Gale Warning 905, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1250 PM AKST FRI NOV 26 2010

.ANALYSIS AND UPPER LEVELS...UPPER LEVEL PATTERN REMAINS VERY
PROGRESSIVE. TROUGH RESPONSIBLE FOR SNOW OVER SOUTHCENTRAL ON
THANKSGIVING DAY IS EXITING TO THE EAST ACROSS SOUTHCENTRAL ALASKA
AS A SHORT-WAVE RIDGE BUILDS IN BEHIND IT. A WEAK LOW AMPLITUDE
TROUGH CROSSING THE BERING SEA IS BEGINNING TO SLIGHTLY DIG
SOUTHEASTWARD AND CONNECT UP WITH A MATURE LOW OVER THE NORTH
CENTRAL PACIFIC. UPSTREAM OF THESE TROUGHS IS ANOTHER SHORT-WAVE
RIDGE OVER THE FAR WESTERN BERING. AT THE SURFACE AN ELONGATED
LOW OVER THE CENTRAL BERING IS TRACKING TOWARD SOUTHWEST ALASKA.
A WARM FRONT EXTENDS WELL OUT AHEAD OF THE LOW WITH SNOW SPREADING
ONSHORE FROM THE KUSKOKWIM DELTA TO BRISTOL BAY. ALL IS QUIET ACROSS
THE REST OF THE FORECAST AREA UNDER THE INFLUENCE OF HIGH PRESSURE.

.MODEL DISCUSSION...THERE IS A KEY DIFFERENCE AMONG THE MODEL
SOLUTIONS IN LOCATION AND EXTENT OF AMPLIFICATION OF UPPER TROUGH
DIGGING ACROSS SOUTHCENTRAL SATURDAY NIGHT AND SUNDAY. THE NAM IS
A BIT OF AN OUTLIER WITH HIGHER AMPLITUDE OVER COOK INLET ALTHOUGH
ECMWF HAS TRENDED THAT DIRECTION. THE GFS/UKMET MAINTAIN A MUCH
LOWER AMPLITUDE TROUGH UNTIL IT REACHES PRINCE WILLIAM SOUND. THIS
WILL HAVE AN IMPACT ON LOCATION AND AMOUNT OF SNOWFALL ACROSS
SOUTHCENTRAL...ESPECIALLY FOR THE WESTERN KENAI TO SUSITNA VALLEY.
FOR NOW WILL TAKE A MIDDLE GROUND SOLUTION. NO MATTER WHAT SOLUTION
YOU GO WITH ANY SNOW ACCUMULATION WILL BE LIGHT.

OTHER THAN THAT MODELS REMAIN IN GENERAL AGREEMENT THE NEXT FEW
DAYS WITH SYNOPTIC FEATURES.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE WEAK LOW OVER THE BERING WILL TRACK
ACROSS SOUTHWEST ALASKA AND INTO THE GULF FRIDAY NIGHT INTO
SATURDAY. THERE WON'T BE A WHOLE LOT OF MOISTURE OR LIFT TO WORK
WITH UNDER BROAD WESTERLY FLOW...SO MAIN IMPACT WILL BE AN INCREASE
IN CLOUDS. A MORE SUBSTANTIVE UPPER TROUGH WILL DROP OUT OF THE
ARCTIC SATURDAY AND BEGIN TO DOG SOUTHEASTWARD TOWARD SOUTHCENTRAL
SATURDAY NIGHT. THERE IS SOME UNCERTAINTY IN THE EVOLUTION OF THIS
TROUGH...BUT LOOKS LIKE THERE WILL BE ENOUGH LIFT AHEAD OF THIS
TROUGH TO PRODUCE A QUICK SHOT OF SNOW ACROSS MUCH OF SOUTHCENTRAL
SATURDAY NIGHT INTO SUNDAY. THE TROUGH WILL CONTINUE TO DIG
SOUTHWARD ACROSS THE GULF AND DEVELOP INTO A CLOSED LOW. ARCTIC
AIR WILL BE USHERED SOUTHWARD BEHIND THE TROUGH SETTING UP A WIND
EVENT ACROSS SOUTHCENTRAL AND THE GULF LATE SUNDAY THROUGH MONDAY.
THIS WILL BE ENHANCED BY A PACIFIC LOW WHICH THEN TRACKS INTO THE
GULF MONDAY...RAPIDLY DEEPENING AS COLD AIR FEEDS INTO IT. IT IS
TOO EARLY TO DETERMINE EXACT WIND SPEEDS...BUT THERE IS SOME
POTENTIAL FOR HIGH WIND WARNING CONDITIONS IN THOMPSON PASS/VALDEZ.
FOR NOW WILL TREND HEAVILY TOWARD STRONGER WINDS IN THE LATEST
FORECAST.

SOUTHWEST ALASKA...PRECIP WILL CONTINUE TO SPREAD INLAND THIS
AFTERNOON AND EVENING. AIRMASS BEHIND THE WARM FRONT LOOKS WARM
ENOUGH TO CHANGE PRECIP TO A MIX OF RAIN AND SNOW OR EVEN ALL RAIN
ALONG COASTAL AREAS. PERSISTENT ONSHORE FLOW WILL ALSO CONTRIBUTE
TO WIDESPREAD LOW CEILINGS AND VISIBILITIES. COLDER AIR WILL SLOWLY
FILTER SOUTHWARD TONIGHT THROUGH SATURDAY CHANGING ANY REMAINING
PRECIP BACK TO SNOW. A MORE SIGNIFICANT ARCTIC BLAST WILL THEN
ACCOMPANY AN UPPER TROUGH AS IT DIGS SOUTHEASTWARD ACROSS SOUTHWEST
ALASKA SATURDAY NIGHT AND SUNDAY. COMBINATION OF THE COLD ADVECTION
AND A PACIFIC LOW MOVING TOWARD THE GULF WILL PRODUCE GUSTY
NORTHERLIES...PRIMARILY FOR EASTERN PORTIONS OF THE KUSKOKWIM
VALLEY AND BRISTOL BAY ZONES. OTHERWISE...HIGH PRESSURE WILL
PROVIDE FOR DRY CONDITIONS THROUGH AT LEAST EARLY NEXT WEEK.

BERING SEA/ALEUTIANS...THE LOW OVER THE CENTRAL BERING WILL EXIT TO
SOUTHWEST ALASKA TONIGHT AND HIGH PRESSURE WILL BUILD IN ONCE AGAIN.
A PACIFIC LOW WILL TRACK TOWARD THE GULF THE NEXT COUPLE DAYS BUT
MOST OF THE IMPACT FROM THIS WILL BE SOUTH OF THE ALEUTIANS AND
ALASKA PENINSULA. THE RIDGE WILL PROGRESS EASTWARD OVER THE WEEKEND
AND EARLY NEXT WEEK ALLOWING A SYSTEM TO MOVE UP ITS WEST SIDE INTO
THE BERING SEA.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE OUT OF PHASE AS WE
HEAD THROUGH NEXT WEEK. HOWEVER...THE BOTTOM LINE IS UPPER LEVEL
PATTERN REMAINS PROGRESSIVE SO WEATHER WILL CONTINUE TO CHANGE
EVERY TWO OR THREE DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...155 160 165 170 176.
FIRE WEATHER...NONE.

SEB NOV 10