Small Craft Advisory 882, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
451 PM AKST THU NOV 5 2015

.ANALYSIS AND UPPER LEVELS...
A MASSIVE UPPER LEVEL LOW CENTERED OVER THE EASTERN BERING
CONTINUES TO BE THE FOCAL POINT FOR WEATHER THROUGHOUT THE REGION.
AN ASSOCIATED STORM FORCE FRONT IS PRESSING NORTHWARD UP THE KENAI
PENINSULA ON ITS WAY TO THE NORTH GULF COAST WHERE PRESSURE RISES
AHEAD OF THE FRONT CONTINUE TO BRING GUSTY GAP WINDS TO PRINCE
WILLIAM SOUND AND TURNAGAIN ARM. THIS FRONT IS ALSO BRINGING
WIDESPREAD RAIN TO THE LOWER ELEVATIONS OF THE GULF COAST...WHICH
BECOMES WET SNOW ABOVE ABOUT 1500 FT. ON THE LEE SIDE OF THE
CHUGACH RANGE...DOWNSLOPING IS PREVENTING MOST OF THE RAIN/SNOW
FROM REACHING THE GROUND IN THE ANCHORAGE BOWL AND MATANUSKA
VALLEY. THIS DOWNSLOPING THEN RAPIDLY ENDS AS YOU REACH THE
SUSITNA VALLEY ALLOWING FOR WIDESPREAD ACCUMULATION
SNOWFALL...ESPECIALLY WEST OF THE PARKS HIGHWAY WHERE A SNOW
ADVISORY IS IN EFFECT.

OVER THE BERING SEA...RAIN AND SNOW SHOWERS ARE ROTATING AROUND
THE WEAKENING LOW OVER THE SOUTHWEST MAINLAND...WHILE BROAD
NORTHWESTERLY FLOW AND COLD AIR ADVECTION SHOWERS ARE SPREADING
THROUGH THE BERING BEHIND THE LOW.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD AGREEMENT IN THE SHORT TERM AS THE BROAD
LOW OVER THE BERING CONTINUES TO WEAKEN AND MOVES INTO THE GULF.
THERE ARE THEN SOME MINOR DIFFERENCES THAT ARISE ON SATURDAY AS
THE LOW MOVES INTO THE EASTERN GULF...BUT THIS IS LARGELY OUT OF
OUR AOR AND WILL HAVE MINIMAL IMPACTS ON OVERALL FORECAST CONFIDENCE
THIS WEEKEND. AS A RESULT THE HIGHER RESOLUTION NAM AND GEM
REGIONAL WERE PRIMARILY USED IN THE EARLY TERM.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE LARGE BERING LOW WILL BE CROSSING OVER THE ALASKA PENINSULA
THIS EVENING....MOVING SOUTH OF KODIAK ISLAND AND INTO THE NORTH
CENTRAL GULF BY TOMORROW EVENING. THE ASSOCIATED FRONT IS
CURRENTLY MOVING INTO SOUTH CENTRAL ALASKA...BRINGING STRONG WINDS
AND HEAVY PRECIPITATION TO COASTAL AREAS AS WELL AS GAP AREAS
ALONG TURNAGAIN ARM. HEAVY SNOW WILL BEGIN TO TAPER OFF IN THE
SUSITNA VALLEY WEST OF THE PARKS HIGHWAY TONIGHT. HEAVY SNOW IS
EXPECTED TO CONTINUE ALONG THE RICHARDSON HIGHWAY SOUTH OF COPPER
CENTER THROUGH EARLY FRIDAY MORNING BEFORE TAPERING OFF INTO
SHOWERS AS THE FRONT MOVES THROUGH. REGARDING PRECIPITATION
TYPE...COASTAL AREAS SHOULD SEE MOSTLY RAIN OVERNIGHT WITH SNOW
EXPECTED OVER THE COPPER RIVER BASIN AND A RAIN/SNOW MIX IN THE
SUSITNA VALLEY. IN THE ANCHORAGE AND MATANUSKA VALLEY...PRECIPITATION
SHOULD REMAIN A RAIN AND SNOW MIX WITH A REASONABLE WARM LAYER
APPARENT ON THE ANCHORAGE 00Z SOUNDING. WINDS WILL BEGIN TO
RAPIDLY DECREASE THIS EVENING AS THE FRONT PUSHES THROUGH TONIGHT.
NORTHWEST FLOW WILL DEVELOP OVER THE REGION SATURDAY AS THE LOW
MOVES INTO SOUTHEASTERN ALASKA...BRINGING COOLER TEMPERATURES TO
THE REGION WITH DECREASING CLOUDS OVER THE WESTERN PORTION OF THE
FORECAST AREA. THIS WILL ALSO INCREASE WINDS THROUGH CHANNELED
AREAS ALONG SOUTHERN KENAI PENINSULA...PRINCE WILLIAM SOUND...AND
THE COPPER RIVER DELTA.

OVER THE MARINE AREAS...STORM FORCE WINDS WILL BE DECREASING
RAPIDLY ALONG THE NORTH GULF COAST/PRINCE WILLIAM SOUND THIS
EVENING AS THE FRONT MOVES INLAND. WITH THE NORTHWEST FLOW...WINDS
WILL BEGIN TO INCREASE AGAIN TOMORROW EVENING THROUGH THE BARREN
ISLANDS AND INTO THE GULF OF ALASKA TO GALE FORCE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
RAIN AND GUSTY EASTERLY WINDS WILL CONTINUE TO DIMINISH THIS
EVENING AS THE LOW OVER THE FAR EASTERN BERING TRACKS ACROSS THE
AKPEN TONIGHT AND INTO THE WESTERN GULF BY FRIDAY MORNING. GUSTY
WINDS WILL PICK BACK UP ALONG THE BRISTOL BAY ZONE AND LOWER
KUSKOKWIM DELTA FRIDAY MORNING THROUGH SATURDAY MORNING AS COLDER
NORTHWESTERLY FLOW BEHIND THIS SYSTEM HELPS TO MIX GUSTY WINDS
ALOFT DOWN TO THE SURFACE. WITH THE COLDER NORTHWESTERLY FLOW
SETTING UP OVER THE SOUTHWEST MAINLAND FRIDAY...THE KUSKOKWIM
DELTA AND VALLEY ALONG WITH PARTS OF INTERIOR BRISTOL BAY COULD
SEE SOME LIGHT SNOW SHOWERS FRIDAY THROUGH FRIDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
RAIN SHOWERS ALONG WITH GALES AND STORM FORCE WINDS WILL PERSIST
OVER THE EASTERN BERING AND ALEUTIANS THROUGH FRIDAY AFTERNOON...AS
THE LOW OVER THE FAR EASTERN BERING TRACKS ACROSS THE AKPEN
TONIGHT AND INTO THE WESTERN GULF BY FRIDAY MORNING. AS WEAK
RIDGING TRACKS OVER THE EASTERN ALEUTIANS FRIDAY...WINDS AND
SHOWERY CONDITIONS OVER THE AREA ARE EXPECTED TO SLOWLY DIMINISH
THROUGH FRIDAY MORNING. HOWEVER...ANOTHER ROUND OF STRONG WINDS
IS IN STORE FOR THE ALEUTIANS AS A COLD FRONT MARCHES EASTWARD
FRIDAY NIGHT AND SATURDAY. THE AIR MASS BEHIND THE COLD FRONT WILL
BE COLD ENOUGH TO CHANGE PRECIPITATION TO A MIX OF RAIN AND SNOW
OR EVEN ALL SNOW IN THE COLDEST AREAS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
IN THE MID TERM THERE IS DECENT AGREEMENT WITH THE LOW OVER THE
NORTHERN BERING AND ITS FRONT THAT EXTENDS THROUGH THE CENTRAL
BERING AND CENTRAL ALEUTIANS. THE FRONT LOOKS TO REACH THE
SOUTHWEST COAST SATURDAY NIGHT AND THEN THE SOUTHCENTRAL SUNDAY
AFTERNOON. THE BIGGEST QUESTION WITH THIS SYSTEM IS WHAT TYPE OF
PRECIPITATION IT WILL BRING. THERE IS GOOD AGREEMENT THAT IT WILL
PULL UP ENOUGH WARM AIR FROM THE SOUTH TO TRANSITION TO RAIN FOR
MUCH OF THE SOUTHWEST. HOWEVER...THERE IS LESS CONFIDENCE FOR THE
LOWER KUSKOKWIM VALLEY WHERE PRECIP WILL LIKELY REMAIN IN THE FORM
OF SNOW INTO SUNDAY THEN EITHER TRANSITION OVER TO RAIN...OR IF
THE SURFACE TEMPERATURES STAY COLD ENOUGH THERE COULD BE SOME
FREEZING RAIN. AT THIS TIME CONFIDENCE IN PRECIP TYPE IS LOW.

AS THE FRONT MOVES THROUGH SOUTHCENTRAL ALASKA ON SUNDAY THE
QUESTION OF HOW MUCH WARM AIR MOVES IN REMAINS THE ISSUE. THE
MAJORITY OF THE GUIDANCE LOOKS TO KEEP SNOW FOR THE MAJORITY OF
THE AREAS WITH THE EXCEPTION OF PLACES RIGHT ALONG THE NORTH GULF
COAST. BY MONDAY THE FRONT WILL HAVE PUSHED THROUGH LEAVING
WESTERLY FLOW FOR SOUTHERN ALASKA THROUGH EARLY NEXT WEEK. THE
AMOUNT OF PRECIPITATION WILL DIMINISH QUITE A BIT WITH THIS SHIFT
BUT SOME SNOW WILL REMAIN FOR SOUTHERN ALASKA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 119 125 155.
         GALE WARNING 120 130 131 132 150 160 165 170 171 172
                      173 174 175 176 179 180 181.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...RF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DK