Brisk Wind Advisory 62, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1245 PM AKST TUE DEC 9 2008

.ANALYSIS AND UPPER LEVELS...REX BLOCK IN PLACE OVER THE REGION
WITH A STRONG CLOSED UPPER HIGH CENTERED OVER THE BEAFORT SEA AND
A CLOSED LOW OVER THE SOUTHERN MAINLAND. THE UPPER LOW HAS DEVELOPED
MULTIPLE CENTERS THIS MORNING...PRIMARILY THE GULF LOW CENTER AND
A NEW CENTER OVER WESTERN ALASKA WHICH IS FORMING IN RESPONSE A
STRONG VORTICITY MAXIMUM RIDING ACROSS NORTHERN ALASKA ON THE
SOUTHERN PERIPHERY OF THE RIDGE. THE GULF LOW CONTINUES TO WEAKEN
AS IT TRACKS TOWARD SEWARD AND WINDS ARE NOW DIMINISHING RAPIDLY
ACROSS THE REGION. THE BULK OF THE PRECIPITATION WITH THIS LOW
REMAINS OVER THE PRINCE WILLIAM SOUND REGION FOR THE TIME BEING.
GUSTY NORTHWESTERLY FLOW AND SNOW SHOWERS DOMINATE THE BERING SEA
REGION AS COLD AIR ADVECTS FROM SIBERIA ACROSS THE BERING AND DOWN
THE BACK SIDE OF THE GULF LOW.

.MODEL DISCUSSION...MODELS INITIALIZED WELL AND AND ARE IN GOOD
AGREEMENT WITH SYNOPTIC FEATURES THROUGH FRIDAY. THERE IS ALSO
VERY GOOD RUN-TO-RUN CONSISTENCY SO FORECAST CONFIDENCE IS MODERATE.
THERE ARE SOME DIFFERENCES IN THE DETAILS OF TIMING AND PLACEMENT
WEAK UPPER TROUGHS SWINGING THROUGH THE SOUTHERN MAINLAND THE NEXT
COUPLE DAYS AND SMALL ADJUSTMENTS WILL BE MADE TO PRECIPITATION
FORECAST BASED ON LATEST MODEL GUIDANCE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE UPPER LOW CENTER FORMING OVER WESTERN
ALASKA WILL BECOME DOMINANT TONIGHT WHILE THE GULF LOW OPENS INTO
A TROUGH. THIS TROUGH WILL SWING NORTHWARD ACROSS SOUTHCENTRAL
ALONG WITH SURFACE LOW TONIGHT. AS THIS OCCURS FLOW WILL SHIFT
TO THE SOUTH MOVING THE AREA OF HEAVIEST PRECIPITATION TO THE
NORTHERN TO EASTERN SIDES OF PRINCE WILLIAM SOUND. AREAS IN THE
VICINITY OF THE LOW BACK OVER WESTERN SOUTHCENTRAL WILL ALSO SEE
SNOW OVERSPREAD THE AREA...BUT IT WILL BE LIGHT. SOME WEAK COLD
ADVECTION WILL OCCUR BEHIND THE UPPER TROUGH AND AID IN GENERATING
SNOW. ADDITIONAL WEAK UPPER TROUGHS WILL ROTATE FROM THE BERING
SEA ACROSS SOUTHCENTRAL THROUGH THURSDAY. STRONGER COLD ADVECTION
WILL COMMENCE WEDNESDAY AND CONTINUE THROUGH THURSDAY...HELPING TO
PRODUCE A PROLONGED LIGHT SNOW EVENT ACROSS SOUTHCENTRAL. SINCE
UPPER LEVEL DYNAMICS ARE FAIRLY WEAK EXPECT LIGHT ACCUMULATION
ACROSS MOST OF SOUTHCENTRAL. UPSLOPE AREAS RIGHT ALONG THE MOUNTAINS
WILL SEE HIGHEST AMOUNTS. NORTHEAST PRINCE WILLIAM SOUND CAN EXPECT
THE HEAVIEST TOTALS WITH LOTS OF MOISTURE IN PLACE AND UPSLOPE
FLOW...BUT LACK OF STRONG UPPER DYNAMICS WILL KEEP TOTALS BELOW
WARNING LEVELS. THE REGION WILL DRY OUT THURSDAY INTO THURSDAY NIGHT
AS A RIDGE BUILDS IN FROM THE WEST.

SOUTHWEST ALASKA...WEAK UPPER LEVEL WAVES WILL MOVE ACROSS SOUTHWEST
ALASKA THROUGH THURSDAY...BUT LOWER LEVELS ARE FAIRLY DRY.
THUS...EXPECT AREAS OF LIGHT SNOW OR FLURRIES. BEST CHANCE FOR
ACCUMULATING SNOW WILL BE IN UPSLOPE AREAS ALONG THE MOUNTAINS. A
FRONT FROM A STRONG WESTERN BERING LOW WILL MOVE TO SOUTHWEST ALASKA
THURSDAY NIGHT INTO FRIDAY...BRINGING STEADIER PRECIPITATION AND
WINDS ALONG THE COAST.

BERING SEA/ALEUTIANS...COLD ADVECTION SNOW SHOWERS WILL CONTINUE
ACROSS THE CENTRAL TO EASTERN BERING TONIGHT AND THEN GRADUALLY
DIMINISH WEDNESDAY AS FLOW THE UPPER TROUGH BEGINS TO LIFT AND
RIDGE BUILDS INTO THE WESTERN BERING. THERE IS POTENTIAL FOR
BLIZZARD CONDITIONS ON THE PRIBILOF ISLANDS LATE THIS AFTERNOON
THROUGH TONIGHT AS WINDS INCREASE. THERE IS CURRENTLY NOT MUCH SNOW
ON THE GROUND TO BLOW AROUND...BUT A LITTLE ADDITIONAL SNOW TO BLOW
AROUND WOULD ALLOW VISIBILITIES TO DROP TO NEAR ZERO. THIS WILL BE
RE-EVALUATED RIGHT BEFORE TH NEW FORECAST GOES OUT AT 4PM. THERE IS
NOW MUCH HIGHER CONFIDENCE IN FORECAST OF THE NEXT MAJOR SYSTEM
FORMING NEAR THE KAMCHATKA PENINSULA. EXPECT A STRONG FRONT TO
QUICKLY CROSS THE BERING SEA LATE WEDNESDAY THROUGH LATE THURSDAY
WITH THE LOW TRACKING ACROSS THE NORTHERN BERING TO NORTHWEST ALASKA
ON FRIDAY.

.LONG TERM FORECAST...MODELS ARE NOW VERY CONSISTENT IN INDICATING A
RIDGE BUILDING FROM THE EAST PACIFIC NORTHWARD TO MAINLAND ALASKA
THROUGH THE EXTENDED PERIOD. THIS WILL SET UP AN ACTIVE STORM TRACK
FROM KAMCHATKA TO NORTHERN ALASKA. SOME OF THESE SYSTEMS MAY AFFECT
MAINLAND ALASKA AS THEY MOVE OVER TOP OF THE RIDGE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...175 176.
         GALE WARNING...120 130 179 185.
         HEAVY FREEZING SPRAY WARNING...160 185.
FIRE WEATHER...NONE.

SEB DEC 08