Small Craft Advisory 59, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
100 PM AKST FRI JAN 18 2013

.ANALYSIS AND UPPER LEVELS...
A FAIRLY COMPLEX UPPER-LEVEL PATTERN CONTINUES TO AFFECT THE ALASKAN
AOR THIS AFTERNOON. AN UPPER TROUGH REMAINS OVER MUCH OF MAINLAND
ALASKA AT THIS TIME...BUT IS BEING PUSHED NORTHEASTWARD BY A SHARP
MEDIUM-AMPLITUDE TROUGH CURRENTLY OVER THE ALASKA PENINSULA. A 100 KT
BRANCH OF THE JET STREAM IS DRIVING THE MOVEMENT OF THE RIDGE TO THE
NORTH. FURTHER WEST...COLD AIR ASSOCIATED WITH ANOTHER SHARP
UPPER-LEVEL TROUGH IS DIGGING SOUTHWARD WELL SOUTH OF THE BERING
SEA...TRYING TO UNDERCUT THE RIDGE NEAR 40N LATITUDE. AT THE
SURFACE...A 983 MB LOW SOUTH OF THE ALASKA PENINSULA IS MOVING
NORTHWARD AND BRINGING RAIN AND WIND TO THE EASTERN HALF OF THE
ALEUTIANS. FURTHER NORTH...MIDLEVEL CLOUDINESS IS LINGERING ACROSS
MANY OF THE INLAND AREAS OF SOUTHCENTRAL AS RELATIVELY WEAK
SUBSIDENCE ASSOCIATED WITH THE RIDGE IS HAVING A HARD TIME CLEARING
SKIES ACROSS THE AREA.

.MODEL DISCUSSION...
MODELS REMAIN IN ABOVE-AVERAGE SYNOPTIC AGREEMENT. THE NAM HAS BEEN
AN OUTLIER OVER THE LAST SEVERAL DAYS...BUT HAS COME INTO MUCH MORE
REASONABLE AGREEMENT TODAY WITH THE EVOLUTION OF THE COMPLEX LOW OVER
THE SOUTHERN BERING SEA THIS WEEKEND. ALL MODELS NOW AGREE ON THE LOW
CURRENTLY APPROACHING THE ALASKA PENINSULA AND ANOTHER LOW MOVING IN
FROM SOUTHWEST OF SHEMYA MERGING TOGETHER INTO ONE LARGE AND COMPLEX
LOW OVER THE EASTERN ALEUTIANS. DESPITE THE WELL-KNOWN COMPLEXITIES
OF SUCH AN INTERACTION...THERE IS EVEN SURPRISINGLY GOOD AGREEMENT
WITH THE LONGEVITY AND POSITION OF THE INDIVIDUAL SURFACE LOWS.
FURTHER TO THE EAST...MODELS AGREE THE FRONT ASSOCIATED WITH THE
ALASKA PENINSULA LOW WILL MOVE INTO THE GULF SATURDAY MORNING AND
BRING A PERIOD OF MODERATE TO HEAVY SNOWFALL TO THE EASTERN KENAI
PENINSULA SATURDAY NIGHT...SHIFTING TO NORTHERN PRINCE WILLIAM SOUND
ON SUNDAY AND TOWARD THE PANHANDLE SUNDAY NIGHT. MODEL CONSENSUS OVER
THE LAST SEVERAL DAYS HAS TRENDED A BIT COLDER WITH THE FRONT MOVING
INTO THE GULF...AND THUS EXPECT PRECIPITATION TO STAY SNOW DOWN TO
SEA LEVEL IN MOST LOCATIONS FOR AT LEAST THE MAJORITY OF THE EVENT.

.SHORT TERM FORECAST...
SOUTHCENTRAL...MIDLEVEL CLOUDINESS WILL CONTINUE TO SLOWLY DECREASE
THIS EVENING...BUT QUICKLY BE REPLACED BY HIGH LEVEL CLOUDS
ASSOCIATED WITH THE APPROACHING STORM. OVERALL FLOW THROUGH THE
ATMOSPHERE WITH THIS STORM WILL BE MORE SOUTHEASTERLY AND MUCH COOLER
THAN THE STORM LAST WEEKEND...AND THUS EXPECT A TYPICAL
UPSLOPE/DOWNLSOPE PATTERN TO DEVELOP AS WINDS INCREASE AHEAD OF THE
FRONT. THE COLDER TREND IN THE MODELS MAKES IT MORE LIKELY THAT THE
PORTAGE AREA MAY SEE SIGNIFICANT AREAS OF BLOWING SNOW DEVELOP LATE
SATURDAY AFTERNOON AND PERSIST THROUGH THE NIGHT...AND WILL NEED TO
BE MONITORED FOR POSSIBLE BLIZZARD POTENTIAL. THE COOK INLET AREA MAY
SEE A BRIEF PERIOD OF LIGHT PRECIPITATION IMMEDIATELY BEFORE THE
WINDS INCREASE...BUT NOT EXPECTING ANYTHING SUBSTANTIAL AT THIS TIME.
THE MORE NOTABLE ISSUE FOR THE ANCHORAGE AREA WILL PROBABLY BE RECENT
LOW-DENSITY SNOWFALL BEING PICKED UP AND BLOWN ALONG TURNAGAIN ARM
AND THE HILLSIDE. NOT EXPECTING WINDS TO MAKE IT TOO FAR DOWN THE
HILLSIDE...BUT THE HIGHER ELEVATIONS WILL LIKELY BE AFFECTED.

SOUTHWEST MAINLAND...A STEADY INCREASE IN NORTHEASTERLY OFFSHORE
WINDS WILL CONTINUE AS THE LOW AND FRONT APPROACH FRIDAY NIGHT AND
SATURDAY. PRECIP MOVES INTO THE AREA SATURDAY...AND SHOULD BE SNOW AT
MOST LOCATIONS EXCEPT ALONG THE ALASKA PENINSULA. WESTERN PORTIONS OF
THE BRISTOL BAY ZONE...AS WELL AS THE DELTA COAST WILL SEE
TEMPERATURES STAY COLD ENOUGH TO CREATE ISSUES WITH REDUCED
VISIBILITIES IN BLOWING SNOW AS THE STORM UNFOLDS. CONFIDENCE IS
HIGHER IN PORTIONS OF THE DELTA COAST SEEING BLIZZARD
CONDITIONS...THUS A BLIZZARD WARNING WILL BE ISSUED WITH THE
AFTERNOON PACKAGE.

BERING SEA AND ALEUTIANS...PRECIP SHIELD ASSOCIATED WITH THE LOW HAS
MOVED INTO THE EASTERN ALEUTIANS AND ALASKA PENINSULA TODAY.
TEMPERATURES HAVE WARMED FAIRLY QUICKLY AND RAIN IS NOW FALLING AT
MOST LOCATIONS WITH GUSTY EASTERLY WINDS. TEMPERATURES ARE REMAINING
MUCH COLDER OVER THE PRIBILOF ISLANDS...AND CONFIDENCE IS HIGH THAT
BLIZZARD CONDITIONS WILL DEVELOP THIS EVENING AS STEADY SNOW BEGINS.
AS THE TWO LOWS MENTIONED ABOVE WEAKEN AND COMBINE BY SUNDAY MORNING
OVER THE CENTRAL ALEUTIANS...THE REGION WILL FALL INTO A MORE SHOWERY
PATTERN THAT IS CHARACTERIZED BY COLD AIR ADVECTION AND SNOW SHOWERS
OVER THE WESTERN BERING SEA/ALEUTIANS...WITH WARMER TEMPERATURES AND
A RAIN/SNOW MIX OVER MUCH OF THE EASTERN BERING.

.LONG TERM FORECAST...
LONGWAVE TROUGH WITH COMPLEX LOW DEVELOPING OVER THE BERING SEA WILL
GRADUALLY SLIDE EASTWARD THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL
KEEP TEMPERATURES ACROSS MUCH OF THE MAINLAND NEAR OR SLIGHTLY
ABOVE-AVERAGE...WITH SHOWERS ALONG THE COAST AND MAINLY DRY
CONDITIONS INLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155 195
         BLIZZARD WATCH 125
MARINE...STORM 185
         GALE 120 130 132 136 137 138 140 150 155 160 165 170 179 180
         HEAVY FREEZING SPRAY 140 160 179 185
FIRE WEATHER...NONE

AMD JAN 13