Small Craft Advisory 717, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
410 PM AKDT SAT SEP 12 2015

.ANALYSIS AND UPPER LEVELS...
THE FLOW ALOFT IS WESTERLY WITH AN UPPER LEVEL LOW OVER NORTHERN
ALASKA AND A FLAT RIDGE OVER THE NORTHERN PACIFIC. THERE IS AN
UPPER LEVEL TROUGH ACROSS SOUTH CENTRAL ALASKA MOVING SLOWLY EAST.
A WEAK UPPER LEVEL VORT-MAX IS MOVING INTO THE KUSKOKWIM DELTA.
THERE IS WEAK RIDGING BETWEEN THIS SYSTEM AND A MUCH STRONGER LOW
OVER THE NORTHERN SEA OF OKHOTSK. A FRONT ASSOCIATED WITH THIS LOW
IS OVER THE WESTERN BERING SEA.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT. THEY BEGIN TO
DIFFER ON THE TIMING OF A LOW MOVING ACROSS THE NORTHERN BERING
AT ABOUT 48 HOURS MODEL TIME (EARLY MONDAY MORNING). THE ECMWF AND
CANADIAN MODELS ARE KEEPING A FAIRLY DISTINCT LOW THAT IS OVER
NORTON SOUND 12Z MONDAY. THE GFS SPLITS THE SURFACE LOW...WITH ONE
CENTER NEAR SAINT MATTHEW ISLAND AND THE OTHER NEAR GALENA. THE
NAM HAS THE CENTER TO THE WEST OF SAINT MATTHEW WITH A BROAD
TROUGH STRETCHING INTO WEST CENTRAL ALASKA. THESE ARE NOT HUGE
DIFFERENCES...BUT DO CREATE SOME CHALLENGES. THUS THE FORECAST
CONFIDENCE IS NEAR NORMAL TODAY.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
SHOWER ACTIVITY OVER THE SOUTHCENTRAL WILL CONTINUE TO LIGHTEN UP
AND PUSH OFF TO THE EAST AS THE UPPER LEVEL TROUGH MOVES OUT OF
THE AREA SUNDAY MORNING. THERE WILL THEN BE A BIT OF A BREAK IN
THE RAIN BEFORE THE NEXT FRONT MOVES IN FROM THE WEST BRINGING
RAIN TO AREAS ALL AROUND THE SOUTHCENTRAL BEGINNING SUNDAY
AFTERNOON/EVENING. THE FRONT WILL TRACK FROM WEST TO EAST AND
BRING RAIN TO AREAS AROUND PRINCE WILLIAM SOUND AND THE COPPER
RIVER BASIN SUNDAY NIGHT. WET WESTERLY FLOW WILL CONTINUE BUT
LIGHTEN THROUGH MONDAY. STRONGER WINDS CAN ALSO BE EXPECTED AS THE
FRONT PUSHES THROUGH.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
AN UPPER LEVEL SHORTWAVE CONTINUES TO BRING WIDESPREAD RAIN AND
PATCHY FOG THROUGH THE KUSKOKWIM DELTA BEFORE SPREADING EASTWARD
INTO THE INTERIOR BRISTOL BAY AND LOWER KUSKOKWIM VALLEY LATER
TONIGHT. BY SUNDAY MORNING A WEATHER FRONT WILL MOVE INTO THE
SOUTHWEST COASTLINE FROM THE NORTHERN BERING SEA. THIS WILL BRING
ANOTHER ROUND OF WETTING RAINS THAT WILL SPREAD FROM THE WEST TO
THE EAST THROUGH THE SOUTHWEST ALASKA REGION. THE HEAVIEST
RAINFALL WILL LIKELY BE ALONG THE ALEUTIAN RANGE THROUGH THE
WEEKEND. THIS WILL BE AIDED WITH THE OROGRAPHIC LIFT ALONG THE
ALEUTIAN RANGE AS THE FRONTAL BOUNDARY TRACKS FARTHER EASTWARD
AND ONSHORE WESTERLY FLOW. THE WINDS ALONG THE SOUTHWEST
COASTLINE WILL INCREASE TO WESTERLY GALE FORCE WINDS BY SUNDAY AS
THE WEATHER FRONT MOVES THROUGH THE REGION.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE BERING SEA AND THE ALEUTIAN CHAIN WILL BE UNDER THE INFLUENCE
OF SOUTHWESTERLY TO WESTERLY WINDS AS A FRONT MOVES THROUGH THE
WESTERN TO NORTHERN BERING SEA TONIGHT. THIS WILL BRING GALE FORCE
WINDS THROUGH THE CENTRAL AND SOUTHERN BERING SEA AS THE WEATHER
FRONT MOVES TO THE SOUTHWESTERN COASTLINE BY SUNDAY AFTERNOON. THE
AFOREMENTIONED SYNOPTIC FEATURE WILL BRING PATCHY FOG/STRATUS WITH
STEADY RAIN THROUGH REST OF THE WEEKEND.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AN ARCTIC TROUGH OVER THE NORTHERN MAINLAND EARLY NEXT WEEK WILL
SLOWLY DESCEND TO THE SOUTHERN MAINLAND BY MID WEEK. THIS WILL
DIRECT SHORTWAVES FROM SIBERIA THROUGH THE NORTHERN STREAM AND
INTO THE EASTERN BERING/ALEUTIANS...CREATING A SHOWERY REGIME
UNDER PERSISTENT COLD AIR ADVECTION AND NORTHWESTERLY FLOW. OVER
THE MAINLAND...THE ARCTIC TROUGH WILL REMAIN OVERHEAD INTO THE
END OF NEXT WEEK...PREVENTING ANY SIGNIFICANT SYSTEMS OUT OF THE
AREA...BUT PRODUCING ENOUGH FORCING FOR AT LEAST A CHANCE OF RAIN WITH
LIGHT WINDS. AFTERWARDS THE MODELS STRUGGLE WITH THE EXACT
PLACEMENT OF THE TROUGH...BUT ARE IN GENERAL AGREEMENT WITH A
TROUGH AXIS PERSISTING OVER THE MAINLAND INTO NEXT WEEK. THIS
MEANS THAT THERE DOES NOT APPEAR TO BE A RETURN TO WARM AND SUNNY
WEATHER IN THE NEXT WEEK.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 130 131 150 155 160 165 170 179 180 181
FIRE WEATHER...NONE.

&&

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