Gale Warning 120, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1250 PM AKST WED FEB 6 2013

.ANALYSIS AND UPPER LEVELS...A SHORT-WAVE TROUGH IS TRACKING EASTWARD
ACROSS SOUTHCENTRAL TODAY BRINGING WIDESPREAD LIGHT SNOW TO MUCH OF
THE REGION. A MUCH LARGER SYSTEM IS AFFECTING THE BERING SEA THIS
MORNING WITH A MATURE DEEP LOW NEARLY STATIONARY JUST SOUTH OF THE
WESTERN ALEUTIANS AND AN OCCLUDED FRONT EXTENDING EASTWARD ACROSS
THE SOUTHERN BERING AND THEN SOUTHWARD ACROSS THE EASTERN ALEUTIANS.
THIS FRONT IS VERY SLOWLY WEAKENING AS IT SPREADS NORTH AND EAST.
BLIZZARD CONDITIONS ARE DEVELOPING THIS MORNING ALONG THE PRIBILOFS
WHILE FURTHER SOUTH PRECIPITATION IS TRANSITIONING FROM SNOW TO RAIN
AS THE FRONT PUSHES THROUGH. IN BETWEEN THESE TWO SYSTEMS ACROSS
SOUTHWEST ALASKA WEAK RIDGING IS SUPPORTING LOW CLOUDS AND AREAS
OF FOG.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT WITH HANDLING OF
SYNOPTIC SCALE FEATURES THROUGH FRIDAY AND SHOW GOOD RUN-TO-RUN
CONSISTENCY. THE ONE FEATURE THAT MODELS CONTINUE TO DIFFER ON IS
THE TRACK OF THE TRIPLE POINT LOW THURSDAY AFTERNOON AND EVENING.
ON THE 12Z MODEL CYCLE ALL BUT THE GFS TRACKED THIS LOW UP COOK
INLET AND THE WESTERN KENAI. THE 18Z NAM HAS NOW COME IN FURTHER
EAST...TRACKING IT ALONG THE EASTERN KENAI INTO PRINCE WILLIAM
SOUND. THE TRACK OF THIS LOW IS CRITICAL TO DETERMINING THE STRENGTH
OF DOWNSLOPE WINDS FROM THE WESTERN KENAI TO ANCHORAGE AND THE MAT
VALLEY WHICH IN TURN AFFECTS HOW MUCH PRECIP WILL FALL. FOR NOW
WILL LEAN HEAVILY TOWARD THE WESTERN SOLUTION...BUT WILL WATCH
NEWER MODEL RUNS CLOSELY TO SEE HOW THEY HANDLE THIS FEATURE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...SNOW WILL END FROM WEST TO EAST ACROSS
SOUTHCENTRAL ALASKA THIS AFTERNOON AND EVENING AS UPPER TROUGH
TRACKS QUICKLY OFF TO THE EAST. WITH LOTS OF LOW LEVEL MOISTURE
IN PLACE EXPECT LOW CLOUDS AND FOG TO QUICKLY DEVELOP BEHIND THE
TROUGH AND HOLD IN UNTIL CLOUDS AND PRECIP WITH NEXT SYSTEM ARRIVE
THURSDAY MORNING. THE FRONT CURRENTLY CROSSING THE BERING WILL
ARRIVE IN THE WESTERN GULF THURSDAY MORNING AND TRACK QUICKLY
NORTHWARD AND EASTWARD THURSDAY AFTERNOON AND EVENING. SOUTH TO
SOUTHWEST FLOW ALOFT ALONG WITH MULTIPLE EMBEDDED WAVES IS FAVORABLE
FOR PRODUCING PRECIP IN MOST AREAS. THE UNCERTAINTY LIES IN THE
TRACK OF THE TRIPLE POINT LOW WHICH WILL PRODUCE STRONG EASTERLY
WINDS ACROSS THE CHUGACH AND KENAI MOUNTAINS. CURRENTLY MOST OF THE
MODELS SUPPORT A MORE WESTERN TRACK TO THIS LOW WHICH WILL PRODUCE
STRONG DOWNSLOPING WINDS FOR MUCH O FTHE DAY TOMORROW. EVEN WITH
THIS...THINK THE UPPER LEVEL LIFT AND MOISTURE WILL BE ENOUGH TO
PRODUCE SOME PRECIP IN THE TYPICAL DOWNSLOPE AREAS. IF THE LOW
TRACKS A LITTLE FURTHER EAST THEN DOWNSLOPING WILL BE REDUCED AND
THERE WILL BE MORE PRECIP. UNLESS THE TRACK VARIES SIGNIFICANTLY
FROM CURRENT THINKING...EXPECT A PERIOD OF BLIZZARD CONDITIONS
THROUGH PORTAGE VALLEY AND EASTERN TURNAGAIN ARM WHERE SNOW WILL
COINCIDE WITH THE STRONG EASTERLY WINDS. NO MATTER WHERE THE LOW
TRACK LOW LEVEL THICKNESSES WILL SUPPORT MOSTLY SNOW ACROSS
SOUTHCENTRAL...WITH RAIN FROM KODIAK ISLAND TO THE NORTH GULF COAST.
THIS SYSTEM WILL EXIT TO THE NORTH AND EAST THURSDAY NIGHT...
ALTHOUGH CYCLONIC FLOW ALOFT WILL PERSIST THROUGH FRIDAY WITH WEAK
UPPER WAVES MOVING THROUGH. THEREFORE AREAS OF LIGHT SNOW WILL
ALSO CONTINUE.

SOUTHWEST ALASKA...CURRENT FORECAST FOR SOUTHWEST ALASKA LOOKS ON
TRACK WITH SNOW ARRIVING ALONG THE COASTAL ZONE OVERNIGHT TONIGHT
AND SPREADING INLAND THURSDAY. BLOWING SNOW FROM THE WESTERN CAPES
TO THE KUSKOKWIM DELTA COAST WILL RESULT IN LOW VISIBILITIES...BUT
WILL BE FAIRLY SHORT-LIVED AS THE FRONT CONTINUES TO WEAKEN AS IT
MOVES THROUGH. CONDITIONS WILL DRY OUT FOR MOST AREAS BY THURSDAY
EVENING ALTHOUGH THERE MAY BE SOME BRIEF PERIODS OF SNOW THROUGH
FRIDAY AS WEAK UPPER WAVES PASS OVERHEAD.

BERING SEA/ALEUTIANS...THE ALEUTIAN LOW WILL BE VERY SLOW TO
WEAKEN AS IT TRACKS EASTWARD JUST SOUTH OF THE CHAIN. WINDS WILL
BE SLOW TO DIMINISH NORTH AND WEST OF THE LOW CENTER WHERE THE
PRESSURE GRADIENT IS VERY TIGHT BETWEEN THE ALEUTIAN LOW AND A
STRONG RIDGE OVER SIBERIA. THE OCCLUDED FRONT WILL MAKE A LITTLE
PROGRESS NORTHWARD TONIGHT AND STALL RIGHT NEAR THE PRIBILOFS
WHERE IT WILL DISSIPATE. THE ALEUTIAN LOW WILL EVENTUALLY MERGE
WITH ANOTHER LOW MOVING UP FROM THE PACIFIC ON FRIDAY. ALL MODELS
INDICATE THIS SYSTEM WILL HEAD TOWARD BRISTOL BAY THIS WEEKEND
WHILE ANOTHER STRONG SYSTEM APPROACHES THE WESTERN ALEUTIANS.

.LONG TERM FORECAST...UPPER LEVEL FLOW WILL REMAIN PROGRESSIVE
THROUGH THE EXTENDED FORECAST PERIOD WITH STRONG STORMS TRACKING
QUICKLY ACROSS THE FORECAST AREA. EXPECT RAPIDLY CHANGING WEATHER
WITH POTENTIAL FOR ADVISORIES AND WARNINGS AS THESE SYSTEMS MOVE
THROUGH.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 125 195.
MARINE...GALE WARNING...120 125 130 172 175 176 179 185.
FIRE WEATHER...NONE.

SEB FEB 13