Small Craft Advisory 782, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
431 PM AKDT WED OCT 8 2014

.ANALYSIS AND UPPER LEVELS...
A LARGE AND VERTICALLY STACKED 948 MB STORM FORCE LOW WAS LOCATED
SOUTH OF THE EASTERN ALEUTIANS. A WEAKER LOW WAS PRESENT SW OF
ATTU. RAIN WAS EVIDENT ALONG THE ASSOCIATED FRONTAL BOUNDARIES
EXTENDING FROM THE ALASKA PENINSULA TO THE FAR WESTERN ALEUTIANS.
GALE TO STORM FORCE WINDS WERE EVIDENT FROM THE COASTAL WATERS
NEAR THE AK PEN TO THE CENTRAL ALEUTIANS AND ACROSS MUCH OF THE
EASTERN BERING SEA. NORTHEAST GALES WITH LOCALIZED STORM GUSTS
WERE ALSO OBSERVED NEAR TOGIAK BAY THIS MORNING.

GENERALLY FAIR SKIES SKIES WITH BRISK NORTHERLY FLOW WAS EVIDENT
ACROSS MUCH OF THE SOUTHWEST MAINLAND. FURTHER EAST...SNOW SHOWERS
ASSOCIATED WITH LIFT FROM AN UPPER LOW WERE EVIDENT OVER THE
COPPER RIVER BASIN AND ALONG THE NORTH GULF COAST. THE REMAINDER
OF SOUTHCENTRAL ALASKA WERE UNDER RELATIVELY FAIR SKIES WITH A FEW
ISOLATED SNOW SHOWERS TRACKING NORTH ALONG THE TURNAGAIN ARM.

.MODEL DISCUSSION...
OOZ MODEL RUNS ARE IN VERY GOOD AGREEMENT FROM INITIALIZATION
THROUGH THE SHORT TERM. THE ASSOCIATED WIND AND QPF FIELDS SHOW
SIMILAR TIMING AND INTENSITY. THE NAM MODEL WITH THE GREATER
DETAIL WILL BE USED OVERALL FOR AFTERNOON PACKAGES THROUGH THE
SHORT TERM.

&&

.SHORT TERM FORECAST...
SOUTHCENTRAL ALASKA... THE LARGE UPPER TROUGH WILL DIG SOUTH
BRIEFLY AND SET UP SW FLOW ACROSS SOUTHCENTRAL ALASKA THIS EVENING
THEN DRIFT AS A RIDGE BUILDS NORTH ACROSS THE NORTHERN GULF IN
ADVANCE OF THE PACIFIC STORM CENTER. A FAIRLY STRONG SW JET
BUILDS ACROSS THE SUSITNA VALLEY AND COPPER RIVER BASIN WITH THE
DIGGING UPPER TROUGH THIS EVENING AND HELPS ENHANCE SNOW SHOWERS
ACROSS THE COPPER RIVER BASIN AND ALASKA RANGE. THE FULLY
OCCLUDED LOW SOUTH OF CENTRAL ALEUTIANS WILL WEAKEN AS IT TRACKS
SLOWLY TO SOUTHERN GULF OF ALASKA FRI NIGHT. THE ASSOCIATED
FRONTAL SYSTEM...CURRENTLY EXTENDING ACROSS THE CENTRAL ALEUTIANS
AND SOUTH OF THE AK PEN...WILL MOVE NORTH AND EAST AND EXTEND
EASTWARD TO A TRIPLE POINT LOW CENTER OVER THE SOUTHERN GULF ON
THU AFTERNOON. THE TRIPLE POINT WILL THEN MOVE SLOWLY NORTH AND
PUSH THE FRONTAL TROUGH OVER THE SOUTHCENTRAL MAINLAND THU NIGHT
AND FRI. PRECIPITATION WITH THESE FEATURES WILL LIKELY BE MOSTLY
RAIN ALONG THE GULF COASTS. PRECIPITATION WILL BE SOMEWHAT MORE
PROBLEMATIC INLAND OF THE COASTAL RANGE AND CHUGACH AS MIXED
PRECIPITATION TYPES ARE LIKELY THU NIGHT AND INTO FRI. THE COPPER
RIVER BASIN WILL LIKELY INITIALLY SEE SNOW WITH OVERRUNNING
MOISTURE THU NIGHT...BUT COULD SEE MIXED OR LIGHT FREEZING RAIN
WITH THE SLOW EROSION OF THE COLD LAYER FRI. PRECIPITATION WILL
LIKELY SPILL OVER THE CHUGACH THU NIGHT WITH LITTLE CROSS BARRIER
FLOW. PRECIPITATION WILL LIKELY START AS LIGHT SNOW THEN BECOME
MIXED. A SHALLOW LAYER OF COLD AIR WILL CONTINUE THROUGH FRI
MORNING AS SURFACE GRADIENTS SUPPORT NORTHERLY LOW LEVEL FLOW
WHILE THE AIR ABOVE CONTINUES TO WARM. THESE CONDITIONS WILL
INCREASE CHANCES OF LIGHT FREEZING RAIN FRI MORNING. THE FREEZING
RAIN THREAT SHOULD DIMINISH FRI AFTERNOON WITH THE CONTINUED
EROSION OF THE COLD NEAR SURFACE LAYER. GALE TO STORM FORCE WINDS
WILL INCREASE ACROSS MUCH OF THE GULF AHEAD OF THE FRONT TONIGHT
AND THU. WINDS SHOULD DIMINISH THU NIGHT AS THE FRONT MOVES INLAND
OVER SOUTHCENTRAL. WINDS...THOUGH NOT AS STRONG...WILL INCREASE
AGAIN ACROSS THE NORTH GULF FRI/FRI NIGHT WITH THE APPROACH OF THE
MAIN LOW CENTER.

.SOUTHWEST ALASKA (CONTINUED FROM SOUTHCENTRAL)...

NORTHERLY WINDS WILL LIKELY INCREASE ACROSS THE SOUTHWEST
MAINLAND THROUGH TONIGHT WITH BUILDING PRESSURE GRADIENTS AHEAD OF
THE FRONT. GALES TO STORMS ARE EXPECTED ACROSS THE AK PEN/BRISTOL
BAY DOMAIN WITH STRONG WIND HEADLINES INLAND. WINDS WILL DIMINISH
ACROSS BRISTOL BAY AND THE EASTERN AK PEN THU TONIGHT BUT WILL
REMAIN RELATIVELY STRONG ACROSS THE DELTA. PRECIPITATION WILL
LIKELY REMAIN RAIN ALONG THE AK PEN TONIGHT BUT SHOULD BECOME
SHOWERY AND MIXED ON THU NIGHT WITH COLD ADVECTION. THE
PRECIPITATIONCOULD BECOME MIXED AS FAR NORTH AS KING SALMON
THU...BUT WHAT MAKES IT FURTHER NORTH WILL LIKELY BE SNOW AND
SHOULD REMAIN GENERALLY EAST OF DILLINGHAM.

BERING SEA/ALEUTIANS...
GALES TO STORMS OVER THE CENTRAL AND EASTERN BERING SEA AND
ALEUTIANS WILL SLOWLY DIMINISH FROM THE WEST ON THU WITH GALES
LIKELY HOLDING ON OVER THE EASTERN ALEUTIANS THROUGH THU NIGHT
WITH GOOD COLD ADVECTION ON THE BACKSIDE OF THE LOW. RAIN TONIGHT
WILL SHIFT MORE TOWARD SHOWERS THU AND MAY BECOME MIXED LATE THU
NIGHT AND FRI AS COLD AIR PUSHES SOUTH.

&&

.LONG TERM FORECAST (SUN THROUGH WED)...THE HIGHLIGHTS OF THE
EXTENDED CONTINUE TO BE A COLD TROUGH STRETCHING FROM THE AK WEST
COAST THROUGH THE GULF AND A SHARP RIDGE OVER THE BERING. THE
RIDGE IS BUILDING IN RESPONSE TO MODERATELY STRONG PIECES OF
ENERGY BREAKING OFF THE POLAR VORTEX AND PUSHING THROUGH THE
KAMCHATKA PENINSULA. WHILE THESE PIECES ARE NOT DIRECTLY AFFECTING THE
MAINLAND AT THIS POINT...THEY DO REVEAL THE STRENGTH OF THE VORTEX
AND ITS SOUTHWARD MOVEMENT. FURTHER DOWNSTREAM...MODELS ARE
STARTING TO COME INTO BETTER AGREEMENT FOR LATER IN THE WEEKEND
AND EARLY NEXT WEEK REGARDING THE CLOSED UPPER LOW NEAR BRISTOL
BAY. RATHER THAN PUNCHING UP THROUGH THE COOK INLET AS THE EC
DEPICTED YESTERDAY...MODELS NOW GENERALLY PAINT THE ENERGY
ASSOCIATED WITH THE CLOSED LOW GETTING SHEARED OUT STRETCHING FROM
THE SEWARD PENINSULA INTO THE GULF.

THE PATTERN GETS EVEN MORE COMPLICATED TO START NEXT WEEK AS
REMNANTS OF SUPER TYPHOON VONGFONG GET SWEPT UP IN OUR 120-130KT
JET. THIS WILL SERVE TO ULTIMATELY REINFORCE SOME TROUGHING OVER
THE GULF. BUT...UNLIKE YESTERDAY...ALL OF THE OPERATIONAL MODELS
WOULD NOW STOP THE TRULY COLD AIR ON THE WEST SIDE OF THE AK
RANGE. IN FACT...MUCH OF SOUTHCENTRAL WOULD LIKELY BE IN A
NEUTRAL-ADVECTION OR WARM-AIR-ADVECTION SCENARIO WITH A SURFACE
LOW IN THE GULF. THE EXACT LOCATION OF THIS LOW VARIES VASTLY
FROM MODEL TO MODEL BY MID-WEEK. BUT MOST MODELS DO AGREE THAT BY
THAT TIME...RIDGING FROM THE BERING WILL START TO PUSH EAST AND
SHOULD BRING A DRYING TREND TO MUCH OF SOUTHCENTRAL.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 150 155 170 172 173 130 131 138.
GALE WARNING 160 165 171 174-181 185 119 120 132 136 137.
FIRE WEATHER...NONE

RMC/MO OCT 14