Small Craft Advisory 619, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
142 PM AKDT FRI AUG 15 2014

.ANALYSIS AND UPPER LEVELS...

UPPER TROUGH LIFTING NORTH AND NORTHWEST TODAY SHOULD BE OUT OF
THE AREA LATER TONIGHT. SHOWERS WILL BECOME MORE SCATTERED THIS
EVENING AND OVERNIGHT BUT WONT END COMPLETELY ALONG THE NORTH GULF
COAST AND SOUTHEAST COPPER RIVER BASIN, AND, WESTERN SUSITNA
VALLEY. NEXT LOW CENTERED NEAR THE EASTERN ALEUTIANS WILL SPREAD
MORE RAIN IN TONIGHT AND SATURDAY AND THE SURFACE TRACKS NORTHEAST
INTO BRISTOL BAY BY SATURDAY AFTERNOON.

&&

.MODEL DISCUSSION...

THERE IS AGREEMENT THAT THE STACKED CENTRAL ALEUTIAN UPPER AND
SURFACE LOW WILL MOVE TO BRISTOL BAY SAT AFTERNOON AND THEN SLOWLY
WEAKEN OVER SOUTHWEST AK THROUGH SUN. AN ASSOCIATED FRONT WILL
WORK ITS WAY ACROSS THE EASTERN ALEUTIANS AND AKPEN TODAY...ENTER
THE WESTERN GULF TONIGHT...AND REACH THE NORTH GULF COAST SAT
MORNING THROUGH SAT NIGHT. A TRIPLE POINT LOW FORMS OVER THE GULF
AND SLOWS THE NORTHEAST PROGRESSION OF THE FRONT AND PREVENTS IT
FROM MOVING INLAND OVER SOUTHEAST UNTIL LATER ON SUN.

LOW PRESSURE WEAKENS OVER THE MAINLAND WHILE HIGH PRESSURE BUILDS
OVER THE BERING SUN INTO MON. THE GFS THROUGH THE SHORT TERM HAS
PRETTY GOOD RUN TO RUN CONSISTENCY AND GREATER DETAIL THAN THE
EC.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...

RAIN AND SHOWERS CAN BE EXPECTED TODAY WITH SOME BRIEF BREAKS THIS
EVENING. THE NEXT FRONT WILL BRING MORE PRECIPITATION TONIGHT
THROUGH SUN BEFORE TAPERING OFF MON. STRONG WINDS THROUGH
CHANNELED TERRAIN AND GALES OVER THE NORTHERN GULF WILL ACCOMPANY
THE ARRIVAL OF THE FRONT.

SOUTHWEST ALASKA...

SHOWERS ARE EXPECTED AGAIN TODAY WITH SOME ISOLATED AFTERNOON AND
EVENING THUNDERSTORMS MAINLY OVER THE KUSKOKWIM VALLEY AND DELTA. THE
ARRIVAL OF THE CENTRAL ALEUTIAN LOW AND ASSOCIATED FRONT WILL
RETURN PRECIPITATION TO THE REGION LATER TONIGHT INTO SAT...WITH
STRONG WINDS THROUGH CHANNELED TERRAIN. ALTHOUGH WINDS WILL
DIMINISH LATER ON SAT...THE SLOW DECAY OF THE LOW OVER SW AK WILL
KEEP SHOWERS IN THE AREA UNTIL HIGH PRESSURE ARRIVES ON SUN AND
BEGINS TO DRY THE ATMOSPHERE INTO MON.

BERING SEA/ALEUTIANS...

SIGNIFICANT RAIN AND SHOWERS WILL AFFECT THE EASTERN HALF OF THE
REGION AS THE LOW MOVES EAST TODAY. BY SAT MORNING PRECIPITATION
WILL BE REDUCED TO SHOWERS ACROSS THE BERING AND ALEUTIANS AS
HIGH PRESSURE BUILDS INTO MON.

&&

.LONG TERM FORECAST...

THE LONG TERM FORECAST PERIOD IS CHARACTERIZED BY A JET STREAM
THAT IS LARGELY SOUTH OF THE AOR WITH THE ABSENCE OF STRONG
WEATHER FEATURES OVERALL. FLAT/ZONAL FLOW ESTABLISHES ITSELF
ACROSS THE SOUTHERN MAINLAND FOR A TIME WHICH SHOULD LEAD TO SOME
SUNNY BREAKS...BUT ALSO TOUGH TO PINPOINT PERIODS OF RAIN AS
SUBTLE DISTURBANCES TRAVERSE THROUGH THE MID-LVL FLOW. OUT
WEST...AN UPPER TROUGH WILL BE CENTERED OVER THE WESTERN BERING
SEA. MODELS SUGGEST THAT THIS TROUGH WILL BEGIN TO TO DIG A BIT
SOUTHWARDS AND CUT OFF MID TO LATE NEXT WEEK. THIS MAY ALLOW THE
INITIALLY FLAT JET STREAM TO NOSE NORTHWARD AND BECOME MORE
SOUTHWEST TO NORTHEAST ORIENTED TOWARDS THE GULF OR SW MAINLAND.
TO WHAT DEGREE IS STILL VERY UNCERTAIN THOUGH.

THE OPERATIONAL GFS IS ESPECIALLY BULLISH IN BRINGING A BROAD SW
FETCH OF MOISTURE THROUGH SOUTHWEST AND SOUTHCENTRAL AK WITH
WIDESPREAD MODERATE QPF/PRECIPITATION...BUT THIS IS NOT SUPPORTED
SUBSTANTIALLY BY IT'S ENSEMBLE MEMBERS AT THIS JUNCTURE. THAT
SAID...IT IS A PLAUSIBLE SOLUTION GIVEN WE ARE NOW MOVING INTO
THE RAINIER SEASON. THE OPERATIONAL ECMWF IS CONSIDERABLY DRIER
DURING THIS TIME PERIOD... BUT RUN TO RUN CONSISTENCY HAS BEEN
POOR. THUS HAVE KEPT THE FORECAST IN THE LONG TERM PERIOD CLOSE TO
A HEAVY ENSEMBLE BLEND PER WPC GUIDANCE. THIS KEEPS THE SOUTHERN
MAINLAND MOSTLY DRY SAVE FOR PASSING SHOWERS TUE AND WED WHILE
ACKNOWLEDGING THAT FORECAST CONFIDENCE IS LOW. LIGHT PRECIPITATION
WITH TEMPERED WINDS/SEAS EXPECTED FOR THE BERING SEA AND CHAIN
UNDER THE INFLUENCE OF THE WEAK UPPER- LOW. FORECAST CONFIDENCE
OUT WEST IS AVERAGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD ADVISORY...121
MARINE...GALE...119 120 125 129 130 131 132 139 150 160 351 352
FIRE WEATHER...NONE

&&

PERCY/JAM