Small Craft Advisory 1003, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
509 PM AKST WED DEC 16 2015

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LEVEL TROUGH EXTENDS FROM THE NORTHERN BERING SEA
INTO THE NORTH PACIFIC. A WEAKENING SURFACE LOW EMBEDDED IN THE
UPPER TROUGH IS EVIDENT SOUTHWEST OF SAINT MATTHEW ISLAND.
SATELLITE IMAGERY SHOWS A BROAD AREA OF OPEN AND CLOSED CELL
CUMULUS(SHOWERS) INDICATIVE OF COLD ADVECTION AND UNSTABLE
CONDITIONS ACROSS MUCH OF THE BERING SEA. A SECONDARY SURFACE LOW
INFLUENCED BY THE UPPER TROUGH IS SOUTH OF KODIAK ISLAND. THE
ASSOCIATED OCCLUDED FRONT EXTENDS NORTH AND EAST ACROSS THE GULF
WITH THE TRIPLE POINT MOVING RAPIDLY EAST TOWARD HAIDA GWAII UNDER
A STRONG WESTERLY JET. THE SOUTHWEST GULF LOW IS PRODUCING STRONG
EAST TO NORTH WINDS ACROSS THE GULF AND BRISK NORTHERLY WINDS
ACROSS BRISTOL BAY AND THE AK PEN. PRECIPITATION WITH THIS FEATURE
IS MAINLY IMPACTING KODIAK ISLAND WITH STEADY RAIN...THOUGH RAIN
AND SNOW ARE HEADING TOWARD THE NORTH GULF COAST WITH THE SURFACE
OCCLUSION.

&&

.MODEL DISCUSSION...
IN THE EAST...MODELS ARE EXCELLENT AGREEMENT IN GENERAL LOW
POSITION...WIND FIELDS...AND QPF PATTERN. GALES TO STORM FORCE
WINDS ACROSS THE GULF AND GAP FLOWS ACROSS THE SOUTHCENTRAL
MAINLAND WILL BE THE MAIN IMPACTS THROUGH THE SHORT TERM. THE GFS
AND GEM REGIONAL WILL BE USED THE FORECAST PACKAGE.

OUT WEST...MODELS DIFFER SOME ON THE TRACK AND POSITION OF THE
DEVELOPING LOW MOVING INTO THE BERING SEA ON THU. HOWEVER...THE
GENERAL WIND FIELDS ARE SIMILAR. THE GFS WILL BE USED THIS
FORECAST PACKAGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE MAIN IMPACTS THROUGH THE SHORT TERM WILL BE STRONG WINDS
ACROSS THE GULF AND MINOR OUTFLOW CONDITIONS OVER THE MAINLAND
THROUGH EARLY THU. THE MAIN CULPRITS ARE A DEEPENING LOW OVER THE
SOUTHWEST GULF AND ITS ASSOCIATED OCCLUDED FRONT. GALES TO STORM
FORCE WINDS WILL SPREAD NORTH ACROSS ACROSS THE GULF TONIGHT AHEAD
OF THE FRONT IMPACTING THE MARINE COASTAL AREAS. WINDS ARE
EXPECTED TO DIMINISH ON THU AS THE LOW AND FRONT START TO PUSH
EASTWARD AND WEAKEN. BRISK GAP FLOWS AREA ALSO EXPECTED ACROSS THE
MAINLAND TONIGHT IN CONJUNCTION WITH THE INCREASED GULF
WINDS...THEN DECREASE SOME ON THU. THE BRUNT OF THE PRECIPITATION
ASSOCIATED WITH GULF LOW AND OCCLUDED FRONT WILL FALL ACROSS THE
GULF WITH VERY LITTLE MAKING IT INLAND. A SECONDARY FRONT
ASSOCIATED WITH A DEVELOPING LOW TRACKING ACROSS THE BERING SEA
WILL BRING ANOTHER SHOT OF RAIN AND SNOW AND INCREASED WINDS TO
THE WESTERN GULF AND SOUTHCENTRAL ON FRI.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A FRONT ASSOCIATED WITH THE DEEP LOW OVER THE WESTERN GULF WILL
SUPPORT A CHANCE OF SNOW ALONG THE ALASKA PENINSULA AND THE
ALEUTIAN RANGE THROUGH TONIGHT BEFORE THE LOW BEGINS TO PULL AWAY
FROM THE AREA ON THURSDAY MORNING. OTHERWISE...THE SOUTHWEST
MAINLAND WILL REMAIN DRY THROUGH THURSDAY EVENING WITH RELATIVELY
BENIGN CONDITIONS BENEATH TRANSITORY UPPER LEVEL RIDGING.
PRECIPITATION WILL RETURN TO THE AREA ON FRIDAY MORNING AS A FRONT
ARRIVES ALONG THE COAST. TEMPERATURES WILL REMAIN COLD ENOUGH TO
SUPPORT ALL SNOW...WITH A BRIEF WINDOW OF BLOWING SNOW POSSIBLE
ALONG THE COAST AS GUSTY EAST TO SOUTHEAST WINDS ACCOMPANY THE
FRONT. HOWEVER...THESE CONDITIONS WOULD BE SHORT LIVED AS THE
FRONT QUICKLY WEAKENS AND PUSHES INLAND.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
NORTHERLY FLOW AND AND A WEAK UPPER LEVEL TROUGH WILL CONTINUE TO
SUPPORT SNOW SHOWERS THROUGH TONIGHT ACROSS THE EASTERN HALF OF
THE BERING BEFORE THESE SHOWERS QUICKLY TAPER OFF ON THURSDAY
MORNING AS RIDGING TEMPORARILY MOVES OVERHEAD. ATTENTION THEN
TURNS TO THE POWERFUL LOW AND ASSOCIATED FRONT POISED TO MOVE INTO
THE WESTERN BERING TONIGHT. GALE FORCE SOUTHERLY WINDS AND A MIX
OF RAIN AND SNOW WILL ACCOMPANY THE ARRIVAL OF THE FRONT...WITH
PRECIPITATION QUICKLY CHANGING TO ALL RAIN AS WARM NORTH PACIFIC
AIR SURGES NORTHWARD. THE FRONT WILL CONTINUE EASTWARD ACROSS THE
BERING THROUGH THURSDAY NIGHT...EVENTUALLY SPREADING PRECIPITATION
AND GALE FORCE WINDS TO THE EASTERN ALEUTIANS AND THE AKPEN.

HOWEVER...THE MAIN FORECAST CHALLENGE WITH THIS SYSTEM WILL BE THE
POTENTIAL FOR WARNING LEVEL WINDS ACROSS THE WESTERN AND CENTRAL
ALEUTIANS FROM THURSDAY NIGHT INTO FRIDAY NIGHT AS WINDS TURN
SOUTHWESTERLY BEHIND THE FRONT AS THE LOW CENTER BEGINS TO MOVE
INTO THE BERING WITH FAVORABLE UPPER LEVEL JET SUPPORT. THE BEST
HIGH WIND POTENTIAL FOR NOW APPEARS TO BE OVER THE WESTERN PART OF
THE CHAIN THURSDAY NIGHT INTO FRIDAY MORNING AS COLD ADVECTION
HELPS THE STRONGEST WINDS TO MIX DOWN TO THE SURFACE. THEREFORE
HAVE UPGRADED THE HIGH WIND WATCH TO A HIGH WIND WARNING FOR THE
WESTERN ALEUTIANS WITH ISSUANCE OF THE AFTERNOON PACKAGE.
CONFIDENCE REMAINS LOWER FOR THE CENTRAL ALEUTIANS AS 12Z MODEL
RUNS HAVE SHOWN SOME UNCERTAINTY REGARDING THE TRACK OF THE
LOW...LEAVING OPEN THE POSSIBILITY THAT THE CORE OF STRONGEST
WINDS WILL REMAIN NORTH OF ADAK AND ATKA. THEREFORE CONTINUED THE
HIGH WIND WATCH FOR THE CENTRAL ALEUTIANS AS OPPOSED TO ISSUING A
WARNING AT THIS TIME.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
WEAKENING LOW PRESSURE WITH STORM-FORCE WINDS DIMINISHING TO
WIDESPREAD GALES WILL TRANSITION TO THE GULF WITH SECONDARY LOW
DEVELOPMENT OVER THE NORTHERN OR CENTRAL GULF. CONFIDENCE IN THE
EXACT LOCATION IS DEPENDENT ON THE LOCATION OF THE ACCOMPANYING
JET STREAM. SNOW CHANCES FOR SOUTHCENTRAL INCLUDING THE LARGER
POPULATION CENTERS WILL BE HIGHLY DEPENDENT ON HOW FAR NORTH
TOWARD PRINCE WILLIAM SOUND THIS SECONDARY LOW DEVELOPMENT
OCCURS...AS WELL AS ANY SOUTHEASTERLY MOISTURE PUSH PROVIDED BY
POTENTIAL JET DEVELOPMENT ON THE DOWNSTREAM SIDE OF THE NEGATIVE-
TILTED UPPER LEVEL TROUGH. OVERALL...CONFIDENCE IN SNOW CHANCES
FOR ANCHORAGE AND VICINITY HAVE DIMINISHED SOMEWHAT IN THE LAST
DAY...ESPECIALLY FOR SUNDAY INTO MONDAY.

MEANWHILE OVER THE BERING A SURFACE FRONT WILL ELONGATE FROM WEST
TO EAST ACROSS THE SOUTHERN BERING AND SERVE AS A FOCUSING
MECHANISM FOR SHOWERS AND GUSTY WINDS. BEHIND THIS FRONT...COLD
ADVECTION WITH SCATTERED SNOW SHOWERS WILL BE COMMON OVER THE
NORTHERN AND CENTRAL BERING.

BY THE EARLY TO MIDDLE PART OF NEXT WEEK...AN ARCTIC AIR MASS WILL
SETTLE OVER MUCH OF THE REGION...BRINGING BELOW NORMAL
TEMPERATURES (BY DECEMBER STANDARDS) TO MOST AREAS THAT MAY
PERSIST UNTIL THE END OF THE YEAR.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 191.
 HIGH WIND WATCH 187.
MARINE...STORM WARNING 119 120 130 131 132 138 139 150 175 176 177
178 179 185.
 GALE WARNING 121 127 128 136 137 141 155 165 170 172
173 174 180 181.
 HEAVY FREEZING SPRAY 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...CC