Small Craft Advisory 943, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
550 AM AKST WED NOV 18 2009

.ANALYSIS AND UPPER LEVELS...
IN THE UPPER-LVLS A RIDGE IS BUILDING OVER THE WESTERN AND CENTRAL
BERING...WHILE A LARGE TROF REMAINS DOMINANT OVER THE SOUTHERN
MAINLAND AND GULF OF AK. THE UPPER-LOW OFF THE S TIP OF KENAI
PENINSULA HAS DIPPED INTO THE GULF OF AK...WITH SHORTWAVES ROTATING
AROUND IT. AT THE SURFACE A WAVE OF LOW PRESSURE SOUTH OF YAKUTAT IS
MOVING WEST AND WEAKENING. OVER THE WESTERN AOR...A LOW 550 NM
SOUTHWEST OF SHEMYA IS DEEPENING TO HURRICANE-WIND FORCE STRENGTH AND
MOVING NORTHEAST TOWARDS THE WESTERN BERING. THIS DEEP LOW AND THE
ASSOCIATED FRONT WILL BECOME PRIMARY WEATHER FEATURES OVER THE AOR IN
THE COMING DAYS.

.MODEL DISCUSSION...
MODELS CAPTURE THE SYNOPTIC PICTURE ADEQUATELY THROUGH THE MID-RANGE
PERIOD. THE MODEL DISCREPANCIES IN THE EASTERN PART OF THE AOR CENTER
ON RESOLVING THE WAVES ROTATING AROUND THE GULF OF AK. IN GENERAL THE
WAVE OF LOW PRESSURE SOUTH OF YAKUTAT WILL CONTINUE TO MOVE WEST
TOWARDS MIDDLETON ISLAND THROUGH WEDNESDAY AND WEAKEN. THE MEAN
UPPER-TROF WILL CONTINUE TO DIP SOUTHEAST AND CARRY WITH IT MUCH OF
THE SHORTWAVE ENERGY AWAY FROM THE MAINLAND. FURTHER WEST...MODELS
HAVE THE STRONG LOW HANGING AROUND THE WESTERN BERING INTO THE
WEEKEND. SOME DIFFERENCES BEGIN TO ARISE WITH REGARDS TO A TRIPLE
POINT LOW ALONG THE FRONT THAT DEVELOPS ON FRIDAY NEAR KODIAK AND ITS
PATH AS IT WORKS INTO THE GULF THIS WEEKEND. THE GFS WAS EMPLOYED IN
THE SHORT TERM WITH A TREND TO THE EC SOLUTION BY THE MID-RANGE
PERIOD IN THE MORNING FORECAST PACKAGE.

.SHORT TERM FORECAST...
.SOUTHCENTRAL...
PERIODS OF SNOW SHOWERS ACROSS PRINCE WILLIAM SOUND DOWN THROUGH THE
S KENAI PENINSULA AND KODIAK ISLAND AS MOISTURE ROTATES AROUND THE
UPPER-LOW. CLOUDS POKING INTO INTERIOR SOUTHCENTRAL ON WEDNESDAY...
BUT DEEP MOISTURE NOT AVAILABLE TO YIELD ANY PRECIPITATION FOR THE
ANCHORAGE BOWL AND MAT-SU VALLEYS...WHERE CONDITIONS WILL REMAIN
RATHER COLD AND DRY THROUGH FRIDAY. A STRONG PRESSURE GRADIENT
THROUGH THE COPPER RIVER DELTA AND THOMPSON PASS WILL WEAKEN AS THE
LOW IN THE GULF ROTATES AWAY LATE THURSDAY HELPING WINDS TO SUBSIDE.
LOW WIND CHILLS OVER THE NORTHERN SUSITNA VALLEY AND THOMPSON PASS
ALSO DIMINISHING AS THE PRESSURE GRADIENT WEAKENS.

.SOUTHWEST...
COLD AND DRY ACROSS SW ALASKA THROUGH THURSDAY. FRONT FROM STRONG LOW
IN THE BERING WILL BRING MOISTURE ACROSS COASTAL AREAS OF BRISTOL
BAY...THE KUSKOWIM DELTA AND SOUTHERN AKPEN ON FRIDAY WITH AN
INCREASED THREAT OF SNOW AND STRONG WINDS.

.BERING SEA/ALEUTIANS...
STRONG LOW AND ASSOCIATED FRONT CONTINUE TO MARCH EAST THROUGH
FRIDAY...WITH SNOW AHEAD OF THE FRONT AND MIXING WITH OR CHANGING TO
RAIN BEHIND IT. AROUND THE SOUTHERN PERIPHERY OF THE LOW...HURRICANE
FORCE WIND GUSTS PARTICULARLY LATE WEDNESDAY NIGHT INTO EARLY FRIDAY
MORNING OVER THE FAR WESTERN ALEUTIANS...AND WESTERN MARINE ZONES.
SOLID GALES AND OR STORM-LEVEL WINDS THROUGH FRIDAY FOR THE CENTRAL
BERING AND ALEUTIANS AS THE SYSTEM EDGES CLOSER.

.LONG TERM FORECAST...
THE PATTERN IS SHIFTING...AND MODERATING TEMPERATURES SHOULD BE IN
STORE FOR THE SOUTHERN MAINLAND AS THE BERING LOW ENTERS THE GULF OF
AK. WITH THIS WILL ALSO BRING AN INCREASE IN CLOUDINESS AND A CHANCE
FOR SNOW...THOUGH DIFFERENCES IN MODELS EXIST ON WHERE A TRIPLE POINT
LOW MAY DEVELOP AND MOVE THIS WEEKEND...AND HOW IT MOVES INTO THE
GULF. REGARDLESS...AS THE OLD BERING LOW INCHES CLOSER TO THE
MAINLAND...THE DRY ENTRENCHED AIRMASS SHOULD GIVE WAY. CONDITIONS
REMAINING UNSETTLED OVER THE WESTERN AOR.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING...191
MARINE...HURRICANE FORCE WIND WARNING...176
         STORM WARNING...411 412 413 414 175 185
         GALE WARNING...352 130 132 150 155 160 165 170 171 172 179
                        180
HEAVY FREEZING SPRAY...121 130 138 140 141 150 160 165 180 185

JAM NOV 09