Gale Warning 405, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT SAT MAY 8 2010

.UPPER LEVEL ANALYSIS...
CYCLONIC FLOW AROUND A VIGOROUS UPPER LEVEL POLAR LOW OVER VICTORIA
ISLAND IN CANADA HAS BEEN ACTING AS A SHORTWAVE TROUGH CONVEYOR BELT
OVER THE MAINLAND FOR THE PAST FEW DAYS. THE FIRST OF THESE TROUGHS
THAT IMPACTED SOUTH CENTRAL AND SOUTHWEST ALASKA LATE THIS PAST WEEK
IS SWINGING SOUTHWARD INTO THE GULF OF ALASKA AS IT WRAPS AROUND ITS
PARENT LOW. AN EMBEDDED YET TIGHT 500 MB CIRCULATION IS EVIDENT ON
BOTH THE VISIBLE AND IR SATELLITE CHANNELS. ANOTHER SHARP SHORTWAVE
TROUGH IS DIVING SOUTHWARD OVER THE BERING STRAIT AND HAS ALSO
DEVELOPED A MID-LEVEL LOW AS IF MIMICKING ITS PREDECESSOR. A THIRD
TROUGH A FEW DAYS AWAY FROM IMPACTING THE REGION STRETCHES NORTHWARD
FROM THE LOW TOWARDS THE NORTH POLE. OUT INTO THE BERING SEA...A
PERSISTENT HIGH PRESSURE RIDGE IS CREEPING SLOWLY WESTWARD AS A
BARBELL LOW UNDERCUTS IT TO THE SOUTH OF THE ALEUTIANS.

.SURFACE ANALYSIS...
SURFACE LOW PRESSURE COVERS MUCH OF THE STATE AS A RESULT OF BOTH
THERMAL TROUGHING IN THE INTERIOR AND A SURFACE LOW ACCOMPANYING THE
NEXT WEATHER SYSTEM MOVING SOUTH OUT OF THE ARCTIC. A BROAD REGION OF
LOW PRESSURE OFFSET 200 MILES TO THE EAST OF ITS PARENT MID-LEVEL LOW
ENCOMPASSES MUCH OF THE WESTERN GULF OF ALASKA. HIGH PRESSURE
DOMINATES THE BERING WITH A SHALLOW SHORTWAVE RIDGE POKING INTO
SOUTHWESTERN ALASKA. A TEMPORARILY STALLED 991 MB LOW RESIDES WELL
SOUTH OF THE WESTERN ALEUTIANS.

.MODEL DISCUSSION...
MODELS INITIALIZED WELL ACROSS THE BOARD TODAY AND ARE IN GOOD
AGREEMENT OUT THROUGH 48 HOURS BEFORE THINGS START TO GET INTERESTING
OUT TOWARDS SOUTHWESTERN ALASKA. UNCERTAINTY ARISES AS THE MID-LEVEL
SHORTWAVE TROUGH DIGGING SOUTHWARD ACROSS WESTERN ALASKA BEGINS TO
INTERACT WITH A LOW JUST SOUTH OF COLD BAY. THE MODELS AGREE THAT
THESE TWO SYSTEMS WILL MERGE INTO A BROAD MID-LEVEL LOW CENTERED OVER
THE AKPEN...BUT DIFFER ON TIMING OF THE ASSOCIATED SHORTWAVES
WRAPPING AROUND THIS SYSTEM. THE PREDICTED TRACK OF THE ASSOCIATED
SURFACE LOW ALSO DIVERGES AROUND THIS TIME FRAME...WITH THE GFS
TAKING THE LOW INLAND NEAR KODIAK WHILE THE ECMWF IS FURTHER WEST
TOWARDS SAND POINT. DESPITE THESE DIFFERENCES...THE END RESULT FOR
THE NORTHERN GULF COAST IS THE SAME...NUMEROUS SHOWERS ALONG THE
COAST WITH CLOUDS FURTHER INLAND STARTING ON TUESDAY. THE SHORT-TERM
FORECAST USES A BLEND OF THE NAM AND GFS.

.SHORT TERM FORECAST...
.SOUTH CENTRAL ALASKA...CUMULUS CLOUDS WILL CONTINUE TO BUILD ACROSS
THE COPPER RIVER BASIN AND THE MAT-SU VALLEY/ANCHORAGE BOWL THIS
AFTERNOON AS SURFACE HEATING ONCE AGAIN PUSHES THE SURFACE AIR MASS
PAST ITS CONVECTIVE TEMPERATURE. UPPER LEVEL RIDGING BUILDING IN FROM
THE WEST WILL HELP TO MODERATE CLOUD DEVELOPMENT AND CONFINE SHOWERS
TO THE MOUNTAINS WEST OF THE CHUGACH AND TALKEETNA MOUNTAIN
RANGES...WITH WIDESPREAD SHOWERS MORE LIKELY IN THE COPPER RIVER
BASIN WHERE THE RIDGE IS SLIGHTLY WEAKER. EXPECT ANOTHER WARM DAY
ACROSS SOUTH CENTRAL AS LIGHT OFFSHORE FLOW PERSISTS ACROSS THE
REGION. TOMORROW WILL MIRROR TODAY WEATHER-WISE FOR THE MOST
PART...BUT WINDS WILL BEGIN TO SWITCH TO A MORE ONSHORE FLOW AS A LOW
BEGINS TO TRACK INTO THE WESTERN GULF OF ALASKA. COOLER TEMPERATURES
AND CLOUDY SKIES WILL FOLLOW SUIT ON MONDAY MORNING...WITH UPSLOPE
MOUNTAIN RANGES EXPERIENCING WIDESPREAD SHOWERS. COASTAL AREAS OF THE
NORTH GULF COAST AND KODIAK ISLAND WILL ALSO SEE PLENTY OF RAIN FROM
THIS SYSTEM...WHICH WILL WILL STALL OUT OVER THE SOUTHEASTERN BERING
SEA ON TUESDAY AND PUMP PLENTY OF MOISTURE ACROSS SOUTHERN ALASKA.

.SOUTHWEST ALASKA...A WEAK UPPER LEVEL SHORTWAVE TROUGH PROGRESSING
OUT AHEAD OF THE MAIN LOW OVER THE BERING STRAIT IS INSTIGATING A
BAND OF LIGHT RAIN THAT IS SLOWLY WORKING SOUTHWARD ACROSS THE
EASTERN BERING SEA AND PORTIONS OF WESTERN ALASKA. THE BETHEL RADAR
INDICATES THAT THESE LIGHT SHOWERS WILL MOVE INTO THE BETHEL AREA
EARLY THIS AFTERNOON AND PUSH FURTHER SOUTH AND EAST ACROSS THE
KUSKOKWIM DELTA AND POINTS SOUTH LATER THIS AFTERNOON AND EVENING. A
NEW LOW PUSHES NORTHWARD OUT OF THE FAR WESTERN GULF AND ACROSS THE
BRISTOL BAY REGION EARLY IN THE WEEK AND THEN STALLS IN THE
SOUTHEASTERN BERING SHORTLY THEREAFTER...SPELLING A WET BEGINNING TO
THE WEEK OVER SOUTHWESTERN ALASKA.

.ALEUTIANS AND BERING SEA...THE WEATHER OVER THE ALEUTIANS REMAINS
RELATIVELY QUIET THROUGH THE FORECAST PERIOD. THE LOW PRESENTLY SOUTH
OF THE WESTERN ALEUTIANS STALLS TODAY BEFORE COMMENCING AN EASTWARD
TRACK WELL SOUTH OF THE ISLANDS. PRECIPITATION ASSOCIATED WITH THIS
SYSTEM REMAINS SOUTH OF THE ISLAND CHAIN. A WEAK FRONT DROPPING SOUTH
OVER THE EASTERN BERING WILL BRING LITTLE MORE THAN LIGHT RAIN TO THE
PRIBILOFS AND THE AKPEN TODAY AND TOMORROW. SHOWERS GRADUALLY FILL IN
OVER THE EASTERN ISLANDS FROM THE EAST STARTING ON MONDAY EVENING AS
THE AFOREMENTIONED LOW WRAPS NORTHWARD TOWARDS THE AKPEN AND THEN
STALLS OVER THE EASTERN BERING SEA ON TUESDAY AFTERNOON.

.LONG TERM FORECAST...
CLOUDS AND SHOWERS WILL PERSIST OVER SOUTHERN ALASKA THROUGH THE WEEK
AS A REX BLOCK TAKES SHAPE OVER THE WESTERN UNITED STATES...FORCING
THE STACKED LOW OVER THE SOUTHEASTERN BERING SEA TO REMAIN STALLED
AND FEED A CONTINUOUS SUPPLY OF MOISTURE AND CLOUDS TO THE REGION.
EXPECT SLIGHTLY COOLER TEMPERATURES AS WELL DUE TO THE INFLUX OF THE
COLDER MARITIME AIR MASS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...175 176.
FIRE WEATHER...NONE.

KS MAY 10