Gale Warning 654, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
215 PM AKDT WED SEP 23 2009

.MODEL DISCUSSION...

THE GFS WAS THE MODEL OF CHOICE FOR THE AFTERNOON PACKAGE THROUGH
SATURDAY MORNING...AS THE NAM IS A SLOW OUTLIER WITH RESPECT TO
PROGRESSION OF THE NORTH PACIFIC LOW THAT WILL MOVE TOWARDS AND
THROUGH THE WESTERN GULF OF ALASKA THURSDAY NIGHT THROUGH FRIDAY
NIGHT. THE OTHER AREA OF INTEREST IS A SECONDARY LOW DEVELOPING IN
THE FAR NORTHWEST BERING SEA THAT WILL BE MOVING SOUTHEASTTOWARDS THE
EASTERN ALEUTIANS AND SOUTHERN AKPEN...ARRIVING SOMETIME FRIDAY
NIGHT. THE GFS MODEL WAS PREFERRED WITH THIS FEATURE AS WELL. PAST
SATURDAY MORNING SIGNIFICANT DIFFERENCES ARISE AS THIS SECONDARY LOW
MOVES INTO THE GULF. THE GFS AND EC HAVE BEEN CONSISTENT IN THEIR
SOLUTIONS...WITH THE GFS BRINGING THIS LOW ON SUNDAY UP TO A POINT
BETWEEN KODIAK AND MIDDLETON ISLAND MUCH CLOSER TO
SOUTHCENTRAL...WHILE THE EC BRINGS THIS LOW INTO THE SOUTHERN GULF.
THE OO UTC EC WAS USED WITH THE SOUTHERN TRACK PREFERRED GIVEN GOOD
AGREEMENT WITH MOST GFS ENSEMBLE MEMBERS...WITH THE GFS OPERATIONAL
THE FARTHEST NORTH SOLUTION. THIS REPRESENTED LITTLE CHANGE FROM
EXISTING GRIDS IN THE MEDIUM TO LONG RANGE...SO THOSE GRIDS WERE LEFT
ALONE.

.ANALYSIS AND UPPER LEVELS...

THE BIG WEATHER FEATURE AFFECTING OUR AREA OF RESPONSIBILITY IS A 982
MB LOW...THE REMNANTS OF SUPER TYPHOON CHOI-WAN...LOCATED ABOUT 350
MILES SOUTH OF UNALASKA ISLAND. THIS LOW IS MOVING NORTHEAST TOWARDS
THE WESTERN GULF OF ALASKA...AND IS CO-LOCATED WITH A MID-LEVEL LOW.
ANOTHER STACKED LOW IS LOCATED OVER THE LOWER YUKON VALLEY BETWEEN
MCGRATH AND NORTON SOUND. THIS FEATURE IS BRINGING SNOW CHANGING TO
SNOW AND RAIN SHOWERS TO THE MIDDLE AND UPPER KUSKOKWIM RIVER VALLEY
TODAY. A SHORTWAVE RIDGE IS LOCATED OVER SOUTHCENTRAL...PROVIDING FOR
A BEAUTIFUL DAY FROM THE MATANUSKA AND SUSITNA VALLEYS DOWN THROUGH
THE KENAI PENINSULA AND KODIAK ISLAND...AND EXTENDING OVER INTO THE
PARTS OF THE BRISTOL BAY REGION. A 1018 MB LOW IS LOCATED EAST OF THE
NORTHEASTERN KAMCHATKA PENINSULA...AND THIS FEATURE WILL MOVE
SOUTHEAST THROUGH THE BERING SEA OVER THE NEXT FEW DAYS.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

A SHORTWAVE EXITING THE COPPER RIVER BASIN BY THIS AFTERNOON SHOULD
IMPROVE CONDITIONS THERE DRASTICALLY OVER THE NEXT FEW HOURS...MAINLY
FROM SOUTH TO NORTH. ELSEWHERE...LOW PRESSURE OVER THE YUKON RIVER
VALLEY WILL KEEP PRECIPITATION CONFINED TO THE WESTERN SLOPES OF THE
ALASKA RANGE...WITH NO SIGNIFICANT EFFECT ON THE WEATHER IN THE
SUSITNA VALLEY EXCEPT PERHAPS A FEW CLOUDS AS A SHORTWAVE STAYS JUST
NORTH OF THE REGION DURING THE OVERNIGHT HOURS TONIGHT.
OTHERWISE...EXPECT MOSTLY NICE WEATHER FOR THE NEXT 12 HOURS OR SO
UNTIL A FRONT ASSOCIATED WITH THE APPROACHING GULF LOW BEGINS TO MOVE
ACROSS THE GULF ON THURSDAY. BY THURSDAY NIGHT...WITH A RIDGE TO THE
NORTH OVER THE COPPER RIVER BASIN AND THE APPROACHING STRONG
FRONT...STORM-FORCE WINDS WILL BE POSSIBLE AS A BARRIER JET INCREASES
IN STRENGTH LATE THURSDAY AND LASTS FOR A GOOD PART OF THE OVERNIGHT
PERIOD THURSDAY NIGHT. OTHERWISE...WITH SOUTHERLY FLOW OVER THE
REGION TEMPERATURES WILL BE WARM ENOUGH TO SUPPORT RAIN EXCEPT THERE
COULD BE A MIX OF RAIN AND SNOW IN THE COPPER RIVER BASIN THURSDAY
NIGHT AS COLDER AIR IS SCOURED OUT. AS THE LOW MOVES TO THE EAST OF
ANCHORAGE IN PRINCE WILLIAM SOUND...WE SHOULD START TO SEE RAIN
INCREASE IN COVERAGE ON THE BACK SIDE FOR ANCHORAGE BEFORE MOVING OUT
FRIDAY NIGHT...BEING REPLACED BY WEAK HIGH PRESSURE FOR THE DAY ON
SATURDAY.

SOUTHWEST...

SHORTWAVE ENERGY MOVING ACROSS THE AREA WILL LIFT OUT THIS EVENING
BRINGING A BRIEF PERIOD OF RELATIVELY TRANQUIL WEATHER TO THE REGION.
THE EXCEPTION MIGHT BE ALONG THE COAST OF THE NORTHWEST DELTA REGION
WHERE SHOWERS WILL BE POSSIBLE. FOR THURSDAY...EXPECT INCREASINGLY
OFFSHORE FLOW AND MOSTLY CLEAR TO PARTLY CLOUDY SKIES AS LOW PRESSURE
MOVES INTO THE WESTERN GULF AND WEAK RIDGING BUILDS OVER THE MIDDLE
KUSKOKWIM RIVER VALLEY FOR THURSDAY. HOWEVER...WITH STRONG FORCING
FOR ASCENT WILL LIKELY SEE RAIN FOR THE EASTERN BRISTOL BAY ZONE
MOSTLY FROM KING SALMON EAST...WITH UPSLOPE SHOWERS FORMING ON THE
BACK SIDE OF THE LOW ON FRIDAY ALONG THE ALASKA RANGE. ANOTHER IN A
SERIES OF LOWS MOVES INTO THE DELTA REGION AS WELL FOR FRIDAY...SO A
CHANCE OF RAIN AND SNOW SHOWERS APPEARS TO RETURN BEFORE QUICKLY
MOVING UP THE KUSKOKWIM RIVER VALLEY FRIDAY NIGHT.

AKPEN/ALEUTIANS/BERING SEA...

GALES WILL CONTINUE ALONG THE SOUTHERN AKPEN COASTAL ZONES AND
ALEUTIANS AS LOW PRESSURE MOVES TOWARDS THE GULF. ATTENTION THEN
FOCUSES ON ANOTHER LOW THAT WILL MOVE SOUTHEAST THROUGH THE BERING
SEA THROUGH FRIDAY. STRONG COLD ADVECTION ON THE BACK SIDE OF THIS
LOW SHOULD BRING GALE-FORCE WINDS AS IT PROGRESSES THROUGH THE
REGION. BY EARLY SATURDAY MORNING...THIS LOW WILL MOVE ACROSS THE
SOUTHERN AKPEN HEADED TOWARDS THE WESTERN GULF.

.LONG TERM FORECAST...

AS MENTIONED EARLIER...SIGNIFICANT DIFFERENCES REMAIN WITH RESPECT TO
THE TRACK OF LOW PRESSURE IN THE GULF FROM SATURDAY NIGHT THROUGH
MONDAY. THE GFS OPERATIONAL APPEARS TO BE A NORTHERLY
OUTLIER...KEEPING IT NEAR THE COAST...WHILE THE EC AND MANY GFS
ENSEMBLE MEMBERS KEEP THE LOW IN THE SOUTHERN GULF AND WELL AWAY FROM
SOUTHCENTRAL ALASKA. NO CHANGES WERE MADE TO EXISTING GRIDS AS THEY
DEPICT THE SOUTHERN TRACK PRETTY WELL. ON THE WEST SIDE...MODELS ARE
IN GOOD AGREEMENT ON A STRONG FRONT AND LOW PRESSURE SYSTEM BEGINNING
TO AFFECT THE WESTERN ALEUTIANS AND BERING SEA AS EARLY AS SUNDAY AND
THEN MOVING EAST ACROSS THE BERING SEA OVER THE FOLLOWING DAYS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...125 130 132 138 140 150 155 170 171 172
         STORM WARNING...120
FIRE WEATHER...NONE.

CC SEP 09