Small Craft Advisory 316, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
439 PM AKDT FRI APR 10 2015

.ANALYSIS AND UPPER LEVELS...

TWO UPPER LOW CENTERS...ONE OVER THE EASTERN BERING AND OVER THE
GULF...ARE CREATING BROAD CYCLONIC FLOW OVER MUCH OF THE AOR. COLD
AIR FLOWING SOUTH ACROSS THE ALEUTIANS/BERING SEA HAS DEPRESSED
THE NEARLY ZONAL JET STREAM WELL SOUTH OF ALASKAN WATERS. UNSTABLE
CONDITIONS AND COLD ADVECTION HAVE GIVEN RISE TO WIDESPREAD OPEN
CELL CUMULUS AND SNOW SHOWERS ACROSS MUCH OF THE BERING SEA AND
ALEUTIANS. IN THE GULF A WEAKENING LOW AND ASSOCIATED BROAD
CYCLONIC FLOW ARE PRODUCING WIDESPREAD RAIN AND SNOW SHOWERS
ACROSS THE NORTH GULF AND EASTERN KENAI. NORTHWESTERLY GALES
CONTINUE ACROSS THE ALEUTIANS...BERING SEA...AND AK PEN.

&&

.MODEL DISCUSSION (THROUGH SUNDAY)...

THE MODELS ARE IN EXCELLENT AGREEMENT WITH THE LARGE SCALE PATTERN
THROUGH THE WEEKEND. MODEL DIFFERENCES POSITION DIFFERENCES CREEK
IN EARLY NEXT WEEK AS DEVELOPING LOW TRACK RAPIDLY EAST UNDER A
NEARLY ZONAL JET.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE UPPER LOW OVER THE GULF OF ALASKA WILL CONTINUE TO DRIFT EAST
AND WEAKEN THROUGH TOMORROW. AS A RESULT OF BEING UNDER THE CYCLONIC
FLOW OF THIS SYSTEM...SOME LINGERING SHOWERS REMAIN ALONG THE
GULF COAST AREAS THROUGH TONIGHT. SOME AREAS AROUND THE WESTERN
KENAI AND ANCHORAGE HAD A BRIEF BREAK FROM THE CLOUDINESS
TODAY...DUE TO SOME DRIER NORTHERLY FLOW AND SUBSIDENCE BEHIND THE
UPPER LOW. HOWEVER THIS WILL BE A SHORT LIVED BREAK WITH THE ENHANCED
INSTABILITY AND DIURNAL HEATING OVER THESE AREAS TODAY...MAKING
WAY FOR SOME CONVECTIVE SHOWERS TO DEVELOP. CURRENT RADAR AND
SATELLITE IMAGERY IS ALREADY SHOWING SOME HEAVY CONVECTIVE
SHOWERS DEVELOPING ALONG THE SUSITNA VALLEY THROUGH KENAI
PENINSULA...INCLUDING THE ANCHORAGE AREA. THE 2200 FT FREEZING
LEVEL MAKES THE ATMOSPHERE CONDUCIVE FOR SOME SMALL HAIL IN THESE
SHOWERS IN THESE AREAS AS WELL. THE GULF LOW WILL THEN TRANSITION
INTO A WEAK FRONT AND BEGIN TO MOVE ONSHORE OF THE GULF COAST
SATURDAY NIGHT. THIS IS IN RESPONSE TO ANOTHER UPPER LOW
APPROACHING FROM THE WEST THAT BEGINS TO PUSH INTO THE GULF NEAR
KODIAK ISLAND SUNDAY NIGHT. IN GENERAL SOUTH CENTRAL ALASKA WILL
REMAIN IN WEAK CYCLONIC FLOW WITH SOME RESIDUAL MOISTURE AND
FAIRLY COLD AIR ALOFT THROUGH MUCH OF THE WEEKEND. THIS WILL
RESULT IN SOME LIGHT SHOWERS...POSSIBLY DIURNALLY ENHANCED...TO
CONTINUE TO POP-UP ALONG SOUTHCENTRAL THROUGH THE WEEKEND.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH SUNDAY)...
AN UPPER LEVEL TROUGH APPROACHING THE SOUTHWEST COAST OVERNIGHT
WILL BRING CONTINUED SNOW SHOWERS...ESPECIALLY FROM SOUTHERN
BRISTOL BAY INTO THE KUSKOKWIM DELTA. THE HEAVIEST SHOWERS ARE
EXPECTED OVER BRISTOL BAY...AND ESPECIALLY TO THE EAST OF KING
SALMON WHERE A FEW INCHES OF NEW SNOWFALL IS POSSIBLE BY MORNING.
NORTHWESTERLY WINDS STRETCHING FROM THE KUSKOKWIM DELTA COAST INTO
THE AKPENN WILL DIMINISH LATE TONIGHT AS THE GULF LOW CONTINUES
TO WEAKEN AND THE PRESSURE GRADIENT DIMINISHES. THIS MAY CREATE A
FEW ISOLATED AREAS OF BLOWING SNOW THIS EVENING...BUT WITH LITTLE
ADDITIONAL ACCUMULATION EXPECTED THESE ARE NOT EXPECTED TO BE LONG
LIVED. FOR THIS WEEKEND...THE WEAKENING UPPER LEVEL TROUGH WILL
MOVE JUST SOUTH OF THE AREA WHICH WILL KEEP MOSTLY CLOUDY SKIES
AND SHOWERS IN THE AREA...BUT NOT AS HEAVY OR WIDESPREAD AS THE
LAST 2 DAYS. THE MAJORITY OF THESE SHOWERS SHOULD OCCUR DURING THE
AFTERNOON-EVENING HOURS AS DIURNAL SURFACE HEATING SUPPLIES SOME
ADDITIONAL INSTABILITY TO THE ATMOSPHERE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH SUNDAY)...
A WEAK SHORTWAVE MOVING THROUGH THE ALEUTIANS WILL BRING SNOW
SHOWERS TO THE AREA INTO TOMORROW MORNING...WITH ACCUMULATIONS
LIMITED MOSTLY TO THE BERING SEA COAST. NORTHWESTERLY FLOW WILL
ALSO CONTINUE THROUGHOUT THE REGION THIS WEEKEND...BUT WITH LIGHT
ACCUMULATIONS AND DIMINISHING WINDS EXPECTED SIGNIFICANT AREAS OF
BLOWING SNOW ARE NOT LIKELY. THIS PATTERN WILL THEN BEING TO
CHANGE LATE SUNDAY AS THE NEXT LOW APPROACHES THE WESTERN
ALEUTIANS FOR EARLY NEXT WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODEL GUIDANCE IS IN PRETTY GOOD AGREEMENT WITH THE EVOLUTION OF
THE SYNOPTIC PATTERN FOR THE EXTENDED PERIOD. THE BEGINNING OF
THIS PERIOD WILL BE DEFINED BY A WEAKENING UPPER LEVEL LOW
PRESSURE ALOFT...KEEPING SHOWERS ALONG THE MOUNTAINS AROUND COOK
INLET AND THE NORTH GULF COAST. WINDS SHOULD BE WEAKENING SUNDAY
NIGHT INTO MONDAY IN MOST AREAS...WHILE COLDER AIR MOVES OVERHEAD.
THE NEXT SYSTEM COMING ACROSS THE ALEUTIANS WILL SHAPE THE
EXTENDED FORECAST. THE LOW PRESSURE SYSTEM AND FRONT WILL MOVE
JUST SOUTH OF THE CHAIN SUNDAY AND MONDAY SPREADING LIGHT SNOW
OVER THE CENTRAL AND EASTERN ALEUTIANS FOLLOWED BY INSTABILITY
SNOW SHOWERS ON THE BACK SIDE OF THE SYSTEM. ON TUESDAY THE
FRONT/LOW COMBO WILL MOVE INTO THE GULF OF ALASKA WHERE IT WILL
SLOWLY WEAKEN OVER THE COURSE OF NEXT WEEK. EXPECT NEAR TO
SLIGHTLY BELOW NORMAL TEMPERATURES AS TEMPERATURES ALOFT COOL
BEHIND THE FIRST SYSTEM THIS WEEK. LINGERING SHOWERS CAN BE
EXPECTED OVER MOUNTAINOUS AREAS WHILE STEADY PRECIPITATION CAN BE
EXPECTED ALONG THE NORTH GULF COAST WITH THE APPROACHING FRONT
NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 130 132 138 150 155 160 173 174 176 177.
		 HEAVY FREEZING SPRAY 180.
FIRE WEATHER...NONE.

&&

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