Small Craft Advisory 738, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
440 PM AKDT MON SEP 21 2015

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH CONTINUES TO SIT OVER MAINLAND ALASKA STRETCHING
DOWN FROM THE ARCTIC INTO THE GULF OF AK. THE MAIN LOW MOVING
THROUGH THIS TROUGH HAS PUSHED TO THE SOUTH OF THE GULF AND NOW
TRACKS TO THE EAST. BEHIND THE LOW COLD AIR HAS BEEN PULLED DOWN
FROM THE NORTH ALONG THE WEST COAST OF THE STATE WHICH ALLOWED FOR
SNOW TO MAKE IT AS FAR SOUTH AS ILIAMNA LAST NIGHT. THE CORE OF
THE JET ALSO RUNS DOWN THE WESTERN SIDE OF THE MAIN TROUGH JUST
OFF THE COASTLINE HELPING TO AID IN THE NORTHERLY FLOW. THIS
STRONG NORTHERLY PUSH HAS BROUGHT IN STRONGER WINDS THROUGH THE
GAPS OF THE ALASKA PENINSULA. FURTHER OUT WEST WARM HIGH PRESSURE
SITS OVER THE WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD SYNOPTIC AGREEMENT IN THE SHORT TERM WHICH
LEADS TO HIGH CONFIDENCE IN THE FORECAST FOR THE MOVEMENT OF MAJOR
FEATURES. THE NAM WAS THE MODEL OF CHOICE FOR ITS BETTER
RESOLUTION FOR MESOSCALE FEATURES.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2...TUE AND
WED)...THE BIG STORY FOR THE NEXT FEW DAYS WILL BE GUSTY OUTFLOW
WINDS. OUR PATTERN HAS FINALLY SHIFTED FROM THE DAYS UPON DAYS OF
WET TO MORE OF A DRY OFFSHORE FLOW. THIS WILL MAKE FOR CLEARING
SKIES AND LIKELY OUR COLDEST OVERNIGHT TEMPERATURES OF THE YEAR
FOR MOST PLACES. BUT WITH A RIDGE BUILDING IN FROM THE WEST...THIS
WILL HELP TO INCREASE THE NORTH TO SOUTH GRADIENT. ALSO...WITH
LONGER AND COLDER NIGHTS...THIS WILL HELP TO BUILD UP SOME COLD
AIR IN THE COPPER RIVER BASIN. AS A FEW WEAK "RIDGE-RIDING"
SHORTWAVES COME OVER THE RIDGE FROM THE ARCTIC...THESE SHOULD
HELP ADD SOME UPPER LEVEL FORCING TO THE PICTURE. SO...ALL THESE
THINGS COMBINED SHOULD MAKE FOR A MODEST EARLY-SEASON OUTFLOW
WIND EVENT. THE STRONGEST WINDS SHOULD BLOW THROUGH THE FAVORED
GAPS...INCLUDING THOMPSON PASS...VALDEZ...AND THE COPPER RIVER
DELTA. WHITTIER AND SEWARD WILL GET IN ON THE ACTION AS WELL...BUT
THE BEST DOWNWARD FORCING WILL BE CENTERED FURTHER TO THE EAST.
THESE WINDS SHOULD START TO INCREASE ON TUESDAY AND PEAK EARLY
WEDNESDAY. AS THE RIDGE BUILDS AND PUSHES FURTHER EAST BY
THU...THIS SHOULD ALLOW THE WINDS TO SLOWLY SUBSIDE. THERE IS SOME
INCREASING UNCERTAINTY IN THE TIMING OF THE END OF THE WINDS THOUGH
AS NEW MODEL RUNS ARE SHOWING MORE ARCTIC ENERGY MAKING IT OVER
THE RIDGE AND POURING THROUGH THOSE GAPS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A COLD UPPER TROUGH WILL CONTINUE TO LINGER OVER THE SOUTHWEST
MAINLAND THROUGH TOMORROW MORNING BEFORE TRACKING EASTWARD OVER
THE GULF. THIS WILL ALLOW FOR RIDGING TO BUILD OVER THE SOUTHWEST
MAINLAND THROUGH WEDNESDAY. SOME LINGERING DAY-TIME INSTABILITY
WILL KEEP ISOLATED SHOWERS IN THE FORECAST OVER THE SOUTHWEST
MAINLAND THROUGH TONIGHT. THE LONE EXCEPTION WILL BE THE
KUSKOKWIM DELTA COAST WHICH WILL SEE SCATTERED SHOWERS AS THIS
NORTHERLY FLOW CONTINUES. GUSTY WINDS MAINLY OVER THE KUSKOKWIM
DELTA AND BRISTOL BAY AREA WILL PERSIST THROUGH TUESDAY
EVENING...WITH GOOD UPPER LEVEL SUPPORT AND A FAIRLY TIGHT
PRESSURE GRADIENT OVER THE AREA. THE NORTHERLY FLOW AHEAD OF THE
RIDGE WILL THEN USHER IN DRIER CONDITIONS OVER MUCH OF THE
SOUTHWEST MAINLAND THROUGH EARLY WEDNESDAY MORNING. AT THAT POINT THE
COLDER AIR ALOFT BEGINS TO MODERATE AS THE UPPER TROUGH EXITS TO
THE EAST AND A WEAK FRONT APPROACHES FROM THE WEST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A COLD UPPER LEVEL TROUGH OVER THE EASTERN BERING AND ALASKA
PENINSULA WILL PUSH FURTHER OVER THE INLAND EARLY THIS
EVENING...WITH AN UPPER LEVEL DISTURBANCE OVER THE EASTERN
ALEUTIANS PROPAGATING THROUGH THE NORTHWESTERLY FLOW AND EXITING
INTO THE NORTHERN PACIFIC TONIGHT. AS THESE SYSTEMS PROGRESS
THROUGH THIS EVENING...GUSTY NORTHERLY WINDS WILL DIMINISH OVER
THE EASTERN ALEUTIANS TONIGHT AS THE BERING SEA RIDGE BUILDS
FURTHER EASTWARD. THE GUSTY NORTHERLY WINDS WILL LINGER OVER THE
FAR EASTERN BERING AND ALASKA PENINSULA THROUGH TUESDAY
EVENING UNTIL WE BEGIN TO LOSE UPPER LEVEL SUPPORT AND THE
GRADIENT OVER THE AREA STARTS TO RELAX WITH THE LOW OVER THE GULF
TRACKING FURTHER EASTWARD. THIS COLD NORTHERLY FLOW REGIME WILL
ALSO PROMOTE INSTABILITY SHOWERS TO DEVELOP OVER THE EASTERN MOST
ALEUTIAN CHAIN...AS THE COLD AIR FLOWS OVER WARM SEA SURFACE
TEMPERATURES. THE NEXT ROUND OF STEADY RAIN WILL ACCOMPANY AN
UPPER LEVEL DISTURBANCE AND FRONT TRACKING THROUGH THE NORTHERN
BERING LATE TUESDAY...BEFORE ROUNDING THE TOP OF THE RIDGE
COVERING MUCH OF THE WESTERN BERING/ALEUTIANS AND DROPPING INTO
THE EASTERN BERING WEDNESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

BEGINNING THE EXTENDED PERIOD WEDNESDAY EVENING...NORTHERLY AND
DRY OFFSHORE FLOW ACROSS ALASKA WILL BEGIN TO GIVE WAY TO MORE
ZONAL FLOW ALOFT AS A SERIES OF JET STREAKS/WAVE DISTURBANCES
ALOFT ORIGINATING FROM RUSSIA MOVE INTO ALASKA. THIS GENERAL
PATTERN REGIME WILL LEAD TO INCREASED CLOUDINESS AND WET
WEATHER...ESPECIALLY ACROSS THE BERING SEA AND WESTERN ALASKA
WEDNESDAY NIGHT INTO THURSDAY. UNFORTUNATELY...THE LOW AMPLITUDE
NATURE OF THE UPPER LEVEL FLOW CONTINUES TO RESULT IN A NOISY
SIGNAL IN TERMS OF SPEED AND STRENGTH OF THESE RUSSIAN WAVE
DISTURBANCES...WHICH EVENTUALLY RESULTS IN LARGER UNCERTAINTY
HEADING INTO LATE WEEK WITH RAIN CHANCES...ESPECIALLY ACROSS
SOUTHCENTRAL. WITH THAT SAID...THE UPPER LEVEL FLOW WILL
EVENTUALLY BECOME MORE SOUTHWESTERLY WITH TIME HEADING INTO THE
LATE WEEKEND...WHICH SHOULD BRING IN A MORE WIDESPREAD SWATH OF
MOISTURE...WITH RAIN BECOMING MORE WIDESPREAD SOMETIME LATE SUNDAY
INTO EARLY NEXT WEEK. THEREAFTER...MUCH UNCERTAINTY DEVELOPS WITH
THE FLOW PATTERN AS THE GLOBAL NUMERICAL GUIDANCE CONTINUES TO
STRUGGLE WITH HOW MUCH TROPICAL ENERGY ASSOCIATED WITH THE
CURRENTLY DEVELOPING TROPICAL STORM MALIA MOVES INTO THE NORTHERN
LATITUDES. CURRENT GUIDANCE IS DEPICTING THE POSSIBILITY OF A
POWERFUL EXTRATROPICAL TRANSITION SOMEWHERE NEAR THE FAR WESTERN
BERING SEA NEXT WEEK...BUT THERE IS VERY HIGH UNCERTAINTY AT THIS
TIME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 127 130 131 150.
FIRE WEATHER...NONE.

&&

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