Gale Warning 369, NWS Anchorage, AK

AREA FORECAST DISCUSSION CORRECTION
SOUTHCENTRAL AND SOUTHWEST ALASKA
125 PM AKDT TUE APR 28 2009

CORRECTED FOR TYPOS

.ANALYSIS AND UPPER LEVELS...BLOCKING RIDGE CENTERED ALONG 140W
IS BUILDING NORTHWARD OVER EASTERN ALASKA AND THE YUKON. THE BOTTOM
OF THE RIDGE IS BEGINNING TO BE PINCHED WHICH WILL EVENTUALLY LEAD
TO FORMATION OF A CUT-OFF HIGH. AREAS OF STRATUS AND FOG ARE MOVING
AROUND THE GULF WHILE MOST OF SOUTHCENTRAL IS ENJOYING A CLEAR AND
DRY DAY. LONG-WAVE TROUGH IS CENTERED OVER THE BERING WITH MULTIPLE
SHORT-WAVES MOVING THROUGH IT. A 165 KT ZONAL JET EXTENDS ACROSS
THE NORTH PACIFIC ALONG 40N THEN TURNS NORTHWARD AROUND
155W...TRANSPORTING LOTS OF TROPICAL MOISTURE NORTHWARD ACROSS THE
ALASKA PENINSULA AND SOUTHWEST ALASKA COAST. THE BULK OF THE RAIN
IS FALLING ALONG THE ALASKA PENINSULA WITH LIGHTER RAIN ALONG THE
SOUTHWEST COAST. A MODERATE LOW NEAR THE FAR WESTERN ALEUTIANS IS
SITTING RIGHT IN THE MIDDLE OF THE LONG-WAVE TROUGH WITH LITTLE
STEERING FLOW...AND IS MAKING VERY SLOW EASTWARD PROGRESS.

.MODEL DISCUSSION...MODELS ARE IN GOOD AGREEMENT WITH FEATURES
AFFECTING ALASKA WEATHER THROUGH ABOUT THURSDAY NIGHT. IN
PARTICULAR MODELS HAVE CONVERGED ON A SIMILAR SOLUTION FOR SURFACE
WAVE TRACKING TO THE SOUTHERN ALASKA PENINSULA/EASTERN ALEUTIANS
WEDNESDAY MORNING AND THEN INTO THE BERING SEA. WILL MODIFY FORECAST
TO FULLY REFLECT THIS FEATURE. OTHERWISE...NO MAJOR CHANGES IN THE
SHORT-TERM.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE MAIN FORECAST CHALLENGE FOR SOUTHCENTRAL
IS FORECASTING THE MOVEMENT OF THE MARINE STRATUS. WITH FULL SUN
OVER LAND EXPECT SEA BREEZE TO DEVELOP ALONG THE COAST WHICH WILL
HELP BRING SOME OF THE STRATUS ONSHORE. HOWEVER...THE SURFACE HIGH
WILL MOVE OVER LAND TONIGHT...SO ANY STRATUS THAT DOES MOVE ONSHORE
SHOULD NOT MAKE IT VERY FAR AND WILL MOVE BACK OFFSHORE QUICKLY.
THE SURFACE RIDGE AXIS WILL SET UP SHOP RIGHT ALONG THE NORTH GULF
COASTAL REGION FOR THE NEXT COUPLE DAYS...WHICH SHOULD KEEP MOST
OF THE STRATUS JUST OFFSHORE. HOWEVER...THE POSITIONING OF THE
RIDGE WILL ALLOW FOR A TIGHTENING PRESSURE GRADIENT AS THE FRONT
DOWN OVER THE SOUTHERN ALASKA PENINSULA MOVES BACK NORTHEASTWARD
A BIT. THUS...GUSTY SOUTHEAST WINDS ARE EXPECTED TO DEVELOP DURING
THE AFTERNOON AND EVENING ON WEDNESDAY AND THURSDAY THROUGH
TURNAGAIN ARM INTO SOUTH TO WEST ANCHORAGE...THROUGH THE KNIK RIVER
VALLEY INTO PALMER...AND ALONG THE COPPER RIVER. THIS WILL SHIFT
THE FOCUS TO FIRE WEATHER CONCERNS. RIGHT NOW IT LOOKS LIKE THE
MATANUSKA VALLEY WILL MEET RED FLAG THRESHOLDS WEDNESDAY
AFTERNOON...SO WILL ISSUE A RED FLAG WARNING WITH THE AFTERNOON
FIRE WEATHER FORECASTS. THURSDAY ALSO HAS POTENTIAL FOR SIMILAR
CONDITIONS. ON FRIDAY THE PRESSURE GRADIENT WILL WEAKEN AS THE
RIDGE BUILDS WESTWARD AND WINDS SHOULD REMAIN BELOW RED FLAG
THRESHOLDS. TEMPERATURES HOWEVER...WILL CONTINUE TO WARM A LITTLE
MORE EACH DAY.

SOUTHWEST ALASKA...THE STATIONARY FRONT OVER THE SOUTHERN ALASKA
PENINSULA AND ALONG THE SOUTHWEST COAST WILL MOVE BACK EAST A
LITTLE BIT TONIGHT...SPREADING RAIN FARTHER INLAND. A SURFACE WAVE
DOWN OVER THE PACIFIC WILL MOVE TO THE WEST OF COLD BAY WEDNESDAY
MORNING AND THEN DISSIPATE AS IT HEADS NORTHWEST...PULLING THE BAND
OF PRECIPITATION WESTWARD AGAIN. ADDITIONAL WAVES WILL CONTINUE TO
MOVE NORTHWARD THROUGH THIS CORRIDOR THROUGH THURSDAY...WITH THE
SOUTHERN ALASKA PENINSULA RECEIVING THE BULK OF THE RAIN AS THE
MOISTURE TRAJECTORY REMAINS AIMED RIGHT AT THAT AREA. THE RIDGE
OVER MAINLAND ALASKA WILL BUILD WESTWARD FRIDAY HELPING TO DRY
OUT MOST OF SOUTHWEST ALASKA...ALTHOUGH RAIN WILL HOLD ON ALONG
THE SOUTHERN ALASKA PENINSULA A BIT LONGER.

BERING SEA/ALEUTIANS...THE WESTERN ALEUTIAN LOW WILL DRIFT EASTWARD
UNTIL AN UPPER CLOSED LOW FORMS LATE WEDNESDAY AND PULLS IT
SOUTHEASTWARD INTO THE NORTH PACIFIC. AS THE ALASKA RIDGE DEVELOPS
A CLOSED CENTER ENERGY WILL HAVE ACCESS TO MOVES EASTWARD BENEATH
IT (DOWN OVER THE NORTHEAST PACIFIC). SO...THE WESTERN TROUGH WILL
ELONGATE TO THE EAST AS WE HEAD INTO THE WEEKEND WHILE THE RIDGE
BUILDS WESTWARD ACROSS MAINLAND ALASKA AND INTO THE BERING SEA.
THUS...UNSETTLED WEATHER WILL CONTINUE ACROSS THE BERING REGION
THROUGH THE END OF THE WEEK BUT A DRYING TREND WILL BEGIN AT WEEK'S
END.

.LONG TERM FORECAST...MEDIUM RANGE MODELS INDICATE THAT ALASKA
RIDGE WILL WEAKEN OVER THE WEEKEND AS IT ELONGATES EAST-WEST. EVEN
WITH THAT...IT LOOKS LIKE A MOSTLY DRY WEEKEND ACROSS ALASKA AND
THE BERING SEA. BY THE BEGINNING OF NEXT WEEK THE PATTERN CHANGE
WILL LIKELY BE IN PROGRESS OR IN PLACE...BRINGING A CHANCE OF
PRECIPITATION AND COOLER TEMPERATURES BACK TO THE STATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...150 155 160 165 176 180.
FIRE WEATHER...NONE.

SEB APR 09