Small Craft Advisory 1053, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1200 PM AST FRI DEC 14 2007

.ANALYSIS AND UPPER LEVELS...THERE ARE TWO MAJOR LOWS ON THE WEATHER
MAP TODAY. ONE IS SOUTH OF THE EASTERN GULF TRACKING NORTHEASTWARD
TOWARD SOUTHEAST ALASKA. THE SURFACE PRESSURE GRADIENT HAS BEEN
TIGHTENING ACROSS THE GULF AND SOUTHCENTRAL ALASKA. WEAK COLD AIR
ADVECTION IS ALSO OCCURRING ACROSS THE SOUTHERN MAINLAND AS WEAK
UPPER LEVEL WAVES MOVE IN FROM THE WEST AND NORTHWEST. THIS INITIAL
COLD ADVECTION COMBINED WITH THE TIGHTENING SURFACE PRESSURE GRADIENT

IS RESULTING IN GUSTY GAP WINDS...MOST NOTABLY FOR RESURRECTION BAY
AND PASSAGE CANAL WHERE GUSTS OF 30 KT OR GREATER HAVE BEEN OBSERVED.
THE SECOND MAJOR LOW IS NOW SOUTH OF THE EASTERN ALEUTIANS TRACKING
EASTWARD. RAIN AND SNOW ALONG WITH GALE FORCE WINDS ARE BEING
OBSERVED ACROSS THE CENTRAL AND EASTERN ALEUTIANS.

.MODEL DISCUSSION...MODELS INITIALIZED WELL AND ARE IN VERY GOOD
AGREEMENT THROUGH THE SHORT-TERM. THERE ARE SOME MINOR DIFFERENCES
IN POSITION OF LOW FORMING OVER NORTHERN GULF SATURDAY...BUT LITTLE
OR NO EFFECT ON FORECAST FOR THE REGION. LARGE MODEL DIFFERENCES AND
RUN-TO-RUN DIFFERENCES BEGIN TO EMERGE BY SUNDAY...ESPECIALLY WITH A
LOW APPROACHING THE WESTERN ALEUTIANS. THEREFORE...WILL STICK WITH
THE EXISTING FORECAST FROM THIS POINT ONWARD.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND...A BLOCKING PATTERN IS BEGINNING TO TAKE SHAPE
AS A RIDGE BUILDS OVER THE WESTERN BERING SEA. THIS RIDGE WILL MOVE
TO THE CENTRAL BERING SATURDAY. THIS IN TURN WILL FORCE SHORT-WAVES
TO DROP SOUTHWARD AND CARVE OUT A HIGH AMPLITUDE TROUGH OVER MAINLAND
ALASKA AND THE GULF. THIS WILL TRANSPORT VERY COLD AIR SOUTHWARD
ACROSS THE STATE INTO THE GULF WHICH WILL HELP MAINTAIN LOW PRESSURE
OVER THE GULF WHICH IN TURN WILL MAINTAIN A TIGHT PRESSURE GRADIENT
AND GUSTY WINDS. SO...THROUGH THE SHORT-TERM OVER THE SOUTHERN
MAINLAND EXPECT DROPPING TEMPERATURES AND STRONG GUSTY GAP WINDS...
ESPECIALLY ALONG THE GULF COASTAL REGION AS ARCTIC COLD AIR IS FORCED
THROUGH GAPS IN THE COASTAL MOUNTAIN RANGES. THE STRONGEST WINDS CAN
BE EXPECTED THROUGH THE AKPEN AND KODIAK ISLAND WATERS WHERE A JET
SETS UP ON THE EAST SIDE OF THE RIDGE AND MAXIMUM COLD ADVECTION
OCCURS. LOOKS LIKE WINDS WILL PEAK ON SATURDAY MOST PLACES...THEN
DROP A BIT SUNDAY AND LEVEL OFF AS COLD ADVECTION WEAKENS...BUT
REMAIN STRONG THROUGH THE GAPS DUE TO PRESSURE GRADIENT. THERE WILL
NOT BE ANY MAJOR CHANGES MADE TO EXISTING FORECAST...JUST MINOR
ADJUSTMENTS TO WIND SPEEDS...MAINLY TO INCREASE THEM.

BERING SEA/ALEUTIANS...THE LOW AFFECTING THE ALEUTIANS TODAY WILL
QUICKLY MOVE AWAY FROM THE REGION THIS EVENING. SO PRECIPITATION
WILL END WINDS WILL SHIFT TO THE NORTH AND COLD ADVECTION WILL
BEGIN...RESULTING IN GUSTY WINDS. AS THE UPPER RIDGE MOVES TO THE
CENTRAL BERING SATURDAY THE COLD ADVECTION AND GUSTY WINDS WILL BE
PUSHED EASTWARD TO THE FAR EASTERN BERING AND SOUTHERN AKPEN. COLD
ADVECTION ACROSS THE RELATIVELY WARMER WATERS WILL PRODUCE THE USUAL
SNOW SHOWERS. A STRONG FRONT WILL PUSH ACROSS THE WESTERN ALEUTIANS
SATURDAY AND WEAKEN AS IT MOVES TOWARD THE RIDGE IN THE CENTRAL
ALEUTIANS/BERING. SYSTEMS WILL CONTINUE TO MOVE THROUGH THIS AREA
AS THE RIDGE SERVES TO BLOCK THEM FROM MOVING FARTHER EAST.

.LONG TERM FORECAST...GFS CONTINUES TO SHOW BERING SEA RIDGE BREAKING
DOWN BY THE END OF NEXT WEEK AS SYSTEMS PUSH AGAINST IT FROM THE
EAST AND WEST AND THE REMNANTS OF THE RIDGE ARE PUSHED OFF TO THE
NORTH. 500MB 5-WAVE INDICATES TROUGH SETTING BACK UP OVER THE BERING.
MODELS DONT USUALLY HANDLE THE BREAKDOWN OF A BLOCKING HIGH TOO
WELL(USUALLY BREAK IT DOWN TO QUICKLY). IN ANY CASE THROUGH MOST OF
THE EXTENDED PERIOD EXPECT CONTINUATION OF COLD AND DRY OVER MAINLAND
ALASKA WITH ACTIVE WEATHER OVER THE CENTRAL TO WESTERN BERING SEA
AND ALEUTIANS. PERHAPS A CHANGE OF PATTERN BY WEEKS END.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING 130 150.
         GALE WARNING 121 129 132 138 155 170 172 175 176.
         HEAVY FREEZING SPRAY WARNING...121 125 129 130 138 140 160
                                        180.
FIRE WEATHER...NONE.

SEB DEC 07