Gale Warning 522, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1230 PM AKDT THU AUG 12 2010

.ANALYSIS AND UPPER LEVELS...AMPLIFICATION OF THE UPPER LEVELS
CONTINUES AS BERING SEA TROUGH DIGS SOUTHWARD AND DOWNSTREAM
RIDGE OVER THE FAR NORTHEAST PACIFIC BUILDS NORTHWARD OVER
SOUTHEAST ALASKA AND WESTERN CANADA. WATER VAPOR IMAGERY SHOWS
A LONG FETCH OF TROPICAL MOISTURE FLOWING NORTHWARD BETWEEN THE
TROUGH AND RIDGE. RIGHT NOW THE JET IS FAIRLY WEAK THROUGH THIS
AREA...BUT THIS IS EXPECTED TO STRENGTHEN AS THE PATTERN CONTINUES
TO AMPLIFY. THE MAIN FEATURES OF CONCERN ARE RIGHT IN THIS CORRIDOR.
A SHORT-WAVE OVER BRISTOL BAY IS TRACKING QUICKLY INLAND WITH RAIN
SPREADING OUT AHEAD OF IT ACROSS SOUTHWEST ALASKA AND WESTERN
PORTION OF SOUTHCENTRAL. AT THE SURFACE A WEAK LOW PRESSURE SYSTEM
IS MOVING INTO THE SOUTHWESTERN GULF. THE FRONT EDGE OF RAIN WITH
THIS SYSTEM IS JUST BEGINNING TO SHOW UP ON THE MIDDLETON ISLAND
RADAR. ELSEWHERE...A WEAK VERTICALLY STACKED LOW NEAR ADAK IS
TRACKING SOUTHEASTWARD. A 150 KT JET ON THE BACK SIDE OF THIS
LOW IS THE CAUSE OF THE AMPLIFYING TROUGH.

.MODEL DISCUSSION...THE BIGGEST FORECAST CHALLENGE OVER THE NEXT
COUPLE DAYS IS DETERMINING EXACTLY WHERE THE STRONG SOUTHERLY FLOW
SETS UP BETWEEN THE UPPER TROUGH AND RIDGE. ALL SOLUTIONS HAVE
TRENDED EASTWARD...BUT THE GFS IS MUCH FARTHER EAST THAN ANY OF
THE OTHER SOLUTIONS. THIS WILL DETERMINE WHETHER SOUTHCENTRAL ALASKA
HAS A COUPLE NICE DAYS OR WHETHER THE CLOUDY COOL AND WET WEATHER
WILL CONTINUE. FOR NOW WILL IGNORE THE GFS SOLUTION AND STICK CLOSE
TO CURRENTLY ADVERTISED FORECAST...WHICH IS FAIRLY CLOSE TO SOLUTION
OF OTHER MODELS.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...RAIN ASSOCIATED WITH THE UPPER LEVEL SHORT-WAVE
WILL EXIT TO THE NORTH THIS EVENING. HOWEVER...RAIN ASSOCIATED WITH
THE SURFACE LOW OVER THE GULF WILL SPREAD NORTHWARD TO THE PRINCE
WILLIAM SOUND REGION THIS AFTERNOON AND SOME OF THIS COULD SPILL
OVER INTO OTHER PORTIONS OF SOUTHCENTRAL. THE UPPER LEVEL RIDGE
WILL AMPLIFY SATURDAY...BUT THERE IS UNCERTAINTY IN WHETHER IT WILL
BECOME AMPLIFIED ENOUGH TO PREVENT RAIN FROM NEXT PACIFIC SYSTEM
FROM MOVING INTO SOUTHCENTRAL. FOR NOW WILL STICK WITH A MOSTLY DRY
FORECAST ACROSS THE REGION ON FRIDAY...RECOGNIZING THAT THERE IS
POTENTIAL FOR THIS TO CHANGE. IN ANY CASE...WHETHER THERE IS MUCH OF
A BREAK OR NOT ON FRIDAY...THE TROUGH IS EXPECTED TO PUSH EASTWARD
SATURDAY AND SUNDAY AND BRING ANOTHER ROUND OF RAIN TO THE REGION.

SOUTHWEST ALASKA...SOUTHWEST ALASKA WILL SEE ANOTHER BRIEF BREAK
IN RAIN TONIGHT INTO FRIDAY IN BETWEEN SYSTEMS. HOWEVER...IT THEN
LOOKS LIKE THE FIRE HOSE OF TROPICAL MOISTURE WILL BE AIMED RIGHT
AT SOUTHWEST ALASKA LATE FRIDAY INTO SATURDAY WHILE A STRENGTHENING
SURFACE LOW TRACKS NORTHWARD INTO THE EASTERN BERING SEA. THERE IS
UNCERTAINTY IN THE EXACT PLACEMENT OF THE FIRE HOSE AND LOW PRESSURE
SYSTEM...BUT THE VARIETY OF SOLUTIONS ALL INDICATE VERY WET
CONDITIONS FOR THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT WITH
IMPROVING CONDITIONS LIKELY ON SUNDAY AS EVERYTHING MOVES EASTWARD.

BERING SEA/ALEUTIANS...THE BERING SEA WILL REMAIN QUIET THE NEXT
FEW DAYS UNDERNEATH THE UPPER TROUGH AS STORMS TRACK ALONG THE
PERIPHERY OF THE TROUGH. A LOW WILL TRACK SOUTH OF THE ALEUTIANS
SATURDAY AND SUNDAY...BRINGING GALE FORCE WINDS AND RAIN TO THE
WESTERN TO CENTRAL ALEUTIANS.

.LONG TERM FORECAST...THE PATTERN LOOKS LIKE IT WILL BECOME QUITE
PROGRESSIVE NEXT WEEK. THE TROUGH AFFECTING THE SOUTHERN MAINLAND
THIS WEEKEND WILL EXIT TO THE NORTH EARLY NEXT WEEK WHILE THE
SYSTEM ALONG THE ALEUTIANS RAPIDLY MOVES IN TO TAKE ITS PLACE.
AFTER THIS SYSTEM EXITS MODELS INDICATE A MORE ZONAL FLOW SETTING
UP. MODEL PERFORMANCE IN THIS TIME RANGE HAS NOT BEEN VERY GOOD AS
OF LATE...BUT MEDIUM RANGE MODELS DO SUPPORT PROGRESSION OF A RIDGE
ACROSS THE BERING SEA EARLY TO MID WEEK AND THEN OVER MAINLAND
MID TO LATE WEEK. THIS WOULD PROVIDE FOR A LONGER DURATION OF
NICE WEATHER BEFORE THE NEXT SYSTEM MOVES IN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...150 155 160 165.
FIRE WEATHER...NONE.

SEB AUG 10