Gale Warning 640, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 PM AKDT SUN SEP 5 2010

.ANALYSIS AND UPPER LEVELS...
VERTICALLY STACKED LOW PRESSURE IN THE NORTHERN GULF IS SLOWLY
FILLING AND MOVING TO THE SOUTHEAST. THE TRIPLE POINT LOW SOUTH OF
PRINCE WILLIAM SOUND DEVELOPED STRONGER THAN ANTICIPATED IN PREVIOUS
MODEL RUNS...WITH RESULTING BARRIER JET SPEEDS UPWARDS OF 40 KNOTS
OBSERVED THIS MORNING NEAR THE COAST. OUT WEST...THE EXTRATROPICAL
REMNANTS OF A WEST PACIFIC TYPHOON ARE HELPING A LOW NEAR THE WESTERN
ALEUTIANS DEVELOP INTO A POTENT EARLY FALL STORM. DEEP TROPICAL
MOISTURE IS NOTED ON SATELLITE WITH THIS SYSTEM...WITH DERIVED TOTAL
PRECIPITABLE WATER EXCEEDING 200 PERCENT OF NORMAL. BETWEEN THE
BERING AND GULF LOWS...A RIDGE OF HIGH PRESSURE IS ATTEMPTING TO
BUILD INTO SOUTHWEST ALASKA.

.MODEL DISCUSSION...MODELS ARE IN OVERALL GOOD AGREEMENT...WITH ONLY
A FEW SIGNIFICANT ISSUES. FIRST...TIMING REMAINS A CONCERN WITH THE
ONSET OF PRECIPITATION OVER SOUTHCENTRAL LATE MONDAY NIGHT AS THE
NEXT FRONT APPROACHES FROM THE SOUTHWEST. THE NAM REMAINS THE SLOWEST
SOLUTION...WHILE THE GFS IS THE FASTEST...AND THE ECMWF IS SOMEWHERE
IN THE MIDDLE. OVERALL TIMING SPREAD REMAINS ABOUT 6 HOURS...AND FOR
THIS PACKAGE A COMPROMISE SOLUTION BETWEEN THE ECMWF AND NAM WERE
USED. THE SECOND MODEL DISCREPANCY IS THE POSITION OF THE BERING LOW
AS IT MOVES INTO THE NORTHERN BERING SEA MONDAY NIGHT.
FORTUNATELY...ALL SOLUTIONS RESULT IN SIMILAR WEATHER FOR THE
PRIBILOF ISLANDS AND SOUTH WEST ALASKA...SOUTHWEST FLOW WITH FOG AND
RAIN. OVERALL MODEL CONFIDENCE IS SLIGHTLY ABOVE AVERAGE.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...THE STRONGER THAN EXPECTED TRIPLE POINT LOW IN THE
GULF IS DELAYING THE DEMISE OF LOW TO MIDLEVEL CLOUDS ACROSS THE
ANCHORAGE BOWL AND KENAI PENINSULA. HOWEVER...CONDITIONS ARE SLOWLY
IMPROVING AND THE TREND SHOULD CONTINUE THROUGH THE EVENING AND
OVERNIGHT. AS HIGH PRESSURE BUILDS IN TONIGHT AND TOMORROW...SKIES
SHOULD BECOME PARTLY CLOUDY ACROSS THE REGION...MAKING MONDAY AN
OASIS OF PLEASANT WEATHER BEFORE RAIN RETURNS TO THE AREA LATE MONDAY
NIGHT. THE MAIN FORECAST CHALLENGE SHOULD OCCUR AS PRESSURE RISES
BEHIND THE DEPARTING SYSTEM SPREAD INTO COOK INLET...CREATING GUSTY
WINDS AT SEWARD...WHITTER...AND POSSIBLY EVEN VALDEZ LATER THIS
EVENING AND OVERNIGHT.

.SOUTHWEST...DESPITE HIGH PRESSURE BUILDING UP FROM THE NORTH THIS
AFTERNOON CONDITIONS WILL ONLY SLOWLY IMPROVE AS SOUTHWEST ONSHORE
FLOW CONTINUES TO PUMP ABUNDANT MOISTURE WELL INLAND. BREAKS IN THE
WIDESPREAD LOW CLOUDS SHOULD INCREASE THIS EVENING...BEFORE MORE
CLOUDS AND A CHANCE OF RAIN ARRIVE BY MORNING. AT THIS TIME IT DOES
NOT APPEAR SIGNIFICANT AMOUNTS OF RAIN WILL FALL AS THE BERING FRONT
FALLS APART JUST OFFSHORE. HOWEVER...A SECOND FRONT WILL RAPIDLY
DEVELOP MONDAY EVENING AND BRING SUBSTANTIAL RAINS TO ALL AREAS
THROUGH TUESDAY MORNING.

.BERING SEA/ALEUTIANS...THE MOST SIGNIFICANT FEATURE IN THE AREA
CURRENTLY IS AND WILL REMAIN THE LOW CROSSING INTO THE BERING SEA
JUST WEST OF ADAK. WINDS HAVE BEEN SURPRISINGLY STRONG...UPWARDS OF
50 KNOTS...ALONG THE FRONT. THIS FRONT WILL SLOWLY WEAKEN OVERNIGHT
AS IT MOVES TO THE NORTH AND EAST. NEVERTHELESS...STRONG WINDS ARE
EXPECTED THIS EVENING AND OVERNIGHT FROM THE EASTERN ALEUTIANS AND
ALASKA PENINSULA TO THE PRIBILOF ISLANDS. WIDESPREAD GALE FORCE WINDS
ON THE SOUTH SIDE OF THE LOW SHOULD BRING ANOTHER PERIOD OF WINDY
CONDITIONS TO THE CENTRAL AND EASTERN BERING DURING THE DAY TUESDAY.

.LONG TERM FORECAST...
THE LONGWAVE TROUGH IN THE BERING SEA LOOKS TO REMAIN ENTRENCHED
THROUGH THE END OF THE WEEK. WITH WEST AND SOUTHWEST FLOW ALOFT
CONTINUING OVER MAINLAND ALASKA...EXPECT GENERALLY ALTERNATING
PERIODS OF RAIN AND MORE BENIGN WEATHER...WITH TEMPERATURES NEAR
NORMAL AT MOST LOCATIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE 120 170 172 175 185 179.
FIRE WEATHER...NONE.

AMD SEP 10