE LONGWAVE PATTERN IS UNDERWAY AS
SATELLITE IMAGERY SHOWS THE WESTERN NORTH AMERICAN RIDGE EXPANDING
NORTHWARD INTO MAINLAND ALASKA...WHILE COLD AIR AND NORTHERLY FLOW
DIGS ALL THE WAY DOWN TO 30N ACROSS THE NORTH CENTRAL PACIFIC.
SINKING AIR AND MOSTLY SUNNY SKIES ACROSS SOUTHCENTRAL HAVE ALLOWED
AREAS OF FOG TO FORM AROUND COOK INLET AND PRINCE WILLIAM SOUND.
FURTHER WEST...A STACKED LOW SOUTH OF THE CENTRAL ALEUTIANS IS
WEAKENING AS THE ASSOCIATED STRONG WARM FRONT SURGES NORTHWARD BEHIND
A ROBUST 180+ KT SOUTHERLY JET. STRONG WINDS AND RAIN OVER THE
EASTERN ALEUTIANS AND ALASKA PENINSULA ARE HEADED EAST TOWARD THE
BRISTOL BAY ZONE...WHERE A HIGH WIND WARNING REMAINS IN EFFECT.

.MODEL DISCUSSION...
MODELS REMAIN IN FAIRLY GOOD AGREEMENT FOR THE FIRST PHASE OF THE
APPROACHING STORM (FIRST 30 HOURS OF THE FORECAST) AS THE ROBUST WARM
FRONT MOVES THROUGH THE SOUTHERN MAINLAND DURING THE DAY SUNDAY. THE
OVERALL TREND AMONG THE MODELS FROM THE OVERNIGHT FORECAST HAS BEEN
TO SPEED UP THE WARM FRONT BY SEVERAL HOURS...AND WITH INCREASING
CONFIDENCE THE HIGH WIND WATCH FOR TURNAGAIN ARM WILL BE UPGRADED TO
A WARNING WITH THE AFTERNOON PACKAGE FOR THE EARLY SUNDAY TIME-FRAME.
MEANWHILE...A FRUSTRATING LEVEL OF MODEL DISAGREEMENT CONTINUES WITH
THE SECONDARY WAVE MOVING THROUGH SOUTHERN ALASKA ON MONDAY. THE
OVERNIGHT MODEL RUNS BEGAN TO TREND TOWARD STRONGER SURFACE LOW
DEVELOPMENT UNDERNEATH THE ROBUST UPPER SHORTWAVE OVER SOUTHWEST
ALASKA ON MONDAY MORNING. THIS MORNING...EACH NEW MODEL RUN IS NOW
INDICATING A WEAKER SUPPORTING UPPER SHORTWAVE...WHICH IN TURN MOVES
THROUGH THE AREA FASTER AND SUPPORTS A WEAKER SURFACE REFLECTION. THE
NAM IS NOW ALONE WITH A MORE SIGNIFICANT SURFACE LOW MOVING INTO
BRISTOL BAY ON MONDAY...AND HAS BEEN EXCLUDED FROM THE FORECAST
DEVELOPMENT TODAY. BOTTOM LINE...LOWER FORECAST CONFIDENCE CONTINUES
REGARDING HIGH WIND POTENTIAL THROUGH TURNAGAIN ARM ON MONDAY.

.SHORT TERM FORECAST...
SOUTHCENTRAL...HIGH CLOUDS INFILTRATING THE AREA ARE THE FIRST SIGN
OF THE APPROACHING STORM. RAIN WILL MOVE INTO KODIAK ISLAND THIS
EVENING AS PRESSURE GRADIENTS ACROSS THE REGION AS A WHOLE INTENSIFY
RAPIDLY. STRONGEST WINDS ARE EXPECTED THROUGH TURNAGAIN ARM...WHERE A
HIGH WIND WARNING WILL BE ISSUED WITH THE AFTERNOON FORECAST FOR THE
SUNDAY PHASE OF THE STORM. ALL MODELS ARE NOW SUGGESTING SOME DEGREE
OF A TRAPPING INVERSION/CRITICAL LAYER ABOVE MOUNTAINTOP LEVEL ON
SUNDAY...WHICH RAISES THE POTENTIAL FOR SOME HIGHER WIND GUSTS TO
SPREAD DOWN TO THE LOWER HILLSIDE AND EAST ANCHORAGE DURING THE
MORNING HOURS ON SUNDAY. AS FOR MONDAY...STRONG WINDS WILL DEVELOP
THROUGH TURNAGAIN ARM...BUT WILL BE HELD BELOW WARNING LEVEL AT THIS
TIME DUE TO THE AFOREMENTIONED MODEL UNCERTAINTY. OF NOTE...THE
OVERALL ORIENTATION OF THE WEATHER PATTERN ON MONDAY CONTINUES TO
LOOK FAVORABLE FOR SOUTH AND WEST ANCHORAGE TO EXPERIENCE SOME WINDS
COMING FROM TURNAGAIN ARM...WHILE EAST ANCHORAGE AND THE LOWER
HILLSIDE MAY BE ON THE MORE BENIGN END OF THE SPECTRUM OF WINDS.

THE DUAL THREAT ACROSS THE REGION WITH THE APPROACHING STORM COMPLEX
WILL BE HEAVY RAIN. HIGHEST RAINFALL TOTALS AND HIGHEST FLOODING
POTENTIAL WILL BE CONFINED TO COASTAL LOCATIONS ALONG THE GULF WITH
THIS STORM. HOWEVER...EVEN INLAND AREAS MAY SEE ENOUGH RAIN TO BUMP
SOME RIVERS AND STREAMS TOWARD BANKFULL. POTENTIAL FOR FLOODING WILL
CONTINUE TO BE EVALUATED AS THE EVENT BEGINS TO UNFOLD LATE TONIGHT.

SOUTHWEST MAINLAND...THE WARM FRONT SURGING NORTHWARD HAS TIGHTENED
PRESSURE GRADIENTS IN A SIGNIFICANT WAY ACROSS PORTIONS OF THE
BRISTOL BAY ZONE WHERE A HIGH WIND WARNING REMAINS IN EFFECT. HEAVY
RAINFALL IS SPREADING UP THE ALASKA PENINSULA...WHERE EVEN STRONG
CROSS-BARRIER/DOWNSLOPING FLOW WILL NOT BE ENOUGH TO KEEP THE WEST
SIDE OF THE MOUNTAINS FROM SEEING MEASURABLE PRECIPITATION. AFTER A
BREAK IN THE RAIN DURING THE DAY SUNDAY...STEADY PRECIP WILL MOVE
BACK IN SUNDAY NIGHT AS THE TROPICAL FIRE-HOSE PUMPS COPIOUS AMOUNTS
OF MOISTURE INTO THE MAJORITY OF THE STATE.

BERING SEA AND ALEUTIANS...BY RELATIVE STANDARDS THE LARGE AND
COMPLEX LOW PRESSURE CIRCULATION THAT WILL BE OVER THE REGION FOR THE
NEXT SEVERAL DAYS WILL BE ON THE LIGHT SIDE. THE WESTERN BERING SEA
WILL SEE CHILLY NORTHERLY WINDS...WHILE THE EASTERN HALF OF THE
BERING WILL SEE WARM SOUTHERLY FLOW. SHOWERS WILL BE PREVALENT ACROSS
THE WHOLE REGION...THOUGH NO SPECIFIC AREAS OF HEAVY PRECIP ARE
EXPECTED ONCE THE WARM FRONT CLEARS THE AREA THIS EVENING.

.LONG TERM FORECAST...
THE OVERALL WEATHER PATTERN LOOKS SET TO CONTINUE FEATURING A STRONG
JET SOUTH OF THE ALEUTIANS CURVING NORTHWARD AND CARRYING MOST OF THE
ACTIVE WEATHER INTO THE MAINLAND. THIS WILL ALSO CONTINUE TO BRING
MOISTURE-LADEN FORMER TROPICAL SYSTEMS FROM LOWER LATITUDES INTO THE
ALASKAN DOMAIN. THUS WHILE DIMINISHING DAYLIGHT WILL NECESSARILY LEAD
TO LESS DAYTIME HEATING ACROSS THE GREAT LAND...NO DISCERNIBLE
PATTERN SHIFT TO MORE WINTRY WEATHER IS FORESEEABLE AT THIS TIME.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101
MARINE...STORM 130 131 150 160 180
         GALE 119 120 125 130 136 137 138 165 181 185
FIRE WEATHER...NONE

AMD OCT 13