Small Craft Advisory 877, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
538 AM AKST WED NOV 4 2015

.ANALYSIS AND UPPER LEVELS...
THE CONTROLLING FEATURE ALOFT IS A BROAD LONGWAVE TROUGH
STRETCHING FROM THE CHUKCHI SEA SOUTHWARD THROUGH THE WESTERN
BERING SEA/ALEUTIANS. ROUNDING THE BASE OF THE PLANETARY WAVE...A
VERY STRONG SHORTWAVE TROUGH/SURFACE LOW PRESSURE SYSTEM IS
IMPACTING MUCH OF THE BERING SEA WITH STEADY RAIN AND STRONG
WINDS. A 140 KT JET STREAK IS FEEDING INTO THE SYSTEM WHICH IS SUPPORTING
FALLING SURFACE PRESSURES. THE SATELLITE PRESENTATION ALOFT SHOWS
A BEAUTY OF AN INSTANT OCCLUSION SYSTEM...WHILE SHOWING A FAIRLY
NARROW MOIST/WARM CONVEYOR BELT. IT HAS THE APPEARANCE OF A VERY
MATURE SYSTEM...YET CONTINUES TO DYNAMICALLY DROP ITS SURFACE
PRESSURE AT IMPRESSIVE RATES.

FURTHER DOWNSTREAM TOWARD THE MAINLAND...THE REMNANTS OF A
PREVIOUS SYSTEM IMPACT THE SOUTHWESTERN MAINLAND WITH SHOWERY
PRECIPITATION. THE SOUTHCENTRAL IS CHARACTERIZED WITH A WEAKENING
PRESSURE GRADIENT...WEAK HIGH PRESSURE OVER THE COOK INLET
REGION...AND LINGERING LOW CLOUDS BANKING UP AGAINST THE TERRAIN.

&&

.MODEL DISCUSSION...
GUIDANCE IS IN LOCK STEP WITH EACH OTHER IN THE UPPER LEVELS AS
THE BERING SEA SYSTEM FULLY MATURES AND SLOWLY BEGINS TO
FILL AND PROPAGATE EASTWARD. THERE ARE ONLY SLIGHT DIFFERENCES IN
SURFACE STRENGTH AND TRACK...HOWEVER THE OVERALL PROGRESSION AND
WEAKENING EASTWARD IS PRETTY WELL AGREED UPON. BOTH DOMAINS
PREFERRED A GFS-BASED FORECAST.

&&

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

DRY CONDITIONS AND LIGHT WINDS PREVAIL ACROSS THE SOUTHCENTRAL
REGION THIS MORNING...WITH SURFACE HIGH PRESSURE IN PLACE OVER
EAST MAINLAND ALASKA. HOWEVER...CLOUDS ARE EXPECTED TO
INCREASE...ALONG WITH WINDS...AS THE NEXT FRONT APPROACHES THE
GULF OF ALASKA THIS EVENING. THE ORIENTATION OF THE FRONT AND
ASSOCIATED STRONG PRESSURE GRADIENTS WILL FAVOR THE DEVELOPMENT OF
STRONG TURNAGAIN ARM WINDS BY THIS EVENING THAT WILL FURTHER
STRENGTHEN THROUGHOUT THE DAY THURSDAY.

THE FRONT IS ASSOCIATED WITH A HEALTHY MOISTURE SUPPLY...AND AS A
RESULT PRECIPITATION WILL BE HEAVY AT TIMES THURSDAY ACROSS
PORTIONS OF EASTERN KENAI...PRINCE WILLIAM SOUND...AND SUSITANA
VALLEY WEST OF THE PARKS HIGHWAY. ENOUGH WARM AIR WILL WORK ITS
WAY NORTHWARD TO SUPPORT MAINLY A RAIN AND SNOW MIX AS
PRECIPITATION BECOMES HEAVY...BUT A FEW QUICK INCHES OF WET SNOW
IS POSSIBLE IN INLAND PORTIONS OF THESE AREAS. DUE TO THE STRONG
WINDS ASSOCIATED WITH THIS FRONT...DOWNSLOPING IS EXPECTED TO
LIMIT RAIN AND SNOWFALL ACROSS PORTIONS OF THE ANCHORAGE
BOWL...MATANUSKA VALLEY...AND WESTERN KENAI PENINSULA.

&&

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

A DECAYING FRONT WILL BRING SOME RAIN AND SNOW INTO SW AK TODAY
BEFORE THE NEXT FRONTAL SYSTEM ARRIVES FROM THE BERING TONIGHT.
THIS IS ASSOCIATED WITH A DEEP LOW OVER THE ALEUTIANS THAT WILL
BRING WARMER AIR AND ABUNDANT RAIN TO THE REGION THROUGH THU. BY
THAT TIME THE LOW WILL MOVE EAST OF THE AKPEN...WITH RESIDUAL
RAIN SHOWER ACTIVITY BEGINNING TO CHANGING OVER TO SNOW SHOWERS
BY FRI MORNING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

AS THE ALEUTIAN LOW MIGRATES EAST IT WILL SPREAD STORM AND
HURRICANE FORCE WINDS AS WELL. A HIGH WIND WARNING HAS BEEN ISSUED ACROSS
THE CENTRAL ALEUTIANS FOR TODAY AND TONIGHT. GALES AND STORM
FORCE WINDS OVER THE EASTERN ALEUTIANS WILL PERSIST THU INTO FRI.
WHILE WINDS SLOWLY TAPER OFF FROM THE WEST...THIS SYSTEM WILL
BRING ABUNDANT RAIN TO THE ISLANDS INTO FRIDAY AS THE LOW MAKES
ITS WAY EAST.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...FRI THROUGH TUE)...
THE FORECAST AREA IS EXPECTED TO REMAIN IN AN ACTIVE PATTERN IN
THE MID TO LONG TERM AS A SERIES OF ROBUST LOWS MOVE THROUGH THE
REGION. FRIDAY EVENING...THE STRONG LOW MOVING THROUGH THE
ALEUTIANS WILL ENTER THE GULF OF ALASKA WITH THE WITH THE
ASSOCIATED FRONT PUSHING INTO THE NORTHERN GULF COAST THURSDAY
NIGHT INTO FRIDAY MORNING. AT THE SAME TIME...A WEAK RIDGE WILL BE
BUILDING INTO THE CENTRAL BERING BY SATURDAY MORNING. THE LOW
WILL SLOWLY WEAKEN AS IT DRIFTS TOWARD PRINCE WILLIAM SOUND
THROUGH SATURDAY MORNING...KEEPING SOUTHWEST ALASKA IN A SHOWERY
NORTHWEST FLOW. THIS PATTERN WILL ALSO INTRODUCE DRIER OFFSHORE
FLOW OVER THE SUSITNA VALLEY/WESTERN KENAI PENINSULA AND THE
ANCHORAGE BOWL WITH PRECIPITATION REMAINING IN THE FORECAST MOSTLY
ALONG THE GULF COAST AS WELL AS PARTS OF THE COPPER RIVER BASIN.
THE RIDGE OVER THE CENTRAL BERING WILL PUSH EASTWARD ON
SATURDAY...FORCING THE LOW INTO THE FAR NORTHEAST PORTION OF THE
GULF BY SUN.

BY MON...THE UPPER LEVEL PATTERN IS STARTING TO SHOW SOME SIGNS OF
BRINGING ANOTHER ROUND OF SNOW TO SOUTHCENTRAL AK. COLD AIR WILL
BE ENTRENCHED ACROSS THE DOMAIN AS NORTHWEST FLOW DOMINATES
THROUGH THE WEEKEND. A LARGE POTENT VERTICALLY STACKED LOW WILL BE
CENTERED NEAR THE BERING STRAIT. AS THIS LOW DROPS
SOUTHEAST...SOME OF THE MODELS ARE HINTING AT A TRIPLE POINT LOW
FORMING NEAR KODIAK ISLAND. IF THIS SECONDARY LOW WERE TO TAKE A
FAVORABLE TRACK AND BRING ENOUGH MOISTURE WITHOUT BRINGING
ABUNDANT WARM AIR...THIS COULD SET THE STAGE FOR A DECENT SNOW
EVENT. A LOT OF VARIABLES STILL HAVE TO COME INTO PLACE FOR THIS
SCENARIO TO UNFOLD...BUT IT IS SOMETHING WE WILL BE WATCHING.

OUT WEST...A WEAK LOW DEVELOPING OVER THE NORTHWEST PACIFIC ON
SATURDAY MORNING WILL MOVE INTO THE WESTERN ALEUTIANS WHERE IT
WILL MERGE WITH A STRONGER LOW DEVELOPING OVER THE NORTHWESTERN
BERING SEA. THIS DEEPER LOW IS EXPECTED TO STRENGTHEN FURTHER AND
MOVE INTO THE CENTRAL BERING BY MONDAY MORNING. GLOBAL MODELS
HAVING VARIOUS REPRESENTATIONS OF THIS STRONG LOW OVER THE
NORTHERN BERING BY 18Z MONDAY. THE GFS IS PLACING A 966 MB LOW
NEAR GAMBELL WHILE THE EC SOLUTION BRINGS THE LOW TO 970 MB AT A
POSITION SOUTHWEST OF SAINT MATTHEW ISLAND WITH NEAR-STORM FORCE
WINDS OVER THE CENTRAL BERING. THE EC HAS BEEN REASONABLY
CONSISTENT WITH THE POSITIONING OF THIS LOW AND THE EC ENSEMBLE
SHOWED A CLOSED LOW AT THIS TIME AS WELL. WITH THIS IN MIND...THE
EXTENDED FORECAST LEANED HEAVY ON THE WPC FORECAST WHICH UTILIZED
THE EC ENSEMBLE. THIS BRINGS THE WINDS OVER THE ALEUTIANS/BERING
TO GALE FORCE SUNDAY INTO MONDAY TO SHOW AN UPWARD TREND FROM THE
PREVIOUS FORECAST PACKAGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 187.
MARINE...HURRICANE WARNING 175 176 177.
	     STORM WARNING 119 155 170 171 172 173 174 178.
		 GALE WARNING 120 125 130 131 132 137 141 150 160 165 179 180.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...RF/MSO