Small Craft Advisory 769, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
145 PM AKDT FRI OCT 3 2014

.ANALYSIS AND UPPER LEVELS...
A BROAD UPPER TROUGH EXTENDS SOUTH ACROSS THE CENTRAL MAINLAND TO
OVER THE WESTERN GULF. SNOW ASSOCIATED WITH A WEAKENING LOW OVER
THE GULF AND ASSOCIATED FRONTAL BOUNDARY WAS EVIDENT ACROSS MUCH
OF THE COPPER RIVER BASIN. LIGHT RAIN WITH WEAK CYCLONIC FLOW
PERSISTED ACROSS THE GULF COAST. GUSTY GAP FLOWS CONTINUED INTO
THIS AFTERNOON OVER THE GULF COAST...KENAI PEN...AND MAT VALLEY
WITH BRISK NORTHWEST WINDS OVER THE WESTERN GULF MARINE AREAS.

A LARGE RIDGE OVER THE BERING SEA AND A WEAKENING LOW COMPLEX
OVER THE NORTH PACIFIC PRODUCED BRISK NORTH TO NORTHEAST WINDS
ACROSS THE EASTERN BERING SEA...SW MAINLAND...AND AK PEN. AREAS OF
STRATUS AND STRATO CU ARE EVIDENT ACROSS THE BERING SEA.

&&

.MODEL DISCUSSION...
ALTHOUGH THERE ARE SOME MINOR DIFFERENCES IN POSITIONING AND
TIME...OVERALL THE MODELS ARE IN GENERALLY GOOD SYNOPTIC AGREEMENT
THROUGH THE SHORT TERM.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
THE LOW OVER THE EASTERN GULF WILL CONTINUE TO WEAKEN AND DRIFT
NORTH TOWARD THE COPPER RIVER BASIN. MOIST SOUTHEASTERLY FLOW IN
THE LOWER LEVELS WILL SPREAD WEST ACROSS SOUTHCENTRAL THROUGH
TONIGHT. OVERRUNNING SNOW WILL CONTINUE OVER THE COPPER RIVER
BASIN THROUGH TONIGHT. RAIN LIKELY TO HOLD ALONG THE COAST AS
TEMPS SHOULD REMAIN WELL ABOVE FREEZING. TEMPS WEST OF THE CHUGACH
RANGE WILL COOL TO BELOW FREEZING THIS EVENING WITH THE ONSET OF
LOW LEVEL COLD ADVECTION. RAIN AND SNOW MIXES WHICH CREEP OVER
THE MOUNTAINS THIS AFTERNOON AND SHOULD SHIFT TO ALL SNOW THIS
EVENING. FAIRLY STRONG DYNAMICS WITH THE DIGGING UPPER NEGATIVELY
TILTED TROUGH...LOW LEVEL MOISTURE ADVECTION...WILL PRODUCE
ADVISORY LEVEL SNOWS ACROSS THE HIGHER ELEVATIONS OF THE THE
ANCHORAGE BOWL AND MATANUSKA VALLEY THROUGH TONIGHT. UPPER
DYNAMICS WEAKEN SOME SAT...SO SNOW SHOULD DIMINISH SOME. THOUGH
THERE IS STILL SOME CONCERN WITH MORE SNOW POTENTIAL FOR THE
HIGHER ELEVATIONS OF 111 AS THE MID LEVEL FLOWS SHIFTS TO THE SW
SAT. ELSEWHERE...SNOW SHOULD CONTINUE ACROSS THE COPPER RIVER
BASIN THROUGH TONIGHT THEN SLOWLY DIMINISH THROUGH SAT MORNING.
THE THREAT OF SNOW AND RAIN/SHOWERS WILL LIKELY CONTINUE THROUGH
THE WEEKEND WITH THE LONG WAVE TROUGH CONTINUING ACROSS
SOUTHCENTRAL.

SOUTHWEST ALASKA... WIND AND SOME
NORTHERLY WINDS AND HIGH PRESSURE WILL CONTINUE RELATIVELY DRY
AND LOWLY WINDY CONDITIONS ACROSS THE SW MAINLAND THROUGH SUN.

BERING SEA/ALEUTIANS...

A LOW DEVELOPS NEAR KAMCHATKA AND MOVES WSW OF ATTU ON SUN
AFTERNOON. ITS ASSOCIATED FRONTAL TROUGH MOVES TO NEAR THE WESTERN
ALDIN'S/WEST BERING SEA SAT EVENING AND THE CENTRAL ALDIN'SBERING
SEA ON SUN NIGHT. RAIN AND GALE TO STORM FORCE WINDS CAN BE
EXPECTED ALONG THE IN ADVANCE OF THIS FRONTAL ZONE.

&&

.LONG TERM FORECAST...

MODELS CONTINUE TO SHOW AND AMPLIFYING TROUGH OF LOW PRESSURE OVER
THE WESTERN HALF OF THE BERING SEA AT THE BEGINNING OF THE LONG
TERM FORECAST (TUESDAY) WITH A RIDGE BUILDING OVER THE EASTERN
BERING SEA. A MATURE LOW PRESSURE SYSTEM WITHIN THE AMPLIFYING
TROUGH WILL BE LOCATED OVER THE WESTERN ALEUTIANS ON TUESDAY AND
SLOWLY DRIFT TO THE SOUTH THROUGH EARLY TUESDAY MORNING. THINGS
BEGIN TO GET A BIT COMPLICATED FROM THIS POINT. THE EXTRATROPICAL
REMNANTS OF TYPHOON PHANFONE (CURRENTLY LOCATED ABOUT 740 NM SOUTH
OF YOKOSUKA JAPAN) WILL RE-CURVE INTO THE NORTH PACIFIC EARLY
TUESDAY MORNING AND PHASE WITH THE AMPLIFIED UPPER TROUGH/MATURE
SURFACE LOW. THE MODELS CONTINUE TO SHOW THE EXTRATROPICAL SYSTEM
UNDERGOING RAPID CYCLOGENESIS. DETERMINISTIC MODELS AND ENSEMBLE
MEMBERS ARE IN EVEN BETTER AGREEMENT THAN THEY WERE IN PREVIOUS
DAYS WHICH INCREASES THE CONFIDENCE OF THE SCENARIO TAKING PLACE
EARLY NEXT WEEK. THE ONLY SIGNIFICANT CHANGE IS THAT THE LOW IS ON
A SLIGHTLY SLOWER AND SOUTHERN TRACK. IT APPEARS THAT GALE TO
STORM FORCE WINDS WILL BE POSSIBLE OVER PARTS OF THE BERING SEA
AND COASTAL WATER SHOULD THIS PAN OUT WITH STRONG WINDS AND HEAVY
RAINFALL ALONG THE ALEUTIAN ISLANDS. THE PHASING OF THE SYSTEMS
WILL END UP AFFECTING THE OVERALL LONGWAVE PATTERN...WITH A
SIGNIFICANT TROUGH OF LOW PRESSURE EXTENDING FROM THE KAMCHATKA
PENINSULA ALL THE WAY TO THE ALASKA PANHANDLE.

WEAK RIDGING OVER THE EASTERN BERING SEA ON MONDAY WILL BE SHUNTED
INTO SOUTHWEST AND SOUTHCENTRAL ALASKA AS THE RAPIDLY DEVELOPING
LOW PRESSURE SYSTEM SHUNTS THE RIDGE EASTWARD. THIS WILL BRING A
PERIOD OF CLEARER...DRIER AND COOLER WEATHER TO THE MAINLAND
THROUGH TUESDAY. AFTER TUESDAY...CLOUD COVER AND PRECIPITATION
CHANCES WILL BE ON THE RISE AS A WARM FRONT ASSOCIATED WITH THE
NEWLY FORMED LOW PUSHES INLAND AND BRINGS SIGNIFICANT CHANCES OF
RAINFALL. THE WARM FRONT WILL END UP BRINGING NORMAL TO ABOVE
NORMAL TEMPERATURES TO SOUTHWEST AND SOUTHCENTRAL ALASKA AND ACT
AS A BARRIER AND KEEP THE COLDER ARCTIC AIR TRAPPED OVER THE
NORTHERN HALF OF THE STATE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM 178. GALE 177.
FIRE WEATHER...NONE. &&

RMC/MC OCT 14