Small Craft Advisory 819, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
125 PM ADT WED OCT 3 2007

.ANALYSIS AND UPPER LEVELS...A SHORT-WAVE TROUGH OVER THE WESTERN
BERING IS AIDING IN THE STRENGTHENING OF A SURFACE LOW WHICH IS
CROSSING THE WESTERN ALEUTIANS THIS MORNING. MODELS INDICATE MAX
GALE TO MIN STORM FORCE WINDS ALONG THE FRONT. HOWEVER...THERE ARE
NO OBS AVAILABLE TO VERIFY THAT. TO THE EAST IS A SHORT-WAVE RIDGE
OVER THE EASTERN BERING SEA AND THEN ANOTHER SHORTWAVE TROUGH
CENTERED OVER SOUTHEAST ALASKA. A STRONG UPPER JET WITH MAX AROUND
170 KT EXTENDS FROM THE TOP OF THE RIDGE AXIS SOUTHEASTWARD ACROSS
THE AKPENN INTO THE PACIFIC. 140 TO 145 KT OBSERVED IN SAINT PAUL
AND COLD BAYS MORNING SOUNDINGS. THE UPPER JET IS CONTRIBUTING TO
STRONG WINDS AT THE SURFACE THROUGH THE AKPENN AND KODIAK ISLAND
WATERS INTO THE GULF. WINDS ARE BEGINNING TO DIMINISH AS EVERYTHING
PROGRESSES EASTWARD. A SHORT-WAVE TROUGH IS ALSO DROPPING SOUTHWARD
ACROSS THE STATE THIS MORNING...ALLOWING COLDER AIR TO FILTER
SOUTHWARD. THE COLD ADVECTION IS CONTRIBUTING TO GUSTY WINDS
THROUGH CHANNELED AREAS SUCH AS THOMPSON PASS...PASSAGE CANAL...AND
RESURRECTION BAY. THERE ARE ALSO SOME UPSLOPE SNOW SHOWERS ALONG
THE ALASKA RANGE WITH SNOW BEING REPORTED NORTH OF CANTWELL AND IN
PUNTILLA. THE SOUTHWARD PROGRESS OF THE TROUGH HAS SLOWED AS THE
BERING RIDGE NUDGES EASTWARD SO COLD ADVECTION WILL BE COMING TO
A HALT BY LATER TODAY. WITH THE ADVECTION OF A MORE STABLE AIRMASS
MUCH OF THE SOUTHERN MAINLAND HAS CLEARED OUT THIS MORNING WITH JUST
A FEW SHOWERS ALONG THE SOUTHWEST COAST AND IN UPSLOPE AREAS.

.MODEL DISCUSSION...MODELS INITIALIZED WELL WITH THE INITIAL
SYNOPTIC POSITIONS. THERE ARE STILL DIFFERENCES IN TRACKING OF THE
ALEUTIAN LOW ACROSS THE BERING SEA AND INTO THE GULF AS WELL AS
WITH THE EVOLUTION OF TRIPLE POINT LOW THAT FORMS NEAR KODIAK ISLAND.
HOWEVER...THE SOLUTIONS ARE MUCH CLOSER TOGETHER THAN THEY HAVE
BEEN THE PAST FEW DAYS. THE TRACK OF THE MAIN LOW IS VERY
SIMILAR...BUT THE SPEED DIFFERS WITH THE ECMWF THE FASTEST...NAM
THE SLOWEST...AND UKMET/GFS IN BETWEEN. GFS ACTUALLY SHOWS VERY
GOOD CONSISTENCY ON THE LAST TWO SYNOPTIC RUNS AND UKMET MATCHES UP
ALMOST EXACTLY SO WILL GO WITH THIS SOLUTION. ALL OF THESE
OPERATIONAL MODELS INDICATE TRIPLE POINT LOW WILL STRENGTHEN AND
TRACK FROM KODIAK ISLAND TO THE NORTHEAST GULF. CONTRADICTORY TO
THIS IS THE GFS ENSEMBLE WITH MOST MEMBER AND THE ENSEMBLE MEAN
TRACKING A WEAKER TRIPLE POINT LOW NORTHWARD TO COOK INLET. WITH
PROGRESSIVE UPPER LEVELS AND A DECENT JET THE OPERATIONAL SOLUTION
IS PREFERRED. WILL AGAIN GO WITH THE GFS SOLUTION.

.SHORT TERM FORECAST...

BERING SEA/ALEUTIANS/AKPENN...THE ALEUTIAN LOW WILL CONTINUE TO
STRENGTHEN AS IT TRACKS NORTHEASTWARD. WITH ADDITIONAL SHORT-WAVES
BACK TO THE WEST AND NORTHWEST THIS SYSTEM WILL NOT HAVE ACCESS TO
ARCTIC AIR. HOWEVER...THERE IS A LOT OF WARM AND JUICY AIR BEING
PUMPED UP FROM THE TROPICS AHEAD OF THE LOW...SO THERE WILL BE A
RELATIVELY LARGE TEMPERATURE DIFFERENCE ACROSS THE COLD FRONT.
ABUNDANT MOISTURE WILL PRODUCE MODERATE TO HEAVY RAIN ALONG THE
FRONT. THE SYSTEM WILL FULLY OCCLUDE BY THURSDAY MORNING WHILE THE
TRIPLE POINT AND WARM/COLD FRONT ARE PUSHED QUICKLY OFF TO THE EAST.
AS THE LOW TRACKS TO THE WESTERN ALASKA COAST ON FRIDAY ANOTHER
SHORT-WAVE WILL DROP OUT OF RUSSIA AND HELP BUILD A RIDGE OVER THE
NORTHERN BERING SEA. THIS WILL ALLOW ARCTIC AIR TO
BE PULLED DOWN ON THE BACK SIDE OF THE SYSTEM ACROSS THE CENTRAL
TO EASTERN BERING. WITH COLD AIR MOVING OVER WARM WATERS EXPECT
WIDESPREAD SHOWERS ACROSS THE EASTERN BERING/SOUTHWEST
COASTLINE...AND AKPENN FRIDAY AND SATURDAY. SOME OF THESE SHOWERS
MAY CONTAIN SNOW OR ICE PELLETS IN NORTHERN AREAS. THE SHORT-WAVE
THAT DROPS OUT OF RUSSIA FRIDAY WILL VERY QUICKLY TRACK ACROSS THE
BERING SEA SATURDAY AND AKPENN SATURDAY NIGHT AS THE UPPER FLOW
REMAINS PROGRESSIVE.

SOUTHERN MAINLAND...WINDS WILL DIMINISH ACROSS SOUTHCENTRAL AND THE
KODIAK AND GULF WATERS TONIGHT AS THE UPPER RIDGE BUILDS IN FROM THE
WEST. COLD ADVECTION WILL ALSO COME TO A HALT AS UPPER TROUGH
DROPPING SOUTHWARD ACROSS MAINLAND IS STOPPED NORTH OF THE ALASKA
RANGE. MOSTLY CLEAR SKIES...DIMINISHING WINDS...AND A DRY AIRMASS
WILL PRODUCE MINIMUM TEMPS AT OR BELOW THIS MORNINGS TEMPS. CLOUDS
WILL INCREASE RAPIDLY OVER SOUTHWEST ALASKA OVERNIGHT AND INTO
SOUTHCENTRAL THURSDAY WITH PRECIPITATION NOT FAR BEHIND. BECAUSE
THERE IS A LOT OF WARM AIR BEING PUMPED NORTHWARD OVER THE REGION
MOST OF THE PRECIPITATION WILL BE IN THE FORM OF RAIN. THE EXCEPTION
MAY BE INLAND LOCATIONS AND HIGHER ELEVATIONS WHEN PRECIPITATION
REACHES THOSE AREAS LATE THURSDAY. AS MAIN LOW AND TRIPLE POINT LOW
TRACK THROUGH THE REGION THE NEXT COUPLE DAYS ALL LOCATIONS WILL
SEE SOME PRECIP AS FLOW SHIFTS AROUND TO DIFFERENT DIRECTIONS. THE
SOUTHERN MAINLAND WILL BEGIN TO DRY OUT FRIDAY NIGHT AND SATURDAY AS
THE MAIN LOW MOVES ACROSS THE NORTHERN GULF TOWARD SOUTHEAST ALASKA.
THE COLDEST AIR OF THE SEASON WILL BE USHERED SOUTHWARD BEHIND THE
SYSTEM SETTING UP WINDY CONDITIONS IN THE USUAL PLACES. ANY REMAINING
SHOWERS OVER THE REGION FRIDAY NIGHT INTO SATURDAY MAY CONTAIN SNOW.
RIGHT NOW IT LOOKS LIKE MOST OF THESE SHOWERS WILL BE ALONG THE
MOUNTAINS...SO LIKELY JUST BECOMING COLD AND DRY FOR MOST LOCATIONS.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE CONSISTENT IN DEPICTING
A MEAN RIDGE OVER THE BERING SEA AND MEAN TROUGH OVER MAINLAND ALASKA
THROUGH MOST OF THE EXTENDED FORECAST PERIOD. THIS WILL SET UP A DRY
AND COLD PERIOD OVER MAINLAND ALASKA AND CALM CONDITIONS ACROSS THE
BERING SEA AND ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORMS 160 165 170 179 185.
         GALES 120 132 150 155 171 172 175 180.
FIRE WEATHER...NONE.

SEB OCT 07