Small Craft Advisory 381, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
130 PM ADT TUE APR 24 2007

.MODEL DISCUSSION...MODELS HAVE GOOD HANDLE ON WEAKENING LOW SOUTH
OF KODIAK AND SHORT-WAVES EMBEDDED IN CYCLONIC FLOW. THERE IS ALSO
VERY GOOD AGREEMENT ON EVOLUTION OF LOW RIDING THE UPPER JET EASTWARD
ACROSS THE NORTH PACIFIC AND INTO THE GULF. SOLUTIONS BEGIN TO
DIVERGE AFTER 60 HOURS WITH REGARD TO THE EXACT POSITION OF THE
LOW...HOWEVER THE MEAN POSITION IS SOMEWHERE OVER THE SOUTHERN GULF
AND THESE DIFFERENCES HAVE LITTLE IMPACT ON THE OVERALL FORECAST.
FOR THIS AFTERNOONS FORECAST WILL GO WITH THE GFS/UKMET SOLUTION.

THERE ARE VERY LARGE MODEL DIFFERENCES IN HANDLING OF NEXT SYSTEM
MOVING TO ALEUTIANS AT THE END OF THE WEEK AND VERY POOR RUN-TO-RUN
CONSISTENCY. DUE TO THIS INCONSISTENCY THE PAST TWO SHIFTS DECIDED
TO STICK WITH SOLUTION FROM A COUPLE DAYS AGO UNTIL MODELS CONVERGED
ON A SOLUTION. FOR THIS AFTERNOONS FORECAST WILL TREND TOWARD THE
NEW GFS SOLUTION IN ORDER TO MAINTAIN CONTINUITY IN FORECAST FROM
THE SHORT-TERM TO THE LONG-TERM.

.ANALYSIS AND UPPER LEVELS...A NEAR ZONAL 150 KT JET EXTENDS FROM
JAPAN ACROSS THE NORTH PACIFIC BETWEEN 30N AND 50N AND THEN SPLITS
AS IT HEADS INTO WESTERN U.S. AND SOUTHERN CANADA. THERE IS ONE
NOTABLE BUCKLE IN THE JET BETWEEN 170W AND 170E WHERE A SHORT-WAVE
TROUGH IS TRACKING EAST WITH A DEVELOPING LOW AT THE SURFACE. A
LONG-WAVE TROUGH ENCOMPASSES ALMOST ALL OF ALASKA...EXTENDING FROM
EASTERN ASIA TO SOUTHEAST ALASKA AND WESTERN CANADA...WHILE A RIDGE
EXTENDS FROM CENTRAL CANADA NORTHWESTWARD TO THE BEAFORT SEA. ANY
SYSTEMS TRACKING EASTWARD ALONG THE JET ARE PUSHED NORTHWARD AHEAD
OF THIS RIDGE. EMBEDDED WITHIN THE LONG-WAVE TROUGH ARE SEVERAL
CLOSED LOWS...MOST NOTABLY THE ONE ALONG THE AKPENN WHICH HAS BEEN
NEARLY STATIONARY THE PAST 3 DAYS SOUTH OF KODIAK ISLAND. THIS LOW
FINALLY SHOWS SIGNS OF FILLING AND DRIFTING OFF TO THE WEST. SIMILAR
TO YESTERDAY...A SHORT-WAVE TROUGH IS ROTATING ACROSS THE GULF THIS
MORNING BRINGING ANOTHER BATCH OF RAIN TO THE GULF COAST. THE
PRESSURE GRADIENT IS TIGHTENING OUT AHEAD OF THE SHORT-WAVE WITH LOW
LEVEL RIDGEING FROM THE COPPER RIVER BASIN WESTWARD TO THE KUSKOKWIM
VALLEY. AS EASTERLY FLOW INCREASES ACROSS THE MOUNTAINS CLOUD BREAKS
ARE DEVELOPING ALONG THE LEE SIDE. THE BREAKS IN CLOUDS WILL AGAIN
HELP HEAT THE SURFACE AND DESTABILIZE THE ATMOSPHERE. THERE WERE
REPORTS OF TOWERING CUMULUS AND MINI CBS LATE MONDAY AFTERNOON.
LOOKS LIKE A SIMILAR SET-UP TODAY...ALTHOUGH THE SHORT-WAVE IS WEAKER
THAN YESTERDAY SO WILL NOT GET AS MUCH FORCING FROM THE UPPER LEVELS.

OUT WEST OVER THE BERING SEA THERE IS A WEAK SURFACE LOWSOUTHWEST
OF CAPE NEWENHAM (JUST AHEAD OF AN UPPER VORT-MAX) DRIFTING WESTWARD.
WEAK FLOW ALOFT AND NORTERLY FLOW AT THE SURFACE DOMINATES THE
CENTRAL TO WESTERN BERING SEA WITH LOTS OF LOW CLOUDS AND AREAS OF
LIGHT RAIN AND SNOW.

.SHORT TERM FORECAST...AS SHORT-WAVE ROTATES WESTWARD ACROSS KENAI
PENINSULA TODAY AND SOUTHWEST ALASKA TONIGHT RAIN WILL CONTINUE
ALONG THE COAST AND ISOLATED TO SCATTERED SHOWERS WILL DEVELOP
INLAND...ESPECIALLY ALONG THE MOUNTAINS. MEANWHILE...THE LOW SOUTH
OF KODIAK WILL DISSIPATE AS IT MOVES WESTWARD TOWARD THE AKPENN.
AS EVERYTHING PUSHES TO THE WEST SURFACE RIDGE WILL BUILD BACK OVER
SOUTHCENTRAL. THIS WILL TIGHTEN UP THE EAST-WEST PRESSURE GRADIENT.
COMBINATION OF PRESSURE GRADIENT AND RISING PRESSURE WILL RESULT IN
GUSTY WINDS. ONE MORE SHORT-WAVE WILL MOVE ACROSS KODIAK ISLAND LATE
TONIGHT AND SOUTHWEST ALASKA WEDNESDAY...AGAIN BRING RAIN TO THE
COAST AND ISOLATED TO SCATTERED SHOWERS ELSEWHERE. A CHANGE WILL
OCCUR WEDNESDAY NIGHT AND THURSDAY AS STRONG LOW MOVES TO THE
SOUTHERN GULF AND FLOW OVER THE MAINLAND SHIFTS TO THE
NORTH...BRINGING MARGINALLY DRIER CONDITIONS. ISOLATED TO SCATTERED
AFTERNOON/EVENING CONVECTION WILL STILL BE LIKELY ALONG THE
MOUNTAINS. OTHERWISE MOST OF THE IMPACT OF GULF LOW WILL BE ALONG
THE IMMEDIATE COASTLINE.

OUT WEST...AN WEAK UPPER LOW WILL DROP ACROSS THE WESTERN ALEUTIANS
TONIGHT AND INTO THE PACIFIC WEDNESDAY...HELPING TO AMPLIFY THE UPPER
TROUGH. THE SURFACE GRADIENT WILL TIGHTEN UP ACROSS THE ALEUTIANS AS
THIS MOVES THROUGH AND COLD ADVECTION WILL FOLLOW...SO THERE WILL BE
A PERIOD OF GUSTY NORTHWESTERLIES IN THE MAX SMALL CRAFT TO MIN GALE
RANGE. OTHER THAN THAT...LOW CLOUDS AND AREAS OF RAIN AND SNOW WILL
CONTINUE ACROSS THE BERING REGION THROUGH THE END OF THE WEEK. A
SHORT-WAVE RIDGE WILL NUDGE INTO THE WESTERN BERING BY WEEKS END
AHEAD OF THE NEXT STORM SYSTEM.

.LONG TERM FORECAST...LONG-WAVE PATTERN IS STABLE AND ALASKA/BERING
SEA WILL REMAIN UNDER THE INFLUENCE OF LONG-WAVE TROUGH WITH JET DOWN
TO THE SOUTH THROUGH THE EXTENDED PERIOD. ORGANIZED STORM SYSTEMS
LOOK LIKE THEY WILL REMAIN OVER THE SOUTHERN PORTION OF THE FORECAST
AREA. OVER THE REST OF THE AREA (INCLUDING MAINLAND ALASKA) FLOW
LOOKS TO BE GENERALLY WEAK AND FORCING ALOFT LOOKS WEAK (UPPER
LOWS/SHORT-WAVES). MARGINALLY COOLER AIR ALOFT DOES FILTER OVER THE
MAINLAND WHICH COULD HELP SET OFF DAILY AFTERNOON/EVENING CONVECTION
WITH ENOUGH SURFACE HEATING. OTHERWISE VARIABLE CLOUDS WITH A CHANCE
OF SHOWERS LOOKS TO BE THE GENERAL THEME THROUGH THE BEGINNING OF
NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALES 120 130 132 172 175.
FIRE WEATHER...NONE.

SEB APR 07