Gale Warning 140, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKST THU FEB 11 2010

.ANALYSIS AND UPPER LEVELS...
A LARGE UPPER LEVEL RIDGE EXTENDS NORTH FROM THE WEST COAST OF THE
US...THROUGH WESTERN CANADA...AND INTO THE BEAUFORT SEA. SOUTHERLY
WINDS ON THE UPSTREAM SIDE OF THE RIDGE CONTINUE TO FEED WARM GULF
AIR UP INTO MUCH OF MAINLAND ALASKA. OUT WEST...A LARGE UPPER LEVEL
TROUGH ORIGINATING FROM A LOW IN SIBERIA IS DRAPED ACROSS MUCH OF THE
BERING SEA...THE ALEUTIANS...AND THE SOUTHERN GULF OF ALASKA. A
NUMBER OF WEAK UPPER LEVEL SHORTWAVES ARE ROTATING UP AND AROUND THIS
TROUGH.

AT THE SURFACE...A SERIES OF SURFACE LOWS ARE TRAINING AROUND THE
UPPER LEVEL TROUGH ACROSS THE NORTH PACIFIC. A 965MB LOW IS ROTATING
INTO THE GULF AND STARTING TO SPREAD SHOWERS ACROSS THE NORTHERN GULF
WHILE A SECOND 974MB LOW IS MOVING WESTWARD NEAR THE PRIBILOF
ISLANDS.

.MODEL DISCUSSION...
MODELS IN GENERAL ARE IN GOOD AGREEMENT THROUGH THE SHORT
TERM...ALTHOUGH THE GFS IS SLIGHTLY STRONGER WITH THE CURRENT LOW IN
THE GULF. MODELS ARE GRADUALLY CONVERGING ON A SOLUTION FOR THE TRACK
OF THE LOW NEAR THE PRIBILOFS...WITH THE ECMWF ALIGNING MORE WITH THE
GFS AND NAM. HOWEVER...AS THE LOW DEVOLVES INTO A SHORTWAVE
TOMORROW...THE MODELS BEGIN TO DIVERGE WITH REGARDS TO THE TRACK AND
STRENGTH OF THE RESIDUAL SHORTWAVE. SOME PROBLEMS BEGIN TO ARISE WITH
THE NEXT LOW MOVING INTO THE GULF OVER THE WEEKEND...WITH THE NAM
BEING THE ONLY MODEL SPLITTING THIS SYSTEM INTO A DOUBLE BARREL LOW.
BY SUNDAY THE ECMWF LOW LAGS A GOOD 12 HOURS BEHIND THE GFS...AND THE
MODELS CONTINUE TO DIVERGE INTO NEXT WEEK. THE GFS WAS THE MODEL OF
CHOICE IN THE SHORT TERM. HOWEVER...THE DEPICTION OF A DOUBLE BARREL
LOW IN THE GULF OVER THE WEEKEND SEEMS MORE REALISTIC...THUS A BLEND
TOWARDS THE NAM WAS USED FURTHER OUT.

.SHORT TERM FORECAST...

.SOUTHCENTRAL...THE NEXT ROUND OF PRECIPITATION FOR THE GULF COAST IS
ALREADY VISIBLE ON THE MIDDLETON ISLAND RADAR AND SHOULD MOVE ONSHORE
LATER THIS EVENING IN ASSOCIATION WITH THE GULF LOW. EASTERLY
DOWNSLOPING FLOW SHOULD HELP ANCHORAGE AND REGIONS WEST AND NORTH OF
THE CHUGACH REMAIN RELATIVELY DRY...THOUGH A STRAY SNOW SHOWER CANNOT
BE RULED OUT. THUS WIDESPREAD PRECIPITATION SHOULD MOSTLY BE CONFINED
TO UPSLOPE REGIONS OF THE KENAI PENINSULA AND THE NORTH CENTRAL GULF
COAST. THE WARM AIR MASS CURRENTLY OVER THE REGION WILL RESULT IN A
RAIN EVENT FOR THE GULF COAST...WITH SNOW AT HIGHER ELEVATIONS. THE
BIGGEST IMPACT THIS SYSTEM WILL HAVE IS STRONG GUSTY WINDS THROUGH
BAYS AND PASSES...SUCH AS TURNAGAIN ARM AND THE PORTAGE PASS. THE LOW
WILL TURN WEST TOMORROW AND REMAIN WELL SOUTH OF THE GULF COAST.

.SOUTHWEST...MOSTLY CLOUDY SKIES SHOULD REMAIN IN PLACE TODAY AS A
LOW NEAR THE PRIBILOF ISLANDS CONTINUES TO TRACK WEST AND WEAKEN.
WINDS SHOULD TURN MORE NORTHERLY IN ADVANCE OF THE LOW MOVING UP IN
THE GULF AND HELP USHER IN A SLIGHTLY COLDER AIR MASS. THE NEXT SHOT
OF PRECIPITATION WILL BE OVER THE WEEKEND AS THE GULF LOW TRACKS
ACROSS THE AKPEN AND INTO BRISTOL BAY.

.ALEUTIANS...GALE FORCE WINDS CAN BE EXPECTED IN THE CENTRAL BERING
OUT AHEAD OF THE RETROGRADING LOW NEAR THE PRIBILOFS. ISOLATED
SHOWERS WILL PERSIST ACROSS THE ISLAND CHAIN AS WEAK SHORTWAVES
ROTATE AROUND THE UPPER LEVEL TROUGH FIRMLY ENTRENCHED OVER THE AREA.
SNOW SHOWERS ARE MORE LIKELY OVER THE EASTERN ALEUTIANS AND THE AKPEN
AS THE GULF LOW PULLS DOWN COLDER MAINLAND AIR OVER THE SOUTHEAST
BERING.

.LONG TERM FORECAST...
NO REAL CHANGES IN STORE FOR THE UPCOMING WEEK...WITH THE UPPER LEVEL
HIGH PRESSURE RIDGE REMAINING MORE OR LESS STATIONARY OVER WESTERN
CANADA WHILE A PARADE OF SHORTWAVES WRAP AROUND THE TROUGH OVER THE
BERING AND SOUTHERN GULF.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 125 132 140 150 172 175.
         STORM WARNING...130 138.
FIRE WEATHER...NONE.

KS FEB 10