Heavy Freezing Spray Warning 166, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST FRI DEC 2 2011

.ANALYSIS AND UPPER LEVELS...THE UPPER LEVEL PATTERN REMAINS WITH THE
LARGE RIDGE OVER THE EASTERN GULF UP TOWARD THE ALCAN BORDER AND LOW
EXTENDING OUT OF THE ARCTIC INTO THE WESTERN BERING SEA. IN BETWEEN
THESE FEATURES THERE IS A FAIRLY STRONG JET STREAM RUNNING FROM
SOUTHWEST TO NORTHEAST AND THEN CURVING EASTWARD OVER THE TOP OF THE
RIDGE. AS EXPECTED BOTH OF THESE FEATURES ARE AMPLIFYING WITH THE
RIDGE BECOMING MORE NARROW AND PUSHING NORTHWARD AS THE TROUGH
BECOMES STRONGER AND DIGS FARTHER SOUTH AND EAST. THIS AMPLIFICATION
WILL CAUSE THE JET STREAM TO BECOME MORE SOUTH TO NORTH ORIENTATED
AND INCREASE IN STRENGTH.

.MODEL DISCUSSION...AFTER A NUMBER OF DAYS WITH THE MODELS STRUGGLING
THEY HAVE CONVERGED ON A COMMON AND CONSISTENT SOLUTION WITH THE
LARGE LOW MOVING THROUGH THE BERING SEA. OTHER MAJOR FEATURES LOOS TO
BE HANDLED WELL ALSO. THE ONLY DIFFERENCE THAT WILL MAKE AN IMPACT ON
THE FORECAST IS ON SUNDAY WITH THE FRONTAL PASSAGE OVER SOUTH CENTRAL
ALASKA. AT THAT TIME THE NAM AND ECMWF ARE FASTER IN BRINGING THROUGH
THE COLD AIR WHILE THE GFS DELAYS IT SOME. THIS IS NOT A HUGE
DIFFERENCE BUT IT WILL BE THE DIFFERENCE WITH RAIN TURNING TO SNOW
DURING THE AFTERNOON SUNDAY OR THE CHANGE NOT OCCURRING UNTIL
OVERNIGHT.

.SHORT TERM FORECAST...BIG WARM UP IS RUNNING ON SCHEDULE WITH THE
SURGE MOVING INTO SOUTHWEST ALASKA TONIGHT AND INTO SOUTH CENTRAL
ALASKA TOMORROW. PRECIPITATION TYPE THROUGH TOMORROW AFTERNOON
CONTINUES TO BE DIFFICULT IN SOUTH CENTRAL. WHAT IS FAIRLY CERTAIN IS
THAT WINDS WILL INCREASE TO HIGH WIND WARNING LEVELS IN TURNAGAIN ARM
AND HIGHER ELEVATIONS AROUND ANCHORAGE THROUGH THE MATANUSKA VALLEY.
WINDS WILL ALSO BECOME SOUTHEAST DURING THE AFTERNOON TOMORROW IN
THOSE AREAS WHICH WILL BRING TEMPERATURES INTO THE 40S IN MANY
PLACES. WINDS IN THE ANCHORAGE BOWL AND MATSU VALLEY WILL ALSO BE
SIGNIFICANT WITH SOUTHEAST WINDS GUSTING IN THE 45 TO 60 MPH RANGE
ARE POSSIBLE SATURDAY AFTERNOON INTO SUNDAY MORNING. THE HIGHEST
WINDS WILL STILL BE ALONG TURNAGAIN ARM AND AT HIGHER ELEVATIONS.
THE OTHER CONCERN IS FOR FREEZING RAIN IN THE ANCHORAGE AREA TOMORROW
EARLY MORNING WITH THE INITIAL SHORT WAVE THAT GOES THROUGH BEFORE
THE MAIN PUSH OF PRECIPITATION AROUND MIDDAY. THE LATEST DATA SHOWS
AN INCREASED CHANCE OF FREEZING RAIN DEVELOPING IN THE EARLY STAGES
OF THE MAIN PRECIPITATION IN ANCHORAGE IN THE LATE MORNING THROUGH
EARLY AFTERNOON. THE LATEST MODEL DATA SHOWS WINDS REMAINING
NORTHEAST IN TOWN INTO EARLY AFTERNOON WHICH WOULD KEEP TEMPERATURES
BELOW FREEZING DURING THE BEGINNING OF THE PRECIPITATION WHICH WOULD
FALL AS FREEZING RAIN. THIS SHOULD BE WATCHED AS IT COULD DEVELOP
INTO A TRAVEL HAZARD IN ANCHORAGE AND INTO THE MATSU VALLEY.

THE PRINCE WILLIAM SOUND AREA WILL BE ALL RAIN WITH THE POSSIBLE
EXCEPTION OF VALDEZ. RECENT MODEL RUNS HAVE TEMPERATURES THERE COOLER
THAN PREVIOUS RUNS WHICH OPENS UP THE POSSIBILITY OF PRECIPITATION
REMAINING MOSTLY SNOW OR REMAINING SNOW LONGER THAN PREVIOUSLY
EXPECTED. IF IT DOES REMAIN SNOW IT WILL BE A SIGNIFICANT SNOWFALL
EVEN FOR VALDEZ STANDARDS.

.LONG TERM FORECAST...COLD AIR WILL WILL MOVE BACK INTO SOUTHWEST
ALASKA SATURDAY NIGHT INTO SUNDAY AND THEN SWEEP INTO SOUTH CENTRAL
ALASKA SUNDAY EVENING. ANOTHER LESS SIGNIFICANT WARM UP COULD OCCUR
DURING THE MIDDLE OF NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101. WINTER STORM WATCH 145.
MARINE...GALE 130 132 150 155 160 165 170 172 175 176 180.
         STORM 179 185.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

DEC 11