Small Craft Advisory 867, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
544 AM AKST SUN NOV 1 2015

.ANALYSIS AND UPPER LEVELS...

A LARGE VERTICALLY STACKED CLOSED LOW SYSTEM SPANS FROM EASTERN
RUSSIA THROUGH THE EASTERN BERING SEA. DOWNSTREAM IN THE UPPER
LEVELS...A RIDGE IS BUILDING IN OVER WESTERN ALASKA WHILE A TROUGH
OVER THE EASTERN PART OF THE STATE MOVES INTO CANADA.

AT THE SURFACE...A LARGE BERING CYCLONE IS CENTERED JUST EAST OF
THE KAMCHATKA PENINSULA. A FAST MOVING COLD FRONT ASSOCIATED WITH
THE LOW IS QUICKLY TRACKING EASTWARD ACROSS THE EASTERN BERING
AND INTO THE WESTERN MAINLAND. THIS FRONT IS BRINGING SOME GUSTY
SOUTHWESTERLY GALES ACROSS THE BERING AND ALEUTIANS AS IT TRACKS
EAST. STRONG PRESSURE GRADIENTS BETWEEN HIGH PRESSURE UNDER THE
RIDGE OVER SOUTHWEST ALASKA AND LEE TROUGHING ALONG THE NORTHERN
GULF COAST ARE SUPPORTING SOME STRONG NORTHWESTERLY OUTFLOW WINDS
FROM THE ALASKA RANGE EAST. THE STRONGEST WINDS ALONG FAVORABLE
GAPS IN THE EASTERN KENAI PENINSULA AND PRINCE WILLIAM SOUND ARE
SUBSIDING AS SUPPORT FROM THE UPPER-LEVEL JET WEAKENS AND SLIDES
EAST.

&&

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT SYNOPTICALLY THROUGH THE MID TERM.
SOME SLIGHT DIFFERENCES ARISE IN THE TRACK OF A NORTH PACIFIC LOW
AS IT MOVES FROM SOUTH OF THE CENTRAL ALEUTIANS TOWARDS THE GULF
MON AFTERNOON. THE GFS IS THE NORTHERN OUTLIER...TRACKING THE
SYSTEM NORTH OF THE ALASKA PENINSULA AND INTO THE BRISTOL BAY. THE
GEM...WHICH TRACKS THE SYSTEM SOUTH OF KODIAK ISLAND...IS THE
SOUTHERN OUTLIER. THE PREFERRED SOLUTION WAS THE MIDDLE GROUND
NAM/EC BLEND...WHICH TAKES THE SYSTEM ALONG OR JUST SOUTH OF THE
ALASKA PENINSULA INTO THE WESTERN GULF MON NIGHT.

&&

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

GENERALLY CLEAR SKIES COVER MUCH OF SOUTHCENTRAL THIS
MORNING...BUT AN APPROACHING FRONT WILL BRING WIDESPREAD SNOW BY
LATE THIS EVENING THROUGH EARLY MONDAY MORNING. WHILE THE
APPROACHING FRONT IS NOT PARTICULARLY STRONG...WESTERLY UPSLOPE
FLOW IS EXPECTED TO LOCALLY ENHANCE SNOWFALL AMOUNTS. IN
ADDITION...WITH WIDESPREAD COLD AIR STILL IN PLACE...TEMPERATURES
ARE EXPECTED TO STAY BELOW FREEZING THROUGHOUT THE DURATION OF THE
EVENT. AS A RESULT...MODERATE SNOWFALL SHOULD PERSIST LONG ENOUGH
EARLY MONDAY MORNING FOR A FEW QUICK INCHES OF SNOW...JUST BEFORE
THE START OF THE MONDAY COMMUTE. SEE THE SPECIAL WEATHER STATEMENT
FOR MORE DETAILS.

WITH A MORE ACTIVE WEATHER PATTERN IN PLACE...CONDITIONS WILL
DRY OUT BRIEFLY...BEFORE THE NEXT LOW PRESSURE SYSTEM APPROACHES
THE GULF OF ALASKA EARLY TUESDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SUN AND MON)...
THE NORTH/SOUTH FRONTAL BOUNDARY IS BEGINNING TO PUSH ONSHORE
EARLY THIS MORNING SPREADING RAIN OVER THE KUSKOKWIM DELTA. IT
WILL CONTINUE TO MOVE EASTWARD TODAY ALONG WITH WARMER SOUTHERLY
WINDS AND RAIN. LINGERING COLD AIR IN THE KUSKOKWIM VALLEY AND
NORTH/EAST GREATER BRISTOL BAY WILL PROMOTE PRECIPITATION STAYING
AS SNOW FOR A BIT LONGER THOUGH. ACCUMULATIONS OF 1 TO 3 INCHES
ARE POSSIBLE IN THESE LOCATIONS. THE FRONT WILL EXIT BY THE
EVENING HOURS WITH LINGERING RAIN ALONG THE ALASKA/ALEUTIAN
RANGES. AN ACTIVE AND UNSTABLE FLOW ALOFT WILL KEEP SCATTERED RAIN
SHOWERS IN THE FORECAST IN MOST OF THE MAINLAND LOCATIONS
OVERNIGHT INTO MONDAY. ON MONDAY...A DEVELOPING SYSTEM MOVING
TOWARD THE ALASKA PENINSULA WILL BRING ANOTHER ROUND OF
RAIN...POSSIBLY MIXED WITH SNOW FLAKES AT TIMES...TO THE GREATER
BRISTOL BAY AREA.

BEHIND THE ORIGINAL FRONTAL BOUNDARY A LONG FETCH OF GALE FORCE
WINDS WILL BRING HIGH SEAS AND COASTAL STORM SURGE TO THE
KUSKOKWIM DELTA COAST. A HIGH SURF ADVISORY REMAINS IN EFFECT FOR
THESE AREAS WITH A SURGE OF 1 TO 2 FEET ABOVE HIGHEST ASTRONOMICAL
TIDE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SUN AND
MON)... THE FRONTAL BOUNDARY EXITS THE EASTERN BERING TODAY
LEAVING MUCH OF THE AREA IN AN UNSTABLE AND GUSTY WESTERLY FLOW.
GALE FORCE WINDS AND RAIN SHOWERS TODAY BEFORE TAPERING OFF
OVERNIGHT. A QUICK AND COMPACT LOW PRESSURE SYSTEM WILL DEVELOP
NEAR THE EASTERN ALEUTIANS/ALASKA PENINSULA EARLY MONDAY MORNING
BRINGING A QUICK SHOW OF RAIN AND WIND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...LATE MON THROUGH FRI)...

AN ACTIVE WEATHER PATTERN IS ON THE HORIZON AS A SERIES OF
SIGNIFICANT STORM SYSTEMS WILL PUSH ACROSS MUCH OF THE FORECAST
AREA. THE FIRST STORM OF NOTE BEGINS MONDAY NIGHT AS A SHORTWAVE
ENHANCED TROUGH INTERACTS WITH A WEAK SURFACE LOW SOUTH AND WEST
OF THE ALASKA PENINSULA. THE JET DYNAMICS ARE QUITE IMPRESSIVE
WITH THIS SHORTWAVE AND SHOULD QUICKLY SPIN A DECENT SURFACE LOW
UP DURING THE OVERNIGHT HOURS MONDAY HEADING INTO TUESDAY. THERE
WILL BE A GOOD BIT OF WARM SOUTHERLY FLOW ASSOCIATED WITH THIS LOW
WHICH SHOULD DRIVE A WARM FRONT ACROSS SOUTHWEST ALASKA. THE
MAJORITY OF PRECIPITATION LOOKS LIKE IT WILL FALL AS RAIN BUT THE
LOWER KUSKOKWIM VALLEY LOOKS LIKE IT WILL INITIALLY SEE SNOW AS
THE VALLEY TRAPS IN SOME COLDER AIR AND IT TAKES A WHILE TO BE
DISPLACED. THIS LOW WILL CONTINUE INTO SOUTHCENTRAL ALASKA TUESDAY
MORNING AND LOOKS LIKE A DECENT SNOWFALL EVENT WILL UNFOLD FOR
MOST INLAND LOCATIONS. INITIALLY...IT LOOKS LIKE DOWNSLOPING WILL
KEEP THE NORMAL LOCATIONS ALONG THE CHUGACH AND KENAI MOUNTAINS
DRY. HOWEVER...AS THE LOW MOVES TOWARD PRINCE WILLIAM SOUND...LOW
LEVEL FLOW SHOULD SWITCH TO THE NORTH WHILE UPPER LEVEL FLOW KEEPS
THE MOISTURE FEED FROM THE SOUTHWEST. THIS COULD LEAD TO A QUICK
COUPLE OF INCHES ACROSS THE ANCHORAGE BOWL AND MAT-SU VALLEYS.
OTHER LOCATIONS ACROSS SOUTHCENTRAL ALASKA WILL SEE DECENT SNOW
AMOUNTS BUT IT IS A BIT TOO EARLY TO GARNER A FAIR ESTIMATE.

ONCE THIS SYSTEM EXITS TO THE EAST TUESDAY NIGHT...THE NEXT SYSTEM
WILL HAVE ALREADY BEGUN TO SPIN UP SOUTH OF SHEMYA. NOW THIS
SYSTEM LOOKS QUITE IMPRESSIVE THROUGH MODEL DATA AS A SPLIT JET
MERGES TWO JET STREAKS TOGETHER AND DEVELOPS A VERY DEEP LOW OVER
A SHORT DURATION (RAPID CYCLOGENESIS). THIS LOW WILL MOVE
EAST/NORTHEAST TOWARD THE CENTRAL ALEUTIANS ON WEDNESDAY AND
CONDITIONS WILL RAPIDLY DETERIORATE AS THE LOW APPROACHES. IN THE
CURRENT FORECAST...WIDESPREAD GALES HAVE BEEN INTRODUCED TO THE
COASTAL WATERS OF THE ALEUTIANS. STORM FORCE WINDS WILL BE LIKELY
BUT MAY IMPACT SOUTH OF OUR AREA OF RESPONSIBILITY. THE TRACK OF
THE LOW WILL BE CRUCIAL WHEN IT COMES TO FORECASTING WINDS ACROSS
THE EASTERN HALF OF THE BERING SEA. MARINERS SHOULD MONITOR THIS
SYSTEM CLOSELY OVER THE NEXT SEVERAL DAYS. IN ADDITION TO THE
WINDS...HEAVY RAIN (SNOW OVER THE LOWER KUSKOKWIM VALLEY) LOOKS
POSSIBLE OVER THE ALEUTIANS AND SOUTHWEST ALASKA WITH A LARGE TAP
INTO SOME SUBTROPICAL MOISTURE. LAST BUT NOT LEAST...THIS LOW
CURRENTLY LOOKS TO PUSH INLAND OVER SOUTHWEST ALASKA THURSDAY
NIGHT WHICH COULD CREATE SOME STORM SURGE AND COASTAL FLOODING
ISSUES. THE DETAILS WILL CONTINUE TO BE IRONED OUT OVER THE COMING
DAYS BUT IT SEEMS A CHANGE IN WEATHER PATTERN IS UPON US.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH SURF ADVISORY 155.
MARINE...GALE WARNING 155 172 175 177 178 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...RD
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...MC