Small Craft Advisory 298, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
447 PM AKDT SAT APR 4 2015

.ANALYSIS AND UPPER LEVELS...
THE OVERALL UPPER LEVEL PATTERN OVER THE STATE IS BECOMING MORE
PROGRESSIVE WITH A TROUGH OVER THE KAMCHATKA PENINSULA...A RIDGE
OVER THE EASTERN BERING SEA...AND ANOTHER TROUGH OVER SOUTHEAST
ALASKA. THE 250 MB JET STREAM IS RUNNING THROUGH THE SOUTHERN
BERING SEA AS IT TRAVERSES SOUTH OF THE KAMCHATKA AND THEN OVER
THE TOP OF THE EASTERN BERING SEA RIDGE BEFORE HEADING SOUTHEAST
ACROSS THE WESTERN GULF OF ALASKA. THERE ARE ALSO A NUMBER OF
SHORT WAVES EMBEDDED IN THIS FLOW WHICH WILL HAVE SOME IMPACT ON
PRECIPITATION OVER SOUTHWEST AND SOUTHCENTRAL ALASKA.

AT THE SURFACE THE RIDGE OVER MAINLAND ALASKA IS RAPIDLY WEAKENING
AND BEING PUSHED EASTWARD AS A SERIES OF LOWS IN THE BERING SEA
MOVE INTO IT OVER THE NEXT FEW DAYS. THE FRONT ASSOCIATED WITH THE
FIRST LOW IN THE EASTERN BERING SEA HAS ALREADY MOVED THROUGH MOST
OF SOUTHWEST ALASKA BRINING SOME SNOW TO THE AREA LAST NIGHT THROUGH
THIS MORNING.

&&

.MODEL DISCUSSION...
MODELS ARE IN EXCELLENT AGREEMENT THROUGH MONDAY AFTERNOON. WHILE
THE OVERALL SYNOPTIC AGREEMENT REMAINS VERY GOOD THERE ARE SOME
DETAILS THAT CROP UP THAT WILL MAKE A DIFFERENCE IN THE FORECAST.
THE FIRST INVOLVES A WAVE MOVING OVER KODIAK ISLAND ON MONDAY
NIGHT INTO TUESDAY. THE NAM HAS A SOLUTION THAT IS A BIT STRONGER
THAN OTHER MODELS AND EVEN CLOSES OFF THE LOW CIRCULATION IN
SHELIKOF STRAIT WHICH IS UNLIKELY TO HAPPEN. THE ECMWF SOLUTION OF
AN OPEN WAVE THAT IS NOT AS STRONG IS PREFERRED. THIS SOLUTION IS
WHAT THE GFS AND GEM MODELS ARE ALSO INDICATING AS MOST LIKELY.
THE ECMWF WAS ALSO PREFERRED DURING THAT TIME FRAME DUE TO THE WAY
THE GFS IS CONSOLIDATING THE ENERGY FROM THE BERING SEA LOW INTO
ONE LOW OVER SOUTHWEST ALASKA INSTEAD OF THE PARENT LOW BEING NEAR
NUNIVAK ISLAND WITH THE TRIPLE POINT OVER KODIAK ISLAND. THE PATTERN
SUPPORTS THE PARENT LOW AND TRIPLE POINT SOLUTION SHOWN BY THE
ECMWF NAM AND GEM MODELS. IN SHORT ALL MODELS ARE PERFORMING WELL
THROUGH MONDAY WITH THE ECMWF TAKING CENTER STAGE AFTER THAT.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL WAVE AND ASSOCIATED WEAK SURFACE FRONT WILL SPREAD
LIGHT SNOW OVER THE COOK INLET REGION AND INTO THE MAT-SU TONIGHT.
ANY ACCUMULATION IS EXPECTED TO REMAIN MINIMAL...WITH VALUES
GENERALLY AROUND OR LESS THAN 1 INCH POSSIBLE FOR MOST AREAS AND
SLIGHTLY HIGHER LOCAL AMOUNTS POSSIBLE AT HIGHER ELEVATIONS SUCH
AS ALONG THE ANCHORAGE HILLSIDE. TRANSITORY SHORT WAVE RIDGING
WILL THEN GIVE WAY TO A BRIEF BREAK IN THE WEATHER ON SUNDAY
AFTERNOON BEFORE THE NEXT WAVE APPROACHES ON SUNDAY NIGHT IN DEEP
SOUTHWEST FLOW. THIS WILL YIELD WIDESPREAD PRECIPITATION ACROSS
SOUTHCENTRAL AK...WITH ANY SNOW ACCUMULATION ONCE AGAIN REMAINING
MINIMAL AS TEMPERATURES GRADUALLY WARM AND ALLOW FOR A CHANGEOVER
TO MOSTLY RAIN BY LATE MONDAY.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONTAL SYSTEM OVER SOUTHWEST ALASKA WILL CONTINUE TO WEAKEN
AND SHEAR APART TONIGHT AS THE PARENT LOW IN THE NORTH BERING
PULLS BACK TO THE NORTHWEST AND A SECOND FRONTAL WAVE IN THE
WESTERN BERING TRACKS EAST. SNOW SHOWERS WILL TAPER TO SCATTERED
COVERAGE AND MAINLY BE CONFINED TO EASTERN AREAS NEAR AND ALONG
THE ALASKA RANGE BY EARLY SUNDAY MORNING.

THE LEADING EDGE OF THE NEXT FRONTAL SYSTEM WILL REACH THE
WESTERN COAST EARLY SUNDAY AND SPREAD PRECIPITATION INLAND
THROUGH THE DAY. THIS SYSTEM LOOKS TO BE A BIT WARMER THAN THE
LAST WITH MORE WARM ADVECTION WITH THE INITIAL WARM FRONT SO
EXPECTING TO SEE RAIN MIXING IN MORE QUICKLY WITH THE SNOW AND
OVER A BROADER AREA. PRECIPITATION WILL BECOME MORE SHOWERY BUT
REMAIN UNSETTLED SUNDAY NIGHT AND MONDAY BEFORE A COOLER TROUGH
BEGINS TO SHIFT ONSHORE LATE IN THE DAY MONDAY.

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
MODELS REMAIN IN GOOD AGREEMENT REGARDING THE STRONG LOW ENTERING
THE BERING THIS EVENING. THE LOW WILL CONTINUE TO DEEPEN AND
STRENGTHEN AS IT TRACKS NORTHEAST TOWARDS ST MATTHEW ISLAND
TONIGHT AND SUNDAY WHERE IT WILL BECOME VERTICALLY STACKED WITH
A CLOSED UPPER LOW. DURING THIS TIME PERIOD A RATHER COLD UPPER
LEVEL TROUGH DIGS SOUTH FROM THE KAMCHATKA PENINSULA ACROSS THE
WESTERN ALEUTIANS ROTATING AROUND TO THE SOUTHWEST SIDE OF THE
UPPER LOW. THE VERTICALLY STACKED LOW WILL TRACK EAST TO NUNIVAK
ISLAND THROUGH MONDAY. THE UPPER TROUGH WILL CONTINUE TO SWING
AROUND THE LOW...SWEEPING QUICKLY EAST OVER THE ALEUTIANS AND
ALASKA PENINSULA SUNDAY NIGHT AND MONDAY SPREADING A MUCH COLDER
AIR MASS AND ACCOMPANYING SHOWERS EAST ACROSS THE BERING AND INTO
BRISTOL BAY AND OTHER COASTAL WATERS OF SOUTHWEST ALASKA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...TUE THROUGH FRI)...
SEVERAL WEATHER SYSTEMS WILL IMPACT THE STATE DURING THIS PERIOD.
WE WILL START TUESDAY WITH ONE SURFACE LOW PRESSURE CENTER NEAR
NUNIVAK ISLAND WITH AN ASSOCIATED FRONT DRAPED THROUGH BRISTOL
BAY. AN UPPER LEVEL TROUGH WILL UNDERCUT THIS SYSTEM AS IT
STRETCHES ALONG THE ALEUTIAN RANGE. THIS WILL LEAD TO THE ENERGY
SHIFTING INTO THE SHELIKOF STRAIT AREA AND STARTING TO TREK
TOWARDS COOK INLET. MODELS DIFFER IN HANDLING OF THIS WITH THE
NAM BEING THE MOST AGGRESSIVE CREATING A CLOSED LOW JUST WEST OF
KODIAK ISLAND. THE GLOBAL MODELS WERE MORE MODERATE IN KEEPING
JUST AN OPEN WAVE. THIS FORECAST TRENDED TOWARD THE GLOBAL MODELS
AS THE NAM APPEARS TO STRUGGLE WITH HOW THE ENERGY TRANSFERS AND
THE ASSOCIATED COLD AIR ADVECTION NEEDED FOR SUCH RAPID DEVELOPMENT.
AS THIS SYSTEM APPROACHES SOUTHCENTRAL TUE EXPECT WINDS TO REALLY
RAMP UP IN THE TURNAGAIN ARM...PORTAGE VALLEY...AND TO SOME EXTENT
EVEN IN THE MAT VALLEY AND WEST ANCHORAGE. IT WILL ALSO BRING A
HEALTHY DOSE OF PRECIPITATION TO MANY AREAS...ESPECIALLY ALONG THE
COAST. IT LOOKS LIKE TEMPERATURES WILL BE PLENTY WARM TO KEEP THE
PRECIP ALL RAIN FOR MOST POPULATION CENTERS DURING THE DAY...BUT
WE COULD SEE SOME FLAKES MIX IN ON THE BACKSIDE OF IT AS COLD AIR
STARTS TO GET PULLED IN AND WE LOSE DAYTIME HEATING.

THE PROGRESSIVE PATTERN THEN REPEATS ITSELF WITH A NEW LOW IN THE
WESTERN BERING BY LATE TUE. THIS LOW STARTS TO FALL APART WED AS
IT SWINGS ANOTHER AREA OF PRECIPITATION AND WARMER AIR QUICKLY
THROUGH THE ALEUTIANS. A NEW TRIPLE POINT LOW FORMS ALONG THE
REMNANT BOUNDARY OVER THE CENTRAL BERING AND JUST REINFORCES THE
PRECIPITATION AND GALE FORCE WINDS THROUGH THE PRIBILOFS AND
EASTERN ALEUTIANS. BY WED AFTERNOON THIS BATCH OF PRECIPITATION
REACHES THE WEST COAST AND BRISTOL BAY AREAS AS A MIX OF RAIN AND
SNOW. AS THIS SYSTEM PUSHES INLAND...OUR ATTENTION SHIFTS ONCE
AGAIN TO HOW IT WILL MOVE ACROSS THE MOUNTAINS. OVER THE PAST
COUPLE OF RUNS THE MODELS HAVE BEEN TRYING TO SHOW A FAIRLY STRONG
LOW DEVELOPING OVER THE NW GULF AND DRIFTING TOWARDS THE PRINCE
WILLIAM SOUND LATE THU INTO FRI. MODELS HAVE TRENDED SLIGHTLY
FURTHER SOUTH TODAY...WHICH WOULD PULL THE PRECIPITATION SHIELD
SOUTH OF THE COOK INLET AREA AND MAINLY AFFECT THE COAST. WE WILL
BE WATCHING THIS FEATURE CLOSELY. BOTTOM LINE...EXPECT A MUCH
WETTER AND SOMEWHAT WINDIER PATTERN FOR NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 173 175 176 177.
         GALE WARNING...155 165 170 172 174 178 179 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...MO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
147 AM AKDT SUN APR 05 2015

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

0140 AM     SNOW             2 ESE BIRD POINT RECREA 60.92N 149.27W
04/05/2015  M2.0 INCH        PKZ140             AK   NWS EMPLOYEE

&&

KUTZ

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE ANCHORAGE AK
154 AM AKDT SUN APR 05 2015

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

0140 AM     SNOW             3 WNW GLEN ALPS         61.12N 149.76W
04/05/2015  M2.0 INCH                           AK   NWS EMPLOYEE

            CORRECTED LOCATION

&&

KUTZ