Small Craft Advisory 903, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
422 PM AKST FRI NOV 13 2015

.ANALYSIS AND UPPER LEVELS...
LOW PRESSURE CONTINUES TO SLOWLY WEAKEN OVER THE NORTHEASTERN
GULF...WHILE COLD AIR ADVECTION REMAINS ALONG THE WESTERN EDGE OF
THE LOW. OVER THE WESTERN GULF...THIS COLD AIR ADVECTION IS STRONG
ENOUGH TO BRING STORM FORCE GUSTS AROUND KODIAK ISLAND...WHILE THE
THERMAL AND PRESSURE GRADIENT IS ALLOWING STRONG WINDS TO CONTINUE
THROUGH GAP WIND AREAS OF THE GULF COAST (SUCH AS
VALDEZ...SEWARD AND WHITTIER). RIDGING OVER THE EASTERN BERING IS
BEGINNING TO MOVE EASTWARD INTO THE SOUTHWEST MAINLAND...ALLOWING
FOR THE NORTHWESTERLY FLOW AND SNOW SHOWERS IN THE AREA TO BEGIN
TO DIMINISH. THIS RIDGING IS BEING PUSHED EASTWARD IN ADVANCING
SHORTWAVE TROUGH MOVING THROUGH THE CENTRAL BERING...BRINGING SNOW
TO THE PRIBILOFS. THIS SHORTWAVE WILL PROGRESS TOWARDS THE
EASTERN ALEUTIANS THIS EVENING...ALLOWING FOR RIDGING TO SPREAD
INTO THE SOUTHERN MAINLAND BY LATE TONIGHT.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD AGREEMENT WITH THE DISSIPATION OF THE GULF
LOW TONIGHT...AND WITH THE DEVELOPMENT OF THE BERING LOW INTO THIS
WEEKEND. IN PARTICULAR THEY HAVE COME INTO BETTER AGREEMENT THAT
ANY SNOWFALL FROM THE GULF LOW AS IT MAKES LANDFALL SATURDAY
AFTERNOON WILL LARGELY STAY CONFINED TO THE EASTERN COPPER RIVER
BASIN...RATHER THAN SPREADING TOWARDS THE VALDEZ/THOMPSON PASS
AREA AS THE MODELS HAD PREVIOUSLY INDICATED. OVER THE BERING SEA
THE MODELS CONTINUE TO BE IN GOOD AGREEMENT WITH THE GENERAL
INTENSITY...BUT STILL HAVE SOME MINOR DIFFERENCES MAINLY IN
POSITIONING AS IT APPROACHES THE PRIBILOFS ON SUNDAY. AS A RESULT
THERE IS NOW GOOD CONFIDENCE THAT THIS SYSTEM WILL DEEPEN TO A
STRONG GALE...OR POSSIBLY STORM FORCE LOW ON SATURDAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

UPPER TROUGHING OVER SOUTHCENTRAL AND A SURFACE LOW IN THE
NORTHEAST GULF IS PROMOTING A CONTINUED OFFSHORE PRESSURE GRADIENT
THIS EVENING. WITH COLDER AIR CONTINUING TO FILTER IN FROM THE
NORTH...THIS SHOULD KEEP A STRONG PRESSURE GRADIENT ALONG THE
NORTHERN COAST THROUGH SATURDAY BEFORE IT BEGINS TO SLACKEN
OFF...ALLOWING FOR NORTHERLY OUTFLOW WINDS TO DIMINISH AS WELL. A
SHORTWAVE TROUGH OVER SOUTHWEST ALASKA WILL MERGE WITH THE
AFOREMENTIONED GULF LOW TONIGHT...ALLOWING FOR SNOW TO DEVELOP
OVER THE EASTERN COPPER BASIN SATURDAY AND SATURDAY NIGHT WITH
LIGHT ACCUMULATIONS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SURFACE RIDGING TRANSITS THE SOUTHWEST THROUGH THE WEEKEND KEEPING
THE AREA UNDER DRIER CONDITIONS. THE EXCEPTION WILL BE ALONG THE
COASTAL AREAS AND ALASKA PENINSULA WHERE A FRONT STALLS SATURDAY
MORNING BRINGING INCREASED SNOW CHANCES THROUGH SUNDAY. WINDS
ACROSS BRISTOL BAY AND THE KUSKOKWIM SHIFT FROM THE NORTHWEST
TONIGHT TO THE EAST ON SATURDAY. THE COASTAL AREAS WILL SEE GUSTY
CONDITIONS AS A FRONT MOVES INTO THE EASTERN BERING. THE ALASKA
PENINSULA WILL SEE NORTHWEST WINDS SHIFT TO THE WEST TONIGHT WITH
GUSTS PERSISTING INTO LATE SATURDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A SURFACE LOW DEVELOPING IN THE NORTHERN BERING WILL BRING STORM
FORCE WINDS ACROSS THE NORTHERN BERING DURING THE FIRST PART OF
THE WEEKEND. THE LOW PUSHES A FRONT INTO THE CENTRAL BERING
TONIGHT AND THEN DIGS QUICKLY TO THE SOUTH AND EASTERN WATERS
BEFORE STALLING ON SATURDAY. THE SURFACE LOW PICKS UP
SOUTHWARD MOMENTUM SATURDAY MORNING KEEPING THE SAME INTENSITY AS
IT MOVES ACROSS THE PRIBILOF ISLANDS INTO SUNDAY. COLD DENSE AIR
FILTERS IN ON THE BACK SIDE OF THIS SYSTEM BRINGING THE STRONGEST
WINDS ACROSS THE BERING SATURDAY THROUGH SUNDAY AFTERNOON.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE BEGINNING OF NEXT WEEK WILL FEATURE WELL BELOW NORMAL
TEMPERATURES ACROSS THE SOUTHERN MAINLAND AS THE LONGWAVE TROUGH
IS REINFORCED BY AN UPPER LOW DIVING SOUTHEAST ACROSS THE BERING
SEA INTO THE GULF OF ALASKA. THIS WILL KEEP ANY PRECIPITATION
CONFINED TO THE GULF AND KODIAK ISLAND THROUGH TUESDAY AS OUTFLOW
WINDS CONTINUE ALONG THE GULF COAST. FORECAST CONFIDENCE DECREASES
BY THE MIDDLE OF THE WEEK AS THE LONGWAVE TROUGH IS DISPLACED
EASTWARD. THE GFS DEPICTS A TRANSITION TO QUASI ZONAL FLOW WITH
SEVERAL UPPER LEVEL WAVES TRACKING THROUGH THE INTERIOR WHEREAS
EUROPEAN GUIDANCE BUILDS A HIGH AMPLITUDE RIDGE OVER THE MAINLAND.
THIS MORE AMPLIFIED SOLUTION WOULD KEEP SOUTHCENTRAL DRY THROUGH
MUCH OF NEXT WEEK AS MOST OF THE ENERGY WOULD BE HELD BACK OVER
THE BERING AND WEST COAST. THE FORECAST REFLECTS SOMEWHAT OF A
MIDDLE GROUND APPROACH...WITH PRECIPITATION CHANCES GRADUALLY
INCREASING FROM WEST TO EAST DURING THE LATTER HALF OF THE WEEK
AS TEMPERATURES SLOWLY MODERATE TO NEAR NORMAL VALUES IN INCREASING
SOUTHWESTERLY FLOW.

OVER THE BERING...A SHOWERY NORTHWEST FLOW REGIME WILL GIVE WAY
TO A MORE PROGRESSIVE PATTERN EARLY IN THE WEEK AS A KAMCHATKA LOW
SWINGS A GALE FORCE FRONT ACROSS THE BERING AND ALEUTIANS. THIS
WILL BE FOLLOWED CLOSELY BY ANOTHER SYSTEM DURING MIDDLE TO LATTER
PORTIONS OF THE WEEK. MODELS ARE STILL STRUGGLING TO PIN DOWN THE
EXACT DETAILS OF THESE FEATURES...BUT IN GENERAL WET AND WINDY
CONDITIONS CAN BE EXPECTED ACROSS THE BERING FOR MUCH OF THE NEXT
WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...CB