Gale Warning 449, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1230 PM AKDT FRI JUN 18 2010

.ANALYSIS AND UPPER LEVELS...THE STAGNANT PATTERN OF THIS PAST
WEEK...DOMINATED BY A LARGE UPPER LOW CENTERED OVER THE BERING
WITH SHORT-WAVES EMBEDDED IN ITS FLOW ROTATING ACROSS THE ALASKA
REGION WILL LAST ANOTHER DAY BEFORE TRANSITION TO A NEW PATTERN
BEGINS. THIS MORNING A SHORT-WAVE IS EXITING SOUTHCENTRAL ALASKA
TO THE NORTH LEAVING BEHIND JUST A FEW SHOWERS WHILE ANOTHER
SHORT-WAVE IS MOVING ACROSS SOUTHWEST ALASKA RESULTING IN FAIRLY
WIDESPREAD COVERAGE OF SHOWERS FROM WESTERN BRISTOL BAY TO THE
KUSKOKWIM DELTA. THE MOST SIGNIFICANT SHORT-WAVE TROUGH SEEN IN
WATER VAPOR IMAGERY IS OVER THE NORTH CENTRAL PACIFIC. THIS TROUGH
HAS BEEN DIGGING SOUTHEASTWARD AS ROTATED OUT OF THE BERING SEA
AND IS NOW FAR ENOUGH SOUTH THAT IT WILL BE MORE INFLUENCED BY
THE WESTERLIES THAN THE BERING LOW CIRCULATION...AND THEREFORE
WILL END UP TRACKING EAST INSTEAD OF BACK NORTH TOWARD THE MAINLAND.

ALSO OF NOT IS A TROUGH OVER THE NORTHWEST PACIFIC TRACKING EAST
TOWARD THE ALEUTIANS. THIS FEATURE WILL BE A PLAYER IN THE UPCOMING
PATTERN CHANGE.

.MODEL DISCUSSION...THE NAM IS AN OUTLIER TODAY WITH TRACK OF
ALEUTIAN LOW THE NEXT FEW DAYS AS WELL AS IN ITS DEPICTION OF A
MUCH SHARPER TROUGH CROSSING THE SOUTHERN MAINLAND SATURDAY AND
SUNDAY. THEREFORE...WILL BASE FORECAST OFF THE GFS/ECMWF/UKMET
WHICH ARE ALL REASONABLY CLOSE WITH MAJOR FEATURES. THE PRIMARY
CHANGE TO THE FORECAST WILL BE TO INCREASE POPS OVER SOUTHCENTRAL
AHEAD OF THE WEAK TROUGH AXIS SATURDAY NIGHT INTO SUNDAY.
OTHERWISE...FINE-TUNING OF CURRENT FORECAST IS ALL THAT IS NEEDED.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND ALASKA...WEAK VORTICITY MAXIMA EMBEDDED IN THE
UPPER FLOW WILL CONTINUE TO MAINTAIN CLOUDY CONDITIONS ACROSS THE
SOUTHERN MAINLAND THROUGH SATURDAY AND SHOWER COVERAGE WITH THESE
WILL BE MINIMAL (ISOLATED TO SCATTERED). THE ONE EXCEPTION IS THE
KUSKOKWIM DELTA WHICH WILL CONTINUE TO SEE OCCASIONAL SHOWERS
CLOSER TO THE BERING LOW CENTER. ONE FINAL TROUGH WILL SWING
THROUGH SOUTHWEST ALASKA SATURDAY AND SOUTHCENTRAL ALASKA SATURDAY
NIGHT INTO SUNDAY...PRODUCING SHOWERS OUT AHEAD OF IT.
MEANWHILE...THE BERING LOW WILL TRACK WESTWARD AWAY FROM THE
REGION AS A NEW LOW SETS UP SHOP ALONG THE ALEUTIANS...AND THIS
IN TURN WILL ALLOW A RIDGE TO BUILD OVER THE EASTERN BERING AND
SOUTHWEST ALASKA SUNDAY AND MONDAY...BRINGING ALLOWING SUNSHINE
AND WARMER TEMPERATURES TO RETURN. MODELS DO INDICATE THE REMNANTS
OF THE UPPER TROUGH STALLING OVER INTERIOR SOUTHCENTRAL SUNDAY...SO
THIS WILL LIKELY HELP TO TRIGGER DIURNAL CONVECTION AS WE HEAD
THROUGH THE BEGINNING OF NEXT WEEK. SOUTHWEST ALASKA WILL BE RIGHT
UNDERNEATH THE UPPER RIDGE AND WILL LIKELY DEVELOP A CAP THAT WILL
LIMIT ANY CONVECTION.

BERING SEA/ALEUTIANS...THE TROUGH OVER THE NORTHWEST PACIFIC WILL
MOVE TO THE WESTERN ALEUTIANS TONIGHT WHILE ANOTHER TROUGH DROPS
DOWN FROM THE NORTH. THESE WILL MERGE INTO A SINGLE LARGE UPPER
LEVEL CLOSED LOW BY SUNDAY AND SERVE AS THE FOCUS FOR ACTIVE WEATHER
NEXT WEEK. A SURFACE LOW WILL DEVELOP BENEATH THE UPPER CENTER...SO
THE TREND ACROSS THE ALEUTIANS AND WESTERN BERING THE NEXT FEW DAYS
WILL BE WETTER AND WINDIER. THE EASTERN BERING AND ALASKA PENINSULA
WILL INITIALLY REMAIN EAST OF THIS ACTIVITY UNDER THE INFLUENCE OF
THE UPPER RIDGE.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE INCONSISTENT IN THE
SPEED AT WHICH UPPER LOW ALONG THE ALEUTIANS WILL PROGRESS EASTWARD
NEXT WEEK. THIS WILL DETERMINE HOW LONG THE WARM AND SUNNY PATTERN
PERSISTS OVER THE SOUTHERN MAINLAND. BASED ON AN AVERAGE SPEED OF
THE LATEST MODEL SOLUTIONS EXPECT THE NICE WEATHER TO CONTINUE
OVER THE SOUTHERN MAINLAND THROUGH AT LEAST MID WEEK AND THEN
HEAD DOWNHILL BY THE END OF THE WEEK. THE BERING AND ALEUTIANS
ON THE OTHER HAND WILL SEE IMPROVING CONDITIONS AS THE SYSTEM
SHIFTS EASTWARD AND A RIDGE BUILDS IN BEHIND IT.

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

SEB JUN 10