Small Craft Advisory 914, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
516 AM AKST WED NOV 18 2015

.ANALYSIS AND UPPER LEVELS...
THE PATTERN IS PROGRESSIVE WITH TWO MAIN LOWS MOVING THROUGH THE
AREA. THE LEADING LOW IS MOVING THROUGH THE NORTHERN BERING WITH
ITS ASSOCIATED FRONT MOVING IN OVER THE SOUTHWEST WHERE IT IS
BRINGING SNOW TO THE AREA. A SECOND MORE INTENSE LOW IS OVER THE
WESTERN BERING WITH ITS FRONT MOVING IN OVER THE WESTERN ALEUTIANS.
BOTH SYSTEMS ARE BRINGING IN WARMER AIR WITH THE SECOND WARM
ENOUGH TO TRANSITION THE PRECIPITATION OVER TO RAIN. AHEAD OF THE
FRONTS OUT OVER MAINLAND ALASKA AN ARCTIC AIR MASS SITS DROPPING
TEMPERATURES BELOW ZERO BEFORE THE WARMER AIR MOVES IN.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT THROUGH THE MID RANGE WITH
PLACEMENT OF THE SYNOPTIC FEATURES. THE PROBLEMS COME WITH
DIFFERENCES IN PRECIPITATION TYPE FOR THE DEEPER SYSTEM THAT MOVES
IN THURSDAY. THE GFS AND GEM HAVE WARMER SOLUTIONS BRINGING RAIN
AS FAR INLAND AS THE LOWER KUSKOKWIM VALLEY WHILE THE NAM KEEPS
THE AREA MORE SNOW WITH THE EC IN THE MIDDLE. THESE DIFFERENCES
RESULT IN LOWER CONFIDENCE AS TO IF OR WHEN SNOW WILL BECOME MIXED
WITH RAIN.

&&

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

OUTFLOW CONDITIONS ACROSS THE NORTHERN AND WESTERN GULF WILL
DIMINISH THROUGH THIS MORNING AS PRESSURE GRADIENTS BEGIN AS THE
TROUGH OVER THE NORTHERN GULF WEAKENS. A WEATHER FRONT MOVING
ACROSS SW ALASKA WILL BRING SNOW TO MUCH OF SOUTHCENTRAL BEGINNING
THIS AFTERNOON OVER THE SW KENAI PEN THEN SPREAD NORTH AND EAST
TONIGHT. SNOW WILL BRIEFLY DIMINISH THU MORNING AFTER UPPER
TROUGH PASSAGE...THOUGH SW FLOW IN THE 850-500 MB LAYER WILL
CONTINUE SOME UPSLOPE SNOW ALONG THE CHUGACH AND TALKEETNA
MOUNTAINS IN THE MORNING. THIS FIRST ROUND OF SNOW SHOULD REMAIN
BELOW ADVISORY LEVELS. THE MID TO UPPER LEVEL SW FLOW INCREASES
SIGNIFICANTLY ACROSS SOUTHCENTRAL THU AFTERNOON THROUGH THU NIGHT
WITH THE APPROACH OF THE NEXT FRONT FROM THE WEST. FAIRLY SIGNIFICANT
SNOW IS EXPECTED TO DEVELOP OVER THE SUSITNA VALLEY DURING THAT
TIME FRAME. SNOW WILL LIKELY TO BE FAIRLY HEAVY ALSO ALONG THE
EASTERN KENAI (BY THU AFTERNOON) AND VALDEZ THU NIGHT. TEMPS WARM
WITH THE APPROACH OF THE FRONT THU AFTERNOON/THU NIGHT AND WILL
BRING SOME MIXED PRECIPITATION TYPES ACROSS THE COOK INLET
REGION...ANCHORAGE BOWL(THU NIGHT)...AND NORTH GULF COAST. PERIODS
OF BLOWING SNOW MAY DROP VISIBILITIES BECOME ONE HALF MILE AT
TIMES THROUGH PORTAGE VALLEY THURSDAY AFTERNOON...HOWEVER THIS
SHOULD BE FAIRLY SHORT LIVED AS TEMPS WILL WARM UP RATHER QUICKLY
TO ABOVE FREEZING AND EVEN MIX WITH RAIN BY THE EARLY EVENING
HOURS.

GALE TO STORM FORCE SOUTHERLY WINDS ARE EXPECTED IN ADVANCE OF THE
FRONT ACROSS THE GULF WATERS ON THU ALONG WITH STRONG GAP FLOWS
ACROSS TURNAGAIN ARM/PORTAGE VALLEY AND TO A LESSER EXPECTED
ACROSS THE MATANUSKA VALLEY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A VERY ACTIVE AND PROGRESSIVE PATTERN OVER THE REGION WILL USHER
IN A SERIES OF STRONG SYSTEMS TRACKING INTO THE SOUTHWEST MAINLAND
THROUGH THE END OF THE WEEK. THE FIRST SYSTEM IN THIS SERIES IS A
FRONTAL SYSTEM ASSOCIATED WITH A WEAKENING LOW IN THE NORTHERN
BERING THIS MORNING. THIS FRONT WILL CONTINUE TO SPREAD SNOW
ACROSS THE SOUTHWEST INTERIOR TODAY...BEFORE BRIEFLY DIMINISHING
AS THE FRONT TRACKS FURTHER EASTWARD OVERNIGHT TONIGHT INTO
THURSDAY. ALONG THE KUSKOKWIM COAST FROM KIPNUK NORTH...EASTERLY
WINDS AND HEAVIER SNOWFALL THIS MORNING THROUGH THE AFTERNOON.
THIS WILL RESULT IN RAPIDLY DETERIORATING CONDITIONS WITH
VISIBILITY RESTRICTIONS CAUSED BY SNOW AND BLOWING SNOW...DROPPING
VISIBILITIES TO A HALF MILE AT TIMES WITH BLOWING AND DRIFTING
SNOW BEFORE THE FRONT MOVES EAST IN THE AFTERNOON.

INCREASING SOUTHWEST WINDS AND ONSHORE FLOW WILL HELP CHANGE SOME
COASTAL AREAS OVER TO RAIN BY WEDNESDAY AFTERNOON AS WARMER
MARINE AIR MOVES IN. A MUCH STRONGER FRONT MOVES IN WEDNESDAY
NIGHT AND THURSDAY...SPREADING RAIN INTO MOST OF BRISTOL BAY AND
THE KUSKOKWIM DELTA...WITH SNOW MIXING IN ACROSS THE LOWER
KUSKOKWIM VALLEY. SOUTHERLY WINDS AHEAD OF THIS SECOND FRONT WILL
COINCIDE WITH A HIGH TIDE CYCLE...WITH THE THREAT FOR SOME MINOR
COASTAL EROSION FROM THE NORTHERN BRISTOL BAY COAST TO THE
KUSKOKWIM BAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A WEAKENING LOW OVER THE NORTHERN BERING WILL TRACK INLAND AND
DISSIPATE OVER THE NORTHERN KUSKOKWIM DELTA THIS MORNING. A MUCH
STRONGER STORM FORCE LOW TRACKS OVER THE WESTERN BERING THIS
AFTERNOON...WITH THE ASSOCIATED LEADING FRONT TRACKING THROUGH THE
WESTERN AND CENTRAL BERING/ALEUTIANS DURING THE DAY TODAY. COLDER
AIR WILL BEGIN WRAPPING INTO THIS SYSTEM ON THE WESTERN PERIPHERY
OF THE LOW...HELPING TO MIX DOWN SOME STRONGER GUSTS OVER THE
SOUTHERN AND WESTERN FLANK OF THE LOW. THE STRONGEST CORE OF STORM
FORCE WINDS WILL REMAIN OVER THE WESTERN AND CENTRAL
BERING/ALEUTIANS...ALTHOUGH STRONG SOUTHERLY GALES WILL CROSS INTO
THE EASTERN BERING OVERNIGHT TONIGHT. A SWATCH OF MODERATE TO
HEAVY RAIN WILL IMPACT MOST LOCATIONS AS THIS FRONT MOVES EAST
ALONG THE ALEUTIAN CHAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
ENTERING INTO THE MID-TERM...THE PATTERN OVER THE NORTH PACIFIC
BECOMES VERY PROGRESSIVE WITH MULTIPLE ROBUST LOWS MOVING THROUGH
THE FORECAST AREA.

AT THE START OF THE MID-TERM ON THURSDAY EVENING...THE FRONT
ASSOCIATED WITH THE LOW NEAR ST LAWRENCE ISLAND WILL BE PUSHING
INLAND OVER SOUTHWESTERN ALASKA AND RAPIDLY MOVING INTO INTO SOUTH
CENTRAL ALASKA OVERNIGHT THURSDAY NIGHT INTO FRIDAY MORNING.
SYNOPTICALLY...MODELS HAVE COME INTO BETTER AGREEMENT WITH
PRECIPITATION TYPE AND AMOUNTS WITH THIS SYSTEM. MOSTLY SNOW IS
EXPECTED OVER THE SOUTHWEST MAINLAND WITH A RAIN SNOW MIX ALONG
THE BRISTOL BAY COAST. OVER SOUTH CENTRAL ALASKA...PRECIPITATION
SHOULD REMAIN AS ALL SNOW OVER MOST OF THE INTERIOR AREAS WITH A
RAIN/SNOW MIX ALONG COASTAL AREAS. SNOW WILL CONTINUE OVER THE
SUSITNA VALLEY THROUGH MID AFTERNOON ON FRIDAY BEFORE TAPERING OFF
FRIDAY EVENING. FOR THE ANCHORAGE BOWL...MODEL GUIDANCE IS
SUGGESTING STRONG WINDS ALONG TURNAGAIN ARM THURSDAY NIGHT INTO
FRIDAY WITH A FAIR AMOUNT OF DOWNSLOPING OF PRECIPITATION INTO
THE ANCHORAGE AREA. WITH THAT BEING SAID...ANCHORAGE SHOULD STILL
SEE ACCUMULATING SNOW. THE HIGHEST SNOW TOTALS WITH THIS SYSTEM
ARE EXPECTED IN THE SUSITNA VALLEY AND ALONG THE HIGHER TERRAIN OF
PRINCE WILLIAM SOUND.

BEHIND THIS LOW...THE NEXT SYSTEM EXPECTED TO IMPACT THE REGION
WILL BE DEVELOPING OVER THE NORTH CENTRAL PACIFIC SOUTH OF THE
CENTRAL ALEUTIANS ON FRIDAY MORNING. MODELS ARE HAVING A VERY
DIFFICULT TIME RESOLVING THIS FEATURE IN BOTH STRENGTH AND
LOCATION. THE 12Z GFS AND GEM RUNS DEVELOPED A 965MB LOW OVER THE
WESTERN ALEUTIANS THAT MOVES RAPIDLY EASTWARD INTO MAINLAND
ALASKA. THE 12Z NAM AND EC DEVELOPED A WEAKER 990 MB LOW SOUTH OF
THE ALASKA PENINSULA THAT WOULD DEEPEN TO 980MB OVER THE NORTH
CENTRAL GULF BY SATURDAY NIGHT. 18Z RUNS OF THE GFS AND NAM HAVE
NOW SWUNG FROM THOSE SOLUTIONS AS WELL WITH THE NAM PLACING A
975MB LOW IN THE BERING AND THE GFS TRENDING MORE TOWARDS THE EC.
NEEDLESS TO SAY...THIS CREATES LOW CONFIDENCE IN THE FORECAST AT
THIS POINT. AFTER COORDINATION WITH WPC...DECIDED TO NUDGE TO THE
EC SOLUTION WITH SOME GFS OVER THE GULF OF ALASKA ON DAY 3.

WHILE THE MODELS ARE HAVING A GREAT DEAL OF DIFFICULTY WITH THE
FRIDAY SYSTEM...THEY ARE IN FAIRLY GOOD AGREEMENT ON BRINGING A
970-975MB LOW INTO THE WESTERN BERING LATE SUNDAY NIGHT INTO
MONDAY. WPC GUIDANCE CAPTURED THIS FEATURE WELL...THUS WAS USED
HEAVILY FOR DAYS 4-7.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY...155.
         WINTER STORM WATCH...145.
         HIGH SURF ADVISORY...155 161.
MARINE...HEAVY FREEZING SPRAY...121 127-130 139 181
         STORM WARNING...150 155 170 173-175 177 178 185
         GALE WARNING...120 130-132 136-139 141 160 165 171
                        172 176179-181

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...RF/MMC