Small Craft Advisory 891, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
537 AM AKST TUE NOV 10 2015

.ANALYSIS AND UPPER LEVELS...
WESTERLY FLOW AND SCATTERED SNOW SHOWERS CONTINUE FOR SOUTHERN
MAINLAND ALASKA DUE TO THE WEAKENING LOW NEAR THE SEWARD
PENINSULA. THIS LOW IS ALSO CONTINUING TO BRING COLDER AIR OVER
SOUTHERN ALASKA AND THE GULF WHICH HAS BEEN AIDING IN CONVECTION
AND THUNDERSTORM DEVELOPMENT OVER THE GULF. THE LOW IS ALSO
BRINGING ANOTHER SHORTWAVE OVER THE SOUTHCENTRAL THAT IS PUSHING
THROUGH THE SOUTHWEST. OUT WEST A LOW FROM THE NORTH PACIFIC IS
MOVING EAST NEAR THE WESTERN ALEUTIANS AND IS BEGINNING TO PHASE
WITH A SHORTWAVE MOVING IN FROM RUSSIA WHICH WILL RAPIDLY DEEPEN
THE LOW AS IT MOVES INTO THE CENTRAL BERING.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN DECENT AGREEMENT IN THE SHORT TERM WITH THE ONLY
IMPACTFUL DISCREPANCIES HAPPENING ON A SMALL SCALE. ONE OF THE
EARLY STRUGGLES IS WITH SNOW AROUND COOK INLET. THERE ARE VARYING
DEGREES OF HOW MUCH SNOW TO KEEP AROUND THE AREA TODAY WITH THE
GFS BEING THE HEAVIEST. WITH EVIDENCE OF CONVERGENCE ALREADY OVER
COOK INLET CONFIDENCE IS HIGHER WITH GUIDANCE LIKE THE GFS THAT
HAS MORE SHOWERS. OUT WEST THERE IS GOOD AGREEMENT WITH THE STRONG
WINDS ON THE COLD AIR ADVECTION SIDE OF THE LOW MOVING ACROSS THE
BERING BUT THERE ARE SOME ISSUES WITH HOW FAR NORTH PRECIPITATION
MAKES IT AS THE LOW MOVES EAST. THIS MAINLY IMPACTS THE PRIBILOF
ISLANDS WITH QUESTIONS ABOUT WHERE THE RAIN/SNOW LINE IS AND
AMOUNTS OF SNOW. THE CONSENSUS OF THE GUIDANCE IS TO KEEP SAINT
PAUL MOSTLY SNOW AND SAINT GEORGE WITH MORE RAIN.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A SERIES OF UPPER LEVEL DISTURBANCES EMBEDDED WITHIN THE LARGER
SCALE TROUGH WILL COMBINE WITH DEEP LAYER INSTABILITY AND ARCTIC
AIR TO PRODUCE SNOW SHOWERS ACROSS PORTIONS OF SOUTHCENTRAL. WITH
GENERAL WEST TO SOUTHWEST LOW LEVEL FLOW THE WEST SIDE OF KODIAK
ISLAND AND THE WEST SIDE OF THE KENAI/CHUGACH/TALKEETNA MOUNTAINS
WILL BE FAVORED AREAS FOR SHOWERS. SNOW ACCUMULATION WILL
GENERALLY BE LIGHT AND LOCALIZED IN NATURE...DEPENDING ON EXACTLY
WHERE BANDS OF SHOWERS TRACK. THE INSTABILITY WILL ALSO LEAD TO
GOOD VERTICAL MIXING WITH STRONG GUSTY WINDS...PRIMARILY ACROSS
KODIAK ISLAND AND THE GULF WHERE LOW LEVEL INSTABILITY IS
GREATEST.

THE UPPER TROUGH WILL EXIT TO THE NORTH AND EAST TONIGHT BRINGING
AN END TO SNOW SHOWERS. CONDITIONS WILL RAPIDLY CHANGE ACROSS
KODIAK ISLAND AND THE GULF LATE TONIGHT THROUGH WEDNESDAY MORNING
AS A POWERFUL STORM SYSTEM APPROACHES FROM THE BERING SEA. THE
UPPER JET WILL DRIVE THIS SYSTEM QUICKLY EASTWARD...KEEPING THE
WORST OF THE IMPACTS ACROSS THE GULF AND NORTH GULF COAST/KENAI
PENINSULA. ONE NOTEWORTHY ASPECT OF THIS PARTICULAR SYSTEM IS THE
PRESENCE OF A DEEP ARCTIC AIR MASS OVER SOUTHCENTRAL ALASKA. THIS
WILL CONTRIBUTE TO ESPECIALLY STRONG PRESSURE GRADIENTS AND WINDS
ALONG THE NORTH GULF COAST AND SOUTHERN COOK INLET. THERE IS SOME
UNCERTAINTY IN THE TRACK OF THE LOW ACROSS THE GULF...WHICH WILL
DETERMINE HOW STRONG THOSE WINDS GET. RIGHT NOW HAVE ADVERTISED
STORM FORCE WINDS...BUT THERE IS POTENTIAL FOR HURRICANE FORCE
GUSTS...ESPECIALLY ACROSS SOUTHERN COOK INLET AD ARCTIC AIR
ADVECTS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM.

AS FOR PRECIPITATION WITH THIS SYSTEM IT WILL BE HEAVY AT TIMES
ACROSS KODIAK ISLAND AND THE GULF COAST...BUT WILL BE SHORT-LIVED
DUE TO THE RAPID MOVEMENT OF THE SYSTEM. THE OCCLUDED FRONT WILL
STALL JUST OFFSHORE OF THE NORTH GULF COASTLINE...WITH LOW LEVEL
FLOW OUT AHEAD OF IT BACKING FROM THE EAST TO THE NORTH. THIS WILL
KEEP THE VALDEZ AREA DRIER THAN NORMAL (DUE TO CONSTANT SUPPLY OF
LOW LEVEL COOL AND DRY AIR FROM THE COPPER RIVER BASIN) AND WILL
GENERALLY RESULT IN LOWER QPF OVER THE INTERIOR OF THE EASTERN
KENAI PENINSULA (AS PRECIP HANGS UP IN THE MOUNTAINS ALONG PRINCE
WILLIAM SOUND). OF COURSE...THIS FLOW ALSO KEEPS WARMER AIR FROM
PUSHING INLAND FROM THE GULF SO PRECIPITATION WILL MAINLY BE IN
THE FORM OF SNOW. AREAS ON THE INLAND SIDE OF THE COASTAL RANGE
WILL LIKELY REMAIN COMPLETELY DRY DUE TO THE PRESENCE OF THE DRY
ARCTIC AIR MASS.

&&

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

SNOW SHOWER ACTIVITY ACROSS SOUTHWEST ALASKA IS EXPECTED TO WANE
THROUGHOUT THE DAY AS A STACKED LOW OVER NORTON SOUND DRIFTS
NORTHWARD AND WEAKENS. THIS WILL ALLOW THE UPPER LEVEL FLOW TO
SWITCH TO A MORE ZONAL PATTERN VS THE AMPLIFIED PATTERN SEEN OVER
THE PAST SEVERAL DAYS. A VERY STRONG BERING SEA LOW WILL PUSH
ACROSS THE ALASKA PENINSULA WEDNESDAY MORNING AND WILL BRING BACK
SIGNIFICANT RAIN AND SNOW CHANCES TO THE BRISTOL BAY AREA. THE
KUSKOKWIM DELTA AND LOWER KUSKOKWIM VALLEY WILL REMAIN LARGELY ON
THE DRY SIDE AS THE AFOREMENTIONED LOW PRESSURE SYSTEM PUSHES
INTO THE GULF OF ALASKA. IN ADDITION...A PRETTY SIGNIFICANT POCKET
OF NEGATIVE VORTICITY ADVECTION WILL BE MOVING ACROSS THE REGION
STABILIZING THE ATMOSPHERE EVEN MORE. PRECIPITATION TYPE ACROSS
THE BRISTOL BAY AREA WILL VARY FROM SNOW TO A MIX OF RAIN AND SNOW
AS THE AFOREMENTIONED LOW CROSSES THE ALASKA PENINSULA. THE LOW
WILL BRING A POTENT SLUG OF WARMER AIR MAINLY SOUTH OF KING
SALMON. THIS WILL KEEP THE PRECIPITATION SOUTH OF KING SALMON AS
RAIN WHILE THE REST OF THE AREA SEES PERIODS OF SNOW AND SNOW
SHOWERS.

THE BERING SEA LOW LOOKS TO HAVE SHIFTED SLIGHTLY FURTHER NORTH WHEN
COMPARED TO MODEL RUNS FROM THIS TIME YESTERDAY. THIS WILL ALLOW
THE CORE OF STRONGEST WINDS TO NOW PUSH ACROSS COLD BAY...KING
COVE...FALSE PASS AND THE SHUMAGIN ISLANDS. HOWEVER...IT APPEARS
THE STRONGEST WINDS WILL OCCUR WEST OF THE SHUMAGIN ISLANDS BASED
ON THE TRACK OF THE LOW. A HIGH WIND WARNING HAS BEEN ISSUED FOR
THE ALASKA PENINSULA FOR WINDS GUSTS OF 75 TO 85 MPH AND POSSIBLE
STRONGER GUSTS TO 100 MPH POSSIBLE THROUGH NORTHWEST ORIENTED
GAPS.

&&

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

THE LOW THAT HAS BEGUN TO DEVELOP SOUTHEAST OF SHEMYA JUST CONTINUES
TO LOOK MORE AND MORE IMPRESSIVE AS NEWER MODEL RUNS COME IN.
SATELLITE IMAGERY SHOWS A VERY POTENT JET STREAK CURRENTLY
INTERACTING WITH THIS LOW AND RAPID CYCLOGENESIS WILL OCCUR
THROUGHOUT THE DAY TODAY. WITH THE TRACK OF THE LOW HOVERING JUST
NORTH OF THE CENTRAL AND EASTERN ALEUTIANS...THE CORE OF STRONGEST
WINDS WILL BE PUSHING ACROSS ADAK...ATKA AND UNALASKA OVER THE
NEXT 24 HOURS. HURRICANE FORCE WIND WARNINGS HAVE BEEN EXPANDED
ACROSS THE BERING SEA TO INCLUDE PORTIONS OF THE SOUTHCENTRAL
BERING SEA AS WELL AS THE PACIFIC SIDE OF THE ALASKA PENINSULA.
SEAS WILL QUICKLY BE ON THE RISE AS THE LOW RAPIDLY DEVELOPS. SEAS
OF LESS THAN 15 FT ACROSS THE PACIFIC SIDE OF THE ALEUTIANS WILL
RAPIDLY INCREASE TO 30 TO 45 FT OVER THE NEXT 12 TO 24 HOURS.

CONDITIONS LOOK QUITE SLOPPY ACROSS THE PRIBILOF ISLANDS AS A MIX
OF RAIN AND SNOW WILL ACCOMPANY WIND GUSTS UPWARDS TO 70 MPH THIS
EVENING AND WEDNESDAY MORNING. IT LOOKS LIKE ST GEORGE WILL SEE
RAIN WHILE ST PAUL WILL LIKELY SEE SNOW THAT MIXES WITH RAIN AT
TIME. THE REASON THIS IS IMPORTANT IS THAT HEAVY PRECIPITATION
COULD BE SEEN AS THE LOW MOVES JUST SOUTH OF THE PRIBILOF ISLANDS.
ALTHOUGH ST PAUL WILL BE SEEING SNOW...TEMPERATURES WILL LIKELY
REMAIN ABOVE FREEZING DURING THE DURATION OF THE SNOWFALL...LEADING
TO A VERY WET SNOW. WITH LARGE AND WET SNOWFLAKE...EVEN THE
STRONGEST WINDS WILL HAVE A HARD TIME BLOWING THE SNOW AND CREATE
ANY RE-SUSPENSION OF SNOW TO REDUCE VISIBILITIES. THUS...NO
BLOWING SNOW ADVISORY OR BLIZZARD WARNING WAS CONSIDERED FOR THE
MORNING PACKAGE. HOWEVER...A SPECIAL WEATHER STATEMENT WAS ISSUED
TO HIGHLIGHT THIS EVENT AND CONTAINS ADDITIONAL INFORMATION.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE GLOBAL MODELS HAVE NOW COME INTO AGREEMENT WITH BRINGING THE
STRONG LOW OVER THE GULF FURTHER SOUTH OVERNIGHT WEDNESDAY...THEN
CURVING BACK NORTHWARD INTO THE NORTHEASTERN GULF COAST AND
REMAINING STATIONARY THROUGH SATURDAY MORNING. GUSTY OUTFLOW WINDS
AROUND PRINCE WILLIAM SOUND AND THE EASTERN KENAI PENINSULA ARE
EXPECTED TO INCREASE THURSDAY...AS THIS LOW MAKES ITS WAY THROUGH
THE GULF AND COLDER AIR FILTERS IN BEHIND THE SYSTEM. ON THE
OTHER HAND...THE STRONG NORTHWESTERLY FLOW OVER THE EASTERN
BERING/ALEUTIANS AND ALASKA PENINSULA WILL BEGIN TO SLOWLY
DIMINISH THURSDAY AS THIS SYSTEM CONTINUES ITS EASTWARD
PROGRESSION. HOWEVER...THE GUSTY WEST TO NORTHWEST WINDS WILL
PERSIST OVER MUCH OF THE BERING AND ALEUTIANS THROUGH THE
WEEKEND...USHERING IN COOLER TEMPERATURES WITH THE CONTINUE COLD
AIR ADVECTION OVER THE AREA. THIS WILL RESULT IN A SHOWERY REGIME
REMAINING OVER THE AREA...WITH THE POTENTIAL FOR SOME SNOW SHOWERS
ALONG THE EASTERN ALEUTIANS THROUGH THE WEEKEND.

FURTHER WEST...RIDGING BUILDS OVER THE WESTERN BERING AND
ALEUTIANS SUNDAY...BUT IS SHORT LIVED...AS ANOTHER FRONTAL SYSTEM
PUSHES INTO THE WESTERN ALEUTIANS ON MONDAY. THIS WILL BRING
ANOTHER ROUND OF WET AND WINDY WEATHER TO THE AREA FOR THE START
OF NEXT WEEK. HOWEVER...FORECAST CONFIDENCE REMAINS LOW DURING
THIS TIME FRAME...AS MODELS CONTINUE TO STRUGGLE WITH THE DETAILS
REGARDING THE STRENGTH AND POSITIONING OF BOTH THE RIDGE OVER THE
WESTERN BERING AND THE LOW PUSHING OFF OF THE KAMCHATKA PENINSULA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING ZONES 181 185 187.
MARINE...HURRICANE FORCE...155 170 171 172 173 174 175. STORM
WARNING...120 130 131 139 150 165 176 177 178 179. GALE
WARNING...119 125 132 136 137 138 140 141 160 180

&&

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