Small Craft Advisory 929, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1250 PM AKST MON NOV 24 2008

.ANALYSIS AND UPPER LEVELS...THE STRONG LOW THAT TRACKED ACROSS
THE ALEUTIANS SUNDAY HAS MOVED ACROSS THE ALASKA PENINSULA AND
IS NOW SOUTH OF KODIAK ISLAND. THE CENTRAL PRESSURE BOTTOMED OUT
AROUND 969 MB AND THE LOW IS BEGINNING TO FILL. A NEARLY STATIONARY
FRONT EXTENDS NORTHWESTWARD FROM THE LOW CENTER ACROSS SOUTHWEST
ALASKA. STEADY SNOW IS GENERALLY CONFINED RIGHT ALONG THIS FRONT
FROM DILLINGHAM NORTHWESTWARD TO ANIAK. MEANWHILE OCCLUDED FRONT
IS APPROACHING THE NORTH GULF COAST. A BARRIER JET HAS FORMED FROM
THE NORTHEAST GULF TO PRINCE WILLIAM SOUND...BUT WINDS ARE ALREADY
BEGINNING TO COME DOWN AS THE FRONT PUSHES INLAND AND FALLS APART.
MOST SIGNIFICANT SNOWFALL HAS BEEN IN THE UPSLOPE AREAS OF WESTERN
PRINCE WILLIAM SOUND WHERE RATES AS HIGH AS 2 INCHES PER HOUR WERE
REPORTED IN GIRDWOOD. PORTIONS OF THE WESTERN SUSITNA VALLEY HAVE
ALSO SEEN SOME UPSLOPE SNOW. A REPORT FROM SKWENTA INDICATES LIGHT
ACCUMULATION...BUT EXPECT THAT AMOUNTS WERE LIKELY HEAVIER AT HIGHER
ELEVATIONS SUCH AS HAZE RIVER. THERE IS CURRENTLY A WINTER WEATHER
ADVISORY FOR SNOW IN EFFECT FOR THIS REGION THROUGH THIS AFTERNOON
WHICH WILL BE ALLOWED TO EXPIRE. DOWNSLOPE AREAS ACROSS THE REGION
HAVE SEEN LITTLE OR NO PRECIPITATION WITH THIS SYSTEM.

A TROUGH AXIS EXTENDS WESTWARD FROM THE LOW ALONG THE ALEUTIANS TO
ANOTHER VERTICALLY STACKED LOW NORTHWEST OF ADAK AND THEN CONTINUING
WESTWARD TO ANOTHER LOW OFF OF KAMCHATKA. THIS TROUGH IS BEING
PUSHED VERY SLOWLY SOUTHWARD SO THE LOW IS JUST DRIFTING TO THE
SOUTHEAST. NORTH OF THE TROUGH AXIS WEAK COLD ADVECTION DOMINATES
THE BERING SEA...PRODUCING A LOT OF STRATOCU AND SOME SNOW SHOWERS.
MULTIPLE WEAK LOWS ARE EMBEDDED IN ZONAL FLOW SOUTH OF THE ALEUTIANS.

.MODEL DISCUSSION...12Z ECMWF/UKMET/NAM ALL HAVE A DECENT HANDLE ON
LOW SOUTH OF KODIAK ISLAND AND DEPICT A SIMILAR TRACK AS IT MOVES
TO THE NORTHERN GULF TONIGHT AS WELL AS A WEAKER SECONDARY LOW IN
BRISTOL BAY. GFS INCORRECTLY PUTS A BROAD LOW FARTHER NORTH AND
TRACKS THIS TO THE BARREN ISLANDS BEFORE JOINING UP WITH THE REST
OF THE SOLUTIONS IN THE NORTH GULF. A WEAK LOW SOUTH OF THE ALEUTIANS
THIS MORNING WILL TRACK INTO THE GULF TUESDAY. MODEL SOLUTIONS
DIVERGE WITH THIS TRACK. WILL GO WITH THE ECMWF/NAM SOLUTION WHICH
LINE UP WELL. ECMWF IS VERIFYING BEST WITH THE ALEUTIAN LOW NEAR
ADAK. ACTUAL LOW POSITION IS A BIT FARTHER NORTH THAN ECMWF...BUT
ALL OTHER MODELS ARE MUCH TOO FAR EAST. WILL STICK WITH THE ECMWF
SOLUTION WHICH IS SLOWEST IN MOVING THIS LOW SOUTHEASTWARD TONIGHT
AND TUESDAY. MODELS REMAIN FAIRLY CONSISTENT WITH DEVELOPMENT OF A
950S LOW SOUTH OF THE ALEUTIANS WEDNESDAY. EXACT TRACK IS STILL IN
QUESTION...BUT ALL SOLUTIONS ARE GROUPED IN THE SAME GENERAL AREA
AND THE END RESULT OF STORM FORCE WINDS ALONG THE ALEUTIANS AND
ALASKA PENINSULA IS THE SAME. WILL SIMPLY MAKE SOME MINOR ADJUSTMENTS
TO BUMP UP WINDS IN A FEW PLACES. ANOTHER LOW WILL ALSO BE MOVING
INTO THE GULF WEDNESDAY. THE TREND IS TOWARD A FARTHER NORTH AND
WEST TRACK ON ALL MODELS EXCEPT THE GFS. WILL TREND TOWARD THE NAM
SOLUTION WITH THIS LOW.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE FRONT ALONG THE NORTH GULF COAST WILL
QUICKLY FALL APART THIS AFTERNOON...SO WINDS WILL QUICKLY DIMINISH
AND PRECIPITATION WILL LIGHTEN UP IN UPSLOPE AREAS. LOW LEVEL FLOW
ACROSS EASTERN PRINCE WILLIAM SOUND WILL VEER SLIGHTLY TOWARD THE
SOUTH AS REMNANTS OF THE FRONT MOVE ONSHORE. THUS...SNOW WILL
BECOME STEADY IN THE VALDEZ AREA WITH RAIN IN CORDOVA. THE LOW
SOUTH OF KODIAK AND ASSOCIATED UPPER TROUGH WILL MOVE TO THE NORTH
GULF BY EARLY TUESDAY MORNING AND THEN INLAND DURING THE
DAY...BRINING MORE PRECIPITATION TO SOUTHCENTRAL...ESPECIALLY ALONG
THE COAST. EXPECT SOME LIGHT SNOW INLAND AS THE TROUGH MOVES THROUGH.
ALSO OF NOTE...IMMEDIATELY BEHIND THE LOW IS A VERY TIGHT THERMAL
AND PRESSURE GRADIENT...SO AS THE LOW TRACKS NORTHEASTWARD TONIGHT
THERE WILL BE AN AREA OF GALE FORCE WINDS THAT WILL MOVE THROUGH
PORTIONS OF THE KODIAK ISLAND WATERS. WOULD NOT BE SURPRISED IF
THERE ARE LOCALIZED BRIEF GUSTS TO STORM FORCE ALONG THE ALASKA
PENINSULA...SOUTHERN SHELIKOF STRAIT...AND SOUTHERN KODIAK ISLAND.
MODELS INDICATE ANOTHER UPPER LEVEL SHORT-WAVE ROTATING FROM
SOUTHWEST ALASKA TOWARD ANCHORAGE TUESDAY NIGHT. CURRENTLY THE
FORECAST IS FAIRLY DRY SO WILL INTRODUCE AT LEAST A CHANCE OF SNOW
AS THIS MOVES THROUGH. THE LIFT ASSOCIATED WITH THIS FEATURE APPEARS
TO BE OVER A SMALL AREA...SO THE EXACT TRACK WILL DETERMINE WHO GETS
THE MOST SNOW. THERE IS DEFINITE POTENTIAL FOR A SHORT PERIOD OF
MODERATE SNOW FROM ANCHORAGE TO THE MAT-SU TUESDAY NIGHT INTO
WEDNESDAY. MEANWHILE...THE NEXT LOW WILL BE MOVING INTO THE GULF
WEDNESDAY. WITH THE NORTHWEST TREND IN THE TRACK OF THIS LOW WILL
INTRODUCE CHANCES OF SNOW FARTHER NORTH AND WEST INCLUDING ANCHORAGE
WEDNESDAY NIGHT INTO THURSDAY.

SOUTHWEST ALASKA...THE BAND OF SNOW FROM BRISTOL BAY TO THE INLAND
KUSKOKWIM DELTA AND SOUTHERN KUSKOKWIM VALLEY WILL MOVE NORTHEASTWARD
TONIGHT AND TUESDAY ALONG WITH THE UPPER TROUGH...PRODUCING
WIDESPREAD AND GENERALLY LIGHT SNOW. MEANWHILE...ANOTHER TROUGH OVER
THE NORTHERN BERING WILL SWING EASTWARD ACROSS THE KUSKOKWIM DELTA
TUESDAY AFTERNOON AND THEN INLAND TUESDAY NIGHT. THE MODELS INDICATE
LITTLE TO NO QPF AS THIS MOVES THROUGH. WITH ONSHORE FLOW AND A
DECENT STRENGTH TROUGH AXIS WILL GO WITH SCATTERED SNOW SHOWERS FOR
THE DELTA AND JUST ISOLATED SNOW SHOWERS AS IT MOVES INLAND.
CONDITIONS WILL DRY OUT ACROSS THE REGION BEHIND THIS TROUGH ON
TUESDAY NIGHT AND WEDNESDAY. COLD ADVECTION WILL ENSURE BEHIND THE
FIRST TROUGH TONIGHT AND TUESDAY. THUS...WITH THE EXCEPTION OF THE
IMMEDIATE COAST WHERE ONSHORE FLOW WILL KEEP TEMPS FROM DROPPING
MUCH...THERE WILL BE A COOLING TREND OVER THE REST OF SOUTHWEST
ALASKA HEADING THROUGH THE NEXT FEW DAYS.

BERING SEA/ALEUTIANS...QUIKSCAT WINDS SHOWS A TIGHT AREA OF GALE
FORCE WINDS AROUND THE ALEUTIAN LOW. THE LOW WILL TRACK SLOWLY
SOUTHEASTWARD CROSSING OVER THE ALEUTIANS NEAR ADAK EARLY TUESDAY
MORNING. BROAD WEAK NORTHERLY FLOW BEHIND THIS LOW AND SURFACE
TROUGH CURRENTLY ALONG THE ALEUTIANS WILL MAINTAIN WEAK COLD
ADVECTION THROUGH TUESDAY NIGHT...RESULTING IN THE TYPICAL MOSTLY
CLOUDY SKIES WITH SNOW SHOWERS. A PACIFIC LOW WILL RAPIDLY DEEPEN
MONDAY NIGHT THROUGH WEDNESDAY...IN AN IDEAL POSITION BETWEEN TWO
UPPER JETS. IT IS UNCLEAR HOW CLOSE THE LOW WILL COME TO THE
ALEUTIANS. CONDITIONS WILL QUICKLY HEAD DOWNHILL LATE WEDNESDAY
WITH WIDESPREAD STORM FORCE WINDS EXPECTED BY WEDNESDAY NIGHT. RIGHT
NOW IT LOOKS LIKE IT WILL BE COLD ENOUGH FOR PRECIPITATION TO START
AS SNOW AND THEN MIX WITH OR CHANGE TO SNOW. WILL NEED TO WATCH
THIS CLOSELY. IF LOW TRACK IS A LITTLE FARTHER SOUTH PRECIPITATION
COULD STAY ALL SNOW AND POTENTIAL FOR BLIZZARD WOULD NEED TO BE
CONSIDERED.

.LONG TERM FORECAST...THE DEEP LOW SOUTH OF THE ALEUTIANS WILL
TRACK NORTHEASTWARD TOWARD THE MAINLAND THURSDAY AND FRIDAY. IT
IS TOO EARLY TO SAY WHETHER IT WILL TRACK INTO THE GULF OR REMAIN
CLOSE THE ALASKA PENINSULA. BOTTOM LINE...WITH SUCH A STRONG SYSTEM
THERE IS POTENTIAL FOR WARNING LEVEL CONDITIONS...SO THIS WILL BE
CONTINUALLY RE-EVALUATED AS WE GET A BETTER IDEA OF WHERE THE LOW
WILL TRACK. THE LONG-WAVE PATTERN LOOKS LIKE IT WILL REMAIN
PROGRESSIVE THROUGH THE EXTENDED PERIOD...RESULTING IN A CONTINUED
ACTIVE WEATHER PATTERN ACROSS THE FORECAST AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...120 125 132 138 150 175.
         HEAVY FREEZING SPRAY...180 185.
FIRE WEATHER...NONE.

SEB NOV 08