Gale Warning 1092, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKST TUE DEC 28 2010

.ANALYSIS...
THE PATTERN CHANGE IS UNDER WAY. THE TROUGH AXIS THAT HAS BEEN
STATIONARY OVER CENTRAL ALASKA IS SHIFTING EAST...CURRENTLY LOCATED
ALONG THE ALCAN BORDER. THE NEW DOMINANT TROUGH IS DIGGING OVER THE
WESTERN BERING SEA WHILE A LARGE PLUME OF MOISTURE IS STREAMING
NORTHWARD RIDING THE 145 KT JET. AT THE SURFACE...A 963 MB LOW SOUTH
OF THE WESTERN ALEUTIANS IS DRIFTING EAST WHILE THE ASSOCIATED
FRONTAL BOUNDARY EXTENDS EAST ALONG THE ALEUTIAN CHAIN. TWO WEAKER
VERTICALLY STACKED LOWS CONTINUE TO WEAKEN IN THE GULF AS THEY DRIFT
EAST TOWARD THE PANHANDLE.

.MODEL DISCUSSION...
THE NAM AND GFS INITIALIZE POORLY ON THE LARGE BAROCLINIC LEAF ACROSS
THE NORTH PACIFIC. THE ECMWF DOES A SLIGHTLY BETTER JOB WITH THIS
DEVELOPING FEATURE. AT THE SURFACE...VERY FEW DIFFERENCES BETWEEN THE
MODELS UNTIL A TRIPLE POINT LOW DEVELOPS WITHIN THE SOUTHWESTERLY
FLOW OVER THE NORTH PACIFIC. THE NAM AND GFS CONTINUE TO PLACE THIS
LOW NEAR KODIAK ISLAND THURSDAY AFTERNOON WHILE THE ECMWF HAS
CONSISTENTLY PLACING THE LOW IN THE OTHER SIDE OF THE ALASKA
PENINSULA OVER BRISTOL BAY. GIVEN THE POOR INITIALIZATION AND
CONSISTENCY ISSUES...HAVE DECIDED TO LEAN HEAVILY TOWARD THE ECMWF
FOR THIS FORECAST PACKAGE.

.SHORT TERM FORECAST...
.SOUTHCENTRAL ALASKA...TODAY IS THE LAST DAY OF QUIET WEATHER BEFORE
A VERY ACTIVE PATTERN TAKES OVER. AN IMPRESSIVE OPEN SHORTWAVE WILL
MOVE NORTH TOWARD SOUTHCENTRAL THIS EVENING. A LOT OF UNCERTAINTY
ABOUT PRECIPITATION POTENTIAL WITH THIS FEATURE AS MODELS CONTINUE TO
ADVERTISE A DRY PASSAGE. THE SOUTHWESTERLY FLOW WITH OVERRUNNING
MOISTURE USUALLY LENDS ITSELF TO AT LEAST LIGHT PRECIPITATION. SO WE
WILL CONTINUE TO ADVERTISE LIKELY WORDING WITH ACCUMULATION OF AN
INCH OR LESS EXCEPT THE UPSLOPE MOUNTAIN RANGES WHERE ACCUMULATION
WILL BE MORE IMPRESSIVE.

THE FORECAST GETS EVEN MORE CHALLENGING ON WEDNESDAY NIGHT WHEN THE
NEXT FRONTAL BOUNDARY APPROACHES THE SOUTHCENTRAL COAST. IT APPEARS
THAT ENOUGH WARM AIR WILL ACCOMPANY THIS FEATURE TO CHANGE
PRECIPITATION TO RAIN ALONG THE COAST. THE POSITION OF THE LOW BASED
ON THE ECMWF WILL LEAD TO DOWNSLOPING IN ANCHORAGE UNTIL THE COLD AIR
WRAPS BACK AROUND THURSDAY AND FRIDAY.

POTENTIAL HAZARDS WITH THIS STORM INCLUDE BLIZZARD CONDITIONS NEAR
PORTAGE UNTIL THE WARM AIR ARRIVES AND HEAVY SNOW IN THE NORTH AND
WESTERN SUSITNA VALLEY WHERE COLD AIR HAS A BETTER CHANCE OF HOLDING
ON THROUGHOUT THE EVENT. THOMPSON PASS ALSO HAS THE POTENTIAL FOR
BLIZZARD CONDITIONS AS THE GRADIENT TIGHTENS UP ALONG THE GULF COAST
AND THE SNOW INTENSITY INCREASES THROUGH WEDNESDAY NIGHT.

.SOUTHWEST MAINLAND...COLDER THAN NORMAL TEMPERATURES CONTINUE ACROSS
THE SOUTHWEST MAINLAND. AT PLACES LIKE BETHEL AND KING
SALMON...TEMPERATURES ARE AVERAGING ABOUT 10 TO 20 BELOW
CLIMATOLOGICAL NORMAL FOR THIS TIME OF YEAR. THE IMPENDING STORM
SYSTEM...ESPECIALLY IF IT FOLLOWS THE ECMWF TRACK...WILL AT LEAST
BRIEFLY BRING TEMPERATURES MUCH CLOSER TO NORMAL AS WARM AIR SPILLS
THROUGH THE ALEUTIAN AND ALASKA RANGES. WIDESPREAD SNOW WILL
ACCOMPANY THIS SYSTEM WITH THE POTENTIAL FOR ADVISORY LEVELS IN THE
MIDDLE KUSKOKWIM VALLEY...AS WELL AS FREEZING RAIN IN PARTS OF THE
BRISTOL BAY ZONE.

BEYOND WEDNESDAY...THE EXPECTED TRACK OF THE LOWS WILL KEEP SOUTHWEST
ALASKA IN AN ACTIVE REGION WITH ABUNDANT MOISTURE ACCOMPANYING EACH
SYSTEM.

.BERING SEA AND ALEUTIANS...THE WARM FRONT HAS MOVED JUST NORTH OF
THE ALEUTIAN RANGE...SWITCHING THE PRECIPITATION TYPE TO A RAIN AND
SNOW MIX AT MANY LOCATIONS. THE FRONT WILL MOVE A BIT FURTHER NORTH
AND STALL NEAR THE PRIBILOF ISLANDS. THE EASTERLY WINDS AND SNOW
ALONG THIS BOUNDARY WILL BRING POSSIBLE BLIZZARD CONDITIONS TO ST
PAUL AND ST GEORGE ISLANDS.

THE NORTH PACIFIC LOW WILL DRIFT EAST UNDER THE ALEUTIAN CHAIN AS IT
GRADUALLY WEAKENS TO 983 MB THURSDAY AFTERNOON. COLD AIR WILL SPILL
BACK SOUTHWARD ON THE BACK SIDE OF THE LOW...BRINGING COLD AIR
ADVECTION SNOW SHOWERS BACK TO THE CHAIN DURING THE WEEK.

.AER/ALU...WATCH/WARNING/ADVISORY SUMMARY
PUBLIC...BLIZZARD WARNING 195
MARINE...STORMS 175 176
         GALES...132 170 172 352 411 413 414
         HEAVY FREEZING SPRAY...121 129 138 140 141 160 165 179 180
185 412 414
FIRE WEATHER...NONE.

AB DEC 10