Gale Warning 16, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1250 PM AKST TUE JAN 19 2010

.ANALYSIS AND UPPER LEVELS...
AN UPPER LEVEL TROUGH CENTERED ALONG THE WEST COAST OF ALASKA EXTENDS
SOUTHWARD INTO THE WESTERN GULF OF ALASKA AND IS BEGINNING TO WEAKEN
AS A RIDGE OF HIGH PRESSURE OVER THE WESTERN ALEUTIANS SCOOTS
EASTWARD. A WEAK TROUGH SOUTH OF SHEMYA IS ALSO MOVING EASTWARD WITH
THE RIDGE. THE MAIN WEATHER STORY IS A LARGE DEVELOPING STORM SYSTEM
AIDED BY THE POLAR LOW OVER EAST CENTRAL RUSSIA. THIS DEEP TROUGH
WILL DIG SOUTHWARD IN THE COMING DAYS AND BRING SIGNIFICANT WINDS TO
THE WESTERN ALEUTIANS ON THURSDAY AND FRIDAY.

AT THE SURFACE...A WEAKENING LOW PRESSURE SYSTEM NEAR THE SOUTHERN
KENAI PENINSULA IS ROTATING AROUND AND BEING ABSORBED BY A SECOND
LARGE LOW FIXATED 300 MILES SOUTH OF KODIAK ISLAND. THIS LARGE LOW
APPEARS TO BE MORPHING INTO A BROAD CIRCULATION CENTER WITH MULTIPLE
EMBEDDED VORTICIES...SEVERAL OF WHICH ARE ALREADY APPEARING ON
INFRARED SATELLITE IMAGERY. THE NORTHERN LOW AND ITS ASSOCIATED
SHORTWAVE ARE PRIMARILY RESPONSIBLE FOR WIDESPREAD SHOWER ACTIVITY
ACROSS PRINCE WILLIAM SOUND AND SNOW OVER KODIAK ISLAND. COLD AIR
ADVECTION OVER THE BERING SEA CONTINUES TO PRODUCE WIDESPREAD SNOW
SHOWERS ACROSS THE BERING SEA AND ALEUTIANS.

.MODEL DISCUSSION...
THE MODELS DID A DECENT JOB INITIALIZING THIS MORNING...BUT ALL
OF THE MODELS PLACED THE LOW OVER THE NORTHWEST GULF TOO FAR TO
THE SOUTH. THIS LOCATION BIAS PROPAGATES ONWARD IN THE MODELS UNTIL
THE LOW DISSIPATES TOMORROW. THIS IS HAVING A SIGNIFICANT IMPACT ON
THE  TYPE OF PRECIPITATION CURRENTLY FALLING AT KODIAK ISLAND (MOSTLY

SNOW INSTEAD OF RAIN)...WHICH IS NOW UNDER NORTHWESTERLY FLOW INSTEAD
OF NORTHEASTERLY FLOW. THE NAM IS ALSO THE ONLY MODEL WITH A HANDLE
ON THE SUB-SYNOPTIC VORTICIES ROTATING AROUND THE PERIPHERY OF THE
BROAD LOW SOUTH OF KODIAK ISLAND. THE LATEST EUROPEAN MODEL RUN ALSO
BEGINS TO DEPICT THESE FEATURES AS WELL...BUT THE GFS CONTINUES TO
MAINTAIN A SINGLE CORE OF LOW PRESSURE WITH EMBEDDED SHORTWAVES.

FURTHER IN TIME...THE MODELS ARE HAVING A DIFFICULT TIME DIAGNOSING
THE TRACK AND TIMING OF A STORM SYSTEM MOVING INTO THE EASTERN GULF
OF ALASKA LATE IN THE WEEK. THE EUROPEAN IS CURRENTLY THE MOST
AGGRESSIVE IN THE SPEED OF THIS SYSTEM AND TAKES IT ON A NORTHERN
TRACK THROUGH THE GULF WHILE THE GFS HANGS BACK AND TAKES THE STORM
ON A MORE SOUTHERLY TRACK. THE NAM LIES IN-BETWEEN THESE TWO
SOLUTIONS. THE FORECAST WILL TREND HEAVILY TOWARD A TRACK WHICH IS
MORE SOUTHERLY THAN CURRENT FORECAST INDICATES. OUT WEST...THE MODELS

ARE IN GOOD AGREEMENT WITH THE TRACK AND WINDS ASSOCIATED WITH THE
INCOMING STORM SYSTEM OVER THE WESTERN ALEUTIANS LATE IN THE WEEK.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...SURFACE TROUGH EXTENDING FROM A LOW NORTHEAST
OF KODIAK ISLAND ALONG WITH ASSOCIATED UPPER SHORT-WAVE WILL MOVE
WESTWARD ACROSS KODIAK ISLAND AND SOUTHERN PORTIONS OF SOUTHCENTRAL
TONIGHT. MOST OF THE PRECIP WITH THIS WILL REMAIN ALONG THE
COAST...BUT EXPECT A FEW SHOWERS ELSEWHERE RIGHT AS THE TROUGH
MOVES THROUGH. THERE WILL BE ONE MORE UPPER SHORT-WAVE MOVING
THROUGH SOUTHCENTRAL WEDNESDAY AFTERNOON AND EVENING...BUT WITH A
STRONG LOW MOVING INTO THE EASTERN GULF...LOW LEVEL FLOW WILL BE
SHIFTING TO THE NORTH AND LOW LEVELS WILL BEGIN TO DRY OUT. SO
EXPECT VERY LITTLE PRECIP OUT OF THIS SECOND SHORT-WAVE. THERE IS
SOME UNCERTAINTY IN THE TRACK OF THE NEW GULF LOW WEDNESDAY AND
THURSDAY...BUT BOTTOM LINE IS IT WILL REMAIN OUT OVER THE GULF.
THIS LOW...IN COMBINATION WITH COLD AIR ADVECTION ASSOCIATED WITH
AN UPPER LEVEL TROUGH DROPPING DOWN FROM THE ARCTIC AND STALLING
OVER SOUTHCENTRAL...WILL TIGHTEN THE PRESSURE GRADIENT THURSDAY AND
FRIDAY AND RESULT IN THE COMMENCEMENT OF GAP WINDS. BECAUSE
THE TROUGH STALLS...DON'T EXPECT MUCH COLD ADVECTION THROUGH THE
GAPS AND INTO THE GULF. THUS PRESSURE DIFFERENCES COMBINED WITH
DENSITY DIFFERENCES IN AIR MASS OVER THE GULF AND AIR MASS INLAND
WILL DRIVE THE WINDS.

SOUTHWEST ALASKA...UPPER WAVES ROUNDING THE LOW COMPLEX SOUTH OF
KODIAK WILL CONTINUE TO PRODUCE A FEW SHOWERS OVER BRISTOL BAY
THROUGH TUESDAY NIGHT. THE SNOW OCCURRING OVER MOSTLY INLAND
PORTIONS OF THE KUSKOKWIM DELTA WILL GRADUALLY COME TO END TONIGHT
AND WEDNESDAY AS UPPER TROUGH JUST OFF THE SOUTHWEST COAST TRACKS
INLAND...PUSHING ALL OF THE MOISTURE OFF TO THE SOUTHEAST AND
ADVECTING IN A DRIER AIRMASS. HIGH PRESSURE...SURFACE AND
ALOFT...WILL BUILD IN FROM THE WEST THURSDAY AND FRIDAY...BRINGING
A RESUPPLY OF ARCTIC AIR WHICH WILL PRODUCING LOCALLY GUSTY WINDS.

BERING SEA/ALEUTIANS/SOUTHERN ALASKA PENINSULA...STRONG
NORTHERLIES/SNOW SHOWERS/HEAVY FREEZING SPRAY WILL BEGIN TO
DIMINISH OVER THE CENTRAL BERING TONIGHT AS WEAK HIGH PRESSURE
BUILDS IN FROM THE WEST...BRINGING AN END TO THE COLD AIR ADVECTION.
THIS TREND WILL SPREAD EASTWARD THROUGH THE END OF THE WEEK...HANGING
ON LONGEST ALONG THE ALASKA PENINSULA. A STORM FORCE FRONT STEMMING
FROM A MAJOR STORM DEVELOPING OVER THE SEA OF OKHOTSK WILL TRACK
SLOWLY EASTWARD TO THE WESTERN ALEUTIANS WEDNESDAY NIGHT AND THEN
STALL OVER THE CENTRAL BERING FRIDAY AS STRONG RIDGE BUILDING OUT
AHEAD OF IT BLOCKS ANY FURTHER PROGRESSION. THE FRONT WILL ALSO
BEGIN TO WEAKEN BY FRIDAY AS THE FRONT BEGINS TO STRETCH APART
FROM THE ARCTIC DOWN TO THE TROPICS.

.LONG TERM FORECAST...THE HIGH AMPLITUDE RIDGE IN PLACE OVER THE
EASTERN BERING AND WESTERN MAINLAND AT WEEK'S END WILL NOSE OVER THE
TOP OF THE NORTHEAST PACIFIC/GULF TROUGH AND CONNECT UP WITH THE
RIDGE OVER CANADA OVER THE WEEKEND. THIS WILL RESULT IN A STRONG
SURFACE HIGH OVER THE NORTHERN MAINLAND WHICH WILL MAINTAIN A TIGHT
PRESSURE GRADIENT ACROSS THE SOUTHERN MAINLAND AND INTO THE GULF.
THUS...EXPECT DRY AND COLD CONDITIONS TO DOMINATE MAINLAND ALASKA
ALONG WITH THE USUAL STRONG WINDS THROUGH GAPS IN THE COASTAL RANGE.
MEANWHILE THE NORTHEAST PACIFIC TROUGH...NOW IN THE FORM OF A CUT-OFF
LOW...WILL GRADUALLY WORK ITS WAY BACK NORTHWARD TOWARD THE GULF AS
WE HEAD THROUGH NEXT WEEK. THIS WILL BRING A CHANCE OF PRECIP BACK
TO THE SOUTHERN MAINLAND...PRIMARILY ALONG THE COAST. OUT
WEST...ENERGY EXITING OUT OF THE DEEP ASIAN TROUGH WILL HELP PUSH THE
REMNANTS OF THE EASTERN BERING RIDGE OFF TO THE NORTH AND CONNECT
UP WITH GULF TROUGH...EVENTUALLY LEADING TO THE RETURN OF A MEAN
TROUGH OVER MOST OF THE FORECAST AREA AND A RETURN TO MORE ACTIVE
WEATHER.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING 176.
         GALE WARNING...150 155 160 165 170 171 179 180.
         HEAVY FREEZING SPRAY WARNING...155 160 165 170 171 179.
FIRE WEATHER...NONE.

KS/SEB JAN 10