Gale Warning 806, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
110 PM AKST WED DEC 3 2008

.ANALYSIS AND UPPER LEVELS...A LARGE CLOSED UPPER LEVEL CYCLONE
IS NEARLY STATIONARY SOUTH OF THE CENTRAL ALEUTIANS. A STRONG UPPER
JET (ESTIMATED JET MAX OF 160KT) IS RIDING NORTHWARD UP THE EASTERN
SIDE OF THIS CYCLONE/WESTERN SIDE OF A BUILDING RIDGE TO SOUTHWEST
ALASKA...PUMPING LOTS OF MOISTURE AND WARM AIR NORTHWARD ACROSS THE
SOUTHERN MAINLAND. BRISTOL BAY TO KODIAK ISLAND HAVE WARMED UP
SIGNIFICANTLY WITH PRECIPITATION PREDOMINANTLY IN THE FORM OF RAIN.
HOWEVER...FURTHER NORTH THERE IS STILL ARCTIC AIR IN PLACE AT THE
SURFACE. SO THE WARM AIR IS RIDING OVER TOP OF THIS COLD AIR AND
PRODUCING SOME FAIRLY STEEP INVERSIONS (AS SEEN IN 12Z SOUNDINGS
FROM BETHEL...MCGRATH...AND ANCHORAGE. THE EXTENT OF THE WARM AIR
ALOFT IS INDICATED IN BETHELS OBSERVATIONS WHERE FREEZING RAIN
BEGAN MIXING IN WITH A SURFACE TEMPERATURE OF 18 DEGREES.

AT THE SURFACE THERE IS A 960MB LOW UNDERNEATH THE UPPER CENTER
WITH OCCLUDED FRONT EXTENDING EASTWARD JUST SOUTH OF THE ALASKA
PENINSULA. A LOW HAS FORMED ALONG THE FRONT SOUTH OF COLD BAY AND
IS ROTATING NORTH-NORTHWEST AROUND THE UPPER CIRCULATION. GALE TO
STORM FORCE WINDS ARE BEING OBSERVED OUT AHEAD OF THE FRONT OVER
THE GULF WATERS EXTENDING WESTWARD TO BRISTOL BAY AND ACROSS MUCH
OF THE BERING SEA.

.MODEL DISCUSSION...MODELS ALL INITIALIZED WELL AND ALL SHOW THE
SAME GENERAL SOLUTION...BUT THERE ARE SOME KEY DIFFERENCES IN LOW
TRACKS. THE TREND WITH THE MAIN LOW SOUTH OF THE ALEUTIANS IS TO
MAINTAIN A TRACK SOUTH OF THE ALASKA PENINSULA. GFS IS FARTHER
SOUTH THAN UKMET/ECMWF/NAM SO WILL STICK CLOSE TO THE CONSENSUS.
THE SECONDARY LOW THAT HAS FORMED SOUTH OF COLD BAY IS A LITTLE
MORE PROBLEMATIC. ALL MODELS ROTATE THIS NORTHWESTWARD ACROSS THE
EASTERN BERING AND THEN SOUTHWARD AS THE MAIN LOW TRACKS EAST.
HOWEVER THERE ARE TIMING AND PLACEMENT DIFFERENCES. FOR NOW...WILL
TREND TOWARD THE GFS. FOR THE GULF AND SOUTHERN MAINLAND PREFER
THE NAM MODEL FOR THE DETAILS. IT IS THE ONLY MODEL TO DEVELOP A
CLOSED SURFACE LOW AS THE FRONT REACHES THE NORTHERN GULF. WITH
STRONG UPPER LEVEL DYNAMICS THIS SEEMS LIKE A SAFE BET. BASED ON
OBSERVATION OF FREEZING RAIN IN BETHEL...MODELS ARE A BIT WEAK AND
A BIT SLOW WITH WARM ADVECTION. THUS WILL TREND TOWARD WARMING
THINGS UP FASTER AND BRINING WARM AIR FARTHER NORTH. BEYOND DAY 3
THERE IS HUGE UNCERTAINTY DUE TO VERY POOR MODEL CONSISTENCY SO
WILL STICK CLOSE TO CURRENT FORECASTS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...OVERRUNNING PRECIPITATION WILL SPREAD ACROSS
SOUTHCENTRAL THIS AFTERNOON...DROPPING A LITTLE SNOW ON MOST PLACES.
THE UPPER JET WILL CURVE EASTWARD TOWARD SOUTHCENTRAL
TONIGHT...PUSHING THE RIDGE EASTWARD...AND TRANSPORTING A LOT OF
MOISTURE AND WARM AIR OVER SOUTHCENTRAL. THUS EXPECT TRENDS SIMILAR
TO WHAT IS OCCURRING OVER SOUTHWEST ALASKA THIS MORNING. IMMEDIATE
COASTAL AREAS WILL QUICKLY CHANGE TO RAIN WHILE INLAND AREAS THAT
ARE MORE ENTRENCHED IN THE ARCTIC AIRMASS WILL SEE A BIT OF FREEZING
RAIN. STRONG EASTERLY FLOW AHEAD OF THE FRONT WILL LIMIT
PRECIPITATION ON THE LEE SIDE OF THE KENAI AND CHUGACH MOUNTAINS.
BUT THE STRONG DYNAMICS AND ABUNDANT MOISTURE WILL RESULT IN LIGHT
PRECIPITATION DESPITE THE STRONG FLOW. THE SUSITNA VALLEY SHOULD
REMAIN MOSTLY SNOW AND THE USUAL UPSLOPE AREAS OF THE ALASKA RANGE
WILL SEE HEAVIER AMOUNTS...SO HAVE ISSUED A WINTER WEATHER ADVISORY
FOR SNOW FOR ZONE 145. UPPER LEVEL FLOW WILL SHIFT TO SOUTH TO
SOUTHWEST LATE TONIGHT AND AN UPPER LEVEL SHORT-WAVE WILL PUSH ACROSS
SOUTHCENTRAL ON THURSDAY. THIS WILL BRING A BRIEF PERIOD OF SNOW TO
ANCHORAGE AND THE MATANUSKA VALLEY...AS WELL AS THE COPPER RIVER
BASIN. THE REMNANTS OF THE FRONT WILL ALSO PUSH ACROSS THE COPPER
BASIN...SO WILL BE ISSUING A WINTER WEATHER ADVISORY FOR SNOW FOR
THERE ON THURSDAY. DO THINK FREEZING RAIN WILL BE A MAJOR PROBLEM
ANYWHERE BECAUSE AIR IS SO WARM THAT TEMPERATURES ALONG AND NEAR
THE COAST SHOULD QUICKLY RISE ABOVE FREEZING. WILL NEED TO KEEP A
CLOSE EYE ON INLAND LOCATIONS WHERE FREEZING RAIN COULD MIX IN
WITH SNOW. THERE IS ANOTHER SHOT FOR PRECIPITATION THURSDAY NIGHT
AS A WEAK UPPER WAVE MOVES ACROSS THE REGION AND AGAIN LATE FRIDAY.
TEMPERATURES WILL CONTINUE TO WARM...SO PLAIN OLD RAIN WILL LIKELY
EXTEND FARTHER INLAND.

SOUTHWEST ALASKA...WARM AIR AND PRECIPITATION WILL CONTINUE TO
SPREAD NORTHWARD TONIGHT THROUGH THURSDAY AFTERNOON...GRADUALLY
CHANGING PRECIPITATION TO RAIN. AREAS OF FREEZING RAIN WILL ALSO
SPREAD NORTHWARD...SO WILL CONTINUE FREEZING RAIN ADVISORIES THROUGH
THURSDAY MORNING. MAY NEED TO EXTEND ADVISORY FOR NORTHERN KUSKOKWIM
WHICH MAY HOLD OUT A LITTLE LONGER BEFORE WARMING TO FREEZING.
UPPER WAVES WILL ROTATE ACROSS THE REGION THURSDAY NIGHT AND
FRIDAY...MAINTAINING AREAS OF MAINLY RAIN ACROSS THE REGION. AS THE
ALEUTIAN LOW TRACKS SOUTH OF THE ALASKA PENINSULA AND KODIAK ISLAND
FRIDAY NIGHT AND SATURDAY TEMPERATURES WILL FINALLY BEGIN TO COOL
AND THE REMAINING SHOWERS OVER THE REGION WILL SHIFT BACK TOWARD
SNOW. ALTHOUGH THERE IS UNCERTAINTY BEYOND THIS TIM PERIOD WITH
NEXT GULF LOW...IT LOOKS LIKE A VERY GOOD CHANCE SOUTHWEST ALASKA
WILL CONTINUE TO COOL HEADING INTO NEXT WEEK.

BERING SEA/ALEUTIANS...A VERY LARGE AREA OF SOLID GALE FORCE WINDS
WILL PERSIST ON THE BACK SIDE OF THE LOW OVER THE CENTRAL BERING SEA
AND WESTERN TO CENTRAL ALEUTIANS THROUGH THE REST OF THE WEEK. THE
LOW CURRENTLY SOUTH OF COLD BAY WILL ROTATES TO NEAR THE PRIBILOFS
THURSDAY. THEN AS IT ROTATES SOUTHWARD FRIDAY THE PRESSURE GRADIENT
WILL TIGHTEN EVEN FURTHER JUST WEST OF THIS LOW...RESULTING IN A
SMALL AREA OF STORM FORCE WINDS. WINDS WILL QUICKLY DIMINISH FRIDAY
NIGHT INTO SATURDAY AS THIS LOW TRACKS SOUTH OF THE ALEUTIANS. THE
EASTERN ALEUTIANS AND EASTERN BERING WILL REMAIN ON THE WARM SIDE OF
THE SYSTEM WITH PERIODS OF RAIN AND SMALL CRAFT OR LESS WINDS THROUGH
FRIDAY.

.LONG TERM FORECAST...THERE IS LOW CONFIDENCE IN THE EXTENDED
FORECAST DUE TO UNCERTAINTY IN TRACK OF A MAJOR LOW TOWARD THE GULF
OF ALASKA. HOWEVER...MODELS ARE MORE CONSISTENT IN DEPICTION OF A
STRONG RIDGE BUILDING FROM THE NORTHERN BERING SEA OVER NORTHERN
ALASKA AND ARCTIC AIR DIVING SOUTHWARD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...120.
         GALE WARNING...125 129 130 140 175 176 179 180 185.
         HEAVY FREEZING SPRAY WARNING...180 185.
FIRE WEATHER...NONE.

SEB DEC 08