Small Craft Advisory 317, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
430 AM ADT TUE APR 8 2008

.ANALYSIS AND UPPER LEVELS...COLD UPPER LEVEL TROUGH REMAINS IN PLACE
ALONG THE WEST COAST OF ALASKA. HIGH PRESSURE AT THE SFC CAN BE FOUND
IN BRISTOL BAY WITH AN ELONGATED AREA OF LOW PRESSURE SOUTH OF THE
ALEUTIAN CHAIN.

.MODEL DISCUSSION...THE NAM HAS BY FAR BEEN THE SUPERIOR MODEL AS OF
LATE...AND THUS WE WILL RELY HEAVILY ON ITS GUIDANCE OVER THE NEXT
THREE DAYS. FROM LATE WEEK ON...RUN TO RUN CONSISTENCY OF ALL MODELS
HAS BEEN HORRIFIC WITH EACH NEW RUN SHOWING SOMETHING VERY DIFFERENT.
TONIGHTS PLAN WAS TO STICK PRETTY CLOSE TO THE 12Z GFS GUIDANCE AND
HOPE FOR SOME STABILITY IN THE MODELS.

.SHORT TERM FORECAST...A DECAYING FRONT STRETCHED ALONG THE ALEUTIAN
CHAIN WILL BRING RAIN AND SNOW TODAY BEFORE COMPLETELY DISSOLVING
TONIGHT. HIGH PRESSURE THEN RE-ESTABLISHES CONTROL OVER THE BERING
SEA.

FURTHER EAST...ANOTHER IMPENDING ACCUMULATING SNOW EVENT IS BEGINNING
TO TAKE SHAPE FOR THIS EVENING THROUGH THURSDAY FOR SOUTHCENTRAL.
THERE ARE SIMILARITIES TO THIS PAST WEEKENDS STORM...BUT ALSO SEVERAL
NOTABLE DIFFERENCES. THE BIGGEST DIFFERENCE IS THE LACK OF COLD
ADVECTION THIS TIME AROUND. THIS IS DUE TO THE POSITION OF THE UPPER
LOW WHICH IS TOO FAR WEST...AND THE SFC LOW TRACKING WELL SOUTH OF
KODIAK INTO THE SOUTHERN GULF. IT LOOKS LIKE INITIALLY AN INVERTED
TROUGH SETS UP ALONG COOK INLET THIS EVENING BRINGING AN INITIAL BAND
OF SNOW THROUGH THE ANCHORAGE BOWL...THEN SHIFTING WEST OVERNIGHT.
WITH TIME...THE UPPER LOW BECOMES MORE NEGATIVELY TILTED ALLOWING A
SHORTWAVE TO SWING AROUND ITS BASE...ENHANCING COLD ADVECTION. A SFC
LOW IS EXPECTED TO DEVELOP IN RESPONSE TO THIS NEAR SEWARD WED
AFTERNOON/EVENING TIME FRAME. THIS LOW IS EXPECTED TO REMAIN NEARLY
STATIONARY THROUGH EARLY THU...GIVING ANCHORAGE SEVERAL INCHES OF
SNOW.

ELSEWHERE ACROSS SOUTHCENTRAL ALASKA...INCREASING SOUTH TO SOUTHWEST
FLOW ALOFT WILL PROMOTE INCREASING SHOWERS ACTIVITY ALONG THE COAST.
THE UPPER CIRCULATION IS SLOW TO MOVE AND THUS EXPECT AT LEAST
SCATTERED SNOW SHOWERS THROUGH WEEKS END.

.LONG TERM FORECAST...A SEMI-PERMANENT COLD UPPER LOW WILL BE
PREVALENT OVER THE STATE THROUGH EARLY NEXT WEEK. SFC FEATURES ARE
HARD TO RESOLVE AT THIS POINT...BUT THE GENERAL TREND CONTINUES TO
FAVOR COOLER THAN AVERAGE TEMPS. FOR THE LAST TWO DAYS...MODELS HAVE
BEEN TRYING TO DEVELOP A LARGE LOW IN THE WESTERN BERING AND PUSHING
IT INTO THE GULF...BUT EACH MODEL RUN HAS BACKED OFF ON THE EASTWARD
PROGRESSION...STAY TUNED AS THIS MAY CAUSE A SHIFT IN THE OVERALL
PATTERN.

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

JCA