Flood in Alaska, May 8 to 12, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT SUN MAY 8 2011

.MODEL DISCUSSION...

THE GFS HAS STRUGGLED OVERNIGHT WITH THE SHOWER ACTIVITY OVER THE
COOK INLET REGION IN ASSOCIATION WITH AN UPPER DISTURBANCE MOVING
THROUGH THE AREA...WITH THE NAM ONLY SLIGHTLY UNDERDONE WITH ITS QPF
DEPICTION. A SECOND MORE SUBTLE SHORTWAVE WILL APPROACH THE REGION
LATER THIS MORNING FROM THE SOUTHWEST...AND THUS WILL KEEP A CHANCE
OF SHOWERS IN THE FORECAST FOR TODAY. OTHERWISE...MODELS ARE IN GOOD
AGREEMENT.

.ANALYSIS AND UPPER LEVELS...

A NARROW UPPER RIDGE OVER THE FAR NORTH BERING SEA HAS PUSHED THE
NORTHERLY STREAM OF THE PROGRESSIVE FLOW OUT OF THE ANCHORAGE
AOR...AND ALLOWED THE BAGGY UPPER LOW OVER THE CENTRAL BERING
CURRENTLY TO MOVE EAST TODAY THROUGH MONDAY NIGHT FROM THE CENTRAL
BERING TO THE EASTERN GULF AND THEN SOUTH AND EAST DOWN THE PACIFIC
COAST. DISTURBANCES OF VARYING STRENGTH ARE ROTATING AROUND THIS
LOW...AND TIMING AND PREDICTING THESE DISTURBANCES WILL BE THE
TOUGHEST PART OF THIS FORECAST PACKAGE OVER THE NEXT COUPLE OF DAYS.
BEHIND THIS LOW...A STRENGTHENING UPPER LEVEL RIDGE (HIGH PRESSURE
ALOFT) CURRENTLY OVER THE FAR NORTHWEST PACIFIC AND KAMCHATKA
PENINSULA WILL MOVE EAST THROUGH THE BERING AND THEN BEGIN TO SLOW AS
IT BEGINS TO REACH THE EASTERN BERING BY TUESDAY NIGHT.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

A SECOND AND SLIGHTLY WEAKER DISTURBANCE WILL MOVE NORTH AND EAST
ACROSS THE COOK INLET REGION LATER THIS MORNING...KEEPING SHOWERS IN
THE FORECAST...WITH A GRADUAL DECREASING TREND AS THE UPPER LOW
APPROACHES THE GULF AND TURNS THE FLOW MORE SOUTHERLY AND THEN
SOUTHEASTERLY WITH TIME. HIGHEST SHOWER PROBABILITY FOR ANCHORAGE
LOOKS TO BE THROUGH THIS MORNING WITH A DECREASING TREND THROUGH THE
AFTERNOON AND TONIGHT. 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 THROUGH MID WEEK.

SOUTHWEST ALASKA...

RAIN ACTIVITY THROUGH MONDAY SHOULD BE CONFINED MAINLY TO THE BRISTOL
BAY ZONE...NEAREST TO THE TRACK OF THE PARENT UPPER LEVEL LOW THAT
WILL MOVE EAST INTO THE GULF TONIGHT INTO MONDAY. THEN EXPECT A
CLEARING TREND AND WARMER TEMPERATURES WITH OFFSHORE FLOW AS UPPER
LEVEL RIDGING BUILDS IN FROM THE WEST THROUGH MID WEEK.

BERING SEA/ALEUTIANS...

LOW PRESSURE SYSTEM OVER THE CENTRAL BERING WILL MOVE EAST INTO THE
GULF THROUGH MONDAY MORNING...WITH GUSTY WINDS ON THE BACK SIDE
ESPECIALLY THROUGH THE GAPS IN THE ALEUTIAN RANGE OVER THE ALASKA
PENINSULA. HIGH PRESSURE BUILDS OVER THE REGION FROM WEST TO EAST
BEHIND THIS SYSTEM...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 SOUTHCENTRAL BY LATE WEEK. MODELS DIVERGE A BIT WITH
PROGRESSION OF THE RIDGE AFTER LATE WEEK...BUT PREFERRED TO KEEP
THINGS ON THE DRY SIDE OVER SOUTHCENTRAL WITH A SLOWER RIDGE
PROGRESSION EASTWARD GIVEN CLIMATOLOGY AND POOR MODEL AGREEMENT
BEGINNING NEXT WEEKEND.

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

29 MAY 11