Small Craft Advisory 947, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
508 AM AKST SAT NOV 28 2015

.ANALYSIS AND UPPER LEVELS...
THE BROAD LONGWAVE TROUGH THAT HAS PERSISTED OVER THE EASTERN
BERING OVER THE PAST FEW DAYS CONTINUES TO SLOWLY WEAKEN IN PLACE
THIS MORNING. COLD AIR FROM THE BERING SEA CAN BE SEEN STRETCHING
ALONG THE SOUTHERN EDGE OF THIS LOW INTO THE NORTH PACIFIC...AND
IS EVEN BEGINNING TO FIRE SHOWERS OVER THE SOUTHERN GULF AS WEAK
COLD AIR ADVECTION WITHIN THE SOUTHERLY FLOW. AS HAS BEEN THE CASE
OVER THE PAST 2 DAYS WITH THIS LOW...YET ANOTHER SHORTWAVE IS
MOVING THROUGH THE SOUTHERN MAINLAND AND BRINGING EXTENSIVE CLOUD
COVER AND RAIN TO MOST AREAS AS TEMPERATURES REMAIN WELL ABOVE
NORMAL...THOUGH MANY AREAS HAVE COOLED OFF SINCE YESTERDAY WITH
DIMINISHING WARM AIR ADVECTION AND SOUTHERLY FLOW. OVER THE
CENTRAL/EASTERN BERING SEA WIDESPREAD COLD AIR ADVECTION REMAINS
WITH PERSISTENT NORTHWEST FLOW AND RAIN AND SNOW SHOWERS. THIS IS
BEGINNING TO DIMINISH HOWEVER OVER THE WESTERN BERING AS THE NEXT
FRONTAL SYSTEM HAS MOVED INTO THE WESTERN ALEUTIANS. THIS FRONT
WILL CONTINUE TO PROGRESS OFF TO THE EAST TODAY...AND BRING AN END
TO MUCH OF THE COLD AIR ADVECTION OVER THE BERING BY THIS EVENING.

&&

.MODEL DISCUSSION...
AS IS TYPICALLY THE CASE IN PERSISTENT AND SLOWLY PROGRESSING PATTERNS
LIKE THE ONE WE ARE CURRENTLY IN...SYNOPTIC MODEL AGREEMENT
REMAINS VERY GOOD INTO EARLY NEXT WEEK. AS A RESULT THE HIGHER
RESOLUTION MODELS SUCH AS THE NAM AND GEM REGIONAL WERE PREFERRED
FOR THE FORECAST PACKAGE THIS MORNING TO BETTER HANDLE GAP WINDS
AND PRECIPITATION THROUGHOUT THE SOUTH MAINLAND. OVER THE WESTERN
ALEUTIANS THERE ARE SOME RELATIVELY SMALL DIFFERENCES WITH THE
INTENSITY OF THE LOW MOVING INTO THE AREA FOR THIS WEEKEND...BUT
WITH COLD AIR ALREADY IN PLACE IN THAT AREA THE DEEPER GFS/EC
SOLUTIONS WERE USED TO BRING A SMALL INCREASE TO THE WINDS THROUGH
TONIGHT. THERE REMAINS VERY GOOD CONFIDENCE THAT THE MAIN IMPACTS
FROM THIS SYSTEM WILL REMAIN SOUTH OF THE ALEUTIANS THROUGH THE
WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE MAIN UPPER LEVEL LOW WILL REMAIN TO THE WEST WITH A RIDGE
WELL TO THE EAST. THIS WILL KEEP SOUTH CENTRAL ALASKA IN SOUTHERLY
FLOW ALOFT THROUGH SUNDAY NIGHT. TEMPERATURES WILL REMAIN WELL
ABOVE NORMAL...BUT THEY WILL SLOWLY DROP AS 500 MB HEIGHTS LOWER
OVER THE NEXT COUPLE OF DAYS. THE BEST CHANCES OF PRECIPITATION
ARE ALONG THE COAST WITH THE MOIST UP-SLOPE FLOW. INLAND AREAS
WILL GENERALLY HAVE ONLY ISOLATED TO SCATTERED SHOWERS. THESE
SHOWERS WILL BE A LITTLE ENHANCED TONIGHT INTO SUNDAY MORNING WITH
THE PASSAGE OF A WEAK UPPER LEVEL TROUGH. A STRONGER SYSTEM WILL
APPROACH KODIAK ISLAND LATE SUNDAY NIGHT FROM THE SOUTHWEST. THIS
WILL ALSO HELP PRODUCE SOME RIDGING OVER THE SOUTH CENTRAL
MAINLAND WHICH WILL END PRECIPITATION CHANCES FOR INLAND AREAS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE SOUTHWEST REGION WILL HAVE SEVERAL WAVES TRACK OVERHEAD THROUGH
THE WEEKEND ASSOCIATED WITH A LOW PRESSURE SYSTEM POSITIONED JUST
NORTH OF NUNIVAK ISLAND. THIS WILL BRING PERIODS OF SNOW AND RAIN
THROUGHOUT THE SOUTHWEST ALASKA REGION. BY SUNDAY A WEATHER FRONT
WILL MOVE INTO THE ALASKA PENINSULA. THIS WILL BRING WARMER
TEMPERATURES AND GALE FORCE SOUTHEASTERLY WINDS ACROSS THE BRISTOL
BAY AND KUSKOKWIM DELTA REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE NORTHERN TO EASTERN BERING SEA WILL HAVE NORTHWESTERLY WINDS
WHILE BEING ON THE BACKSIDE OF THE LOW PRESSURE SYSTEM LOCATED
JUST NORTH OF NUNIVAK ISLAND TODAY. THE WESTERN ALEUTIANS WILL
HAVE A STORM FORCE LOW TRACKING SOUTHWEST OF SHEMYA BY THIS AFTERNOON.
THE ASSOCIATED FRONT WITH THIS SYSTEM WILL BE MOVING THROUGH THE
WESTERN TO CENTRAL ALEUTIAN CHAIN RESULTING IN GUSTY GALE FORCE
SOUTHEASTERLY TO EASTERLY WINDS. BY SUNDAY THE LOW PRESSURE SYSTEM
WILL BE LOCATED NEAR ADAK WITH THE WEATHER FRONT LOCATED IN THE
EASTERN BERING SEA AND EASTERN ALEUTIANS. THIS WILL BRING WARMER
TEMPERATURES TO THE BRISTOL BAY REGION AND COOLER TEMPERATURES ON
THE BACKSIDE OF THE LOW IN THE CENTRAL BERING/CHAIN AREA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BEGINNING THE EXTENDED PERIOD ON MONDAY MORNING...A BROAD UPPER
TROUGH OVER THE NORTH PACIFIC AND BERING SEA WILL BE MAKING SLOW
EASTWARD PROGRESS...WITH A DEPARTING AND WEAKENING UPPER TROUGH
OVER EASTERN SOUTHCENTRAL ALASKA. THE ASSOCIATED BERING FRONT WILL
MOVE INTO THE GULF OF ALASKA SUNDAY NIGHT AND MONDAY...THEN MERGE
WITH A PREEXISTING CUTOFF LOW NEAR HAIDA GWAII. THE FRONT WILL
REACH GALE FORCE IS IT TRACKS INTO THE GULF...BUT THEN WEAKEN AS
IT MERGES WITH THE AFOREMENTIONED HAIDA GWAII LOW AS IT TRACKS
TOWARD THE NORTHERN GULF. THIS RATHER COMMON SEMIPERMANENT BERING
LOW REGIME WILL FAVOR SHOWERY WEATHER ACROSS COASTAL LOCATIONS IN
THE GULF...WITH THE BULK OF COLD AIR REMAINING OVER THE BERING
SEA...WHICH IN ITSELF TENDS TO ENHANCE THE NORTH PACIFIC POLAR JET
STREAM. SOUTHCENTRAL WILL REMAIN UNDER THE INFLUENCE OF WEAKER
LOWS ROTATING AROUND THE TROUGH INTO THE GULF...WITH EAST TO
SOUTHEAST LOW LEVEL FLOW FAVORING A RATHER DRAMATIC DOWNSLOPE
PRECIPITATION PATTERN ACROSS INLAND LOCALES. THE FIRST LARGE
BERING LOW WILL MOVE EAST AND WEAKEN BY LATE WEEK...ONLY TO BE
REPLACED AGAIN BY ANOTHER LARGE BERING LOW AS THE NORTH PACIFIC
JET STREAM MAKES SLOW EASTWARD PROGRESS HEADING INTO THE
WEEKEND...AND AS THE STOUT NORTHEAST PACIFIC RIDGE (THE CURRENT
SOURCE FOR THE VERY WARM PATTERN IN PLACE NOW) DEAMPLIFIES AND
WEAKENS. WHAT THIS MEANS...IMPACT WISE...IS THERE WILL NOT BE ANY
SIGNIFICANT COLD AIR OUTBREAKS OR SIGNIFICANT INLAND STORMS...BUT
IT WILL RESULT IN A MODERATION OF THE VERY WARM TEMPERATURES
CLOSER TO NORMAL BY THE WEEKEND. FORECAST CONFIDENCE IS EXTREMELY
HIGH WITH THE GENERAL PATTERN AND INLAND IMPACTS...AND MODERATELY
HIGH REGARDING WEAK LOWS ROTATING AROUND THE LARGER TROUGH AS THEY
TREK INTO THE GULF OF ALASKA. THESE DIFFERENCES...HOWEVER...ARE
NOT ALL THAT SIGNIFICANT UNTIL LATE WEEK.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE
MARINE...GALE WARNING 175 176 177 178

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PLD
LONG TERM...JA