Heavy Freezing Spray Warning 183, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST THU NOV 15 2012

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL TROUGH LIES PARKED OVER SOUTHERN ALASKA THIS MORNING.
WITHIN THE LONG-WAVE TROUGH ARE A NUMBER OF SHORTWAVE TROUGHS OF
VARYING STRENGTH. A FILLING SURFACE/UPPER LOW SPINS OVER THE NORTHERN
GULF BRINGING RAIN AND SNOW SHOWERS TO THE NORTHERN GULF COAST. THERE
ARE TWO POTENT DISTURBANCES ROTATING AROUND THE BACKSIDE OF THE
LONG-WAVE. THE MAIN EFFECT ON SENSIBLE WEATHER WILL BE INCREASINGLY
GUSTY NORTHERLY WINDS AS COLD ADVECTION SETS IN BEHIND THE DEPARTING
SHORTWAVES. WHILE THE PRESSURE GRADIENT WILL REMAIN TIGHTENED THESE
DISTURBANCES WILL ONLY ACT TO REINFORCE THE GENERAL CYCLONIC
CIRCULATION IN THE GULF OF ALASKA. A CLOSED OFF UPPER RIDGE SITS OVER
SIBERIA WHILE A POTENT KAMCHATKA LOW MOVES INTO THE FAR WESTERN
BERING FROM THE SOUTH.

.MODEL DISCUSSION...
GUIDANCE IN PRETTY GOOD AGREEMENT SYNOPTICALLY SPEAKING LIKELY DUE TO
A SOMEWHAT BLOCKY TYPE PATTERN WITH CLOSED HIGH OVER SIBERIA AND
UPPER LOW TO THE SOUTHWEST OVER KAMCHATKA. THE SIBERIAN HIGH KEEPS
THE SOUTHWESTERLY FLOW FROM PROGRESSING TOO FAR INTO THE BERING SEA
WHILE THE MAINLAND TROUGHING STAYS IN PLACE AS LOWS FILL IN THE GULF
OF ALASKA.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...STEADY RAIN AND SNOW MAINLY ALONG THE NORTHERN
GULF COAST WILL PERSIST TODAY AS THE SURFACE/UPPER LOW SLOWLY DECAY.
A NEW SURFACE LOW CENTER WILL DEVELOP AS A SHORTWAVE ROUNDS THE BASE
OF THE TROUGH...SHIFTING THE FOCUS FOR PRECIPITATION TO THE EASTERN
GULF. SHOWERS WILL DIMINISH TONIGHT AS THE UPPER TROUGH SHIFTS
SOUTHWARD USHERING IN A COLDER AIR MASS ALOFT INTO THIS WEEKEND. THE
RESPONSE TO THE COLD AIR SPILLING OVER THE ALASKA RANGE WILL BE AN
INCREASE IN OUTFLOW/GAP TYPE WINDS ALONG THE FAVORED REGIONS OF THE
NORTHERN GULF COAST...THOMPSON PASS...COPPER RIVER
DELTA...VALDEZ...AS WELL AS THE MATANUSKA VALLEY AND SEWARD/WHITTIER.
DECREASING PRECIPITATION AND CLOUD COVER FOR MOST LOCATIONS THE REST
OF THE WEEK FOLLOWED BY COOLER TEMPERATURES AND HIGHER WINDS.

SOUTHWEST ALASKA...THE BRISTOL BAY SHORTWAVE CONTINUES TO DROP SOUTH
THIS MORNING LEAVING ONE LAST SHOT OF SNOW TO MAINLY THE COASTAL
AREAS OF BRISTOL BAY. BEHIND THE WAVE...COLD NORTHERLY FLOW WILL MIX
DOWN GUSTY WINDS FROM ALOFT THROUGH THE REST OF THE WEEK. COLDER
TEMPERATURES WILL RETURN THROUGH THE WEEKEND.

BERING SEA AND ALEUTAINS...COLD NORTHERLY FLOW WILL PROMOTE SNOW
SHOWERS OVER THE CENTRAL AND EASTERN ALEUTIANS AS WELL AS GUSTY WINDS
TODAY. A KAMCHATKA LOW WILL SWING A FRONT FROM THE WESTERN ALEUTIANS
TO THE CENTRAL ALEUTIANS BY FRIDAY MORNING.

.LONG TERM FORECAST...
THE EXTENDED PATTERN LOOKS FAIRLY SIMILAR TO THE LONGWAVE PATTERN
ALREADY IN PLACE. UPPER LOW/TROUGHING OVER THE GULF OF ALASKA AND
SOUTHERN MAINLAND WITH A WEAK RIDGE OVER THE BERING SEA AND KAMCHATKA
LOW TO THE WEST. EXPECT CONDITIONS NOT UNLIKE THE CURRENT SITUATION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORM 155 185
         GALE 127 128 130 132 150 160 165 170 176 180
         HEAVY FREEZING SPRAY 160 180
FIRE WEATHER...NONE

MTL NOV 12