Small Craft Advisory 330, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
145 PM AKDT WED APR 15 2009

.ANALYSIS AND UPPER LEVELS...LARGE CUT-OFF LOW IS CENTERED DOWN
AROUND 51N 156W THIS MORNING...DRIFTING EASTWARD. CIRCULATION
AROUND THIS CENTER EXTENDS FROM 40N ALL THE WAY TO 60N AND FROM
135W TO 170W. MULTIPLE UPPER WAVES AND SURFACE LOWS ARE EMBEDDED
WITHIN THIS HUGE CIRCULATION. THE PROBLEM OF THE DAY WILL BE TO
TRY AND FORECAST THESE FEATURES AS THEY ROTATE ACROSS THE GULF.
A DISSIPATING OCCLUDED FRONT IS NEARLY STATIONARY OVER THE NORTHERN
TO WESTERN GULF WITH STEADY PRECIPITATION FALLING FROM PRINCE
WILLIAM SOUND TO KODIAK ISLAND AND ALONG THE ALASKA PENINSULA.
SOUTHEAST FLOW HAS ALSO PUSHED SOME SNOW INTO THE EASTERN COPPER
BASIN. A TIGHT PRESSURE GRADIENT ON THE BACK SIDE OF THE LOW
COMPLEX IS PRODUCING BLOWING SNOW OVER THE SOUTHERN ALASKA
PENINSULA...ALTHOUGH WINDS ARE SLOWLY DIMINISHING AS THE LOW
COMPLEX MOVES EASTWARD.

SATELLITE IMAGERY SHOWS WHAT LOOKS TO BE A WELL DEVELOPED LOW OVER
THE NORTHWEST BERING WITH SURFACE FRONT EXTENDING DOWN ACROSS THE
CENTRAL BERING. IN FACT...THIS IS A WEAK (AROUND 1015 MB) VERTICALLY
STACKED LOW EMBEDDED WITHIN A LARGE UPPER RIDGE. OTHER THAN CLOUDS
ASSOCIATED WITH THIS SYSTEM...SKIES ACROSS THE BERING SEA AND
ALEUTIANS ARE MOSTLY CLEAR. SO THE CLEAR VIEW OF THIS SYSTEM MAKES
IT LOOK A LOT WORSE THAN IT IS.

.MODEL DISCUSSION...THERE CONTINUE TO BE DIFFERENCES IN EXACT
POSITION AND STRENGTH OF LOWS/UPPER WAVES EMBEDDED WITHIN THE LOW
COMPLEX...BUT SOLUTIONS ARE IN FAIR AGREEMENT THROUGH ABOUT 60 HOURS
AND THEN DIVERGE AFTER THAT. WILL FOCUS ON THIS HIGHER CONFIDENCE
PERIOD AND MAKE LITTLE OR NO CHANGE AFTER THAT.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...OCCLUDED FRONT OVER GULF WILL CONTINUE TO
DISSIPATE TONIGHT...RESULTING IN DIMINISHING WINDS. LOW LEVEL WINDS
OVER SOUTHCENTRAL WILL BACK TOWARD THE NORTH WHICH WILL PUSH EDGE
OF PRECIPITATION FARTHER SOUTH ALONG THE IMMEDIATE COAST. HOWEVER...
AN UPPER LEVEL SHORT-WAVE AND ASSOCIATED SURFACE LOW DEVELOPING OVER
THE EASTERN GULF WILL ROTATE WESTWARD ACROSS THE GULF THURSDAY AND
THURSDAY NIGHT BRINGING ANOTHER ROUND OF PRECIPITATION AND WINDS TO
THE COASTAL AREAS. THESE FEATURES APPEAR TO BE FAR ENOUGH SOUTH TO
PREVENT PRECIPITATION FORM MAKING IT INLAND...WITH THE EXCEPTION OF
THE EASTERN COPPER BASIN WHERE SOUTHEASTERLY FLOW USUALLY DOES BRING
IN SOME PRECIPITATION. ANOTHER WEAKER LOW WILL TAKE A FARTHER NORTH
TRACK ON FRIDAY AND SATURDAY..BUT STILL EXPECT THE BULK OF
PRECIPITATION ALONG THE COAST. INLAND AREAS WILL REMAIN MOSTLY
CLOUDY AS THESE FEATURES PASS JUST TO THE SOUTH...ALTHOUGH IN
BETWEEN SYSTEMS THE SUN SHOULD BE ABLE TO BRIEFLY POKE THROUGH
THE CLOUDS.

SOUTHWEST ALASKA...SOUTHWEST ALASKA WILL BE ON THE WESTERN EDGE OF
ALL OF THE ACTIVITY IN THE GULF. ALASKA PENINSULA WILL SEE CLOUDS
AND PERHAPS A FEW SHOWERS SPILLING OVER THE ALEUTIAN RANGE...WHILE
AREAS NORTH AND WEST REMAIN MOSTLY CLEAR. AN UPPER TROUGH WILL DROP
DOWN OUT OF THE NORTH ON FRIDAY ADVECTING COLDER AIR INTO THE
REGION...BUT THERE WONT BE A WHOLE LOT OF MOISTURE TO WORK WITH...
SO WOULD NOT EXPECT ANYTHING MORE THAN ISOLATED SHOWERS WITH THIS.

BERING SEA/ALEUTIANS...THE LOW OVER THE NORTHWEST BERING WILL
RAPIDLY DISSIPATE TONIGHT AS IT SOUTHWARD THROUGH THE HEART OF
THE RIDGE. TRANQUIL CONDITIONS WILL THEN DOMINATE THE CENTRAL
BERING AND ALEUTIANS INTO THE WEEKEND. GUSTY WINDS WILL PERSIST
JUST EAST OF THE RIDGE OVER THE EASTERN BERING/EASTERN ALEUTIANS
AND SOUTHERN ALASKA PENINSULA. HOWEVER...TEMPERATURE ADVECTION IS
NEAR NEUTRAL SO DONT EXPECT MUCH IN THE WAY OF SNOW SHOWERS TO
FORM OFF OF THE ICE EDGE. A STRONG FRONT WILL MOVE TO THE FAR
WESTERN ALEUTIANS LATE THURSDAY...BUT WILL BE BLOCKED FROM MAKING
ANY EASTWARD PROGRESSION.

.LONG TERM FORECAST...HIGH AMPLITUDE PATTERN WILL REMAIN SOLIDLY IN
PLACE THROUGH THE WEEKEND. HEADING INTO NEXT WEEK THERE IS A LOT OF
UNCERTAINTY AS TO WHETHER AND/OR HOW BERING RIDGE WILL BREAK DOWN.
WILL RIDE WITH CURRENT EXTENDED FORECAST AND SEE IF NEXT MODEL
CYCLE SHOWS ANY CONSISTENT TRENDS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 130 132.
         HEAVY FREEZING SPRAY WARNING 179.
FIRE WEATHER...NONE.

SEB APR 09