Storm Warning 180, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT FRI OCT 1 2010

.ANALYSIS AND UPPER LEVELS...
A STRONG LOW IS WRAPPING UP NICELY IN THE SOUTHWESTERN GULF OF ALASKA
THIS MORNING. THE INITIAL FRONT ASSOCIATED WITH THE LOW MOVED ONSHORE
OVERNIGHT AND A SECOND WAVE IS MOVING ONSHORE EARLY THIS AFTERNOON.
THE FINAL OCCLUSION WILL APPROACH THE COAST OVERNIGHT...BRINGING
ANOTHER ROUND OF STRONG WINDS AND HEAVY RAIN. THE SUBTROPICAL FETCH
HAS BEEN PUSHED TO THE EAST TOWARD THE PANHANDLE. THE DYNAMIC SYSTEM
IS STILL VERY CAPABLE OF PRODUCING HEAVY RAIN IN THE COASTAL REGIONS
ALTHOUGH THE REDUCED TROPICAL MOISTURE IS LEADING TO MORE DOWNSLOPED
AREAS ACROSS THE INTERIOR.

.MODEL DISCUSSION...
MODELS IN AGREEMENT IN THE SHORT TERM BRINGING THE MAIN CIRCULATION
TOWARD KACHEMAK BAY AND THEN UP THE INLET...BEFORE WEAKENING INLAND
INTO A LARGE COMPLEX LOW OVER SOUTHWESTERN ALASKA. THE LOW THEN
DEVELOPS A NEW CENTER OFF OF THE KUSKOKWIM DELTA WHERE IT SLOWLY
WEAKENS AS IT DRIFTS TOWARD BRISTOL BAY SUNDAY NIGHT AS A LARGE
VERTICALLY STACKED FEATURE.

A FLY IN THE OINTMENT IS AN OBSERVATION AT BUOY 01. THE NORTHEASTERLY
WINDS THROUGH 20Z SUGGEST THE LOW IS TO THE EAST OF THE BUOY WHILE
THE MODELS ALL PLACE THE LOW TO THE WEST. I BELIEVE THE MODELS ARE
INITIALIZING OFF OF THE UPPER LOW THAT IS DISPLACED TO THE WEST ABOUT
100 MILES. THIS ADDS A SMALL AMOUNT OF UNCERTAINTY IN THE FIRST
PERIOD OF THE FORECAST AS WE TRY TO ADJUST FOR THIS AND WATCH TO SEE
IF IT BECOMES MORE VERTICALLY STACKED OVER THE NEXT SEVERAL HOURS AS
THE MODELS SUGGEST IT SHOULD BE.

A NEW FEATURE THAT THE 12Z RUNS ARE HITTING HARDER IS A DEVELOPING
LOW ALONG A POTENT SHORTWAVE MOVING UP TOWARD THE NORTHERN GULF
SATURDAY EVENING AND SUNDAY MORNING. MODELS VARY WILDLY ON THE
STRENGTH AND SPEED OF THIS SYSTEM. AT THIS POINT...DID A BLEND TO
INTRODUCE SOME STRONGER WINDS ALONG THE NORTH GULF COAST SATURDAY
NIGHT BUT WILL NEED TO WATCH THE NEXT COUPLE OF RUNS OF THE MODELS TO
MAKE SURE WE WON'T NEED ANYMORE HIGH WIND WARNINGS ALONG THE GULF
COAST.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...SYSTEM NOT QUITE PANNING OUT AS MODELS HAD
SUGGESTED THIS TIME YESTERDAY. WINDS ALONG THE COAST WERE NOT NEARLY
AS STRONG WITH THE INITIAL OCCLUSION TO MOVE INLAND OVERNIGHT. THREAT
STILL EXISTS FOR STORM FORCE WINDS OVER THE COASTAL WATERS AND HIGH
WIND WARNING WINDS THROUGH THE NORMAL CHANNELED TERRAIN LATER THIS
AFTERNOON THROUGH EARLY SATURDAY MORNING. HEAVY RAIN CONTINUES TO
FALL ACROSS THE NORTHWESTERN PRINCE WILLIAM SOUND AREA. COUPLED WITH
THE ELEVATED FREEZING LEVELS...WE ARE SEEING RIVERS RESPOND QUICKLY
THIS MORNING AND HAVE EXTENDED THE FLOOD ADVISORY FOR THE EASTERN
KENAI PENINSULA.

THE GULF LOW WILL WEAKEN AS IT MOVES ACROSS KACHEMAK BAY AND UP THE
INLET SUNDAY MORNING. THE DOWN-INLET PRESSURE GRADIENT WILL WEAKEN
AND ALLOW TURNAGAIN ARM WINDS TO FUNNEL THROUGH MUCH OF ANCHORAGE
SATURDAY...KNOCKING WHAT IS LEFT OF THE LEAVES OFF OF THE TREES. TOO
MUCH UNCERTAINTY REGARDING THE FORECAST SATURDAY NIGHT AND SUNDAY
MORNING BECAUSE OF THE TRACK OF THE LOW INTO THE NORTHERN GULF. WILL
HAVE TO GO WITH GENERAL WORDING TO KEEP THE CHANCE OF PRECIP IN THE
FORECAST FOR NOW BUT AGAIN...WILL NEED TO FINE TUNE THE NEXT COUPLE
OF FORECASTS AS THINGS BECOME MORE CLEAR.

EARLY NEXT WEEK...ANOTHER STRONG LOW WILL DEVELOP IN THE SOUTHERN
GULF BRINGING MORE RAIN AND WIND TO SOUTHCENTRAL.

SOUTHWEST ALASKA...
LARGE DEFORMATION ZONE ASSOCIATED WITH THE INITIAL OCCLUSION TO MOVE
ACROSS SOUTHCENTRAL IS NOW IN PLACE ACROSS SOUTHWEST ALASKA AND THE
ALASKA PENINSULA. THE RAIN AND SNOW THAT IS FALLING UNDER THIS
FEATURE IS GENERALLY LIGHT...BUT COULD BRING A FEW MORE INCHES TO THE
DELTA THIS EVENING BEFORE TAPERING OFF.

AS THE LOW MOVES INLAND OVERNIGHT...WINDS AT THE SURFACE BECOME LIGHT
WEST TO SOUTHWESTERLY. THE WEAK GRADIENT OVER THE REGION AND RECENT
PRECIPITATION SHOULD LEAD TO WIDESPREAD LOW STRATUS AND FOG
OVERNIGHT. SATURDAY...SOUTHWESTERLY WINDS INCREASE BRINGING MORE
CONVECTIVE SHOWERS BACK TO THE REGION WHICH MAY LAST THROUGH EARLY
NEXT WEEK AS THE BROAD AREA OF LOW PRESSURE SLOWLY SPINS AND WEAKENS
OVER BRISTOL BAY.

STRONG NORTHWESTERLY FLOW ACROSS MOST OF THE CENTRAL AND EASTERN
BERING SEA LEAD TO LOCAL GUSTY WINDS THROUGH THE ALASKA PENINSULA AND
EASTERN ALEUTIANS. THE LONG WAVE PATTERN MAKES VERY LITTLE PROGRESS
THROUGH EARLY NEXT WEEK SO EXPECTING MORE OF THE SAME FOR THIS
REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 125 135
         FLOOD ADVISORY 125
MARINE...STORM 120 129 130
         GALE 125 132 138 140 141 150 155 160 165 179 180
FIRE WEATHER...NONE.

AB SEP 10