Small Craft Advisory 901, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
LOW PRESSURE SYSTEM OVER THE NORTHEASTERN GULF CONTINUES TO WEAKEN
STEADILY AND BROADEN...WITH A VERY WEAK UPPER LEVEL RIDGE OVER THE
WESTERN GULF. TO THE NORTH OF THIS RIDGE IS AN UPPER LEVEL TROUGH
DIGGING SOUTH AND EAST TOWARD INTERIOR SOUTHCENTRAL ALASKA. A
SMALLISH JET STREAK MOVING ALONG THE SOUTHERN EDGE OF THIS FEATURE
HAS HELPED TO LOCALLY ENHANCE OUTFLOW WINDS THROUGH THE CHUGACH
RANGE INTO PRINCE WILLIAM SOUND AND THE NORTHERN GULF...WITH A 71
MPH PEAK GUST AT VALDEZ AIRPORT LAST EVENING. MEANWHILE...ANOTHER
UPPER LEVEL TROUGH RESIDES FROM NORTON SOUND SOUTH TO NEAR PORT
HEIDEN ON THE ALASKA PENINSULA. THIS FEATURE LARGELY DELINEATES
THE EDGE OF THE STRONG NORTHWEST JET STREAM FLOW OVER THE BERING
WITH THE PERSISTENT AREA OF DEFORMATION THAT CONTINUES ALONG AND
AHEAD OF THE SLOW-MOVING TROUGH. THE FAST NORTHWEST FLOW
ASSOCIATED WITH THE ACTIVE JET STREAM HAS CONTINUED TO BRING
OCCASIONAL SNOW SQUALLS TO THE BERING REGION. FINALLY...ANOTHER
UPPER LEVEL TROUGH WITH A WEAK SURFACE LOW IS MOVING OFF OF THE
NORTHERN KAMCHATKA PENINSULA TOWARD THE NORTHWEST BERING SEA.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GREAT AGREEMENT IN BROADENING THE SURFACE LOW
OVER THE NORTHEAST GULF THROUGH THE WEEKEND BEFORE SLOWLY
DISSIPATING. THE DISTURBANCE OVER THE SOUTHERN INTERIOR OF STATE
AND ITS ASSOCIATED MID-LEVEL JET STREAK WILL TRACK INTO THE YUKON
BY SATURDAY...BUT WILL LEAVE BEHIND A FAIRLY DEEP TROUGH OVER THE
CENTRAL AND SOUTHERN MAINLAND. THE UPPER LEVEL TROUGH OVER
SOUTHWEST ALASKA AND THE ALASKA PENINSULA WEAKENS THROUGH SATURDAY
AS IT MOVES TO SOUTHCENTRAL AND THE WESTERN GULF BEFORE DEEPENING
AND BROADENING ONCE AGAIN AS THE JET STREAM THE SOUTH OF THE GULF
OF ALASKA STRENGTHENS. FINALLY...THE LOW MOVING OFF THE NORTHERN
COAST OF KAMCHATKA WILL SPIN OVER THE NORTHWEST BERING THROUGH
TONIGHT...THEN BEGIN TO MOVE SOUTH AND EAST ALONG THE NORTHERN
EDGE OF SEVERAL JET STREAKS THAT WILL HELP TO INVIGORATE AND
DIMINISH THE STRENGTH OF THE LOW AT VARYING TIMES AS IT MOVES
SOUTH AND EAST TOWARD THE CENTRAL BERING TOWARD SATURDAY INTO
SUNDAY.

ANOTHER LOW APPEARS POISED TO HELP INITIATE A WEATHER PATTERN
CHANGE AS IT MOVES INTO THE BERING THE EARLY TO MIDDLE PART OF
NEXT WEEK FROM WEST TO EAST...WITH COLD NORTHERLY FLOW OVER THE
AREA OF RESPONSIBILITY SLOWLY SHIFTING TO A MORE WARM AND
SOUTHERLY DIRECTION.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A COUPLE OF UPPER LEVEL SHORT-WAVES WILL CROSS THE REGION
TODAY...ONE THROUGH INTERIOR SOUTHCENTRAL AND ANOTHER ACROSS
KODIAK ISLAND INTO THE GULF. THESE WILL HELP USHER DEEP ARCTIC
AIR OFFSHORE INTO THE GULF OF ALASKA WHICH WILL SUPPORT CONTINUED
STRONG WINDS ALONG THE COAST. THE AIR MASS HAS ALREADY STABILIZED
OVER SOUTHCENTRAL ALASKA...AS INDICATED BY THE 12Z ANCHORAGE
SOUNDING AND BY THE PRESENCE OF STANDING WAVE CLOUDS ALONG THE
EASTERN KENAI PENINSULA OVERNIGHT. THE PRESENCE OF SUCH A STABLE
LAYER ABOVE MOUNTAIN TOP IS FAVORABLE FOR ISOLATED AND ERRATIC
VERY STRONG WIND GUSTS LIKE WHAT WAS BRIEFLY OBSERVED IN VALDEZ
LAST EVENING. WINDS ALONG THE COAST WILL FINALLY BEGIN TO DIMINISH
OVERNIGHT TONIGHT THROUGH SATURDAY AS COLD ADVECTION COMES TO AN
END AND PRESSURE GRADIENTS SLACKEN A BIT. HOWEVER...WEAKER GAP
WINDS WILL PERSIST AS A SURFACE LOW LINGERS ALONG THE NORTHEAST
GULF COAST.

MEANWHILE...WINDS HAVE DIED DOWN OVER MUCH OF INTERIOR SOUTHCENTRAL
AND THE ARCTIC AIR IS SETTLING IN. WITH THE DIMINISHED SOLAR
RADIATION THIS TIME OF YEAR THERE WILL NOT BE MUCH RECOVERY OF
TEMPERATURES DURING THE DAY. AN OVERALL DOWNWARD TREND IN
TEMPERATURES WILL CONTINUE WITH WIDESPREAD SUB-ZERO TEMPERATURES
EXPECTED AS WE HEAD THROUGH THE WEEKEND.

AS THE SHORT-WAVE TROUGH MOVING INTO THE GULF CONTINUES EASTWARD
IT WILL BEGIN TO LIFT NORTHEASTWARD THANKS TO RISING HEIGHTS
DOWNSTREAM. THERE IS INCREASING CONFIDENCE THAT THIS WILL PULL
SOME MOISTURE FROM THE LOW OVER THE NORTHEAST GULF BACK NORTH AND
WEST TOWARD THE EASTERN COPPER RIVER BASIN AND EASTERN PRINCE
WILLIAM SOUND ON SATURDAY. FOR NOW HAVE JUST INTRODUCED A CHANCE
OF SNOW FOR THESE AREAS. THERE IS HIGHER CONFIDENCE IN CLOUD COVER
WHICH COULD KEEP TEMPERATURES FROM PLUMMETING IN PORTIONS OF THE
COPPER RIVER BASIN.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
NORTHWEST FLOW AND COLD AIR ADVECTION CONTINUE FOR SOUTHWEST
ALASKA. THERE IS ALSO ENOUGH UPPER LEVEL SUPPORT IN THE NORTHWEST
FLOW WITH SHORTWAVES MOVING THROUGH FOR OCCASIONAL SNOW SHOWERS
INTO SATURDAY BUT THEY WILL LESSON AS THE UPPER LEVEL ACTIVITY
PUSHES OFF TO THE EAST. THIS WILL HELP TO WEAKEN THE STRONGER
NORTHWEST WINDS ALONG THE COAST THAT WILL DIMINISH THROUGHOUT THE
DAY AS THEY LOSE UPPER LEVEL SUPPORT. EARLY ON SATURDAY A LOW WILL
PUSH EAST ACROSS THE NORTHERN BERING THAT WILL BRING MORE SNOW TO
THE COASTLINE BUT NORTHERLY FLOW OVER THE SOUTHWEST WILL KEEP THE
MAJORITY OF THE SNOW AWAY FROM INTERIOR PORTIONS OF THE SOUTHWEST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
NORTHWEST FLOW WILL KEEP SHOWERS OVER THE BERING AND ALEUTIANS
THROUGH SATURDAY. THE SHOWERS WILL BE ENHANCED AT TIMES WITH TWO
DIFFERENT TROUGHS MOVING THROUGH. THE FIRST IS BRINGING SHOWERS TO
THE ALASKA PENINSULA THAT WILL DIMINISH THROUGHOUT TODAY AS THE
TROUGH MOVES SOUTHEAST. THE OTHER TROUGH WILL MOVE IN OVER THE
WESTERN BERING THIS AFTERNOON AND TRACK TO THE ALASKA PENINSULA BY
SATURDAY AFTERNOON BRINGING HEAVIER SHOWERS AS IT PASSES. THE
ALEUTIANS ARE ALSO WARM ENOUGH TO SEE RAIN MIX WITH THE SNOW
SHOWERS AT TIMES.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
ANOTHER POTENT UPPER LOW DROPPING OUT OF EASTERN RUSSIA THIS
WEEKEND WILL HELP TO REINFORCE THE LONGWAVE TROUGH OVER MAINLAND
ALASKA AND KEEP A VERY COLD AIR MASS OVER MUCH OF THE REGION
THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL RESULT IN WELL BELOW
NORMAL TEMPERATURES WITH LOWS RANGING FROM THE SINGLE DIGITS
ACROSS THE INTERIOR PORTIONS OF THE SOUTHWEST MAINLAND AND AREAS
SURROUNDING COOK INLET...TO WELL BELOW ZERO OVER THE COPPER RIVER
BASIN AND NORTHERN SUSITNA VALLEY. MAINLY DRY CONDITIONS ARE
EXPECTED ACROSS THE SOUTHERN MAINLAND AS THE BULK OF THE ENERGY
REMAINS CONFINED TO THE GULF. THERE ARE SIGNIFICANT MODEL
DISCREPANCIES OVER THE STRENGTH AND PLACEMENT OF A SURFACE LOW
FORMING OVER THE GULF EARLY NEXT WEEK AS THE UPPER LOW DIVES DOWN
FROM THE NORTHWEST. THE EVOLUTION OF THIS FEATURE WILL HAVE A
LARGE IMPACT ON PRECIPITATION CHANCES AND THE STRENGTH OF OUTFLOW
WINDS ALONG THE GULF COAST THROUGH THE MIDDLE OF THE WEEK.
TEMPERATURES WILL BEGIN TO SLOWLY MODERATE DURING THE LATTER HALF
OF THE WEEK AS TRANSITORY RIDGING BUILDS IN FROM THE WEST AND
USHERS IN WESTERLY UPPER LEVEL FLOW.

MEANWHILE...THE BERING WILL REMAIN IN A GUSTY AND SHOWERY REGIME
THROUGH THE EARLY PART OF NEXT WEEK IN UNSTABLE NORTHWEST FLOW ON
THE BACKSIDE OF THE TROUGH. A KAMCHATKA LOW WILL THEN MOVE TOWARDS
THE BERING STRAIT ON TUESDAY AND SWING A GALE FORCE FRONT ACROSS
THE BERING AND ALEUTIANS DURING THE MIDDLE OF THE WEEK. MODELS
CONTINUE TO STRUGGLE WITH THESE FEATURES OUT WEST...WHICH HAS KEPT
FORECAST CONFIDENCE WITH REGARDS TO THE TIMING OF THE WINDS AND
PRECIPITATION ON THE LOWER END OF THE SPECTRUM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 121 126 127 128 129 131 136 137 138 150 155 165 170
               172 173 174 175 177 178 185.
         STORMS 130 132.

&&

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...TP