Areal Flood Warning 22, NWS Anchorage, AK

SOUTH CENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 PM AKDT SUN MAY 8 2011

.MODEL DISCUSSION...

OVERALL MODELS ARE SIMILAR FOR THE ANCHORAGE AOR. DIFFERENCE ARISE AS
THE LOW MOVES INTO THE GULF AND CONSOLIDATES TO A SINGLE MAIN CENTER
IN THE EASTERN GULF OF ALASKA. FOR THE SOUTH CENTRAL REGION AND
PRINCE WILLIAM SOUND THE NET RESULT IS THE SAME WITH A DRY NORTHERLY
FLOW PATTERN SETTING UP MON NIGHT AND TUE. OUT WEST THE MODELS ARE IN
GOOD AGREEMENT WITH THE RIDGE MOVING TO THE BERING SEA COAST BY TUE
NIGHT AND A LARGE LOW MOVING INTO THE WESTERN BERING SEA BY WED
AFTERNOON.

.ANALYSIS AND UPPER LEVELS...

THE MAIN UPPER CENTER NOW OVER BRISTOL BAY SUPPORTING THE SURFACE LOW
DIGS SOUTH AND EAST ACROSS THE GULF IN THE BASE OF THE LARGE UPPER
TROUGH FROM THE ARCTIC. THE LOW LEVEL AIR REMAINS RELATIVELY COOL
OVER THE SOUTHERN MAINLAND AS MORE COOLING ALOFT AROUND 500 MB MOVES
OVER THE REGION RESULTING IN SLIGHTLY MORE UNSTABLE CONDITIONS BY MON
AFTERNOON. THIS WILL RESULT IN SLIGHTLY ENHANCED CONVECTIVE SHOWERY
ACTIVITY MON AS MOISTURE CONTINUES TO ROTATE AROUND THE GULF OF
ALASKA LOW INTO THE REGION. BY TUE THE DRY NORTHERLY FLOW WILL REDUCE
THE COVERAGE OF SHOWERS. THE DRY AIR AND EXPECTED INCREASE IN NORTH
WIND AS THE GRADIENT INCREASE WILL INCREASE CONCERN FOR THE FIRE
WEATHER FORECAST OVER THE MAT-SU AND KENAI PENINSULA TUE FOR STRONG
WIND AND LOW RELATIVE HUMIDITY.

THE PREVIOUSLY MENTIONED RIDGE IS SUPPORTED BY A RIDGE ALOFT AND AN
UPPER LOW SUPPORTS THE INTENSIFYING STORM NOW AT THE SOUTH END OF THE
KAMCHATKA PENINSULA.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

MOISTURE ASSOCIATED WITH THE LOW MOVING FROM BRISTOL BAY INTO THE
GULF WILL CONTINUE TO SPREAD ALONG THE COAST AND KODIAK ISLAND.
COUPLED WITH THE UPPER LEVEL TROUGH EXPECT THE THREAT OF SHOWERS TO
PERSIST THROUGH MON. FLOW BECOMES OFFSHORE DURING THE DAY ON MONDAY
WHICH MEANS ONLY SHOWER CHANCES ACROSS THE REGION WILL BE FROM
DIURNAL CONVECTIVE ACTIVITY THAT FIRES OVER THE MOUNTAINS AND DRIFTS
SOUTH WITH THE FLOW THOUGH CONTINUED DRYING CONDITIONS BY TUE AND WED
RESULTS IN MUCH LESS OF A CHANCE OF ANY SHOWERS MID WEEK.

SOUTHWEST ALASKA...

RAIN ACTIVITY THROUGH MONDAY SHOULD BE CONFINED TO NEAR THE LOW IN
THE BRISTOL BAY AREA THROUGH MON. OFFSHORE AND DRYING CONDITIONS MON
NIGHT WILL LIMIT SHOWERS TO THE BRISTOL BAY SIDE OF THE EASTERN AK
PENINSULA TUE ALTHOUGH THE WESTERN AK PENINSULA ON THE BERING SIDE
SHOULD SEE A CONTINUED THREAT FOR SHOWERS THROUGH TUE.

BERING SEA/ALEUTIANS...

WEAK LOW PRESSURE OVER THE CENTRAL BERING WILL MOVE EAST
CONSOLIDATING WITH THE BRISTOL BAY LOW MOVING INTO THE GULF OF ALASKA
THROUGH TUE. EXPECT GUSTY WINDS ON THE BACK SIDE OF THE LOW
ESPECIALLY THROUGH THE GAPS IN THE ALEUTIAN RANGE OVER THE ALASKA
PENINSULA. THE RIDGE OF HIGH PRESSURE MOVES IN AS THIS LOW EXITS AND
GIVEN THE STRENGTH OF THE RIDGE AND COLD SEA SURFACE TEMPERATURES
EXPECT TO SEE A LOT OF LOW STRATUS AND FOG DEVELOP. THE NEXT SYSTEM
WILL BEGIN TO AFFECT THE WESTERN ALEUTIANS LATE MONDAY INTO TUESDAY
ON THE BACK SIDE OF THE RIDGE BRINGING A CHANCE OF RAIN AND STRONG
SOUTHEASTERLY WINDS.

.LONG TERM FORECAST...

STRONG UPPER LEVEL RIDGE WILL MOVE OVER SOUTHWEST ALASKA MIDWEEK AND
THEN MOVE OVER SOUTH CENTRAL BY LATE WEEK. HPC GUIDANCE AND MODELS
GENERALLY AGREE THROUGH THE END OF THE WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY ZONE 152.
MARINE...GALES...175 176
FIRE WEATHER...NONE.

MAY 11