Small Craft Advisory 309, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
510 PM AKDT WED APR 8 2015

.ANALYSIS AND UPPER LEVELS...
A STRONG UPPER LEVEL NEGATIVELY TILTED TROUGH IS POSITIONED ROUGHLY
ALONG A LINE FROM MCGRATH TO SKWENTNA TO ANCHORAGE TO CORDOVA THIS
AFTERNOON. THIS SYSTEM IS ACCOMPANIED BY SUFFICIENT INSTABILITY
AND SYNOPTIC SCALE LIFT TO PRODUCE A PERIOD OF STEADY SNOW JUST
AHEAD OF IT. UPSTREAM THERE IS WEAK TRANSITORY RIDGING OVER INLAND
BRISTOL BAY AHEAD OF A VERY LARGE CLOSED LOW CENTERED OVER THE
BERING SEA BETWEEN SAINT PAUL AND SAINT MATTHEW ISLANDS. TO THE
SOUTH...A STRONG UPPER LEVEL JET AND A STRONG SURFACE PRESSURE
GRADIENT ARE COMBINING TO PRODUCE STORM FORCE WINDS OVER THE
SOUTHERN BERING SEA APPROACHING THE SOUTHERN ALASKA PENINSULA AND
EASTERN ALEUTIANS. STRATIFORM CLOUDS OUT AHEAD OF THE LOW AND ITS
ASSOCIATED FRONT QUICKLY GIVE WAY TO INSTABILITY CUMULIFORM CLOUDS
AND SHOWERS. PRECIPITATION IS FALLING MOSTLY AS SNOW ACROSS THE
BERING REGION...EXCEPT FALLING AS A MIX OF RAIN AND SNOW ACROSS
THE EASTERN ALEUTIANS AND THE ALASKA PENINSULA.

THE LOW WILL GRADUALLY BEGIN TO WEAKEN THE NEXT COUPLE OF DAYS AS
IT MOVES SLOWLY EAST FROM THE EASTERN BERING TO THE COOK INLET
REGION ON THURSDAY...THEN TO THE NORTHERN GULF OF ALASKA FOR FRIDAY.
A NORTHWEST-SOUTHEAST ORIENTED SURFACE FRONT WILL MOVE THROUGH THE
WESTERN GULF TONIGHT AND THEN PIVOT NORTH INTO THE GULF COAST BY
THURSDAY EVENING OUT AHEAD OF THE LOW.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN VERY GOOD AGREEMENT...WITH THE SYNOPTIC FEATURES
CURRENTLY DOMINATING THE WEATHER MAP GIVING HIGH CONFIDENCE TO THE
FORECAST. THE NAM IS BEING USED MAINLY FOR ITS BETTER RESOLUTION
WITH LOCAL EFFECTS FOR BOTH DOMAINS.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE STRONG UPPER LEVEL TROUGH WILL PUSH NORTH TOWARD INTERIOR
SOUTHCENTRAL THROUGH TONIGHT...BUT WEAKEN CONSIDERABLY AS IT DOES
SO. THUS...THE COPPER RIVER BASIN WILL MISS OUT ON WIDESPREAD
PRECIPITATION...THOUGH A FEW SNOW SHOWERS WILL BE POSSIBLE MAINLY
TOWARD HIGHER ELEVATIONS. A FRONT ASSOCIATED WITH A LOW RACING
EASTWARD ACROSS THE BERING SEA WILL MOVE INTO KODIAK ISLAND AND
THE WESTERN GULF THIS EVENING...THEN PUSH EAST INTO THE REST OF
SOUTHCENTRAL LATE TONIGHT INTO THURSDAY EVENING. THE LOW ITSELF
WILL CONTINUE TO DRIVE EAST AND WILL BE CENTERED JUST NORTH OF
KODIAK ISLAND BY LATE THURSDAY NIGHT. THIS SYSTEM IS ALSO FAIRLY
COLD (ALOFT) BUT DUE TO THE LOCATION OF ITS TRACK AND ITS
ORIENTATION THE FRONT ITSELF WILL NOT PUSH VERY FAR INLAND. THIS
CREATES A BIT OF A CHALLENGE FOR PRECIPITATION FORECASTS FOR
THURSDAY AND THURSDAY NIGHT...IN JUST HOW FAR NORTH THE
PRECIPITATION WILL REACH. DOWNSLOPE CONDITIONS SHOULD PREDOMINATE
AHEAD OF THE FRONT OVER INLAND SECTIONS...BUT AS THE FRONT PASSES
AND DIMINISHES CROSS-BARRIER FLOW WILL DIMINISH RESULTING IN
SHOWERY CONDITIONS OVER MOST OF THE GULF REGION FRIDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (TONIGHT THROUGH FRI NIGHT)...
A FRONTAL SYSTEM ENTERING THE SOUTHWEST COAST WILL BRING
ACCUMULATING SNOW TO MUCH OF THE SOUTHWEST MAINLAND THROUGH
TOMORROW MORNING. THE HEAVIEST ACCUMULATION FROM THIS IS EXPECTED
TO OCCUR OVER NORTHERN BRISTOL BAY STARTING LATE TONIGHT AS
DOWNSLOPING FROM THE ALEUTIAN RANGE BEGINS TO DIMINISH. SNOW
ACCUMULATION WAS INCREASED TO 2 TO 4 INCHES WITH THE AFTERNOON
PACKAGE...BUT THERE IS A POTENTIAL THAT THIS MAY NEED TO BE
INCREASED FURTHER AS ADVISORY LEVEL ACCUMULATIONS ARE POSSIBLE.
BY LATE TONIGHT...THE UPPER LEVEL TROUGH WILL MOVE INTO THE
GULF...LEAVING SCATTERED SNOW SHOWERS AND NORTHWESTERLY FLOW IN
THE AREA THROUGH FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (TONIGHT THROUGH FRI
NIGHT)...
THE UPPER LEVEL LOW MOVING THROUGH THE EASTERN BERING WILL BRING
SNOW SHOWERS AND NORTHWESTERLY WINDS THROUGH FRIDAY. STORM FORCE
WINDS ALONG THE SOUTHERN EDGE OF THIS LOW OVER THE SOUTHERN BERING
WILL QUICKLY MOVE INTO THE DUTCH HARBOR AREA THIS EVENING...WITH
STRONG NORTHWEST WINDS CONTINUING INTO FRIDAY MORNING. AS THE
UPPER LEVEL LOW MOVES SOUTHEAST TOWARDS THE GULF TOMORROW...GUSTY
WINDS WILL ALSO DEVELOP THROUGHOUT THE ALASKA PENINSULA BEFORE
DIMINISHING ON FRIDAY EVENING. FOR THE PRIBILOF ISLANDS...SNOW
SHOWERS WILL CONTINUE TO MOVE THROUGH THE AREA BUT WITH LIGHT
ACCUMULATION EXPECTED AND TEMPERATURES REMAINING FAIRLY WARM
SIGNIFICANT AREAS OF BLOWING SNOW ARE NOT EXPECTED WITH THE
STRONG WINDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A ZONAL TRANS PACIFIC JET WILL BEGIN TO BUCKLE SAT NIGHT...CAUSING
A PATTERN CHANGE THAT WILL AFFECT THE FORECAST AREA AT LEAST
THROUGH THE MIDDLE OF NEXT WEEK. CYCLONIC FLOW OVER MAINLAND AK
WILL GIVE WAY TO A BUILDING RIDGE OVER THE WEST COAST OF NORTH
AMERICA BEGINNING TUE. A DEEPENING TROUGH WILL AFFECT THE
ALEUTIANS SUN THROUGH WED. AT THE SURFACE...A LOW OVER THE
NORTHERN GULF WILL WEAKEN IN PLACE...DISSIPATING MON NIGHT WHEN
SURFACE RIDGING BUILDS INTO THE AREA. NORTHWEST FLOW OVER THE
BERING WILL SLOWLY WEAKEN THROUGH SUN. A LOW SOUTH OF THE WESTERN
ALEUTIANS ON MON WILL BRING A FRONT NEAR THE ALEUTIANS AND AKPEN
THROUGH WED.

ZONAL FLOW WITH UNCERTAIN TIMING OF WAVES IS BEST HANDLED BY AN
ENSEMBLE APPROACH...AND THE FORECAST INITIALLY UTILIZES THE EC AND
THEN RAPIDLY YIELDS TO THE WPC SOLUTION.

THE BERING AND ALEUTIANS CAN EXPECT RAIN AND SNOW SHOWERS...
DIMINISHING ON MON. THIS WILL BE FOLLOWED BY A ROUND OF SNOW
CHANGING TO RAIN...ASSOCIATED WITH THE FRONT APPROACHING THE AREA
THROUGH WED. AT FIRST SHOWERY CONDITIONS WILL PERSIST OVER
SOUTHCENTRAL AND COASTAL LOCATIONS. RAIN WILL BE DOMINANT ALONG
THE COAST WITH A MIX CROSSING THE MOUNTAIN RANGES...WITH SNOW MORE
COMMON AT NIGHT. DRYING WILL THEN OCCUR TUE INTO WED.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 170 171 173.
         GALE WARNING 119 120 125 130 131 132 150 155 160 165
                      172 174 175 176 177 178 179 180 181.
         HEAVY FREEZING SPRAY WARNING 180 185.
FIRE WEATHER...NONE.

&&

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1208 AM AKDT THU APR 09 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1100 PM     NON-TSTM WND GST UNALASKA                53.93N 166.51W
04/08/2015  M76 MPH                             AK   COAST GUARD

            METEOROLOGIST ONBOARD THE USCGC ALEX HALEY REPORTED PEAK
            WIND GUST OF 76 MPH. WINDS HAVE BEEN GUSTING BETWEEN 60
            AND 70 MPH THROUGHOUT THE DAY.

&&

MCLAY