Small Craft Advisory 48, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
120 PM AKST SUN JAN 11 2009

.ANALYSIS AND UPPER LEVELS...SATELLITE IMAGERY SHOWS THE PINEAPPLE
EXPRESS HEADED FOR SOUTHCENTRAL ALASKA. A STRONG UPPER JET IS
RIDING UP THE WEST SIDE OF A HIGH AMPLITUDE EAST PACIFIC
RIDGE...TRANSPORTING LOTS OF MOISTURE AND WARM AIR NORTHWARD TO THE
GULF OF ALASKA. A STRENGTHENING SURFACE LOW IS LOCATED DOWN AROUND
40N...A SECOND LOW IS EXPECTED TO DEVELOP MUCH FARTHER NORTH THIS
AFTERNOON AND TRACK INTO THE GULF TONIGHT. CONDITIONS ARE CURRENTLY
CALM AND COLD OVER SOUTHCENTRAL...BUT THIS SYSTEM WILL BE THE FIRST
STEP IN A MAJOR CHANGE IN THE WEATHER PATTERN. MEANWHILE A WEAK UPPER
SHORT-WAVE IS PUSHING NORTHWARD ACROSS BRISTOL BAY...SPREADING LIGHT
SNOW NORTHWARD ACROSS SOUTHWEST ALASKA. A COUPLE WEAK LOWS REMAIN
ALONG THE ALASKA PENINSULA. HOWEVER...THESE ARE ABOUT TO BE PUSHED
NORTHWARD BY AN AMPLIFYING TROUGH EXTENDING FROM AN UPPER LOW OVER
THE NORTHWEST BERING SOUTHEASTWARD TO THE EASTERN ALEUTIANS.
A LARGE LOW COMPLEX IS TRACKING ACROSS THE NORTH PACIFIC SOUTH OF
THE ALEUTIANS...CURRENTLY TOO FAR SOUTH TO AFFECT THE FORECAST AREA.
THIS SYSTEM WILL HELP REINFORCE THE HIGH AMPLITUDE TROUGH AND
DOWNSTREAM RIDGE.

.MODEL DISCUSSION...MODELS DIFFER IN EXACT TRACK OF LOW ACROSS THE
GULF TONIGHT. PREFER THE VERY CONSISTENT ECMWF/UKMET SOLUTION...AND
18Z NAM IS NOW VERY CLOSE TO THAT. OTHERWISE...MODELS ARE IN VERY
GOOD AGREEMENT THROUGH 48 HOURS. DIFFERENCES THEN SHOW UP WITH LOW
COMPLEX OUT WEST AND POSITION/ORIENTATION OF WARM OCCLUSION PUSHING
TOWARD THE ALEUTIANS. WILL GO WITH A CONSENSUS OF
ECMWF/GFS/UKMET...NAM IS A CLEAR OUTLIER.

.SHORT TERM FORECAST...

SOUTHCENTRAL...WITH A LOW TRACK TO AROUND CAPE SUCKLING...THE BULK
OF WARM AIR WILL BE SHUNTED OFF TOWARD SOUTHEAST ALASKA.
HOWEVER...THERE WILL STILL BE STEADY WARMING ACROSS SOUTHCENTRAL
AS CLOUDS AND PRECIPITATION MOVE IN. THE AMPLIFYING TROUGH OUT WEST
WILL SWING INTO THE GULF TONIGHT AND RAPIDLY PUSH NORTHWARD ACROSS
THE STATE MONDAY UNDER INFLUENCE OF STRONG SOUTHERLY JET...SO
SURFACE STORM WILL BE QUICK TO MOVE THROUGH THE REGION. OVERRUNNING
WILL BRING LIGHT SNOW TO SOUTHCENTRAL BEGINNING LATE THIS AFTERNOON
AND EVENING AND STEADIER SNOW WILL MOVE IN LATER TONIGHT. THE
HEAVIEST PRECIP IN THE VICINITY OF THE LOW WILL SPREAD TO PRINCE
WILLIAM SOUND AND EASTWARD TO SOUTHEAST ALASKA. HOWEVER...THE UPPER
TROUGH IS STRONG AND MOST AREAS WILL SEE SOME SNOW. THE REGION WILL
DRY OUT DURING THE DAY MONDAY. THERE WONT BE MUCH OF A BREAK
BETWEEN SYSTEMS. THE UPPER RIDGE WILL AMPLIFY TUESDAY AND VERY WARM
AIR WILL OVERRUN SOUTHCENTRAL TUESDAY AND WEDNESDAY. THIS WILL
INITIALLY BRING A CHANCE OF SNOW...THEN FREEZING RAIN...AND AS WE
HEAD THROUGH MID WEEK IT SHOULD GET WARM ENOUGH FOR RAIN IN MOST
PLACES.

SOUTHWEST ALASKA/ALASKA PENINSULA...AS THE UPPER TROUGH AMPLIFIES
TONIGHT AND SWINGS TOWARD SOUTHWEST ALASKA SNOW WILL BECOME
HEAVIER..ESPECIALLY FROM DILLINGHAM NORTHWARD TO THE SOUTHERN
KUSKOKWIM VALLEY WHERE 6 INCHES OF SNOW OR MORE ARE LIKELY. WILL
HAVE TO CONSIDER ISSUING A WINTER WEATHER ADVISORY FOR SNOW FOR THE
BRISTOL BAY ZONE. SNOW WILL GRADUALLY END MONDAY AS THE TROUGH EXITS
TO THE NORTH. WARM ADVECTION OUT AHEAD OF THE NORTH PACIFIC LOW WILL
BEGIN TUESDAY AND TURN PRECIPITATION TO RAIN MOST PLACES BY
WEDNESDAY.

BERING SEA/ALEUTIANS...IT IS A BORDERLINE CALL FOR CURRENT BLIZZARD
WATCH IN EFFECT FOR THE CENTRAL ALEUTIANS ON MONDAY. AS THE FRONT
APPROACHES THE ALEUTIANS AND EAST WINDS PICK UP TEMPERATURES SHOULD
QUICKLY RISE. HOWEVER...IT IS VERY COLD NOW WITH TEMPS IN THE TEENS
AND THE QUESTION IS WHETHER IT WILL WARM ENOUGH BY THE TIME SNOW
ARRIVES TO PREVENT BLIZZARD CONDITIONS. FOR NOW WILL HOLD ON TO THE
WATCH AND WAIT UNTIL THE NEXT MODEL CYCLE BEFORE MAKING A DECISION
ON WHETHER TO UPGRADE THE WATCH TO A WARNING.

.LONG TERM FORECAST...WITH HIGH AMPLITUDE RIDGE OVER WESTERN NORTH
AMERICA AND HIGH AMPLITUDE TROUGH OVER THE BERING IT WILL BE VERY
WARM AND WET OVER MAINLAND ALASKA MID TO LATE WEEK AND COLD OUT
WEST. MODELS INDICATE SOME EASTWARD PROGRESSION OF THE PATTERN
BY NEXT WEEKEND...SO COLDER AIR COULD MAKE ITS WAY BACK TO MAINLAND
ALASKA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WATCH 131.
MARINE...STORM WARNING...172 175.
         GALE WARNING...120 130 140 170 171 176.
         HEAVY FREEZING SPRAY WARNING...121 129 130 140 179 185.
FIRE WEATHER...NONE.

SEB JAN 09