Small Craft Advisory 938, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
415 AM AKST THU NOV 27 2008

.MODEL DISCUSSION...MODELS ALL INITIALIZED FAIRLY WELL THIS MORNING.
EVEN THE GFS HAS FINALLY COME INTO LINE WITH THE EC. WENT WITH A
BLEND OF THE GFS/EC OUT WEST AND LEANED TOWARD GFS/PERSISTENCE IN THE
EAST. MAIN THING TO WATCH IS THE GFS TENDENCY TO MOVE THESE SYSTEMS A
LITTLE FASTER THAN THE NAM/EC ESPECIALLY THE UPPER LEVEL TROUGHS.
THIS BECOMES IMPORTANT BY SAT FOR SOUTHCENTRAL. A LINGERING TROUGH
WILL MEAN A LOT MORE CAA AND SNOW..POTENTIALLY ADVISORY TO WARNING
LEVELS FOR THE WEEKEND.

.ANALYSIS AND UPPER LEVELS...A DEFORMATION ZONE HAS SET UP ALONG THE
WESTERN CHUGACH AND TALKEETNAS WITH THE STRONGEST RADAR RETURNS IN A
NORTH/SOUTH LINE FROM HOUSTON TO WEST ANCHORAGE. THIS HAS RESULTED AT
TIMES IN SNOWFALL RATES OF HALF AN INCH PER HOUR OVERNIGHT. THIS
ENHANCED PRECIP ZONE FOLLOWS A CAA LINE ASSOCIATED WITH AN 850 MB LOW
THAT WILL LEAVE THE AREA BY 18Z. THE TROUGH LINGERED MUCH LONGER THAN
ORIGINALLY INDICATED IN THE MODELS. OTHERWISE THE MAIN AREAS OF
PRECIP CONTINUE TO BE ACROSS PRINCE WILLIAM SOUND. VALDEZ HAS SEEN
SNOWFALL RATES OF 1 INCH PER HOUR SINCE WED EVENING. THE TROUGH DID
NOT PUSH FAR ENOUGH EAST TO KEEP CORDOVA COLD ENOUGH FOR SNOW..THEY
HAVE BEEN RAIN ALL NIGHT.

THE TROUGH AND THE INCREASING GRADIENT FROM THE LOW CURRENTLY SOUTH
OF THE EASTERN ALEUTIANS IS HELPING TO ENHANCE NORTHERLY WINDS ALONG
THE COAST. WITH THESE WINDS AND PRECIP HAS COME BLOWING SNOW
ESPECIALLY ALONG THE EASTERN KENAI PENINSULA. OUT WEST THE OCCLUSION
ASSOCIATED WITH THE 950S LOW IN THE NORTH PACIFIC IS BRINGING STORM
FORCE WINDS..SNOW AND BLOWING SNOW AND REDUCED VISIBILITIES ACROSS
THE CENTRAL AND EASTERN ALEUTIANS WITH STRONGEST WINDS THROUGH
CHANNELED TERRAIN.

.SHORT TERM FORECAST...
SOUTHCENTRAL..THE GULF LOW WILL DISSIPATE BY THIS AFTERNOON AND THE
OCCLUDED FRONT FROM THE LOW SOUTH OF THE ALEUTIANS WILL MOVE INTO THE
GULF...QUICKLY SPREADING MORE PRECIPITATION NORTHWARD. THE BULK OF
THE PRECIPITATION WITH  THIS FRONT WILL FALL ALONG THE COAST DUE TO
DOWNSLOPING ON THE LEE OF THE COASTAL RANGE...BUT SHORT-WAVES ALOFT
COMBINED WITH ABUNDANT MOISTURE AND SOME OVERRUNNING WILL BRING A
CHANCE OF PRECIPITATION TO THE REST OF SOUTHCENTRAL. CONTINUED WARM
AIR ADVECTION WILL CHANGE ALL COASTAL AREAS TO RAIN BY FRIDAY WITH
THE POTENTIAL FOR SOME INLAND AREAS WARMING ENOUGH TO AT LEAST MIX
WITH RAIN. THE STORM IS NOW EXPECTED TO TRACK TO PRINCE WILLIAM SOUND
FRIDAY NIGHT WHILE AN UPPER TROUGH SWINGS NORTHEASTWARD TOWARD THE
REGION AND STRONG COLD ADVECTION ENSUES ON THE BACK SIDE OF THE
SYSTEM. IF ALL OF THIS COMES TOGETHER THERE COULD BE A SNOWSTORM IN
STORE FOR MUCH OF SOUTHCENTRAL(INCLUDING ANCHORAGE AND VICINITY) OVER
THE WEEKEND. IF NOT THERE IS STILL THE POTENTIAL FOR SOME FREEZING
RAIN AND/OR SLEET..ESPECIALLY ON FRIDAY.

SOUTHWEST AK..NORTHERLY WINDS WILL INCREASE ACROSS THE REGION TONIGHT
THROUGH THURSDAY AS THE PACIFIC LOW TRACKS SOUTH OF THE ALASKA
PENINSULA. PRECIPITATION AHEAD OF THE OCCLUDED FRONT WILL BACK INTO
EASTERN PORTIONS OF SOUTHWEST ALASKA LATE THURSDAY THROUGH FRIDAY
MORNING. TEMPERATURES WILL REMAIN COLD ENOUGH FOR SNOW AND
ACCUMULATION WILL GENERALLY REMAIN LIGHT AS THE BULK OF THE LIFT
WITH THE SYSTEM STAYS TO THE EAST. AS THE LOW TRACKS TO PRINCE
WILLIAM SOUND FRIDAY AND FRIDAY NIGHT COLD AIR WILL ADVECT ACROSS
SOUTHWEST ALASKA...PRODUCING GUSTY NORTHWEST FLOW AND SNOW IN
UPSLOPE AREAS OF THE ALASKA AND ALEUTIAN RANGES. THE UPPER TROUGH
MAY HELP ENHANCE SNOWFALL OVER PORTIONS OF THE KUSKOKWIM DELTA AS
IT SWINGS NORTHEASTWARD FRIDAY NIGHT AND SATURDAY. OTHERWISE...EXPECT
A DRYING TREND BEHIND THIS TROUGH HEADING INTO THE WEEKEND.

ALEUTIANS AND BERING..COMBINED WITH WIDESPREAD WINDS OF
40 TO 60 MPH LOW VISIBILITIES IN SNOW AND BLOWING SNOW ARE EXPECTED.
FORTUNATELY WATER TEMPERATURES ARE STILL FAIRLY WARM...SO SURFACE
AIR TEMPERATURES SHOULD REMAIN NEAR OR SLIGHTLY ABOVE
FREEZING...ELIMINATING THE THREAT OF BLIZZARD CONDITIONS. THE ALASKA
PENINSULA WILL SEE SOME WARM AIR ADVECTION AS THE OCCLUSION
APPROACHES THIS AFTERNOON...BUT THE FRONT WILL NEVER MOVE
THROUGH. SO IT WILL LIKELY BE MAINLY SNOW. AS THE SYSTEM MOVES TO
NEAR KODIAK ISLAND FRIDAY BROAD NORTHERLY FLOW AND COLD ADVECTION
WILL DOMINATE THE BERING SEA AND ALEUTIANS...CONTINUING INTO THE
WEEKEND. THUS...EXPECT THE TYPICAL GUSTY WINDS AND SNOW SHOWERS.
WINDS AND SNOW SHOWERS WILL GRADUALLY DIMINISH FRIDAY AND FRIDAY
NIGHT FROM WEST TO EAST. MEANWHILE...THE NEXT STORM SYSTEM OR SYSTEMS
WILL ENTER FROM THE WEST FRIDAY AND SATURDAY...BUT THERE IS GREAT
UNCERTAINTY IN THE TIMING AND PLACEMENT OF THESE.

.LONG TERM FORECAST...MEDIUM RANGE MODELS ARE CONSISTENT IN
INDICATING A MORE AMPLIFIED PATTERN WITH RIDGING OVER WESTERN NORTH
AMERICA AND A TROUGH OVER THE BERING/NORTH PACIFIC. THIS WOULD LEAD
TO A LESS ACTIVE PATTERN THAN OF LATE.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...STORMS 155 170 172
         GALES  120 121 130 140 160 165 171 179 180
         HEAVY FREEZING SPRAY 160 179 180
FIRE WEATHER...NONE

RW NOV 08