Small Craft Advisory 911, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
511 PM AKST MON NOV 16 2015

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER LEVEL TROUGH REMAINS CENTERED OVER THE
MAINLAND WITH A SERIES OF SHORTWAVE TROUGHS ROTATING AROUND THE
LOW CENTER. THIS IS A VERY DRY TROUGH HOWEVER...WHICH HAS ALLOWED
FOR CLEAR SKIES...LIGHT WINDS...AND SOME OF THE COLDEST AIR OF THE
SEASON SPREAD INTO THE SOUTHERN MAINLAND. AT THE SURFACE A WEAK
LOW IS FORMING OVER THE GULF...WHICH ALONG WITH A TIGHT THERMAL
GRADIENT PRODUCED FROM COLD AIR ENTRENCHED THROUGHOUT THE SOUTH
MAINLAND IS BRINGING GUSTY GAP WINDS TO THE GULF COAST. THE STRONGEST
OF WHICH ARE OCCURRING FROM WHITTIER TO KODIAK ISLAND WHERE STRONG
COLD AIR ADVECTION AND JET SUPPORT IS PRESENT. THE FIRST OF TWO
SHORTWAVES ROTATING AROUND THE UPPER LEVEL TROUGH IS JUST SOUTH OF
THE ALASKA PENINSULA AND MOVING INTO THE NORTH PACIFIC. THE OTHER
IS BEGINNING TO ENTER THE BERING FROM EASTERN SIBERIA...WHICH CAN
BEGIN TO BE SEEN WITH SNOW SHOWER DEVELOPMENT OVER THE NORTH
CENTRAL BERING SPREADING EASTWARD TOWARDS THE PRIBILOFS. OVER THE
WESTERN BERING THE NEXT FRONTAL SYSTEM ASSOCIATED WITH A LOW NEAR
THE KAMCHATKA COAST. THIS SYSTEM WILL CONTINUE ON THIS EASTWARD
TRACK TODAY AND BRING A PATTERN CHANGE TO THE MAINLAND BY MID
WEEK.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT UNTIL TUESDAY EVENING WHEN
THEY BEGIN TO HAVE PROBLEMS WITH THE LOW CURRENTLY MOVING INTO THE
NORTH CENTRAL BERING. THEY HAVE COME INTO MUCH BETTER AGREEMENT
WITH THIS MORNINGS 12Z MODEL RUNS WITH THE POSITION OF THE UPPER
LEVEL TROUGH OVER THE NORTHERN BERING. PREVIOUS RUNS OF THE GFS
HAD BROUGHT THIS MUCH FURTHER TO THE NORTH INTO SIBERIA...WHILE
THE EC/NAM/GEM GLOBAL WERE ALL IN GOOD AGREEMENT THAT THIS LOW
WOULD MOVE EASTWARD ALONG THE JET. THE 12Z GFS HAS SINCE COME IN
MUCH MORE IN LINE WITH THE REST OF THE MODELS...THOUGH THERE STILL
ARE SOME MINOR TIMING DIFFERENCES...ESPECIALLY WITH REGARDS TO
TIMING OF PRECIPITATION TO THE SOUTHERN MAINLAND ON WEDNESDAY. THE
12Z MODELS HAVE ALSO COME INTO MUCH BETTER AGREEMENT WITH THE
TRACK OF ANOTHER LOW THAT WILL MOVE IN BEHIND THE FIRST LOW IN THE
BERING ON THURSDAY...AND ARE NOW IN GENERALLY GOOD AGREEMENT THAT
THIS LOW WILL MAKE LANDFALL NEAR NUNIVAK ISLAND ON THURSDAY.

&&

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

THE FORMATION OF A SMALL LOW OVER THE NORTHERN GULF THIS EVENING WILL
TIGHTEN THE PRESSURE GRADIENT ACROSS THE REGION. THIS WILL
STRENGTHEN WINDS TO STRONG WIND LEVELS TONIGHT...PARTICULARLY
THROUGH CHANNELED TERRAIN. SOME SNOW SHOWERS ARE ALSO POSSIBLE
ALONG COOK INLET AS PRECIPITATION BAND OSCILLATES NEAR THE KENAI
PENINSULA SHORE. ON TUE WINDS WILL DIMINISH AS SOUTHCENTRAL FINDS
ITSELF BENEATH A WEAK RIDGE BETWEEN SYSTEMS. BY TUE NIGHT THE
NEXT FRONT FROM THE BERING LOW MOVES INTO SOUTHWEST AK...WITH
OVERRUNNING CLOUDS SPREADING EAST OF THE ALEUTIAN RANGE. ON WED
SNOW MOVES ACROSS KODIAK ISLAND AND THE KENAI PENINSULA...BUT DOES NOT
REACH THE ANCHORAGE AREA UNTIL EARLY WED EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...TUE AND
WED)...THE PATTERN WILL REMAIN ACTIVE FOR THE NEXT COUPLE OF DAYS.
MOST OF THE MAINLAND WILL REMAIN UNDER RELATIVELY LIGHT WINDS AND
VERY COLD CONDITIONS TONIGHT. HOWEVER...ALONG THE COAST FROM THE
DELTA SOUTH THROUGH THE ALASKA PENINSULA...A QUICK HITTING "POLAR
FRONT" WILL MAKE FOR DETERIORATING CONDITIONS TONIGHT. A FEW POLAR
VORTICES HAVE DEVELOPED ALONG THIS FEATURE. AS THEY PASSED
THROUGH THE PRIBILOF ISLANDS THEY BROUGHT A VERY BRIEF BLAST OF
BLIZZARD LIKE CONDITIONS. THEY CIRCULATIONS WILL BE VERY
COMPACT...BUT IF THEY WERE TO HIT A POPULATION CENTER...THEY WOULD
BRING VERY GUSTY WINDS AND HEAVY SNOW SHOWERS. THE WORST
CONDITIONS LOOK TO REMAIN OVER THE WATERS OF BRISTOL BAY. AFTER
THIS CLEARS THE AREA TUE MORNING...WE SHIFT OUR ATTENTION TO A
WEAK WARM FRONT COMING ACROSS THE BERING. THIS SHOULD BRING SNOW
TO THE AREA STARTING ALONG THE WESTERN CAPES BY TUE EVENING.
THE ZONAL JET PUSHES THE LOW CENTER ITSELF QUICKLY ACROSS THE
BERING AND BRINGS THE REST OF THE ASSOCIATED PRECIPITATION INTO
THE MAINLAND ON WED. WHILE MOST INLAND LOCATIONS WILL REMAIN
SNOW...WE COULD START TO SEE SOME RAIN MIX IN ALONG THE COAST AND
ALASKA PENINSULA AS A WEAK PUSH OF WARM AIR MOVES IN FROM THE
NORTH PACIFIC.

COASTAL FLOODING COULD ALSO BE A CONCERN LATER THIS WEEK. AS THESE
TWO STORMS TRACK QUICKLY FROM WEST TO EAST...THEY WILL BRING A
LONG FETCH OF WESTERLY SWELL TOWARD THE WEST COAST. THE SECOND
STORM IS THE STRONGER OF THE TWO AND TAKES THE MORE FAVORABLE
TRACK FOR A HIGHER SURGE. MODELS ARE NOW SHOWING THE POTENTIAL FOR
A STORM SURGE 3 TO 5 FEET ABOVE HIGHEST ASTRONIMCAL TIDE. THAT
SAID...THE EXACT SURGE WOULD BE HIGHLY DEPENDENT ON THE STORM
TRACK. MODELS HAVE BEEN STRUGGLING WITH EXACTLY WHERE THE LOW WILL
MOVE INLAND. SO WHILE CONFIDENCE REMAINS LOW IN EXACT TIMING AND
HEIGHT OF THE SURGE...IT IS LIKELY THAT WATER LEVELS WILL RISE
ABOVE NORMAL ALONG THE WEST COAST LATER THIS WEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...TUE AND
WED)...A POTENT ZONAL JET OVER THE ALEUTIANS WILL MAKE FOR AN
ACTIVE PATTERN THE NEXT FEW DAYS. THE FIRST LOW IS DEVELOPING
NORTH OF SHEMYA. IT IS HELPING TO CREATE SOME GALE FORCE
SOUTHERLY WINDS OVER THE WESTERN ALEUTIANS THIS EVENING. IT IS
ALSO BRINGING THE FIRST SHOT OF APPRECIABLE WARM AIR TO THE BERING
THAT WE HAVE SEEN IN ABOUT A WEEK. PRECIPITATION HAS TURNED OVER
TO ALL RAIN FOR SHEMYA. THIS LOW WILL TRACK QUICKLY ACROSS THE
BERING AND DRAG ITS GALE FORCE FRONT ACROSS THE ENTIRE CHAIN. IT
WILL ALSO BRING A FAIRLY BROAD SWATH OF PRECIPITATION THAT WILL
START AS SNOW BUT SHOULD TURN OVER TO RAIN FOR MOST LOCATIONS. THE
NEXT LOW WILL DEVELOP VERY NEAR SHEMYA ON WED. THIS STORM SHOULD
BE SLIGHTLY STRONGER AND BRING SOME STORM FORCE WINDS TO THE
WESTERN ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE MAIN CHALLENGE IN THE LONG RANGE FORECAST IS A STORM SYSTEM
THAT QUICKLY DEVELOPS OVER THE CENTRAL BERING WEDNESDAY...BRINGING
WIDESPREAD PRECIPITATION TO THE SOUTHERN MAINLAND FOR THE SECOND
HALF OF THE WEEK. THIS STACKED SYSTEM ADVECTS A MUCH WARMER AIR
MASS FROM THE NORTH PACIFIC INTO THE BERING WHICH WILL BRING RAIN
ACROSS MUCH OF THE BERING...INITIALLY MIXED WITH SNOW ACROSS THE
PRIBILOFS AND ALASKA PENINSULA WEDNESDAY NIGHT INTO THURSDAY MORNING.

THE FRONT PUSHES INTO THE SOUTHWEST MAINLAND EARLY THURSDAY...WITH
THE WARMER AIR ALOFT SURGING INLAND AT A FASTER PACE. THERE IS
STILL A BIT OF UNCERTAINTY IN HOW FAR NORTH THE SURFACE WARM FRONT
MOVES...SO CONSERVATIVE EDITS WERE MADE TODAY USING A BLEND OF
THE ECMWF AND GFS WHICH INTRODUCES THE WARMER CONDITIONS FURTHER
NORTH. POCKETS OF FREEZING RAIN WILL BE POSSIBLE ACROSS THE
SOUTHWEST ON THURSDAY AND THURSDAY NIGHT AND THEN COLD AIR ADVECTS
IN ON FRIDAY. EARLY THURSDAY RAIN IS EXPECTED TO SPREAD ACROSS
THE WESTERN GULF AND SOUTHERN KENAI WITH SNOW ALONG THE NORTHERN
KENAI BY THE EARLY AFTERNOON. LIGHT SNOW WILL BEGIN TO DEVELOP
ACROSS THE REST OF SOUTHCENTRAL DURING THE AFTERNOON WITH THE
HEAVIEST ACCUMULATIONS DURING THE EVENING HOURS THURSDAY INTO
FRIDAY MORNING. CONTINUED SNOW SHOWERS CAN BE EXPECTED THROUGH THE
WEEKEND AS THE SURFACE LOW LOSES MOMENTUM AS IT CROSSES INTO THE
NORTHEASTERN GULF.

THE NEXT STORM SYSTEM MOVES INTO THE WESTERN BERING ON SUNDAY.
TIMING OF THIS SYSTEM WAS SLOWED DOWN BY THE GLOBAL ENSEMBLES AS
RIDGING IN BETWEEN THE TWO SYSTEMS AMPLIFIES OVER THE MAINLAND
EARLY NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...121 126 127 129 130 138 139 160
								180 181 185.
	GALE...121 126 127 129 130 131 132 136 137 138 150
	155 165 170 172 173 174 175 176 177 178 181 185.

&&

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