Small Craft Advisory 853, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
202 PM AKDT TUE OCT 28 2014

.ANALYSIS AND UPPER LEVELS...

500MB...A STACKED LOW CENTER WAS LOCATED NEAR THE AK PEN WITH A
SECONDARY CENTER OVER HAIDA GWAII. A RIDGE EXTENDED WEST FROM THE
CANADIAN YUKON TO OVER THE CENTRAL MAINLAND. A HIGH AMPLITUDE
RIDGE WAS OVER THE BERING SEA WITH A TROUGH TO THE WEST NEAR THE
KAMCHATKA PEN.

THE LOW NEAR THE AK PEN WEAKENS AS MOVES SOUTHEAST THEN EAST TO
OVER THE PANHANDLE THU AFTERNOON. AT THAT TIME...A BROAD TROUGH
EXTENDS SOUTH ACROSS MUCH OF THE MAINLAND. THE CENTRAL BERING SEA
RIDGE MOVES TO THE EASTERN BERING WITH A HIGH CENTER PINCHING OFF
NEAR THE CHUKCHI SEA THU AFTERNOON. THE KAMCHATKA TROUGH ELONGATES
EAST AS A DEVELOPING CENTER MOVES OVER THE EASTERN ALEUTIANS THU
EVENING. AT THAT TIME...A BROAD WESTERLY JET SETS UP OVER THE
NORTH PACIFIC.

SURFACE...
WIDESPREAD STRATUS WITH AREAS OF FOG AND FLURRIES CONTINUED OVER
THE COPPER RIVER BASIN. OUTFLOW WINDS WERE EVIDENT ALONG THE NORTH
GULF COAST AS WELL AS THE MATANUSKA VALLEY. VISIBLE SATELLITE
IMAGERY SHOWED SILT BLOWING OUT OF THE COPPER RIVER DELTA TO OVER
THE COASTAL WATERS.

FURTHER WEST...A SURFACE LOW NEAR THE AK PEN AND ASSOCIATED
FRONTAL TROUGH BROUGHT RAIN AND SNOW TO THE SOUTHWEST MAINLAND
AND RAIN/SHOWERS TO THE AK PEN. STRONG NORTHERLY WINDS WERE ALSO
PRESENT TO THE WEST OF THE CENTER FROM THE AK PEN TO THE CENTRAL
ALEUTAINS. WINDS OVER THE WESTERN ALEUTIANS SHIFTED TO THE
SOUTHEAST AS A FRONTAL TROUGH MOVED TO THE WESTERN BERING SEA THIS
MORNING.

&&

.MODEL DISCUSSION...
MODEL AGREEMENT VARIES DEPENDING ON AREA. THE ECMWF AND GFS ARE IN
FAIRLY GOOD AGREEMENT ON THE SYNOPTIC FEATURES OVER THE BERING
SEA AND ALEUTAINS...ESPECIALLY THE DEVELOPING LOW WHICH MOVES TO
THE CENTRAL ALEUTIANS THU. AFTERNOON PACKAGES IN THIS REGION WILL
BE BASED IN PART ON THE GFS.

FURTHER EAST...THE GEM REGION HAS A FAIRLY GOOD HANDLE ON
PRESSURE GRADIENTS ALONG THE NORTH GULF COAST AND DID A GOOD JOB
OF CAPTURING OUTFLOW WINDS THIS MORNING. THE ECMWF HAS THE OVER
ALL BEST SYNOPTIC HANDLING OF FEATURES AND WILL USED IN
COMBINATION WITH THE GEM REGIONAL.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...A WAVE MOVING ACROSS THE COPPER RIVER
TONIGHT WILL LIKELY STILL KICK OFF A FEW AREAS OF LIGHT
SNOW/FLURRIES. THIS WAVE WILL DO LITTLE TO BREAK UP THE
STRATUS...BUT MAY PRODUCE ENOUGH MIXING TO RAISE CEILINGS SOME
OVER THE EASTERN BASIN. OUTFLOW WIND ACROSS THE GULF SHOULD
DIMINISH SOME OVERNIGHT AS PRESSURE GRADIENTS WEAKEN AND
SUPPORTING FLOW ALOFT BECOMES LESS FAVORABLE. A WAVE MOVING NORTH
INTO THE NORTHER GULF ON WED AFTERNOON WILL BRING CLOUDS AND SOME
RAIN TO THE GULF COAST...BUT SHOULD NOT MAKE IT INLAND OVER THE
COASTAL/CHUGACH RANGES. SHOWERS SHOULD CONTINUE ALONG THE GULF
COASTS THROUGH THU.

SOUTHWEST ALASKA...

STRONG NORTHERLY WINDS ACROSS THE AK PEN WILL SLOWLY DIMINISH ON
WED. RAIN AND SNOW OVER SW ALASKA WILL MOVE SOUTH AND WEST WITH
THE FRONTAL BOUNDARY OVERNIGHT. DRY NORTHERLY FLOW WILL THEN TAKE
HOLD WED AND PERSIST THROUGH THU. A DEVELOPING LOW AND FRONTAL
TROUGH MOVING ACROSS THE ALEUTIANS WILL LIKELY BRING INCREASED
CHANCES OF RAIN TO THE AK PEN THU EVENING AND SNOW TO THE BRISTOL
BAY COAST FRI. WINDY CONDITIONS WILL ALSO ACCOMPANY THE
PRECIPITATION.

BERING SEA/ALEUTIANS...MOST OF THE AREA IS ON THE BACKSIDE OF THE
LOW PRESSURE SYSTEM UNDER WEAK COLD ADVECTION ALOFT. GALE FORCE
WINDS EXTEND FROM THE CENTRAL TO EASTERN BERING SEA ALONG WITH
RAIN AND SNOW SHOWERS. WINDS WILL SLOWLY TAPER FROM WEST TO EAST
BETWEEN NOW AND WEDNESDAY AFTERNOON. A DEVELOPING LOW OVER THE
NORTH PACIFIC MOVES TO THE CENTRAL ALEUTIANS THU AFTERNOON AND
SOUTH OF THE PRIBILOF'S THU NIGHT. EXPECT GALES IN ADVANCE OF
THIS SYSTEM WITH WESTERLY STORMS ALONG ITS SOUTHERN FLANK.

&&

.LONG TERM FORECAST...
MODEL AGREEMENT CONTINUES TO INCREASE WITH A SLIGHTLY FASTER LOW
TRACK FROM THE EASTERN BERING INTO THE GULF LATE FRIDAY OR EARLY
SATURDAY. THIS SYSTEM WILL BRING RAINY AND STORMY WEATHER TO THE
GULF COAST STARTING ON FRIDAY THAT NOW APPEARS TO PERSIST INTO
EARLY NEXT WEEK. THERE HAS ALSO BEEN A TREND TOWARDS A WETTER
FORECAST FOR SOUTHCENTRAL FOR SUNDAY AND MONDAY AS THE UPPER
TROUGH STALLS OVER THE SOUTHERN GULF. IT IS TOO SOON TO TELL HOW
THIS MAY IMPACT SOUTHCENTRAL...BUT THE MODELS ARE STARTING TO SHOW
ENOUGH COLD AIR ALOFT BY SUNDAY OR MONDAY TO SUPPORT SNOW AROUND
THE ANCHORAGE BOWL. EXACTLY WHEN AND HOW MUCH WILL BECOME A FOCUS
IN THE FORECAST LATER THIS WEEK.

THE MODELS THEN CONTINUE THE STORMIER PATTERN AS A DEEP LOW
CENTERED NEAR EASTERN SIBERIA WILL MOVE THROUGH THE BERING AND
POSSIBLY ONTO THE MAINLAND BY THE MIDDLE OF NEXT WEEK.

AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 150 155 165 170 171 172 173 174.
FIRE WEATHER...NONE.

RMC/DEK OCT 14