Heavy Freezing Spray Warning 169, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1235 PM AKDT THU MAY 3 2012

.ANALYSIS AND UPPER LEVELS...A COLD UPPER LEVEL LOW OVER FAR
NORTHWESTERN ALASKA IS JUST BEGINNING TO DIVE SOUTHWARD TOWARD
THE NORTHERN BERING SEA. CYCLONIC CIRCULATION AROUND THIS LOW
EXTENDS ALL THE WAY SOUTH TO BRISTOL BAY AND THE NORTHERN GULF.
FAST WESTERLIES DOMINATE THE FLOW JUST TO THE SOUTH OF HERE WITH
THE UPPER JET PARALLELING THE ALEUTIANS BEFORE DIPPING SOUTHWARD
INTO THE NORTHEAST PACIFIC. THE PRIMARY PRECIPITATION PRODUCER IN
THE REGION IS A STRONG SHORT-WAVE WHICH IS TRACKING FROM THE
EASTERN BERING ACROSS THE ALASKA PENINSULA INTO THE SOUTHWEST GULF.
A SURFACE LOW IS LOCATED UNDERNEATH THIS WAVE AND IS TAKING A
SIMILAR TRACK. STEADY SNOW IS FALLING OVER EASTERN PORTIONS OF
BRISTOL BAY WITH RAIN ALONG THE ALASKA PENINSULA AND KODIAK ISLAND.
ELSEWHERE ACROSS THE FORECAST AREA WEAK FEATURES ARE PRODUCING A
FEW SHOWERS...BUT CONDITIONS ARE GENERALLY BENIGN.

.MODEL DISCUSSION...MODELS AGREE ON THE BASIC SYNOPTIC EVOLUTION
OVER THE NEXT FEW DAYS BUT DISAGREE ON THE POSITIONS AND STRENGTH
OF TWO KEY SURFACE LOWS. THE FIRST LOW IS THE ONE WHICH FORMS NEAR
THE SOUTHERN END OF THE ALASKA PENINSULA ON SATURDAY IN RESPONSE
TO DIVING UPPER LOW AND THE ARCTIC AIR WHICH WILL ACCOMPANY IT. THE
SECOND IS A LOW THAT DEVELOPS OVER THE NORTHEAST PACIFIC ALONG THE
UPPER JET AND AHEAD OF THE DIGGING TROUGH SATURDAY AND MOVES INTO
THE GULF SUNDAY. THERE IS A TREND TOWARD STRONGER LOWS...BUT
OTHERWISE NONE OF THE MODELS SHOW VERY GOOD RUN-TO-RUN CONSISTENCY.
THEREFORE....FOR NOW WILL USE A MODEL BLEND TO GET AN AVERAGE
POSITION AND TREND TOWARD STRONGER WINDS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE SHORT-WAVE AND SURFACE LOW ALONG THE
ALASKA PENINSULA WILL TRACK TO THE EASTERN GULF TONIGHT AND FRIDAY
WITH THE BULK OF PRECIP REMAINING DOWN OVER THE GULF AND KODIAK
ISLAND. THE 12Z ANCHORAGE SOUNDING SHOWS TEMPERATURES ALOFT ARE
STILL VERY COLD. THEREFORE...THE LITTLE BIT OF SUN THAT DOES POKE
THROUGH THE CLOUDS WILL PROVIDE ENOUGH HEATING TO TRIGGER A FEW
AFTERNOON AND EVENING SHOWERS ACROSS SOUTHCENTRAL TODAY AND
FRIDAY...ESPECIALLY OVER THE MOUNTAINS. THE REMNANTS OF THE TROUGH
OVER THE GULF WILL LIFT NORTHWARD FRIDAY NIGHT AND SATURDAY PROVIDING
MORE WIDESPREAD RAIN OR SHOWERS ALONG THE COAST AND AN INCREASED
CHANCE OF SHOWERS INLAND. EVEN WITH THE MORE FOCUSED LIFT FROM THIS
TROUGH STILL EXPECT SOME BREAKS OF SUN EACH DAY FOR INLAND LOCATIONS.

IT IS LOOKING MORE AND MORE LIKELY THAT A STRONG LOW WILL MOVE INTO
THE GULF SUNDAY BRINGING LOTS OF WIND AND RAIN TO THE GULF
COAST...ALTHOUGH THE DETAILS OF THIS ARE STILL A LITTLE UNCLEAR.

SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...THE SYSTEM ALONG THE ALASKA
PENINSULA WILL EXIT TO THE GULF TONIGHT. YET ANOTHER SHOT OF ARCTIC
AIR WILL THEN USHER SOUTHWARD WITH THE UPPER LEVEL LOW TONIGHT
THROUGH SATURDAY. SINCE THE LOW MOVING INTO THE GULF IS QUITE WEAK
THE SURFACE PRESSURE GRADIENT BETWEEN IT AND HIGH PRESSURE OVER THE
NORTHWEST PACIFIC AND FAR WESTERN BERING SEA WILL NOT BE VERY TIGHT.
THIS MEANS WINDS WILL BE A LOT LESS THAN ONE WOULD NORMALLY EXPECT
WITH THIS TYPE OF COLD ADVECTION. GUSTY NORTHERLIES AND SNOW SHOWERS
CAN STILL BE EXPECTED. AS THE UPPER LOW BOTTOMS OUT ON SATURDAY A
SURFACE LOW WILL DEVELOP NEAR THE SOUTHERN END OF THE ALASKA
PENINSULA. THIS WILL RESULT IN STRONGER WINDS AND STEADIER PRECIP
ALONG THE ALASKA PENINSULA AND EASTERN ALEUTIANS.

.LONG TERM FORECAST...MEDIUM RANGE MODELS SHOW THE SAME EVOLUTION
IN LARGE SCALE FLOW NEXT WEEK BUT DO NOT AGREE ON THE MOVEMENT OF
INDIVIDUAL SYSTEMS WITHIN THIS FLOW. THE LARGE UPPER LEVEL CLOSED
LOW IN PLACE OVER THE SOUTHERN GULF AT THE BEGINNING OF THE WEEK
WILL KICK EASTWARD INTO CANADA BY MID WEEK AS ANOTHER TROUGH DROPS
SOUTHWARD ACROSS THE BERING. MODELS INDICATE THIS TROUGH WILL DIG
SOUTHEASTWARD TOWARD THE GULF BY THE END OF THE WEEK...POSSIBLY
DEVELOPING ANOTHER CUT-OFF LOW. THIS PATTERN WILL KEEP THE UPPER
LEVEL JET AND PRIMARY STORM TRACK FROM THE PACIFIC TO THE GULF.
STEADY PRECIP WILL CONTINUE TO BE CONFINED TO THE GULF COAST WITH
DIURNAL SHOWERS THE NORM FOR INLAND LOCATIONS. THE BERING
SEA/ALEUTIANS/SOUTHWEST ALASKA WILL ALL REMAIN ON THE COLD SIDE
FOR THIS TIME OF YEAR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY ZONE 152 KUSKOKWIM RIVER NEAR SLEETMUTE.
         FLOOD WATCH ZONE 152 KUSKOKWIM RIVER NEAR RED DEVIL.
MARINE...HEAVY FREEZING SPRAY...160 179 180.
FIRE WEATHER...NONE.

SEB MAY 12