Small Craft Advisory 218, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
505 AM AKDT WED MAR 11 2015

.ANALYSIS AND UPPER LEVELS...
GENERALLY FAIR SKIES ARE EVIDENT ACROSS MUCH OF THE SOUTHERN
MAINLAND AND NORTHERN GULF WITH BROAD OFFSHORE FLOW...WITH THE
EXCEPTIONS A NARROW BAND OF INLET-EFFECT SHOWERS FROM LOWER COOK
INLET SOUTH TOWARD THE WESTERN GULF BRUSHING THE NORTH AND EAST
END OF KODIAK ISLAND...AS WELL AS SCATTERED SNOW SHOWERS ALONG THE
OUTER COAST OF THE KUSKOKWIM DELTA. CLOUDY CONDITIONS WITH SNOW
SHOWERS UNDER A BROAD NORTHEASTERLY FLOW WERE EVIDENT ACROSS MUCH
OF THE BERING SEA AND ALEUTIANS.

&&

.MODEL DISCUSSION(THROUGH THU NIGHT)...

MODEL INITIALIZATIONS WERE IN GOOD. THE ECMWF AND GFS WERE IN
FAIR AGREEMENT AND REASONABLE THROUGH THE PERIOD...WITH THE GEM
REGIONAL USED FOR MESOSCALE WINDS IN THE EAST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (WEDNESDAY AND THURSDAY)...

ANOTHER CLEAR AND COLD DAY IS ON TRACK FOR THE AREA TODAY AND
AGAIN TOMORROW. TEMPERATURES ACROSS MANY PARTS OF THE AREA
ACTUALLY REBOUNDED ABOVE MUCH OF THE AVAILABLE GUIDANCE
YESTERDAY...SOMEWHAT SURPRISING GIVEN THE ARCTIC AIRMASS. A KEY
REASON FOR THIS (IN ADDITION TO THE OBVIOUS PLETHORA OF SUNSHINE)
IS SUSPECTED TO BE THE NOTABLE LACK OF SNOW COVER FROM THE
MATANUSKA VALLEY SOUTHWARD. WITH SIMILAR CONDITIONS EXPECTED AGAIN
TODAY WILL HEDGE TOWARD THE HIGHER END OF THE AVAILABLE GUIDANCE
ENVELOP FOR MAX TEMPERATURES THE NEXT 2 DAYS. MEANWHILE...GAP
WINDS HAVE ONLY SLIGHTLY DIMINISHED OVERNIGHT FROM PRINCE WILLIAM
SOUND TO THE EASTERN KENAI PENINSULA AS PRESSURE GRADIENTS REMAIN
FAIRLY TIGHT. ANY DOWNTURN WILL BE SHORT-LIVED AS A REINFORCING
SHOT OF COLD AIR MOVING IN FROM THE NORTHWEST THIS AFTERNOON WILL
CAUSE WIND SPEEDS TO AGAIN TREND UPWARD. OVERALL THIS REMAINS A
MODERATE EVENT OVERALL IN TERMS OF OUTFLOW WIND REGIMES OWING
LARGELY TO LACK OF FAVORABLE UPPER LEVEL SUPPORT.

SPEAKING OF THE UPPER LEVELS...THE BROAD LONGWAVE TROUGH OVER THE
SOUTHERN PORTIONS OF THE STATE WILL BEGIN TO SHARPEN/AMPLIFY TODAY
WITH A DEEP UPPER LOW EVENTUALLY TAKING UP RESIDENCE DIRECTLY
OVERHEAD NORTHERN COOK INLET BY THURSDAY AFTERNOON. THE AIRMASS
REMAINS FAR TOO STARVED TO PRODUCE CLOUDS AT MOST LOCATIONS...WITH
THE EXCEPTION OF THE EASTERN COPPER RIVER BASIN (WRANGELL
MOUNTAINS) WHERE CLOUDS AND EVEN SOME SNOW WILL BECOME POSSIBLE BY
THURSDAY AS THE UPPER FLOW BECOMES MORE SOUTHERLY AND DEEP
MOISTURE SLIPS INTO THE AREA FROM THE NORTHERN PANHANDLE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE UPPER LEVEL TROUGH OVER MAINLAND ALASKA WILL SHARPEN AS A
SHORTWAVE ROTATES AROUND IT FURTHER REINFORCING THE ARCTIC AIR
MASS OVER THE AREA TONIGHT AND THURSDAY. NORTH TO NORTHWEST
SURFACE WINDS WILL ALSO PICK UP AGAIN AS THIS OCCURS...ESPECIALLY
THROUGH GAPS AND PASSES IN THE ALASKA RANGE. SNOW SHOWERS WILL
CONTINUE ALONG THE BERING SIDE OF THE ALASKA PENINSULA AND BRUSH
THE WESTERN CAPES AT TIMES BUT OTHERWISE CONDITIONS WILL REMAIN
COLD AND DRY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE VERTICALLY STACKED LOW SOUTH OF THE ALEUTIANS WILL CONTINUE TO
DROP SOUTH TODAY AND TONIGHT GRADUALLY EASING WINDS AND LIMITING
PRECIPITATION TO INSTABILITY-DRIVEN COLD AIR SHOWERS PRIMARILY
OVER THE BERING. THE NEXT FRONTAL SYSTEM WILL APPROACH THE WESTERN
ALEUTIANS THIS AFTERNOON AND EVENING BRINGING GALES AS WELL AS A
MIX OF RAIN AND SNOW AS IT SLIDES EAST TONIGHT. THE FRONT WILL
WEAKEN AND STALL OVER THE CENTRAL ALEUTIANS THURSDAY BEFORE A
FASTER MOVING WESTERLY SHORTWAVE CATCHES UP WITH IT THURSDAY
NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A DEEP COLD LOW PRESSURE TROUGH OVER THE ALASKA MAINLAND AND GULF
OF ALASKA WILL GRADUALLY DRIFT NORTH AND EAST INTO WESTERN CANADA
THIS WEEKEND...WHILE A WEST-EAST ORIENTED TROUGH OVER THE ALEUTIAN
CHAIN REMAINS LARGELY STATIONARY BUT EXTENDS EAST INTO THE NORTH
PACIFIC SOUTH OF KODIAK BY EARLY NEXT WEEK. AS THE MAINLAND TROUGH
EXITS INTO CANADA A STRONG RIDGE OF HIGH PRESSURE WILL BEGIN
BUILDING NORTH AND WEST INTO THE SOUTHERN MAINLAND FROM WESTERN
NORTH AMERICA. OVERALL...SURFACE TO MID-LEVEL THICKNESSES WILL
REMAIN ON THE LOW SIDE THROUGH EARLY NEXT WEEK...MEANING
TEMPERATURES WILL REMAIN BELOW NORMAL MOST PARTS OF THE SOUTHERN
MAINLAND. HOWEVER...AS A SEASONABLY STRONG LOW PRESSURE SYSTEM
DEVELOPS SOUTH OF KODIAK AND MOVES NORTH AND WEST INTO THE BERING
EARLY NEXT WEEK...STRONG SOUTH TO SOUTHEASTERLY FLOW WILL PUSH
TEMPERATURES QUICKLY ABOVE SEASONAL NORMALS BY THE MIDDLE OF NEXT
WEEK. WITH THOSE WARMER TEMPERATURES THE EARLY TO MIDDLE PART OF
NEXT WEEK WILL COME INCREASED CLOUD COVER AND A GOOD CHANCE FOR
RAIN AND SNOW TO MUCH OF SOUTHERN ALASKA BEGINNING AS EARLY AS
SUNDAY NIGHT.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...127 130-132 150 155 172 175-178
 HVY FRZG SPRY...121 126-131 138 139 150 160 165 179 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...CC