Small Craft Advisory 981, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
414 PM AKST TUE DEC 8 2015

.ANALYSIS AND UPPER LEVELS...
SOUTHCENTRAL AND THE GULF...A VERTICALLY STACKED LOW IS MOVING
NORTHWARD INTO THE GULF THIS AFTERNOON. CURRENTLY THE UPPER LEVEL
DIVERGENCE ASSOCIATED WITH A VERY STRONG UPPER LEVEL JET STREAK IS
DISTANCING ITSELF FROM THE LOW AS THE LOW MOVES NORTH INTO THE
GULF AND THE JET STREAK MOVES EAST INTO THE PACIFIC NORTHWEST.

THE OCCLUDED FRONT NORTH OF THE LOW HAS BEEN CAUSING WINDS TO
GUST TO GALE FORCE ALONG THE NORTHERN GULF COAST. AS COLDER AIR
OVER INTERIOR SOUTHCENTRAL IS DRAWN SOUTHWARD...IT HAS ENHANCED
THE TEMPERATURE GRADIENT NEAR THE COAST WHERE THAT COLD AIR
COLLIDES WITH THE WARMER GULF AIR. AS A RESULT THE PRESSURE
GRADIENT BETWEEN THE TWO AIR MASSES HAS INTENSIFIED...LEADING TO
THE GUSTY WINDS ALONG THE COAST.

FURTHER INLAND...OTHER THAN GRADUALLY INCREASING HIGH
CLOUDINESS...THE WEATHER REMAINS DRY. THE COLD AIR OVER INTERIOR
SOUTHCENTRAL IS SHALLOW...AS EVIDENCED BY THE ANCHORAGE 12Z
SOUNDING SHOWING A VERY STRONG NEAR-SURFACE INVERSION.
OBSERVATIONS AROUND SOUTHCENTRAL SHOW COLD AIR WITH TEMPERATURES
IN THE TEENS FROM THE ANCHORAGE BOWL NORTHWARD THROUGH THE
VALLEY...WHILE THE HILLSIDE AND HIGHER ELEVATIONS EAST OF
ANCHORAGE ARE SHOWING TEMPERATURES APPROACHING THE FREEZING MARK.

SOUTHWEST ALASKA AND THE BERING...THE FORMER PRIMARY LOW CURRENTLY
CENTERED SOUTH OF DUTCH HARBOR IS FILLING AS IT BEGINS TO MERGE
WITH THE STRONGER LOW OVER THE GULF. THIS PATTERN MAKES FOR TWO
NEIGHBORING LOWS IN THE MEAN SEA LEVEL PRESSURE FIELDS...WITH NO
CONCENTRICITY. HIGH PRESSURE OVER SIBERIA AND THE FAR WESTERN
BERING ARE KEEPING THE PRESSURE GRADIENT TIGHT ENOUGH FOR STRONG
NORTH WINDS TO PERSIST OVER THE CENTRAL BERING WITH NORTHEASTERLY
WINDS FROM THE KUSKOKWIM DELTA AND BRISTOL BAY THROUGH SAINT PAUL.
THIS HAS BROUGHT COLDER AIR SOUTH THROUGH AREAS LIKE KING SALMON
EARLIER THIS MORNING...WHILE WARMER AIR REMAINS FURTHER EAST
TOWARD THE ALEUTIAN RANGE.

&&

.MODEL DISCUSSION...
MODELS ARE HAVING DIFFICULTY RESOLVING THE COMPLEX LOW IN THE GULF
OF ALASKA THIS MORNING. GFS HAS THE LOW CENTER LOCATED FURTHEST
WEST WHILE LATEST RUNS OF THE ECMWF/NAM/GEM HAVE A BROADER AREA
OF LOW PRESSURE CENTERED FURTHER EAST. SATELLITE INDICATES THAT
THERE ARE INDEED MULTIPLE LOW CENTERS...SO ECMWF WAS CHOSEN AS THE
MOST INDICATIVE OF CURRENT CONDITIONS FOR THE SHORT TERM. AS THE
MAIN LOW CENTER MOVES WESTWARD THE TIMING OF TROUGHS MOVING
THROUGH THE FORECAST AREA ALSO DIFFERS FROM MODEL TO MODEL. THIS
IS COMPLICATED BY THE FACT THAT RUN TO RUN CONSISTENCY HAS ALSO
BEEN POOR. GFS WAS CHOSEN FOR RESOLUTION AND TIMING OF THE
APPROACHING FRONTS IN THE EAST...WHILE THE WEST FORECASTER CHOSE
TO STICK WITH THE EC SOLUTION FOR TIMING. MODEL CHOICE WILL
PROBABLY HAVE THE GREATEST IMPACTS ON TIMING AND PRECIP TYPE IN
BOTH AREAS...AS PRECIP AMOUNTS DO NOT SEEM TO DIFFER GREATLY
BETWEEN MODELS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE LOW IN THE SOUTHERN GULF WILL SLOWLY TRACK INTO THE WESTERN
GULF AND AS IT DOES IT WILL BRING A PUSH OF WARMER MOIST AIR OVER
THE SOUTHCENTRAL. THE MAIN IMPACT FROM THIS WILL BE SNOW ALONG THE
NORTH GULF COAST THAT WILL MIX WITH RAIN FROM THE CONTINUED WARM
PUSH. WITH THE SUPPORT OF AN UPPER LEVEL TROUGH AND THE SOUTHERN
PUSH OF MOISTURE SOME SNOW WILL START TO MAKE ITS WAY PAST THE
COASTAL RANGES WEDNESDAY. THE OTHER IMPACT FROM THIS LOW IS
STRONGER WINDS IN THE NORTH TO SOUTH ORIENTED GAPS WHICH HAVE
BEEN OCCURRING AND ARE EXPECTED TO CONTINUE THROUGH WEDNESDAY.
THROUGH THOMPSON PASS...THESE STRONGER WINDS COMBINED WITH THE
INCOMING SNOW PROVIDE THE POSSIBILITY FOR BLOWING SNOW.
HOWEVER...WITH MINIMAL NEW SNOWFALL AMOUNTS AND LITTLE TO NO
TRANSPORTABLE SNOW THROUGH THE PASS VISIBILITIES ARE EXPECTED TO
STAY AT OR ABOVE A MILE.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
OFFSHORE FLOW WILL SUPPORT PREDOMINANTLY COLD AND DRY CONDITIONS
ACROSS THE SOUTHWEST MAINLAND THROUGH THURSDAY AS SKIES GRADUALLY
CLEAR BENEATH WEAK UPPER LEVEL RIDGING. PERSISTENT NORTHEAST WINDS
WILL CONTRIBUTE TO WIND CHILL VALUES WELL BELOW ZERO ACROSS THE
KUSKOKWIM DELTA AND LOWER KUSKOKWIM VALLEY THROUGH THURSDAY
MORNING...HOWEVER THESE VALUES ARE NOT EXPECTED TO APPROACH
ADVISORY CRITERIA AT THIS TIME.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A SHOWERY REGIME WILL PERSIST OVER THE WESTERN HALF OF THE BERING
FOR THE NEXT SEVERAL DAYS AS COLD NORTHERLY FLOW REMAINS IN PLACE
IN ADVANCE OF AN UPPER TROUGH THAT WILL APPROACH FROM THE WEST ON
WEDNESDAY. FARTHER EAST...A DECAYING FRONTAL BOUNDARY WILL STALL
OVER THE CENTRAL BERING TONIGHT AND KEEP PRECIPITATION FOCUSED
ALONG A SOMEWHAT NARROW BAND EXTENDING FROM JUST WEST OF THE
PRIBILOF ISLANDS THROUGH THE EASTERN ALEUTIANS. THIS BAND OF
PRECIPITATION WILL BEGIN TO PUSH BACK TOWARDS THE EAST THROUGH THE
PRIBILOFS AND THE ALASKA PENINSULA ON THURSDAY AS THE UPPER
TROUGH PROGRESSES EASTWARD...WITH A RAIN/SNOW MIX GRADUALLY
CHANGING TO ALL SNOW AS COLD ADVECTION TAKES HOLD.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS ARE IN SLIGHTLY BETTER AGREEMENT WITH THE LOW PRESSURE
SYSTEMS CIRCULATING AROUND THE GULF AND EASTERN BERING DURING THE
LATER PART OF THE WEEK...KEEPING PRECIPITATION IN THE FORECAST
THROUGH SATURDAY AFTERNOON FOR THE SOUTHERN MAINLAND AND EASTERN
MOST ALEUTIANS. SOME WEAK RIDGING BUILDS IN BEHIND THIS AREA OF
LOW PRESSURE THAT EXITS TO THE EAST DURING THE DAY SATURDAY...
BRINGING IN A BRIEF PERIOD OF CLEARING SKIES AND DIMINISHED
PRECIPITATION TO THE SOUTHERN MAINLAND SATURDAY NIGHT INTO SUNDAY
MORNING. THIS VERY BRIEF CLEARING IS QUICKLY REPLACED WITH A
STRONG FRONTAL SYSTEM TRACKING THROUGH THE WESTERN/CENTRAL
ALEUTIANS SATURDAY AFTERNOON...THEN INTO THE SOUTHWEST MAINLAND
AND WESTERN GULF BY SUNDAY MORNING. GUSTY SOUTHERLY WINDS AND
WARMER TEMPERATURES ARE EXPECTED ALONG THE LEADING EDGE OF THE
FRONT AS IT TRACKS THROUGH THE ALEUTIANS AND BERING OVER THE
WEEKEND...RESULTING IN RAIN MIXING BACK INTO THE FORECAST OVER
THESE AREAS. AS THE LOW TRACKS INTO THE NORTHEASTERN BERING BY
THE BEGINNING OF NEXT WEEK...COLDER NORTHWESTERLY FLOW ALONG THE
WESTERN FLANK OF THE SYSTEM WILL GRADUALLY FILTER BACK IN OVER THE
AREA. MODELS REGARDING THIS SYSTEM ARE STILL NOT IN FULL
AGREEMENT...WITH THE GFS BRINGING A DEEP LOW THROUGH THE WESTERN
ALEUTIANS AND BERING DURING THE WEEKEND...AND THE ECMWF/CANADIAN
MODELS AND WPC BRINGING THE SYSTEM FURTHER EAST AND INTO THE
KUSKOKWIM COAST BY SUNDAY NIGHT. THE ONE SHINING LIGHT ON ALL
THESE MODEL DIFFERENCES IS THAT THE MODELS STARTED TO TREND TOWARD
THE GFS SOLUTION...BRINGING THE LOW CENTER FURTHER WEST AND
STRONGER. HOWEVER...FORECAST CONFIDENCE STILL REMAINS LOW WITH
THIS FEATURE...AS MODELS CONTINUE TO WORK OUT THE DETAILS
REGARDING THE STRENGTH AND TRACK OF THIS SYSTEM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...160 180 181 185
 		GALE WARNING...119 120 127 128 130 131 132 136 138 139 173 174
		175 176 177 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...JW/LF
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...TP