Brisk Wind Advisory 56, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
100 PM AKDT TUE APR 14 2009

.ANALYSIS AND UPPER LEVELS...A LARGE CUT-OFF LOW POSITIONED SOUTH
OF THE ALASKA PENINSULA THIS MORNING CONTINUES ITS SLOW EASTWARD
PROGRESSION. THIS IS ONE OF MANY CUT-OFF LOWS EMBEDDED WITHIN THE
NORTHERN HEMISPHERIC WAVE TRAIN...WHICH HAS BEEN PROGRESSIVE BUT
IS NOW SHOWING SIGNS OF STALLING AS INDIVIDUAL WAVES BECOME MORE
AMPLIFIED. THE SOUTHERN MAINLAND OF ALASKA IS IN A COL REGION...
WITH A TROUGH OVER NORTHERN ALASKA EXITING TO THE ARCTIC AND HIGH
AMPLITUDE RIDGES ON EITHER SIDE OF THE CUT-OFF LOW.

THERE ARE MULTIPLE SURFACE LOWS BENEATH THE UPPER LOW SWIRLING
AROUND SOUTH OF THE ALASKA PENINSULA WHILE FRONTAL SYSTEM EXTENDS
ALONG THE AKPENN AND THEN EASTWARD INTO THE SOUTHWESTERN GULF. THE
BULK OF PRECIPITATION IS FALLING ALONG AND AHEAD OF THIS FRONT
WITH LITTLE PRECIP AS YOU HEAD INLAND. SURFACE HIGHS EAST AND WEST
OF THE LOW COMPLEX HAVE SET UP TIGHT PRESSURE GRADIENTS ALONG THE
FRONT IN THE GULF AND ON THE BACK SIDE OF THE LOW COMPLEX OVER THE
EASTERN BERING AND EASTERN ALEUTIANS. BLOWING SNOW IS A THREAT BACK
OVER THE EASTERN BERING REGION WITH SURFACE TEMPERATURES AT FREEZING
OR BELOW.

.MODEL DISCUSSION...MODELS REMAIN IN FAIRLY GOOD AGREEMENT THROUGH
THE SHORT-TERM FORECAST PERIOD. THE TROUBLESOME AREA IS PINPOINTING
INDIVIDUAL LOW POSITIONS WITHIN THE LOW COMPLEX THAT SETS UP SHOP
SOUTH OF THE GULF ON WEDNESDAY. SOME OF THESE WILL LIKELY ROTATE
ACROSS THE SOUTHERN GULF...BUT MODELS ARE HAVING THERE USUAL
PROBLEMS WITH THIS SET-UP AND ARE NOT OF MUCH HELP IN THIS.
THEREFORE...THERE IS SOME UNCERTAINTY IN THE WIND FORECAST OVER
THE GULF...BUT HIGH CONFIDENCE BACK OVER THE REST OF THE FORECAST
AREA.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A SURFACE LOW CURRENTLY TRACKING
NORTH-NORTHWEST TOWARD KODIAK ISLAND WILL ROTATE WESTWARD TONIGHT
AROUND THE TOP SIDE OF THE UPPER LOW AND THEN BACK SOUTHWARD ON
WEDNESDAY. THEREFORE...OCCLUDED FRONT EXTENDING FROM THIS LOW TRACK
NORTHWARD TONIGHT AND THEN STALL OVER THE NORTHERN GULF AND BEGIN
TO DISSIPATE WEDNESDAY AS THE FRONT BEGINS TO SHEAR APART. THIS
WILL CONTINUE TO RELEGATE MOST OF THE PRECIPITATION TO COASTAL
AREAS WITH JUST A FEW SHOWERS INLAND. THE LOW COMPLEX WILL SET UP
SHOP JUST SOUTH OF THE GULF WEDNESDAY AND REMAIN THROUGH FRIDAY
AS AN EVOLVING HIGH AMPLITUDE PATTERN STALLS HEMISPHERIC WAVE
PROGRESSION. MODELS DONT TYPICALLY HANDLE THESE LARGE LOW COMPLEXES
WELL SO IT WILL BE VERY DIFFICULT TO FORECAST EXACT LOW POSITIONS
AND WHERE THE UPPER CENTER MIGHT DECIDE TO RE-CENTER ITSELF. WHAT
WE CAN SAY IS THAT OCCASIONAL SHOWERS WILL LIKELY CONTINUE ALONG
COASTAL AREAS AND A CHANCE OF SHOWERS WILL REMAIN FOR INLAND AREAS
DUE TO THE POSSIBILITY OF AN UPPER WAVE ROTATING ACROSS THE REGION.

SOUTHWEST ALASKA...PRECIPITATION ACROSS SOUTHWEST ALASKA...WHICH
CURRENTLY EXTENDS ACROSS BRISTOL BAY AND UP ALONG THE ALASKA
RANGE...WILL DIMINISH TONIGHT INTO WEDNESDAY AS THE LOW COMPLEX
MOVES SOUTH AND EAST AWAY FROM THE REGION. GUSTY WINDS WILL CONTINUE
THROUGH WEDNESDAY PRODUCING AREAS OF BLOWING SNOW AND LOCALLY
REDUCED VISIBILITIES...ESPECIALLY ALONG THE KUSKOKWIM DELTA WHERE
TEMPERATURES MOST LOCATIONS ARE IN THE TEENS. AFTER PRECIPITATION
ENDS DRY CONDITIONS WILL CONTINUE THROUGH THE END OF THE WEEK.
NORTHERLY FLOW WILL CONTINUE TO MAINTAIN COOL TEMPERATURES...ALTHOUGH
THE SUN WILL HELP TO WARM THINGS UP NICELY DURING THE AFTERNOONS.

BERING SEA/ALEUTIANS...A HIGH AMPLITUDE SHORT-WAVE IS MOVING INTO
THE TOP OF THE BERING RIDGE...BUT THIS WILL BE A TEMPORARY SQUASHING
OF THE RIDGE. IT WILL QUICKLY RE-BUILD AHEAD OF A CUT-OFF LOW OVER
EASTERN ASIA. A VERY TIGHT SURFACE PRESSURE GRADIENT BETWEEN WEST
CENTRAL BERING SURFACE HIGH AND THE LOW COMPLEX SOUTH OF THE ALASKA
PENINSULA WILL PRODUCE STRONG WINDS...SNOW SHOWERS...AND BLOWING
SNOW ALONG THE EASTERN ALEUTIANS AND SOUTHERN ALASKA PENINSULA
THROUGH WEDNESDAY. CONDITIONS WILL IMPROVE WEDNESDAY NIGHT AS THE
LOW COMPLEX SETTLES FARTHER EAST. A SURFACE FRONT WILL MOVE TO THE
WESTERN ALEUTIANS THURSDAY NIGHT...BUT BERING RIDGE WILL KEEP IT
FROM MAKING MUSH EASTWARD PROGRESSION.

.LONG TERM FORECAST...HIGH AMPLITUDE PATTERN OF TROUGH OVER MAINLAND
ALASKA AND GULF AND RIDGE OVER THE BERING WILL PERSIST INTO THE
BEGINNING OF NEXT WEEK. THIS WILL MAINTAIN CALM CONDITIONS ACROSS
THE BERING SEA AND ALEUTIANS WITH PERHAPS THE EXCEPTION OF THE
WESTERN ALEUTIANS WHICH WILL BE EXPOSED TO STORMS ON THE WEST
SIDE OF THE RIDGE. LOW COMPLEX/TROUGH WILL MAINTAIN CONSIDERABLE
CLOUDINESS ACROSS THE SOUTHERN MAINLAND ALONG WITH A CONTINUED
CHANCE OF SHOWERS THROUGH THE FORECAST PERIOD.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...170.
         GALE WARNING...120 130 132 138 155 165 171 175.
         HEAVY FREEZING SPRAY WARNING...179.
FIRE WEATHER...NONE.

SEB APR 09