Small Craft Advisory 326, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
447 PM AKDT MON APR 13 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS A DISSIPATING UPPER LOW ALONG THE NORTHWEST GULF
COAST...WITH WEAK CYCLONIC FLOW OVER MUCH OF SOUTHERN ALASKA. THIS
IS CONTINUING THE TREND OF DIURNALLY ENHANCED SHOWERS OVER SOUTH
CENTRAL ALASKA. THERE IS ANOTHER LOW SOUTH OF THE CENTRAL/EASTERN
ALEUTIANS WHICH IS QUICKLY MOVING EASTWARD. THIS LOW IS VERTICALLY
STACKED. THE LEADING FRONT FROM THIS LOW STRETCHES EASTWARD FROM
ABOUT ATKA...THROUGH DUTCH HARBOR TO THE TIP OF THE ALASKA
PENINSULA...THEN TURNS SOUTHEAST INTO THE NORTH PACIFIC. MOST OF
THE UPPER LEVEL DYNAMICS WITH THIS SYSTEM ARE NEAR THE JET...WHICH
IS JUST SOUTH OF THE AREA.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN VERY GOOD AGREEMENT THROUGH THE SHORT
TERM. THERE IS A FEW DIFFERENCES ON HOW THEY HANDLE THE DIURNAL
CONVECTION...AND PRECIPITATION TYPE FORECASTS ARE A BIT TRICKY.
THIS LOWERS THE FORECAST CONFIDENCE A BIT...BUT IT IS STILL A
LITTLE HIGHER THAN NORMAL FOR THE AFTERNOON FORECAST.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
WEAK DIURNALLY DRIVEN SHOWER ACTIVITY WILL REMAIN LARGELY
CONFINED TO THE MOUNTAINS AND SLOWLY DISSIPATE THROUGH THIS
EVENING WITH THE LOSS OF DAYTIME HEATING...YIELDING MOSTLY CLEAR
SKIES TONIGHT ACROSS MUCH OF SOUTHCENTRAL AK. ATTENTION THEN
TURNS TO THE SEASONABLY STRONG LOW MOVING INTO THE WESTERN GULF OF
AK ON TUESDAY AND THE ACCOMPANYING GALE FORCE FRONT THAT WILL
REACH THE NORTH GULF COAST TUESDAY NIGHT. THIS WILL SPREAD LIGHT
SNOW OVER MUCH OF THE GULF COAST REGION...BEGINNING WITH KODIAK
ISLAND LATE TONIGHT WHERE SOME BLOWING SNOW WILL BE POSSIBLE AT
THE ONSET OF PRECIPITATION BEFORE QUICKLY CHANGING OVER TO RAIN.
PRECIPITATION WILL THEN CONTINUE THROUGH THE MIDDLE OF THE WEEK
ALONG THE GULF COAST WITH SNOW GRADUALLY CHANGING OVER TO RAIN AS
TEMPERATURES WARM. MEANWHILE...INLAND LOCATIONS WILL REMAIN MOSTLY
DRY THROUGH WEDNESDAY AS A RESULT OF STRONG CROSS BARRIER FLOW.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE SOUTHWEST ALASKA REGION WILL CONTINUE WITH OFFSHORE FLOW
RESULTING IN DRIER CONDITIONS EXCEPT FOR AN UPPER LEVEL WEAK
DISTURBANCE OVER THE LOWER KUSKOKWIM VALLEY. THIS FEATURE WILL
BRING SOME ISOLATED SNOW SHOWERS TONIGHT INTO THE AREA. AS THE
FRONTAL BOUNDARY ASSOCIATED WITH THE STORM FORCE NORTH PACIFIC LOW
APPROACHING THE EASTERN ALEUTIANS THIS EVENING...THIS WILL BRING
INCREASING CLOUDS TO THE ALASKA PENINSULA THROUGH TUESDAY. THE
MAJORITY OF THE PRECIPITATION WILL REMAIN ALONG THE ALASKA
PENINSULA AND THE ALEUTIAN RANGE. THIS WILL RESULT IN WARMER
TEMPERATURES TO THE BRISTOL BAY REGION...WITH PRECIPITATION
REMAINING MOSTLY ALL RAIN WITH SOME MIXING OF SNOW AT TIMES. BY
WEDNESDAY THE NORTH PACIFIC LOW WILL BE LOCATED IN THE WESTERN
GULF. THIS WILL PRODUCE SOME WRAP-AROUND MOISTURE ALONG THE ALASKA
PENINSULA AND THE ALEUTIAN RANGE WITH CONTINUED NORTH TO
NORTHWESTERLY WINDS FOR THE SOUTHWEST ALASKA REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE STORM FORCE LOW CONTINUES TO TRACK PARALLEL TO THE ALEUTIANS
AND IS POSITIONED JUST SOUTH ATKA THIS EVENING. THIS SYSTEM WILL
TRACK TO THE EASTERN ALEUTIANS BY TUESDAY MORNING JUST SOUTH OF
THE SHUMAGIN ISLANDS BEFORE TRACKING JUST SOUTH OF KODIAK ISLAND
BY LATE TUESDAY EVENING. AS THIS SYSTEM MOVES ALONG THE CHAIN IT
WILL BRING GUSTY WINDS WITH MOISTURE AND WARMER TEMPERATURES. ON
THE BACKSIDE OF THIS SYSTEM THERE WILL AREAS OF BLOWING SNOW
ASSOCIATED WITH THE NORTHERLY WINDS AND THE COOLER TEMPERATURES.
BY TUESDAY THE MAJORITY OF THE BERING SEA WILL HAVE SCATTERED
PRECIPITATION...EXCEPT FOR NUMEROUS SNOW SHOWERS ALONG THE EASTERN
ALEUTIANS WITH THE CONTINUED NORTHERLY WINDS. BY WEDNESDAY THE
CENTRAL BERING SEA WILL HAVE A RIDGE OF HIGH PRESSURE BUILDING
INTO THE AREA...WHILE UPSTREAM ANOTHER NORTH PACIFIC LOW TRACKS
SOUTH OF THE WESTERN ALEUTIANS NEAR SHEMYA.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THERE IS GOOD AGREEMENT IN THE MID TERM WITH A WEAKENING LOW IN
THE NORTHERN GULF MOVING NORTHWEST THROUGH COOK INLET AND INTO THE
ALASKA RANGE ON THURSDAY. THIS WILL BRING A RAIN AND SNOW MIX TO
MUCH OF THE SOUTHCENTRAL. THE MAJOR FEATURE MOVING INTO THE
WEEKEND IS A LOW TRACKING TO THE SOUTH OF THE ALEUTIANS FROM THE
WEST. THERE IS GOOD AGREEMENT WITH ITS EASTERLY TRACK BUT WHEN IT
STARTS TO MOVE NORTH FRIDAY NIGHT SOME DISCREPANCIES ARISE.

THE EC AND ITS ENSEMBLE MOVE THE LOW ALONG THE WEST COAST OF THE
STATE WHILE THE GFS...ITS ENSEMBLE AND THE GEM HAVE A MORE
EASTERLY SOLUTION OVER MAINLAND ALASKA. BECAUSE OF GOOD AGREEMENT
WITH STRONG RIDGING BUILDING IN OVER THE EASTERN PART OF THE STATE
THE MORE WESTERLY TRACK OF THE EC WAS PREFERRED. THE DIFFERENCES
IN THE POSITIONING OF THIS LOW AND ITS ASSOCIATED FRONT WILL
IMPACT THE TIMING OF THE FRONTS ARRIVAL TO THE SOUTHCENTRAL LATE
FRIDAY.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 130-139 150-176 180.
         HEAVY FREEZING SPRAY 179 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DK