Small Craft Advisory 783, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
556 AM AKDT THU OCT 9 2014

.ANALYSIS AND UPPER LEVELS...
THE DOMINANT FEATURE ON SATELLITE IMAGERY THIS MORNING IS THE
STORM FORCE LOW PRESENTLY LOCATED APPROXIMATELY 300 MILES SOUTH OF
DUTCH HARBOR. STORM FORCE WINDS ON THE NORTHERN PERIPHERY OF THIS
SYSTEM EXTEND ALONG THE PACIFIC SIDE OF THE ALASKA PENINSULA
WESTWARD THROUGH THE EASTERN ALEUTIANS AND PRIBILOF ISLANDS...WITH
GALES OVER MUCH OF THE REST OF THE BERING AS A STRONG PRESSURE
GRADIENT PERSISTS BETWEEN THE LOW TO THE SOUTH AND HIGH PRESSURE
OVER THE NORTHERN BERING. A STRONG FRONT IS PUSHING INTO THE
SOUTHERN GULF OF ALASKA...SPREADING RAIN AND GALE FORCE WINDS OVER
KODIAK ISLAND. FAIRLY BENIGN CONDITIONS PERSIST ACROSS THE
SOUTHERN MAINLAND...WITH MOSTLY CLOUDY SKIES OVER SOUTHCENTRAL AK
BENEATH AN UPPER TROUGH THAT IS HELPING TO GENERATE A FEW RAIN AND
SNOW SHOWERS FROM EASTERN PRINCE WILLIAM SOUND INTO THE COPPER
RIVER BASIN AS IT PUSHES EASTWARD. BRISK NORTHERLY WINDS CONTINUE
ACROSS THE SOUTHWEST MAINLAND AND SOUTHCENTRAL AHEAD OF THE
APPROACHING LOW.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT INTO THE WEEKEND...WITH
ALL GUIDANCE PERFORMING SIMILARLY WITH RESPECT TO THE STRENGTH
AND POSITIONING OF THE LOW AS IT TRACKS INTO THE GULF ON FRIDAY
AND ALSO WITH THE TIMING OF THE FRONT AS IT APPROACHES THE GULF
COAST LATER TODAY. UTILIZED THE NAM/GEM EARLY ON FOR ENHANCED
DETAIL AND THEN GENERALLY WENT TOWARDS THE EC FOR THE REMAINDER OF
THE SHORT TERM FORECAST.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
WIDESPREAD RAIN WILL RETURN TO SOUTHCENTRAL AK TODAY AND TONIGHT AS
THE FRONT MOVES OVER THE NORTHERN GULF COAST...WITH RAIN REACHING
THE COAST BY LATER THIS MORNING AND THEN SPREADING INLAND THIS
EVENING. THE MAIN FORECAST CHALLENGE IN THE SHORT TERM WILL BE
DETERMINING PRECIPITATION TYPE LATER TONIGHT. LOCATIONS FROM THE
ANCHORAGE BOWL TO THE MATANUSKA VALLEY WILL LIKELY SEE A MIX OF
RAIN AND SNOW TONIGHT AS TEMPERATURES BEGIN TO COOL...BUT A BRIEF
WINDOW OF LIGHT FREEZING RAIN WILL ALSO BE POSSIBLE AS TEMPERATURES
BEGIN TO WARM ALOFT BUT NORTHERLY WINDS ALLOW COLDER AIR REMAIN IN
PLACE AT THE SURFACE. ALTHOUGH CONFIDENCE REMAINS LOW...THE BEST
CHANCE WILL BE LATE TONIGHT INTO TOMORROW MORNING FOR THE
TYPICALLY COLDER LOCATIONS WHERE THE SUB FREEZING TEMPERATURES MAY
TAKE A BIT LONGER TO BE SCOURED OUT. THIS INCLUDES EAST ANCHORAGE
AND EAGLE RIVER AS WELL AS THE BUTTE AREA IN THE MATANUSKA VALLEY.
LIGHT FREEZING RAIN WILL ALSO BE POSSIBLE FOR PORTIONS OF THE
COPPER RIVER BASIN AS PRECIPITATION BEGINS AS ALL SNOW BUT WARMER
AIR BEGINS TO MOVE IN ALOFT TONIGHT. PRECIPITATION WILL CHANGE
OVER TO ALL RAIN BY LATE FRIDAY MORNING AS TEMPERATURES CONTINUE
TO WARM...WITH SHOWERS CONTINUING INTO THE WEEKEND AS THE LOW
ITSELF MOVES INLAND OVER SOUTHCENTRAL AK.

SOUTHWEST ALASKA...
MOST OF THE SOUTHWEST MAINLAND WILL SEE ONLY A GLANCING BLOW FROM
THE SYSTEM AS IT MOVES TOWARDS THE GULF TODAY...WITH RAIN AND
SNOW POSSIBLE FOR MAINLY COASTAL PORTIONS OF BRISTOL BAY FROM
DILLINGHAM EAST. A PERIOD OF LIGHT FREEZING RAIN WILL BE POSSIBLE
LATER TONIGHT AS WARMER AIR MOVES IN ALOFT...BUT CONFIDENCE IN
THIS SCENARIO REMAINS LOW. THE REMAINDER OF THE AREA WILL
PRIMARILY BE IMPACTED BY STRONG NORTHERLY WINDS THROUGH FRIDAY AS
THE PRESSURE GRADIENT CONTINUES TO INCREASE WITH THE NORTHERLY
PROGRESSION OF THE LOW.

BERING SEA/ALEUTIANS...
RAIN AND STORM FORCE WINDS WILL CONTINUE INTO THIS EVENING BEFORE
SLOWLY DIMINISHING FROM WEST TO EAST OVER THE EASTERN PART OF THE
BERING AND THE ALASKA PENINSULA AS THE LOW TRACKS SOUTH OF THE
AKPEN TOWARDS THE GULF OF ALASKA. THE AREA WILL THEN TRANSITION TO
A MORE SHOWERY REGIME BY FRIDAY WITH GUSTY NORTHWEST WINDS IN
COLD ADVECTION ON THE BACKSIDE OF THE LOW. A FEW SNOW SHOWERS WILL
BEGIN TO MIX IN BY FRIDAY AFTERNOON AS COLDER AIR CONTINUES TO
FILTER IN FROM THE NORTH. FARTHER WEST...RAIN AND GALES WILL GRADUALLY
START TO WIND DOWN TODAY ACROSS THE WESTERN ALEUTIANS AS THE LOW
MOVES OFF TO THE EAST AND HIGH PRESSURE BUILDS IN THROUGH
SATURDAY.

&&

.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 130 131 138 150 155 170 173 179
         GALE WARNING 119 120 132 136 137 139 160 165 172
                      174 175 176 177 180 181 185
FIRE WEATHER...NONE

&&

CB/MO OCT 14