Small Craft Advisory 490, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
447 AM AKDT TUE JUN 9 2015

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH OUT OF THE ARCTIC COVERING MUCH OF THE BERING
AND ALEUTIANS HAS STARTED TO TRACK INTO THE SOUTHWEST
MAINLAND...WITH SOUTHWESTERLY FLOW ALOFT OVER THE SOUTHERN
MAINLAND SHIFTING TO THE SOUTH AND SOUTHEAST TODAY AS THE TROUGH
TRACKS FURTHER EAST. AT THE SURFACE...THE LOW OVER THE EASTERN
ALEUTIANS WILL CONTINUE TO WEAKEN AND TRACK EASTWARD TOWARD THE
GULF TODAY. THE FRONT ASSOCIATED WITH THIS LOW WILL TRACK THROUGH
THE SOUTHWEST MAINLAND AND INTO THE NORTHERN GULF COAST TODAY.
CURRENT RADAR IMAGERY SHOWS THE PRECIPITATION ASSOCIATED WITH THIS
FRONT WORKING THROUGH THE ALASKA PENINSULA AND WESTERN GULF...AND
QUICKLY CATCHING UP TO THE DECAYING WAVE OVER THE NORTHERN GULF
COAST CURRENTLY PRODUCING PRECIPITATION OVER THE AREA AND PARTS OF
THE SOUTHCENTRAL MAINLAND.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD AGREEMENT THROUGH MOST OF THE WEEK...KEEPING
FORECAST CONFIDENCE HIGHER THAN NORMAL THROUGH MUCH OF THE WEEK. THE
NAM AND ECMWF BOTH KEEP A WEAK SURFACE LOW OVER THE GULF WEDNESDAY
NIGHT...WHILE THE GFS WASHES IT OUT INTO A TROUGH. MODELS THEN
INDICATE WEST TO NORTHWEST FLOW SETTING UP OVER THE SOUTHWEST
MAINLAND AND WESTERN GULF...DEVELOPING SOME GUSTY GAP WINDS AROUND
SHELIKOF STRAIT AND PARTS OF SOUTHERN COOK INLET LATER IN THE
WEEK. THE MODELS INTO AND THROUGH THE WEEKEND HAVE CONVERGED ONTO
THE SOLUTION THAT BUILDS A RIDGE OVER MUCH OF THE MAINLAND BY
SATURDAY MORNING. WITH MODELS ALL SHOWING THIS PROGRESSION...IT
FURTHER INCREASES FORECAST CONFIDENCE IN THIS SCENARIO OVER THE
WEEKEND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...TODAY
THROUGH WED)...
VERY LITTLE HAS CHANGED IN THE OVERALL SYNOPTIC SCALE FORECAST
THROUGH WED. THE MAIN FEATURES CONTINUE TO BE THE A 980S LOW
MOVING ACROSS THE AK PEN AND INTO THE WESTERN GULF AND ITS
ASSOCIATED FRONT SYSTEM HEADING TOWARD THE NORTH GULF COAST TODAY.
EASTERLY (SE TO NE) GALES WILL ACCOMPANY THE FRONT AS IT MOVES
NORTH TODAY WITH THE LAST REMNANTS TAPERING OFF ALONG THE NORTH
GULF COAST TONIGHT. BRISK (SUB-GALE) SWLY FLOW BRIEFLY SETS UP
OVER THE OFFSHORE WATERS TONIGHT WITH TRAILING TROUGH BEFORE
SHIFTING TO THE EASTERN GULF WED AFTERNOON. STRONG GAP FLOWS
ACROSS SOUTHCENTRAL...ESPECIALLY FAVOR AREAS (TURNAGAIN/PORTAGE
VALLEY/KNIK/COPPER RIVER)...WILL DIMINISH OVERNIGHT AS PRESSURE
GRADIENTS RELAX SOME AS THE FRONT WEAKENS ALONG THE GULF COAST.
THE NEXT TROUGH MOVING NORTH IN THE GULF ON WED WILL STRENGTHEN
THE COASTAL RIDGE SOME AND ALLOW FOR THE DEVELOPMENT OF GAP
FLOWS...THOUGH WEAKER...WED AFTERNOON AND EVENING.

THE BRUNT OF THE RAIN...WHICH COULD BE MODERATE TO HEAVY AT
TIMES...WITH THE FRONT MOVING NORTH TODAY WILL FALL ALONG THE
COAST AND UPSLOPE AREAS OVER WESTERN COOK INLET/WEST SUSITNA
VALLEY. DOWNSLOPE TO THE LEE OF THE KENAI/CHUGACH MOUNTAINS SHOULD
KEEP RAIN MORE SHOWERY. GENERAL SHOWERS ARE EXPECTED TO CONTINUE
INLAND WITH RAIN ALONG THE COASTS INTO WED.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL LOW PRESSURE SYSTEM WILL DRIFT OVER BRISTOL BAY
TODAY BRINGING WIDESPREAD SHOWERS TO MUCH OF INTERIOR BRISTOL BAY
AND KUSKOKWIM VALLEY. RAIN SHOWERS WILL BE MUCH LESS WIDESPREAD
OVER THE KUSKOKWIM DELTA. GUSTY EASTERLY WINDS WILL GRADUALLY
TAPER OFF THROUGH THE DAY TODAY ACROSS GREATER BRISTOL BAY AND
HIGHER ELEVATIONS. OVERNIGHT TUESDAY INTO WEDNESDAY A RIDGE OF
HIGH PRESSURE FROM THE BERING SEA WILL BUILD OVERHEAD BRINGING
DRIER CONDITIONS AND SOME BREAKS IN THE CLOUDS THOUGH LINGERING
MOISTURE WILL STICK AROUND. A DISTURBANCE ON THE NORTH SIDE OF
THIS SYSTEM WILL FIRE OFF SOME SHOWERS OVER THE KUSKOKWIM VALLEY
AND ALASKA RANGE WEDNESDAY AFTERNOON AND EVENING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A WEAKENING LOW PRESSURE SYSTEM WILL GRADUALLY SLIDE EASTWARD OUT
OF THE AREA TONIGHT. WIDESPREAD SHOWERS FROM THE CENTRAL ALEUTIANS
THOUGH THE ALASKA PENINSULA WILL SLOWLY DECREASE IN
COVERAGE...LINGERING THE LONGEST ALONG THE ALASKA PENINSULA
WEDNESDAY MORNING. A SLUG OF STABLE AIR FROM SIBERIA WILL DRIFT
OVER THE BERING SEA THE NEXT TWO DAYS FROM WEST TO EAST CREATING
FAVORABLE CONDITIONS FOR WIDESPREAD DENSE FOG...ESPECIALLY OVER
COOLER SEA SURFACE TEMPERATURE OVER THE NORTHERN BERING SEA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN UPPER LEVEL CLOSED LOW OVER THE ARCTIC HAS AN ASSOCIATED
TROUGH EXTENDING INTO THE SOUTHWEST ALASKA REGION. THIS WILL
BRING A SHOWERY REGIME ACCOMPANIED BY A WEAK ZONAL JET STREAK
MOVING THROUGH THE NORTON SOUND AREA INTO THE SOUTHWEST REGION.
THERE WILL BE SEVERAL WEAK SHORTWAVES ROTATING AROUND THE LOW THAT
WILL SWING THROUGH THE ALASKA REGION BRINGING MORE SHOWERS
THROUGH FRIDAY MORNING. BY SATURDAY THE BERING SEA WILL HAVE AN
AMPLIFIED RIDGE BUILDING THROUGH THE WEEKEND OVER THE SOUTHWEST
AND SOUTHCENTRAL REGION. AN UPPER LEVEL CLOSED HIGH WILL DEVELOP
SOUTH OF THE EASTERN ALEUTIANS WITH THE RIDGE EXTENDING THROUGH
SOUTHWEST ALASKA INTO THE NORTH SLOPE BY SUNDAY. THIS WILL BRING
WARMER TEMPERATURES THROUGHOUT THE ALASKA REGION HEADING THROUGH
THE WEEKEND AND THE EARLY PART OF NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING...119 120 125 130.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...PD