Small Craft Advisory 764, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT TUE OCT 1 2013

.ANALYSIS AND UPPER LEVELS...
LOW PRESSURE IN THE EASTERN GULF CONTINUES TO WEAKEN...WITH RESULTANT
GAP WINDS AROUND COASTAL SECTIONS OF SOUTHCENTRAL DECREASING
SUBSTANTIALLY. AN UPPER TROUGH OVER SOUTHWEST ALASKA IS BEGINNING TO
SHOW HINTS OF BECOMING A WEAK UPPER LOW CENTER AS THE FEATURE SLOWLY
LIFTS NORTHWARD THROUGH BRISTOL BAY AND THE WESTERN GULF. MOSTLY
SUNNY CONDITIONS CONTINUE FOR ANOTHER DAY ACROSS LARGE SECTIONS OF
THE SOUTHERN MAINLAND...WITH THE EXCEPTION OF THE SUSITNA VALLEY AND
COPPER RIVER BASIN. OUT WEST...SATELLITE IMAGERY SHOWS A MATURE LOW
IN THE 985 MB RANGE OVER THE SOUTHWEST BERING SEA. AN ASSOCIATED
FRONT STRETCHES AHEAD OF THE LOW AND IS CURRENTLY BRINGING GALE-FORCE
WINDS TO THE EASTERN ALEUTIANS AND PRIBILOF ISLANDS. THE CLOUD SHIELD
ASSOCIATED WITH THIS LOW SPREADS FAR NORTH AND EAST AHEAD OF THE
LOW...CURRENTLY SPREADING UP THE ALASKA PENINSULA AND OVER TO KODIAK
ISLAND.

.MODEL DISCUSSION...
THE MAIN FEATURE AFFECTING THE FORECAST DOMAIN IN THE SHORT TERM
PERIOD IS THE LARGE LOW IN THE BERING. WHILE THE LOW IS LIKELY A BIT
DEEPER THAN EXPECTED YESTERDAY...THE MODELS CONTINUE TO SHOW THE SAME
OVERALL EVOLUTION OF THIS LOW AS IT DROPS INTO THE NORTH PACIFIC THIS
EVENING AND THEN CURVES NORTHWARD INTO THE GULF BY THURSDAY MORNING.
THERE IS STILL SIGNIFICANT MODEL DISAGREEMENT WITH THE DEVELOPMENT
AND EVOLUTION OF A TRIPLE POINT LOW AS THE OVERALL CIRCULATION ENTERS
THE GULF ON THURSDAY. THE OVERALL MOVEMENT OF THE MODELS HAS BEEN
TOWARD A STRONGER TRIPLE POINT...BUT THE 12Z ECMWF IS STRONGER THAN
ANY OF THE OTHER MODELS WITH THIS FEATURE. MEANWHILE...THE GFS KEEPS
THE ENERGY ASSOCIATED WITH THE LOW FOCUSED IN A MUCH MORE CONCENTRIC
CIRCULATION THAT REMAINS TO THE SOUTHWEST OF KODIAK ISLAND ON
THURSDAY MORNING. THE JET REMAINS FAR ENOUGH SOUTHEAST THAT A
ELONGATED MULTIPLE-CIRCULATION SOLUTION SEEMS THE MOST
PLAUSIBLE...AND A MIX OF THE EC AND NAM WAS USED TO TWEAK THE
FORECAST IN THIS DIRECTION AS THE LOW MOVES INTO THE GULF.

.SHORT TERM FORECAST...
SOUTHCENTRAL...CLOUDS WILL INCREASE TONIGHT ACROSS THE GULF COAST AND
COOK INLET AS THE UPPER LOW FORMS TO THE WEST OF THE ALASKA RANGE AND
PROVIDES A SOURCE OF LIFT FOR THE DEEP MOISTURE PERSISTING ACROSS THE
AREA. NOT EXPECTING THIS TO BE A SIGNIFICANT RAINFALL...BUT WILL MAKE
FOR A GLOOMIER DAY THAN RECENT SUNNY FALL DAYS. THE MORE SIGNIFICANT
WEATHER WILL OCCUR ON THURSDAY AS THE AFOREMENTIONED STORM MOVES INTO
THE GULF. ENOUGH WARM AIR WILL MOVE INTO THE REGION AHEAD OF THE
STORM THAT EVEN HIGHER ELEVATION TERRAIN AND MOUNTAIN PASSES SHOULD
SEE RAIN...WITH A TYPICAL UPSLOPE-DOWNSLOPE PATTERN CAUSING THE VAST
MAJORITY OF PRECIP TO FALL ALONG THE COASTLINES. THE EXACT TRACK AND
STRENGTH OF THE SECONDARY LOW DEVELOPMENT WILL HAVE LARGE
RAMIFICATIONS ON TIMING AND STRENGTH OF A BARRIER JET ALONG THE NORTH
GULF COAST. WILL KEEP WITH A STRONG GALE-FORCE BARRIER JET AT THIS
TIME...THOUGH A LATER UPGRADE TO STORM FORCE CANNOT BE RULED OUT
PENDING BETTER MODEL AGREEMENT.

SOUTHWEST...SOME HIGH CLOUDS WILL START TO FILTER INTO THE AREA THIS
EVENING. THE BERING LOW WILL PASS FAR ENOUGH SOUTH OF THE AREA TO
RESULT IN MOSTLY DRY OFFSHORE (NORTHERLY) FLOW AT MOST LOCATIONS FOR
THE LATTER HALF OF THE WEEK. TEMPERATURES WILL REMAIN SLIGHTLY BELOW
NORMAL...ESPECIALLY OVER INLAND LOCATIONS.

BERING SEA AND ALEUTIANS...THE SIGNIFICANT LOW WILL CROSS INTO THE
PACIFIC JUST EAST OF ATKA THIS EVENING. STRONG SOUTHEAST WINDS ALONG
THE FRONT WILL MOVE FROM DUTCH HARBOR OVER TO THE ALASKA PENINSULA
OVERNIGHT AS THE FRONT BECOMES INCREASINGLY EAST-WEST ORIENTED.
ALTHOUGH THERE IS MINIMAL COLD AIR BEHIND THE SYSTEM TO BOOST WIND
SPEEDS...NORTHERLIES BEHIND THE LOW WILL BE IN THE 30-50 MPH RANGE
ACROSS A WIDE SWATH OF THE CENTRAL AND EASTERN ALEUTIANS THROUGH
WEDNESDAY NIGHT.

.LONG TERM FORECAST...
MEDIUM RANGE GUIDANCE CONTINUES TO SHOW THE PROGRESSIVE AMPLIFIED
UPPER LEVEL FLOW PATTERN BECOMING EVEN MORE AMPLIFIED AS WE HEAD
THROUGH THIS WEEKEND AND INTO EARLY NEXT WEEK. THIS ENVIRONMENT IS
FAVORABLE FOR DEVELOPMENT OF VERY STRONG STORM SYSTEMS CHARACTERIZED
BY STRONG WINDS AND HEAVY PRECIPITATION. AS THE GULF TROUGH/LOW EXIT
TO THE EAST SATURDAY ANOTHER LARGE AND DEEP UPPER LOW COMPLEX WILL
MOVE OUT OF ASIA AND INTO THE BERING SEA. THE FIRST MAJOR SURFACE LOW
OUT AHEAD OF THIS TROUGH WILL INITIALLY TRACK OVER THE FAR WESTERN
BERING. THE MAIN IMPACT TO ALASKA WILL BE THE ACCOMPANYING FRONTAL
SYSTEM WHICH WILL MARCH EASTWARD ACROSS THE BERING FRIDAY AND
MAINLAND ALASKA OVER THE WEEKEND...BRINGING WIDESPREAD RAIN WITH IT.
THE UPPER LOW COMPLEX WILL GRADUALLY SETTLE OVER THE BERING SEA ALONG
WITH A WEAKENING SURFACE LOW.

MORE SIGNIFICANTLY...MODELS INDICATE A SHORT-WAVE DROPPING INTO THE
BACK SIDE OF THE TROUGH LEADING TO FURTHER AMPLIFICATION OF THE
TROUGH AND DOWNSTREAM RIDGE. THIS IN TURN WILL LEAD TO DEVELOPMENT
OF A STRONG BAROCLINIC ZONE (FAVORABLE FOR CYCLOGENESIS) AND
TRANSPORT OF TROPICAL MOISTURE NORTHWARD TO MAINLAND ALASKA. THERE
IS SOME MODEL SPREAD IN THE POSITION OF THE TROUGH AND RIDGE...BUT
CURRENT INDICATIONS ARE THAT A MAJOR STORM WILL DEVELOP OVER THE
NORTHWEST PACIFIC AND TRACK TO EITHER SOUTHWEST ALASKA OR
SOUTHCENTRAL ALASKA SOME TIME EARLY NEXT WEEK. IN ADDITION TO THE
TYPICAL IMPACT OF HIGH WINDS AND SEAS IN MARINE AREAS THE PRIMARY
IMPACT WILL BE THE HEAVY RAINFALL...SO WILL HAVE TO MONITOR FLOODING
POTENTIAL AS THE STORM NEARS. WARMER AIR ACCOMPANYING THE SYSTEM
WILL ENSURE PRECIPITATION FALLS AS ALL RAIN ACROSS THE SOUTHERN
MAINLAND. DEPENDING ON THE ULTIMATE TRACK OF THE LOW WOULD EXPECT
COLDER AIR TO AGGRESSIVELY MOVE BACK INTO THE REGION BEHIND THE
SYSTEM LATER NEXT WEEK.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 119 132 138 150 155 165 170 172 173 174 175 176 177 179
FIRE WEATHER...NONE

AMD/SEB OCT 13

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1005 AM AKDT TUE OCT 1 2013

AKZ171-020000-

...MINOR ASHFALL REMAINS POSSIBLE ACROSS KODIAK ISLAND...

STRONG NORTHWEST WINDS CONTINUE TO RE-SUSPEND AND PUSH DUST AND ASH
FROM THE 1912 NOVARUPTA/KATMAI VOLCANIC ERUPTION TOWARDS KODIAK
ISLAND. AS SUCH...MINOR DUST OR ASHFALL REMAINS POSSIBLE ACROSS THE
ISLAND. ANY ASHFALL ACCUMULATION SHOULD BE LIMITED TO A TRACE.

AMD