Small Craft Advisory 905, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
135 PM AKST TUE NOV 18 2008

.ANALYSIS AND UPPER LEVELS...A HIGH AMPLITUDE TROUGH WITH EMBEDDED
LOW COMPLEX IS CENTERED SOUTH OF THE GULF OF ALASKA. A TRIPLE POINT
LOW ON THE NORTH SIDE OF THIS CIRCULATION QUICKLY STRENGTHENED THIS
MORNING AND HAS NOW BECOME OCCLUDED. THE FRONT IS BEING PUSHED NORTH
AND WEST INTO THE GULF WHILE THE LOW BEGINS TO CURVE TOWARD THE
SOUTHWEST. A RIDGE DOMINATES THE BERING WITH A TROUGH UNDERCUTTING
THE RIDGE TO THE SOUTH. ANOTHER HIGH AMPLITUDE TROUGH IS CENTERED
OVER EASTERN RUSSIA WITH A 165KT JET HEADED FOR THE WESTERN
ALEUTIANS.

.MODEL DISCUSSION...ALTHOUGH THERE ARE NO SURFACE OBSERVATIONS TO
CONFIRM THIS...BASED ON SATELLITE IMAGERY ALL OF THE MODELS ARE
TOO WEAK WITH THE LOW JUST SOUTH OF THE GULF. THE MARINE FORECAST
WINDS ARE ALREADY HIGHER THAN MODEL GUIDANCE...SO WONT NEED TO MAKE
MANY ADJUSTMENTS. THE MODEL SOLUTIONS ARE INITIALLY IN GOOD AGREEMENT
WITH LOCATION OF THE MULTIPLE LOWS...BUT DIVERGE AS THEY CONSOLIDATE
INTO A SINGLE CENTER WEDNESDAY NIGHT. GFS SHOWS GOOD RUN-TO-RUN
CONSISTENCY AND HAVE STUCK CLOSE TO ITS SOLUTION THROUGH THURSDAY.
THERE HAS BEEN A GENERAL TREND OF PUSHING THE FRONT FARTHER NORTH
AND WEST...SO WILL INCREASE CHANCE OF PRECIPITATION ALONG THE GULF
COASTAL AREAS.

MODELS SHOW POOR RUN-TO-RUN CONSISTENCY WITH LOWS APPROACHING THE
WESTERN BERING THROUGH THE WEEKEND. THUS...NO MAJOR CHANGES WILL BE
MADE TO EXISTING FORECAST. THERE IS NOW GENERAL AGREEMENT IN
DEVELOPMENT OF TRIPLE POINT LOW WEDNESDAY NIGHT AND MOVEMENT
NORTHWARD ACROSS THE WESTERN ALEUTIANS THURSDAY...SO WILL TREND A
LITTLE MORE HEAVILY TOWARD THIS SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL...INCREASING PRESSURE GRADIENT TONIGHT AND WEDNESDAY
AS FRONT MOVES ACROSS THE GULF SHOULD HELP PRODUCE ENOUGH MIXING TO
EITHER WEAKEN OR BREAK THE LOW LEVEL INVERSION IN PLACE OVER MUCH OF
SOUTHCENTRAL. THEREFORE...EXPECT ANY FOG THAT DEVELOPS TONIGHT TO
BE LOCALIZED. PRECIPITATION WILL REACH KODIAK ISLAND EARLY TOMORROW
MORNING IN THE FORM OF SNOW AND ACCOMPANIED BY STRONG NORTHERLY FLOW.

TEMPERATURES ON KODIAK ISLAND ARE CURRENTLY NEAR FREEZING AND DONT
EXPECT MUCH CHANGE BY THE TIME SNOW STARTS. WITH TEMPERATURES AT OR
ABOVE FREEZING DONT ANTICIPATE VISIBILITIES WILL GET LOW ENOUGH TO
PRODUCE BLIZZARD CONDITIONS...BUT SOMEWHERE AROUND 1 MILE IS LIKELY.
THE FRONT WILL DISSIPATE AS IT REACHES THE ISLAND. WHILE THE SURFACE
FLOW WILL REMAIN NORTH TO NORTHWEST FLOW RIGHT ABOVE THE SURFACE WILL
HAVE A NORTHEAST COMPONENT. THERE MIGHT BE JUST ENOUGH WARM AIR TO
MIX IN A LITTLE RAIN ALONG THE GULF...BUT PRECIPITATION WILL REMAIN
PREDOMINANTLY SNOW. SNOW WILL ALSO OVERSPREAD THE PRINCE WILLIAM
SOUND REGION ON WEDNESDAY. HOWEVER...STRONG OFFSHORE FLOW WILL KEEP
IT GENERALLY LIGHT. THE BEST POSSIBILITY FOR ACCUMULATION LOOKS TO
BE WESTERN PRINCE WILLIAM SOUND WHICH WILL BE IN AN AREA OF STRONGER
UPPER LEVEL VERTICAL MOTION AND WILL HAVE AN UPSLOPE COMPONENT TO
THE WINDS ABOVE THE SURFACE. IT WILL BE VERY DIFFICULT FOR
PRECIPITATION TO MAKE IT OVER THE COASTAL MOUNTAINS. VERY DRY AIR
ON THE LEE SIDE OF THE MOUNTAINS WILL CONTINUALLY BE REINFORCED BY
NORTHERLY FLOW SO ANY PRECIPITATION T5HAT FALLS FROM ABOVE WILL
EVAPORATE BEFORE REACHING THE GROUND. AT MOST THERE MIGHT BE A FEW
FLURRIES RIGHT ALONG THE MOUNTAINS. PRECIPITATION CHANCES WILL
CONTINUE ALONG THE COAST INTO THE WEEKEND AS A LOW REMAIN OVER
THE GULF. THE SURFACE PRESSURE GRADIENT WILL REMAIN
STRONG...RESULTING IN A CONTINUATION OF LOCALLY STRONG GAP WINDS
ALONG THE GULF COAST.

SOUTHWEST ALASKA/ALASKA PENINSULA...A TIGHTENING PRESSURE GRADIENT
ASSOCIATED WITH THE GULF SYSTEM WILL PRODUCE LOCALLY GUSTY WINDS
ACROSS SOUTHWEST ALASKA...ESPECIALLY ACROSS BRISTOL BAY AND THE
ALASKA PENINSULA. AN UPPER LEVEL SHORT-WAVE WILL THEN DROP DOWN
FROM THE NORTH WEDNESDAY NIGHT AND THURSDAY RESULTING IN MODERATE
TO STRONG COLD ADVECTION ACROSS SOUTHWEST ALASKA. THIS WILL PRODUCE
MORE WIDESPREAD GUSTY WINDS THURSDAY INTO FRIDAY. CONDITIONS WILL
REMAIN DRY THROUGH THE SHORT-TERM PERIOD.

BERING SEA/ALEUTIANS...HIGH PRESSURE OVER THE BERING WILL GRADUALLY
BE PINCHED AS THE LOW MOVES INTO THE GULF ON THE EAST AND A STRONG
FRONT APPROACHES FROM THE WEST. THIS FRONT WILL REACH THE WESTERN
ALEUTIANS LATE WEDNESDAY AND TRACK TO THE EASTERN ALEUTIANS AND
PRIBILOFS FRIDAY. A LOW IS EXPECTED TO DEVELOP ALONG THE FRONT AND
TRACK ACROSS THE WESTERN ALEUTIANS THURSDAY...BUT THERE IS LOW
CONFIDENCE IN THIS SOLUTION AND THE EVOLUTION OF THE SYSTEM AFTER
THIS POINT. MODELS INDICATE WINDS IN THE STORM FORCE TO NEAR
HURRICANE FORCE STRENGTH...BUT FOR NOW WILL MAINTAIN WINDS NO
HIGHER THAN GALE FORCE.

.LONG TERM FORECAST...THERE IS A LOT OF UNCERTAINTY IN THE EXTENDED
TIME FRAME. HOWEVER...CURRENT MEDIUM RANGE MODELS INDICATE A MEAN
TROUGH SETTING UP OVER THE BERING SEA WITH UPPER JET SETTING UP JUST
SOUTH OF THE ALEUTIANS AND THEN UP INTO THE GULF. IF ACCURATE...THIS
WILL RESULT IN AN ACTIVE STORM PATTERN FOR MUCH OF THE FORECAST AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...130 132 138 140 150.
         GALE WARNING...120 121 141 155 160 165 175 176 180.
         HEAVY FREEZING SPRAY 160 180.
FIRE WEATHER...NONE.

SEB NOV 08