Small Craft Advisory 889, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
449 PM AKST MON NOV 9 2015

.ANALYSIS AND UPPER LEVELS...THE PATTERN IS DOMINATED BY A
POWERFUL VERTICALLY STACKED LOW NEAR THE SEWARD PENINSULA. THE
WELL ADVERTISED FRONT ASSOCIATED WITH THIS SYSTEM MADE ITS WAY
THROUGH SOUTH CENTRAL LAST NIGHT. SNOW AMOUNTS VARIED QUITE WIDELY
FROM THE SUSITNA VALLEY THROUGH THE ANCHORAGE BOWL. PLEASE SEE THE
PUBLIC INFORMATION STATEMENT (PNS) FOR PRELIMINARY TOTALS. WITH
SOME COLDER AIR ALOFT CREEPING OVER THE ALASKA RANGE...THE
UNSTABLE AIR IN THE WAKE OF THE FRONT IS MAKING FOR A FEW SHOWERS
THIS MORNING. THESE ARE ESPECIALLY WIDESPREAD UP IN THE MATANUSKA
VALLEY WHERE SOME WARM MOIST SOUTHWEST FLOW OFF THE COOK INLET IS
BEING LIFTED ALONG THE TERRAIN. FURTHER TO THE WEST...THIS COLD
UNSTABLE FLOW ACROSS THE WARM WATERS OF THE BERING CONTINUES TO
TRIGGER SHOWERS AND GUSTY WINDS ALL THE WAY INLAND TO THE
KUSKOKWIM VALLEY. THE BEST LINE OF SHOWERS AND ISOLATED
THUNDERSTORMS IS ASSOCIATED WITH THE "PARTING SHOT" OF ENERGY IN
THE FORM OF AN UPPER LEVEL WAVE APPROACHING BRISTOL BAY. THIS
SYSTEM PRODUCED HEAVY SNOW SHOWERS FROM THE ALASKA PENINSULA UP
TO BETHEL WITH VISIBILITIES AS LOW AS 1/4 MILE AT TIMES. THIS WAVE
IS RIGHT IN THE "SWEET SPOT" FOR UPPER LEVEL DIVERGENCE OF THE
LEFT EXIT REGION OF A ROBUST 160 KT JET. THE REMAINDER OF THE JET
FLOWS RIGHT ALONG THE ALEUTIAN CHAIN BEFORE TURNING NORTHEAST
THROUGH THE GULF AT ABOUT 110 KTS.

&&

.MODEL DISCUSSION...MODELS ARE IN FAIRLY GOOD AGREEMENT WITH
SYNOPTIC SCALE FEATURES. BUT AS OFTEN IS THE CASE...THE DETAILS
REMAIN SOMEWHAT UNCERTAIN. THE BROAD WESTERLY CYCLONIC FLOW WILL
ALLOW FOR SHOWERS TO CONTINUE TO DEVELOP ACROSS SOUTH
CENTRAL...ESPECIALLY IN UPSLOPE FLOW WEST OF THE MOUNTAINS. THE
QUESTION IS EXACTLY WHERE THE HEAVIER SHOWERS SET UP BASED ON
LOW-LEVEL CONVERGENCE AND MOISTURE. PLANNING TO GO WITH A BROAD
BRUSHED APPROACH WITH SCATTERED TO NUMEROUS SHOWERS TO HANDLE THIS
UNCERTAINTY. THE MORE IMPORTANT CONCERN WITH MODEL DIFFERENCES IS
HOW THEY HANDLE THE POWERFUL CYCLONE THAT DEVELOPS NEAR THE
CENTRAL ALEUTIANS TUE INTO WED. THIS SYSTEM IS VERY UNIQUE IN THAT
IT DEVELOPS FROM THE SURFACE BAROCLINITY UPWARD. IT WILL BE RIGHT
ALONG A 150 KT ZONAL JET. THESE TWO ASPECTS ARE CAUSING MODELS TO
STRUGGLE WITH TIMING AND MINIMUM PRESSURE. THIS WILL LEAVE THE
BIGGEST QUESTIONS AS HOW STRONG WILL THE WINDS BECOME NEAR DUTCH
LATE TUE INTO WED AND WILL THE PRIBILOFS STAY COLD ENOUGH TO HAVE
BLOWING SNOW CONDITIONS. THIS FORECAST PACKAGE LEANS ON THE
AMERICAN MODELS AS THEY HAVE BEEN MORE CONSISTENT TO THIS POINT.

&&

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

A LARGE UPPER TROUGH ENCOMPASSES THE ENTIRE REGION...WITH NUMEROUS
WEAK WAVE DISTURBANCES EMBEDDED WITHIN IT. THIS WILL KEEP A
SHOWERY REGIME IN PLACE AS COLD AIR ALOFT REMAINS ENTRENCHED OVER
THE AREA. MOST SHOWERS WILL BE ALONG COASTAL AREAS AND NEAR COOK
INLET. SOUTHERLY FLOW ALOFT WILL SUPPORT PERIODS OF LIGHT SNOW
OVER THE NORTHERN SUSITNA VALLEY WITH LIGHT ACCUMULATING SNOW.
A WEAK AND ELONGATING TROUGH WILL MOVE INTO SOUTHCENTRAL TOMORROW
MORNING...SPREADING ENOUGH MOISTURE INTO SOUTHCENTRAL TO SUPPORT
LIGHT SNOW AND SNOW SHOWERS...ESPECIALLY ALONG AND NEAR THE
MOUNTAINS. THAT SYSTEM MOVES EAST TUESDAY NIGHT...WITH MOST
PRECIPITATION ENDING AS IT MOVES EAST...ALTHOUGH SNOW SHOWERS WILL
CONTINUE ACROSS THE NORTHERN SUSITNA AND ALONG THE MOUNTAINS. A
STRONG STORM FORCE WARM FRONT MOVES INTO THE GULF OF ALASKA ON
WEDNESDAY...BRINGING HEAVY RAIN TO KODIAK ISLAND...AND RAIN AND
SNOW TO THE NORTHERN GULF COAST. INLAND LOCATIONS WILL EXPERIENCE
A VERY STRONG DOWNSLOPE SHADOW WITH ONLY PASSING FLURRIES AT
TIMES.

&&

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

UNSTABLE SOUTHWEST FLOW OFF THE BERING WILL CONTINUE TO BRING SNOW
SHOWER ACTIVITY TO MUCH OF SOUTHWEST ALASKA THROUGH TUESDAY
NIGHT. BY WEDNESDAY THE ALEUTIAN LOW WILL SPREAD RAIN AND WIND
ACROSS BRISTOL BAY WHILE THE KUSKOKWIM VALLEY AND DELTA REMAIN
DRY.

&&

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

RAIN SHOWERS ARE EXPECTED TONIGHT OVER THE BERING AND ALEUTIANS...WITH
A FEW THUNDERSTORMS IN THE UNSTABLE AIRMASS NORTH OF THE AKPEN. SHOWER
ACTIVITY WILL CONTINUE OVER THE EASTERN PORTION OF THE REGION ON
TUESDAY...BUT THE NEXT BIG PLAYER WILL BE A RAPIDLY INTENSIFYING
LOW CURRENTLY WEST OF SHEMYA THAT WILL REACH BRISTOL BAY AND THE
AKPEN ON WEDNESDAY. THIS SYSTEM HAS STRONG UPPER SUPPORT ON THE
TRAILING SIDE...WHICH WILL BRING STORM AND HURRICANE FORCE WINDS
ALONG WITH HIGH WIND WARNINGS TO THE CENTRAL AND EASTERN ALEUTIANS
THROUGH WEDNESDAY. RAIN WILL BE ASSOCIATED WITH THE EASTERN FLANK
OF THE LOW...CHANGING TO SNOW ON THE WESTERN SIDE. SOME BLOWING
SNOW WILL AFFECT THE PRIBILOFS AS THE LOW HEADS FOR BRISTOL BAY
AND THE AKPEN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE NAM/GFS MODELS CONTINUE TO HAVE BETTER CONSISTENCY WITH PLACEMENT
ON STORM PATH TRAJECTORY WITH THE HURRICANE FORCE LOW POSITIONED IN
THE BRISTOL BAY REGION. WHERE THE ECMWF MODEL IS DEPICTING THE LOW
FARTHER SOUTH AND FARTHER EASTWARD AND HAS BEEN INCONSISTENT BETWEEN
MODEL RUNS. THIS LOW PRESSURE SYSTEM WILL TRACK ACROSS THE ALASKA
PENINSULA INTO THE WESTERN GULF OVER KODIAK ISLAND BY WEDNESDAY
EVENING. THIS WILL BRING IN PREDOMINANTLY GUSTY NORTHWESTERLY WINDS
THROUGH THE BERING AND THE ALEUTIAN CHAIN HEADING INTO THE WEEKEND.
THE NORTHWESTERLY FLOW WILL BRING IN COOLER TEMPERATURES WITH THE
CONTINUE COLD AIR ADVECTION INTO THE BERING SEA. RESULTING IN A
SHOWERY REGIME WITH THE HEAVIEST SNOW SHOWERS ALONG THE EASTERN
ALEUTIANS THROUGH REST OF THE WEEK HEADING INTO THE WEEKEND.

THE STORM FORCE LOW FROM THE BERING SEA TRACKS INTO THE WESTERN
GULF BEFORE TRACKING ACROSS THE KODIAK ISLAND BY WEDNESDAY EVENING.
THE ASSOCIATED WEATHER FRONT WITH THE AFOREMENTIONED SYNOPTIC
FEATURE PUSHES THROUGH THE BARREN ISLAND NORTHWARD ALONG THE
NORTHERN GULF COASTLINE. THIS WILL RESULT IN STORM FORCE WINDS
THROUGH THE BARREN ISLANDS...SOUTHERN COOK INLET AND ALONG THE
NORTHERN GULF COASTLINE GOING INTO THE EARLY THURSDAY MORNING
HOURS. THIS SYNOPTIC FEATURE WILL BE ACCOMPANIED BY WIDESPREAD
RAIN AND STRATUS THROUGH THE GULF AS THIS SYSTEM TRACKS NEAR
YAKUTAT BY THURSDAY EVENING. THE WESTERN GULF WILL TRANSITION TO
NORTHWESTERLY GAP WINDS BY THURSDAY AS THE COLDER AIR FILTERS INTO
THE REGION. THE SOUTHERN MAINLAND WILL HAVE ONSHORE FLOW BRIEFLY
BEFORE TRANSITIONING TO OFFSHORE FLOW BY END OF THIS WEEK. THIS
WILL BRING COLDER TEMPERATURES COINCIDING WITH THE NORTHWESTERLY
TO NORTHERLY WINDS TO THE SOUTHCENTRAL REGION HEADING INTO THE
WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING ZONES 185 187.
MARINE...HURRICANE FORCE...170 172 173. STORMS...155 171 174 175
176 177 179 413 414. GALES 131 132 150 160 165 178 180 181 185 351
352 411 412.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...PD