Small Craft Advisory 128, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
437 PM AKST TUE FEB 10 2015

.ANALYSIS AND UPPER LEVELS...
THE UPPER LEVEL RIDGE OVER THE WEST COAST OF NORTH AMERICA IS
AMPLIFYING AGAIN. THE UPPER LEVEL TROUGH REMAINS OVER SOUTHWEST
ALASKA AND THE BERING SEA. THIS COMBINATION IS SENDING THE STORM
TRACK BACK TOWARD THE GULF OF ALASKA AND SOUTHCENTRAL ALASKA.
THE FIRST OF A NUMBER OF LOWS HAS PUSHED THROUGH THE GULF THIS
MORNING AND IS NOW MOVING INTO SOUTHWEST ALASKA. THIS PATTERN WILL
CONTINUE THROUGH THE WEEK WITH WARMER AIR MOVING INTO THE AREA.

&&

.MODEL DISCUSSION...
MODELS ARE IN GOOD SYNOPTIC AGREEMENT THE NEXT FEW DAYS. HOWEVER
THE GFS AND ECMWF LOOK TO HAVE THE BEST OVERALL HANDLE ON THE
WEATHER SITUATION. THE NAM AND GEM LOOK TO BE TOO STRONG IN
DEVELOPING AN OPEN WAVE INTO A CLOSED OFF LOW IN THE SOUTHEAST OF
THE GULF WEDNESDAY INTO WEDNESDAY NIGHT. THIS SYSTEM WILL BE
COMPLEX IN NATURE AS IT HEADS INTO THE GULF OF ALASKA FRIDAY BUT
THE ECMWF IS MOVING THE SYSTEM THE FARTHEST TO THE WEST WHICH IS
LIKELY TO OCCUR. THE IMPACT THIS WILL AVE ON THE FORECAST WILL BE
TO BRINGING WARMER AIR INTO THE GULF AND GULF COAST THAN SOLUTIONS
THAT SHOW THE MAIN PART OF THE LOW FARTHER EAST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE DEEPENING STORM FORCE LOW THAT WILL RAPIDLY MOVE TOWARDS THE
NORTH GULF BY LATE TONIGHT WILL BRING ANOTHER ROUND OF SNOW TO
THE GULF COAST THROUGH TOMORROW. AN UPPER LEVEL TROUGH ASSOCIATED
WITH THIS SYSTEM WILL THEN PASS OVER SOUTHCENTRAL LATE TOMORROW
MORNING...BRINGING A PERIOD OF LIGHT SNOW FROM THE NORTHERN KENAI
PENINSULA INTO THE ANCHORAGE BOWL AND MATANUSKA VALLEY THAT SHOULD
PERSIST UNTIL THE EARLY EVENING. ACCUMULATIONS IN THESE AREAS ARE
EXPECTED TO BE LIGHT FROM THIS SYSTEM AS MOST OF THE MOISTURE AND
UPPER LEVEL DYNAMICS ARE SHUNTED TO THE EAST...BUT MOST AREAS
SHOULD SEE ACCUMULATING SNOW TOMORROW. HEAVIER SNOWS WILL FALL
FROM THE EASTERN KENAI PENINSULA INTO THE THOMPSON PASS...HOWEVER
SINCE THE SYSTEM WILL BE FALLING APART ONCE THE SURFACE LOW
CRASHES INTO PRINCE WILLIAM SOUND ON WEDNESDAY MORNING THESE
SHOULD ALL STAY WELL BELOW ADVISORY CRITERIA. CONDITIONS THEN
BEGIN TO IMPROVE THROUGHOUT THE AREA ON THURSDAY AS THE UPPER
LEVEL TROUGH MOVES INTO THE INTERIOR...BUT WITH SOUTHERLY FLOW
ALOFT A FEW SHOWERS WILL REMAIN IN THE AREA WITH TEMPERATURES
CONTINUING TO SLOWLY RISE INTO FRIDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
PRECIPITATION OVER THE SOUTHWEST MAINLAND WILL BE LARGELY
CONFINED TO THE BRISTOL BAY REGION THROUGH WEDNESDAY...WITH A
STALLED FRONT OVER THE SOUTHEASTERN BERING AND A WEAK UPPER WAVE
ROTATING NORTHWESTWARD ACROSS THE ALASKA PENINSULA KEEPING A
CHANCE OF SNOW OVER THE AREA FOR THE NEXT SEVERAL DAYS. THE
KUSKOKWIM VALLEY AND DELTA WILL SEE MOSTLY CLOUDY SKIES AS THE
UPPER LEVEL FEATURE PASSES TO THE SOUTH...BUT WILL OTHERWISE STAY
MOSTLY DRY WITH GUSTY NORTHEAST WINDS OVER THE DELTA IN PERSISTENT
OFFSHORE FLOW. ANOTHER UPPER LEVEL WAVE WILL LIFT NORTHWARD OVER
THE ALASKA PENINSULA THURSDAY MORNING...BRINGING A BETTER CHANCE
FOR PRECIPITATION ACROSS THE ENTIRE SOUTHWEST MAINLAND THROUGH
THURSDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STALLED FRONT OVER THE SOUTHEASTERN BERING WILL KEEP RAIN AND
GUSTY NORTHEAST WINDS OVER THE ALASKA PENINSULA AND EASTERN HALF
OF THE ALEUTIAN CHAIN FOR THE NEXT SEVERAL DAYS AS IT SLOWLY
WEAKENS IN PLACE. ELSEWHERE...A TIGHT PRESSURE GRADIENT BETWEEN A
RIDGE OVER THE WESTERN BERING AND THE BROAD NORTH PACIFIC LOW WILL
HELP TO MAINTAIN A LARGE SWATH OF GALE FORCE WINDS OVER THE
CENTRAL BERING...INCLUDING THE PRIBILOF ISLANDS AND CENTRAL
ALEUTIANS THROUGH THURSDAY.

&&

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

BEGINNING FRIDAY...A GENERAL REGIME CHANGE WILL BE UNDERWAY AS A
NORTH PACIFIC LOW...CENTERED OVER 165W...TRACKS IN A SERIES OF
WEAK POTENTIAL VORTICITY ANOMALIES INTO THE GULF OF ALASKA. WITH
THE MAIN BAROCLINIC ZONE OVER THE EASTERN BERING...THE ASSOCIATED
FRONTS WILL BE WEAKENING AS THEY TRACK NORTH. WITH THAT
SAID...EACH FRONTAL PROGRESSION WILL FEATURE A RENEWED SURGE OF WARM
AND MOIST AIR SLIDING INTO SOUTHERN ALASKA...ALLOWING FOR A
GRADUAL WARM-UP TO NEAR AVERAGE ACROSS MOST OF THE REGION. RAIN
AND SNOW CHANCES IN THIS PATTERN WILL GENERALLY REMAIN OVER THE
GULF COAST INTO PRINCE WILLIAM SOUND...AS WELL AS OVER THE BERING
AND ALEUTIANS...WITH GENERALLY DRIER CONDITIONS INLAND. WITH THE
PERSISTENT COLD PATTERN IN PLACE...MOST PRECIPITATION WILL REMAIN
SNOW INLAND...ALTHOUGH RAIN AND POSSIBLY FREEZING RAIN WILL BE
POSSIBLE LATE FRIDAY AS A MORE VIGOROUS LOW TRACKS INLAND.
SHORTWAVE RIDGING BUILDS IN LATE WEEKEND INTO EARLY NEXT
WEEK...WITH THE ACTIVE NORTH PACIFIC POLAR JET REMAINING DISPLACED
NEAR 40N. DISCREPANCY IN THE SUITE OF GLOBAL NUMERICAL GUIDANCE
INCREASES BY MIDWEEK...WITH THE GFS AND CANADIAN GDPS MORE BULLISH
WITH RESPECT TO SOUTHERN STREAM ACTIVITY TRACKING INTO SOUTHERN
ALASKA. FOR NOW...A MORE MIDDLE GROUND WPC APPROACH WAS FAVORED
GIVEN THE UNCERTAINTY WITH THE STRENGTH OF POTENTIAL BLOCKING OVER
THE REGION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 119 130 138
         GALE 120 127 131 132 136 137 139 160 165 170 173
         174 175 176 177 179 180 181 185
         HEAVY FREEZING SPRAY 127 179 185
FIRE WEATHER...NONE.

&&

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