Small Craft Advisory 963, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
514 AM AKST WED DEC 3 2014

.ANALYSIS AND UPPER LEVELS...

A NARROW YET HIGHLY AMPLIFIED UPPER TROUGH (THE REMNANTS OF THE
POWERFUL UPPER LOW OVER THE BERING SEA THE LAST FEW DAYS) RESIDES
OVER THE SOUTHWEST MAINLAND EXTENDING SOUTH OVER BRISTOL BAY AND
THE ALASKA PENINSULA WELL DOWN INTO THE PACIFIC SOUTH OF 45N
LATITUDE...WITH SLOWLY WEAKENING HIGH PRESSURE RIDGING NOW PUSHED
WELL DOWNSTREAM OVER WESTERN CANADA. BEHIND THE TROUGH...ANOTHER
TRANSITORY RIDGE HAS MOVED EASTWARD WITH AXIS FROM THE 180
PARALLEL SOUTH OF THE WESTERN ALEUTIANS EXTENDING NORTHWEST TOWARD
KAMCHATKA. IMMEDIATELY UPSTREAM BETWEEN ATTU AND KAMCHATKA...LOW
PRESSURE IS FORMING ALONG A WEATHER FRONT. A SMALL UPPER LOW IS
MOVING SOUTHWEST TOWARD THE NORTHERN BERING SEA OVER THE BERING
STRAIT.

OVER THE GULF AND SOUTHCENTRAL...A VERY UNSTABLE AIR MASS IS IN
PLACE WITH SOUTHERLY FLOW PUSHING THIS CONVECTION ONSHORE ALONG
THE GULF COAST...AS WELL AS PUSHING UP ALONG COOK INLET TOWARD THE
SUSITNA VALLEY. THE ASSOCIATED CONVECTION BROUGHT REPORTS OF
LIGHTNING ALONG THE GULF COAST AND ALASKA PENINSULA...AS WELL AS
REPORTS OF SNOW FALLING AT OVER 4 INCHES PER HOUR THROUGH THOMPSON
PASS LAST EVENING.

&&

.MODEL DISCUSSION...

MODELS SUGGEST THAT AS THE REMNANT TROUGH OVER THE NORTH PACIFIC
DIGS TO THE EAST WELL SOUTH OF THE GULF THROUGH TONIGHT...SHORTWAVE
RIDGING WELL SOUTH OF THE GULF WILL RAPIDLY BUILD NORTHWARD
THROUGH THURSDAY WITH THE RIDGE AXIS BECOMING SITUATED FROM THE
EASTERN GULF THROUGH PRINCE WILLIAM SOUND TO THE SUSITNA VALLEY.
THIS WILL ALLOW FOR A SERIES OF FRONTS TO BEGIN MOVING FROM
SOUTHEAST TO NORTHWEST FROM THE SOUTHERN GULF NORTHWEST ACROSS
KODIAK ISLAND AND INTO THE SOUTHWEST MAINLAND TO THE SOUTH OF THE
UPPER RIDGE AXIS.

MEANWHILE...THE RIDGING OVER THE FAR SOUTHWEST
BERING WILL RAPIDLY DISSIPATE AS LOW PRESSURE MOVES RAPIDLY EAST
JUST TO THE SOUTH OF THE ALEUTIANS THROUGH THURSDAY. MODELS
DIFFER QUITE A BIT WITH THE PLACEMENT AND STRENGTH OF THIS
LOW...WITH THE NAM A GOOD 10 MB DEEPER THAN ALL OTHER MODELS. THE
EUROPEAN MODEL...A SOUTHERN OUTLIER...HAS A VERY GOOD SUCCESS RATE
WITH LOW PRESSURE SYSTEM IN THIS PARTICULAR AREA AND CAN NOT BE
TOTALLY DISCOUNTED. THE GFS AND CANADIAN MODELS ARE CLOSER TO THE
NAM POSITION WITH THE LOW CLOSER TO THE CENTRAL ALEUTIANS...BUT
NOT AS STRONG AS THE NAM. FOR THIS FORECAST PACKAGE...THE
CANADIAN MODELS ARE PREFERRED EARLY ON WITH A NOD TO THE NAM
POSITIONING AFTER TONIGHT.

FORECAST CONFIDENCE OVERALL IS MODERATE IN THE SHORT TERM.

&&

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

UNSTABLE SOUTHWESTERLY FLOW OVER SOUTHCENTRAL WILL CONTINUE
THROUGH THE DAY TODAY WITH A DISTURBANCE MOVING INLAND EARLY THIS
MORNING BRINGING A BRIEF ROUND OF SCATTERED TO NUMEROUS SNOW
SHOWERS LASTING INTO EARLY THIS AFTERNOON. THE HEAVIEST AMOUNTS
WILL BE CONFINED TO THE GULF COAST...ESPECIALLY TOWARD THOMPSON
PASS...BUT BRIEFLY MODERATE SHOWERS WILL BE POSSIBLE FOR INLAND
AREAS AS WELL.

THE FLOW BACKS TO SOUTHERLY TONIGHT AND THEN SOUTHEASTERLY
THURSDAY FROM THE KENAI PENINSULA SOUTH. THIS WILL ALLOW FOR A
WEATHER FRONT MOVING NORTHWEST TO BRING A ROUND OF MODERATE TO
HEAVY RAIN SHOWERS TO THE SOUTH AND EAST SIDE OF KODIAK ISLAND AND
THE GULF COAST OF THE KENAI PENINSULA AND WESTERN PRINCE WILLIAM
SOUND...WITH LESSER COVERAGE AND INTENSITY INLAND FROM THE
MATANUSKA VALLEY SOUTH INCLUDING ANCHORAGE...KENAI...AND
HOMER...WHERE TEMPERATURES WILL BE COLD ENOUGH FOR THE SHOWERS TO
FALL AS SNOW.

&&

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

ISOLATED TO SCATTERED SNOW SHOWER ACTIVITY WILL BE ALONG THE
KUSKOKWIM THROUGH THU. ISOLATED SNOW SHOWER ACTIVITY IN BRISTOL
BAY WILL BECOME CONCENTRATED NEAR THE ALEUTIAN RANGE
TONIGHT...AND WILL MIX WITH SOME RAIN ON THU. PRECIPITATION OVER
ALL OF SOUTHWEST AK IS EXPECTED TO TAPER OFF BENEATH MOSTLY
CLOUDY SKIES THU NIGHT.

&&

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

RAIN WILL SPREAD ALONG THE ALEUTIANS THROUGH THU NIGHT...MIXING
WITH SNOW AT TIMES OVER THE PRIBILOFS. THE AKPEN WILL REMAIN
FAIRLY DRY UNTIL THU NIGHT WHEN RAIN AND SNOW SHOWERS ARRIVE.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN ACTIVE WEATHER PATTERN CONTINUES THROUGH NEXT WEEK WITH
SEVERAL LOW CENTERS MOVING ALONG BROAD TROUGHING CENTERED OVER
THE BERING. THE SOUTHERN COASTAL AREAS AND SURROUNDING WATERS
WILL BE IN THE WETTER PATTERN INITIALLY AND THEN WEAK RIDGING
ACROSS THE SOUTHERN ALCAN BORDER BEGINS TO BREAK DOWN FOR THE
SECOND HALF OF THE WEEKEND. A WETTER PATTERN THEN ENSUES ACROSS
THE SOUTHERN MAINLAND THROUGH NEXT WEEK AS A CLOSED LOW PATTERN
DEVELOPS ACROSS THE NORTHEASTERN PACIFIC SENDING MULTIPLE WAVES
TOWARD THE COAST. EXPECT A MIX OF RAIN AND SNOW TO REMAIN IN THE
FORECAST ACROSS MUCH OF THE SOUTHERN MAINLAND WITH THE UPCOMING
SHORTWAVES AS THE LOW PRESSURE SYSTEM IN THE PACIFIC TAPS INTO
THE WARMER SUBTROPICAL AIR MASS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 176.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CC
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...KH