Snow Advisory 24, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AST FRI DEC 7 2007

.ANALYSIS AND UPPER LEVELS...
CURRENTLY A STRONG UPPER LOW AND TROUGH IS SUPPORTING THE STRONG
SURFACE LOW NOW MOVING ACROSS THE CENTRAL ALASKA PENINSULA. AN UPPER
LEVEL RIDGE OF HIGH PRESSURE EXTENDS ALONG THE EASTERN GULF OF ALASKA
INTO THE YAKUTAT AREA WITH A WEAK SURFACE LOW OVER PRINCE WILLIAM
SOUND THAT IS DISSIPATING AS IT IS FORCED NORTH ACROSS THE CHUGACH
MOUNTAINS. THE 110 KT JET STREAM FLOWS FROM SOUTHWEST TO NORTHEAST
INTO THE INTERIOR OF ALASKA. THIS WILL CONTINUE TO FUEL NUMEROUS
AREAS OF LOW PRESSURE WHICH FORM SOUTH OF THE ALEUTIANS AND MOVE
NORTH INTO THE EASTERN BERING SEA AND WESTERN MAINLAND ALASKA THE
NEXT SEVERAL DAYS. THIS WILL CONTINUE TO PUMP LOTS OF WARM AIR NORTH
FROM THE TROPICS INTO THE ALASKA MAINLAND.

.MODEL DISCUSSION...
THE CURRENT GFS HAS A GOOD HANDLE ON THE ALASKA PENINSULA LOW AND ITS
TRAJECTORY NORTH NORTHEAST AND THE WESTERN ALEUTIAN LOW AND THE
DEVELOPING TRIPLE POINT SOUTH OF SEGUAM ISLAND. THE LONGER TERM
SOLUTIONS ARE STILL SUSPECT AS MODEL RUN TO RUN CONSISTENCY IS NOT AS
GOOD BUT GENERALLY THE SOLUTIONS ARE SIMILAR CONSIDERING THE HIGHLY
ACTIVE WEATHER PATTERN. THE PRIMARY ISSUE IN THE LOG TERM IS WHETHER
THE LOW WILL BE ONE LARGE STRONG LOW ORE SEVERAL SMALLER WEAKER LOWS.

.SHORT TERM FORECAST...
THE WEAK LOW NOW OVER PRINCE WILLIAM SOUND WILL DISSPATE AS IT MOVES
NORTH. THE INCOMING FRONT ASSOCIATED WITH THE AK PENINSULA LOW IS
SPREADING WARM AIR CLOUDS AND MOISTURE INTO SOUTH CENTRAL ALASKA.
THE LOW CROSSING THE ALASKA PENINSULA WILL MOVE INTO THE KUSKOKWIM
DELTA LATE TONIGHT. THIS WILL MOVE THE PRECIPITATION INTO THE DELTA
FASTER THAN THE MORNING FORECAST HAD INDICATED AND WILL BE REFLECTED
IN THIS AFTERNOONS FOERCAST PACKAGE. THE LOW WILL PUSH NORTH WITH THE
TRAILING SURFACE TROUGH REMAINING OVER THE REGION SATURDAY. THEREFORE
WE EXPECT SNOW TO BE LIKELY THORUGH SATURDAY OVER SOUTHWEST ALASKA.

SNOW AND RAIN WILL CHANGE TO RAIN OVER KODIAK ISLAND AS THE WARM AIR
MOVES IN THROUGH THIS AFTERNOON AND EVENING. WE EXPECT WARMER AIR TO
MOVE INTO THE SOUND RESULTING IN A MIXTURE OF RAIN AND SNOW FOR THE
REGION THROUGH SAT EVENING. THE FLOW ALOFT REMAINS SOUTH TO SOUTHWEST
WHICH SUPPORTS CONTINUED PRECIPITATION FOR THE VALDEZ TO THOMPSON
PASS AREA THROUGH SATURDAY.

EXPECT THE STRONG GAP WINDS ACROSS THE CHUGACH MOUNTAINS TONGIHT
THROUGH SATURDAY AS THE LOW MOVES NORTH ALONG THE BERING COAST. AS IS
USUAL EXPECT THE DOWN SLOPE FLOW ACROSS THE CHUGACH TO LIMIT
PRECIPITATION ALONG THE EAST SIDE OF COOK INLET TO THE PALMER REGION.
AS THE FLOW ALOFT BECOMES MORE SOUTHERLY TONIGHT AND SATURDAY EXPECT
SNOW IN THE NORTHER SUSITNA VALLEY TO BECOME HEAVIER AND WE MAY NEED
TO ISSUE AN ADVISORY FOR THE AREA FROM CHULITNA NORTH.

BERING SEA/ALEUTIANS...
THE MAIN ISSUE IS THE LOW NEAR ADAK WITH ANOTHER CENTER TO THE SOUTH
OF SEGUAM ISLAND WITH A WEAK RIDGE BETWEEN THESE LOW AND THE AK
PENINSULA LOW. WE EXPECT RAIN AND SNOW TO ERSUE OVER THE EASTERN
ALEUTIANS THIS EVENING AND CONTINUE SATURDAY. THE LOW SOUTH OF THE
CHAIN IS EXPECTED TO PRODUCE STORM FORCE WINDS OVER THE ALEUTIANS AS
IT CORSSES THEM TONIGHT. OTHERWISE EXPECT A CONTINUATION OF THE TREND
OF LOWS TO MOVE THROUGH THE WEEKEND.

.LONG TERM FORECAST...
SIMILAR WEATHER PATTERN TO CONTINUE THROUGH THE EARLY PART OF NEXT
WEEK. THE MODELS ARE STARTING TO ADVERTISE A TRANSITION BACK TO A
COLDER PATTERN BY WEDNESDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING ZONES 130 132 138 170.
         GALE WARNING ZONES 120 125 132 140 150 155 160 171 172
         351 352.
FIRE WEATHER...NONE.

SAM DEC 07