Gale Warning 870, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTH CENTRAL AND SOUTHWEST ALASKA
200 PM AST MON NOV 19 2007

.MODEL DISCUSSION AND ANALYSIS...
THE CURRENT SURFACE ANALYSIS HAS A WEAK LOW OVER THE NORTHERN KENAI
PENINSULA THAT IS SLOWLY DISSIPATING AS THE NEXT BIG STORM IS
APPROACHING THE ALASKA PENINSULA FROM THE SOUTH. A WEAK RIDGE OF HIGH
PRESSURE EXTENDS INTO THE CENTRAL TO WESTERN ALEUTIANS AS ANOTHER
LARGE STRONG LOW MOVES INTO THE EXTREME WESTERN ALEUTIANS.

OVERALL THE MODELS ARE IN GOOD AGREEMENT THROUGH WED. BEYOND WED SOME
UNCERTAINTY EXISTS AS THE ENSEMBLE SOLUTIONS DIVERGE AFTER WED.

THE GFS MODEL HAS REMAINED CONSISTENT IN ITS SOLUTION IN THE SHORT
TERM THROUGH WED AFTERNOON. IT STILL HAS ISSUES WITH RESOLVING THE
INTENSITY AND LOCATION OF THE NEXT STORM THAT IS MOVING TOWARD THE
ALASKA PENINSULA FROM THE SOUTH WED NIGHT AND THU. THIS WILL IMPACT
THE FORECAST SOLUTION. AT THIS TIME WE WILL TEND TO LEAN TO THE
LATEST NAM AND ECMWF MODEL SOLUTIONS BEGINNING WED NIGHT THAT RESULTS
IN A WEAKER LOW AND A MORE EAST SOLUTION IN THE PLACEMENT OF THE LOW
WED NIGHT.

.SHORT TERM FORECAST...THE MAIN CONCERN AT THIS TIME IN THE SOUTHWEST
IS THE BRISTOL BAY ZONE. WE EXPECT THE ONSET OF THIS EVENT TO BEGIN
AS A GOOD OVER RUNNING SNOW FALL COUPLED WITH NODERATE NORTHEAST WIND
BEFORE THE WARM AIR MIXES IN FROM THE SOUTH AS THE FRONT PUSHES
NORTH. THIS PRESENTS THE POTENTIAL FOR A BLIZZARD IN THE ZONE IF THE
WIND AND SNOW COINCIDE BEFORE THE ANTICIPATED WARMING. PRECIPITATION
HAS ALREADY BEGUN IN KODIAK IN THE FORM OF RAIN AND SNOW.
TEMPERATURES ARE RISING IN THE BRISTOL BAY ZONE WHICH IS CAUSING US
TO LEAN TO A MORE RAPID INFLUX OF WARM AIR AND THUS IF ANY BLIZZARD
CONDITIONS OCCUR, THEY WILL BE BRIEF AND INCONSEQUENTIAL. WE ARE
LEANING AWAY FROM FREEZING RAIN FOR THIS ZONE AS WE ANTICIPATE
CONDITIONS TO BE WELL MIXED WITH THE EXPECTED STRONG WIND REGIME AND
WARM ADVECTION IN ADVANCE OF AND WITH THE INCOMING FRONT TO REMOVE
THE THREAT OF THE FREEZING RAIN. IF IT DOES OCCUR, WE EXPECT IT TO BE
SPOTTY AND EXTREMELY LIGHT.

OVER SOUTH CENTRAL ALASKA AN IN PARTICULAR PRINCE WILLIAM SOUND THE
FIRST MAJOR QUESTION CONCERNS THE TIMING OF A CHANGE OVER FROM SNOW
TO RAIN. EXPECT HEAVY SNOW INITIALLY IN WESTERN PRINCE WILLIAM SOUND
ACROSS TURNAGAIN ARM INTO TURNAGAIN PASS PRIOR TO THE CHANGE OVER TO
RAIN. THE HEAVY SNOWFALL AND RAPIDLY INCREASING WIND PRESENTS THE
PROBLEM OF BRIEF BLIZZARD CONDITIONS IN EASTERN TURNAGAIN ARM AND
PORTAGE VALLEY TONIGHT. WE DO NOT EXPECT THIS TO BE A WARNING EVENT
SINCE THE DURATION OF THE BLIZZARD CONDITIONS WILL LIKELY BE AN HOUR
OR TWO IF AT ALL BEFORE THE WARM AIR CHANGES THE SEA LEVEL
PRECIPITATION TO RAIN OR A RAIN SNOW MIX TUE MORNING. CURRENT
TEMPERATURES ARE ALREADY ABOVE FREEZING ON THE SOUND SIDE.

FURTHER WEST TO THE ALASKA PENINSULA WE WILL HAVE TO WATCH FOR
REDUCED VISIBILITY IN SNOW SHOWERS AND STRONG NORTHERLY WINDS. EXPECT
LOCALIZED SHORT DURATION BLIZZARD LIKE CONDITIONS ON THE PENINSULA IN
THIS NORTHERLY FLOW PATTERN THROUGH TUESDAY.

HEAVY SNOW IS EXPECTED TO SPREAD INTO THE WESTERN SUSITNA VALLEY
BEGINNING LATE TONIGHT AS UPSLOPE FLOW INCREASES. WE ARE CONTINUING
WITH THE SNOW ADVISORY TO BEGIN TONIGHT INTO TUESDAY. WE ANTICIPATE
RAPID WARMING OF THE AIRMASS TO INHIBIT THE MAGNITUDE OF THIS SNOW
EVENT BEFORE MIXING WITH OR CHANGING TO RAIN AS WARM AIR SURGES
NORTHWARD. SNOWFALL TOTALS THROUGH THOMPSON PASS MAY ALSO BE VERY
HIGH WITH THE RAPID INFLOW OF WARM AIR LIMITING THE SNOW FALL FOR
THIS AREA TUESDAY.

THE NORTHERLY PUSH OF THIS INTENSE STORM WILL BRING WITH IT A GOOD
CHINOOK EVENT ACROSS THE SOUTH CENTRAL REGION BY WED RESULTING IN
CONSIDERABLE WARMING. ON THE FLIP SIDE OF THIS PERSISTENT NORTHERLY
FLOW OVER THE EASTERN BERING WILL KEEP WESTERN ALASKA IN THE COLD
WINTER FLOW AND HELP THE ICE EDGE MOVE SOUTH.

.LONG TERM FORECAST...
THE MODELS REMAIN DIVERGENT AND THUS CONFIDENCE IN ANY LONG TERM
SOLUTION IS MINIMAL. WE WILL CONTINUE ALONG WITH FORECASTS CLOSE TO
THE CLIMATE NORMALS FOR THIS TIME OF YEAR UNTIL WE GET MORE
CONSISTENT SOLUTIONS FROM THE LONGER TERM MODELS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM 120 155 176 351 352.
         GALE 125 130 132 138 140 141 150 160 165 170 175 411 413.
         HEAVY FREEZING SPRAY 180.
FIRE WEATHER...DONE.

SAM