Small Craft Advisory 322, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
453 PM AKDT SUN APR 12 2015

.ANALYSIS AND UPPER LEVELS...
AN UPPER LOW WAS EVIDENT OVER THE NORTH AND WEST GULF OF ALASKA WITH
SEVERAL WAVES OBSERVED IN THE BROAD CYCLONIC LOW. A SURFACE CENTER
ASSOCIATED WITH ONE OF THESE WAVES MOVED INLAND OVER THE SOUTHERN
KENAI PENINSULA EARLY THIS AFTERNOON. RAIN AND SNOW SHOWERS WERE
OBSERVED ACROSS THE KENAI AND NORTHERN GULF. CLEARING OVER THE
WESTERN SUSITNA VALLEY THROUGH MID AFTERNOON CAUSED ENOUGH LOW
LEVEL HEATING TO MAKE THE REGION WEST OF THE PARKS HIGHWAY
CONDUCIVE FOR SOME ISOLATED THUNDERSTORMS THROUGH THE EARLY
EVENING.

OUT WEST...BRISK NORTHWESTERLY FLOW CONTINUED ACROSS THE CENTRAL
BERING SEA TO OVER THE EASTERN BERING SEA AND ALASKA PENINSULA.
NUMEROUS SNOW SHOWERS WERE ALSO EVIDENT ACROSS MUCH OF THE AREA. A
DEVELOPING LOW SOUTH OF THE WESTERN ALEUTIANS IS FULLY OCCLUDED
WITH THE FRONTAL BOUNDARY EXTENDING NORTH AND EAST. CURRENT BOUYS
WELL OUTSIDE OF THE SATELLITE BASED CENTER SHOW A MINIMUM PRESSURE
OF 986 MB...SO A MODEL PROJECTION OF 976 MB SEEMS REASONABLE.

&&

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT ON THE KEY FEATURES. THE NAM AND GEM
REGIONAL ARE DOING A FAIRLY GOOD JOB ON THE LOW MOVING NORTH
ACROSS THE COOK INLET REGION THIS EVENING. THE DEVELOPING LOW
CENTER SOUTH OF THE THE WESTERN ALEUTIANS IS ALSO FAIRLY WELL
HANDLED BY THE MODEL SUITE.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
CONVECTIVE SHOWERS OVER THE NORTHERN GULF THIS AFTERNOON HAVE
STARTED TO BECOME BETTER ORGANIZED ALONG A FRONT...AS THE
ASSOCIATED UPPER LEVEL TROUGH ALONG THE GULF COAST LIFTS FURTHER
NORTH THROUGH TONIGHT. SHOWERS WILL PERSIST ALONG COASTAL
LOCATIONS THROUGH THIS EVENING BEFORE TAPERING OFF AFTER
MIDNIGHT...WITH SOME HEAVIER SHOWERS DEVELOPING INLAND OVER THE
KENAI PENINSULA AND ALONG TURNAGAIN ARM EARLY THIS EVENING.
THERE WILL ALSO BE ISOLATED THUNDERSTORMS WEST OF THE PARKS
HIGHWAY THROUGH THE EARLY EVENING HOURS TONIGHT. PRESSURE RISES
BEHIND THIS SYSTEM WILL BEGIN TO INCREASE SOUTHEAST FLOW THROUGH
FAVORED GAPS...INCLUDING DOWN TURNAGAIN ARM AND INTO PORTIONS OF
ANCHORAGE IN THE EVENING. THESE WINDS WILL QUICKLY DIMINISH BY
MORNING AS THE GRADIENT OVER THE AREA WEAKENS. TOMORROW WILL BE
DRIER AND LESS ACTIVE AS A WEAK OFFSHORE PRESSURE GRADIENT
COMBINES WITH WEAK UPPER RIDGING ALOFT...KEEPING MOST SHOWER
ACTIVITY OVER THE MOUNTAINS. IN OTHER WORDS...MOST INLAND
LOCATIONS WILL EXPERIENCE A RATHER PLEASANT SPRING DAY TOMORROW.

BY TUESDAY MORNING AN ALEUTIAN LOW WILL TRACK JUST SOUTH OF THE
ALASKA PENINSULA...WITH AN ASSOCIATED FRONT PUSHING INTO THE
WESTERN GULF. GUSTY WINDS AND MIXED PRECIPITATION WILL BEGIN TO
BUILD BACK INTO THE AREAS SURROUNDING THE GULF TUESDAY AFTERNOON
AS THIS FRONT TRACKS NORTHWARD THROUGH THE GULF. AREAS JUST WEST
OF THE CHUGACH RANGE HOWEVER WILL LIKELY EXPERIENCE
DOWNSLOPING...WITH SOME DECENT CROSS BARRIER FLOW SETTING UP AS
THIS FRONT MOVES INTO THE NORTHERN GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (THROUGH TUESDAY)...
SNOW SHOWERS WILL DEVELOP ONCE AGAIN THIS EVENING FROM NORTHERN
BRISTOL BAY INTO THE KUSKOKWIM DELTA AS AN UPPER LEVEL TROUGH
PASSES TO THE SOUTH AND ENTERS THE GULF. THE HEAVIEST
ACCUMULATIONS SHOULD OCCUR IN NORTHEAST BRISTOL BAY...WHERE MOIST
EASTERLY FLOW ALOFT IS OVERRUNNING WESTERLY UPSLOPE FLOW AT THE
SURFACE. SNOWFALL HOWEVER WAS DECREASED SLIGHTLY WITH THE
AFTERNOON PACKAGE AS WEBCAMS IMAGERY FROM THIS AFTERNOON
INDICATED THE SNOW WAS STRUGGLING TO ACCUMULATE WITH DAYTIME
HEATING...SO MOST OF THE ACCUMULATION WILL LIKELY OCCUR LATE THIS
EVENING AFTER SUNSET. A FEW RESIDUAL SHOWERS WILL LIKELY CONTINUE
OVER EASTERN BRISTOL BAY INTO MONDAY MORNING...BUT WITH RIDGING
BUILDING THESE SHOULD EASILY DIMINISH AND ALLOW TEMPERATURES
THROUGHOUT THE SOUTHWEST MAINLAND TO RETURN TO ABOVE NORMAL UNDER
CLEARING SKIES. ON TUESDAY A NORTH PACIFIC LOW APPROACHING THE
AKPENN WILL BRING A SLIGHT INCREASE IN CLOUD COVER AND EASTERLY
FLOW...BUT OTHERWISE CONDITIONS SHOULD REMAIN DRY AND WARM.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (THROUGH TUESDAY)...
THE NORTH PACIFIC LOW ENTERING THE WESTERN WILL BEGIN TO DOMINATE
THE SHORT TERM WEATHER OVER THE BERING STARTING THIS EVENING. THE
FRONT FROM THIS SYSTEM WILL SPREAD RAIN AND SNOW WITH STRONG
WINDS INTO THE CENTRAL ALEUTIANS STARTING THIS EVENING...BEFORE
SPREADING INTO THE DUTCH HARBOR AREA BY TOMORROW AFTERNOON. THERE
MAY BE SOME LOCALIZED AREAS OF BLOWING SNOW INITIALLY WITH THE
FRONT...BUT WITH TEMPERATURES AT LEAST IN THE MID 30S AND MIXING
WITH RAIN...WIDESPREAD AREAS OF BLOWING SNOW WILL LIKELY HOLD OFF
UNTIL COLDER NORTHWESTERLY WINDS DEVELOP BEHIND THE LOW. THESE
CONDITIONS WILL LIKELY BEGIN NEAR ADAK TOMORROW AFTERNOON AND
THEN SPREAD INTO DUTCH HARBOR OVERNIGHT MONDAY NIGHT. BY TUESDAY
THIS LOW WILL BE CENTERED JUST SOUTH OF THE AKPENN...LEAVING MUCH
OF THE BERING WITH SNOW SHOWERS UNDER DIMINISHING NORTHWESTERLY
FLOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A PROGRESSIVE PATTERN WILL CONTINUE THROUGH THE END OF THE WEEK.
THE MAIN LOW IN THE GULF WILL PUSH INTO THE NORTH GULF COAST
BRINGING RAIN AND SNOW WITH IT INTO FRIDAY. ANOTHER LOW WILL MOVE
INTO THE AREA FROM THE WEST AND THEN TRACK EAST NEAR THE ALEUTIANS
THROUGH THE LATTER PART OF THE WEEK. SOME DISCREPANCIES THEN
DEVELOP WITH THE TRACK OF THIS LOW ON FRIDAY AS THE EC AND GEM
BRING IT INTO THE BERING WHILE THE GFS KEEPS IT SOUTH OF THE
ALEUTIANS. THIS RESULTS IN TIMING DIFFERENCES WITH THE ASSOCIATED
FRONT AND ITS ARRIVAL TO THE SOUTHWEST AND SOUTHCENTRAL WITH THE
GFS BEING BOTH FASTER AND STRONGER WITH THE FRONT.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 132 150 155 170 171 177 178.
 STORM 172-176.
 HEAVY FREEZING SPRAY 180.
FIRE WEATHER...NONE.

&&

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