Small Craft Advisory 321, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM AKDT WED APR 28 2010

.ANALYSIS AND UPPER LEVELS...
LONG WAVE UPPER LEVEL TROUGH REMAINS IN PLACE OVER WESTERN ALASKA AND
THE BERING SEA. DOWNSTREAM...A HIGH AMPLITUDE UPPER LEVEL RIDGE HAS
BEEN CUT OFF FROM THE MAIN CIRCULATION AND IS DRIFTING NORTHWEST
ACROSS THE NORTHERN YUKON AND NORTHWEST TERRITORIES. THE JET IS STILL
WELL SOUTH OF OUR AREA OF RESPONSIBILITY BUT WILL NUDGE CLOSER LATER
THIS WEEK AS THE RIDGE LOSES GROUND AND THE TROUGH DIGS DEEPER TO THE
WEST...POINTING THE JET TOWARD THE ALASKA PANHANDLE.

AT THE SURFACE...A BROAD AREA OF LOW PRESSURE ENCOMPASSES THE GULF OF
ALASKA AND SOUTHCENTRAL ALASKA. THE ONLY DISCERNIBLE LOW ON SATELLITE
IS EMBEDDED IN THE EASTERLY FLOW ACROSS THE WESTERN GULF. A THERMAL
TROUGH IS ALSO EVIDENT ACROSS THE UPPER YUKON RIVER VALLEY...BRUSHING
UP AGAINST THE ALASKA RANGE AND THE NORTHERN SUSITNA AND COPPER RIVER
VALLEYS. OUT WEST...A WEAK AREA OF HIGH PRESSURE IS PREVALENT OVER
THE REGION WITH COLD NORTHWESTERLY FLOW BRINGING MUCH OF THE
SOUTHWEST COASTAL REGION AND THE EASTERN ALEUTIANS BELOW AVERAGE
TEMPERATURES.

.MODEL DISCUSSION...VERY LITTLE DIFFERENCES IN THE MODEL SOLUTIONS
THIS MORNING THROUGH 48 HOURS. THURSDAY NIGHT...A SURFACE LOW WILL
DEVELOP AND RAPIDLY MOVE NORTHEAST TOWARD THE GULF. THE MODELS HAVE
BEEN WILDLY INCONSISTENT WITH THE PLACEMENT AND STRENGTH OF THIS
FEATURE. THE GFS APPEARS TO BE A BIT MORE CONSISTENT THAN THE NAM OR
EC...SO THE FORECAST IS A BLEND OF THE LATEST GFS WITH THE INHERITED
FORECAST WHICH WAS BASED OFF OF THE PREVIOUS GFS. CONFIDENCE BEYOND
48 HOURS IS AVERAGE TO BELOW AVERAGE.

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA...GIVEN THE UNCERTAINTY IN THE MEDIUM
RANGE...WILL FOCUS ON THE SHORT TERM FORECAST. THE AFOREMENTIONED LOW
IN THE GULF IS MOVING RAPIDLY WEST TOWARD KAMISHAK BAY THIS
AFTERNOON. RAIN WILL BE MAINLY LIMITED TO THE COASTAL ZONES
ASSOCIATED WITH THIS FEATURE. THE CHALLENGE IN THE FORECAST WILL BE
THE EFFECTS OF A THERMAL TROUGH NEAR THE ALASKA RANGE. CUMULUS JUST
NOW DEVELOPING NORTH OF THE RANGE WITH ONLY CIRRUS COVERING THE
NORTHERN PORTIONS OF OUR DOMAIN. THE POTENTIAL FOR AFTERNOON
CONVECTION WITH THE OUTSIDE CHANCE OF A STRAY LIGHTNING STRIKE EXISTS
WHERE THERE HAS BEEN LIMITED CLOUD COVERAGE...ALTHOUGH NOT CONFIDENT
ENOUGH TO MENTION THAT QUITE YET IN THE FORECAST.

THERE WILL BE SLIGHTLY COOLER TEMPERATURES ADVECTING TO THE WEST ON
THE BACKSIDE OF THE LOW MOVING INLAND. CLOUDS WILL THIN OUT AT TIMES
AND THEN INCREASE AGAIN AS THE NEXT WAVE APPROACHES THURSDAY SO
EXPECTING SOMEWHERE BETWEEN PARTLY TO MOSTLY CLOUDY SKIES ACROSS
SOUTHCENTRAL WITH CLOUDS AND RAIN CONTINUING ALONG THE GULF COAST.
STILL MUCH UNCERTAINTY IN THE LOW MOVING INTO THE GULF ON
FRIDAY...ALTHOUGH THE EFFECTS SHOULD MAINLY BE OVER THE WATER AND
ALONG THE COAST.

SOUTHWEST ALASKA...A DEFORMATION ZONE IS IN PLACE FROM THE ALASKA
PENINSULA UP TO THE SEWARD PENINSULA. COLD AIR AT THE SURFACE IS
BEING OVER RUN BY WARM AIR ALOFT...RESULTING IN WIDESPREAD LIGHT SNOW
ACROSS ZONE 161. THIS AREA OF SNOW WILL DISSIPATE AS IT DRIFTS WEST
THIS AFTERNOON...BUT A SECOND AREA WILL DEVELOP LATER THIS EVENING AS
THE MAIN LOW MOVES INLAND. INITIALLY...THIS LOW WILL BRING WARMER AIR
SO SNOW WILL TRANSITION OVER TO RAIN OR A RAIN AND SNOW MIX
OVERNIGHT. COLD AIR WRAPS AROUND THE BACKSIDE OF THE LOW BUT NOT
UNTIL THE MOISTURE IS CUT OFF...RESULTING IN SNOW SHOWERS THROUGH THE
REST OF THE WEEK.

ALEUTIANS/BERING SEA...COLD AIR BEING PUSHED SOUTH UNDER THE DEEP
TROUGH IS LEADING TO 10 TO 15 DEGREE BELOW NORMAL TEMPERATURES FROM
THE MAINLAND COAST TO THE CENTRAL ALEUTIANS. TEMPERATURES WILL SLOWLY
WARM UP AS THE SOURCE OF THE COLD AIR IS SLOWLY PINCHED OFF AND
MODERATES. WEAK HIGH PRESSURE WILL PREVAIL OVER THE WESTERN ALEUTIANS
WITH LOW PRESSURE TO THE EAST. THIS PATTERN WILL CONTINUE THROUGH THE
WEEKEND.

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

AB APR 10