Small Craft Advisory 681, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
457 AM AKDT SAT AUG 29 2015

.ANALYSIS AND UPPER LEVELS...

AN AMPLIFIED UPPER TROUGH OVER THE MAINLAND HAS TWO LOW CENTERS...ONE
AT THE BASE SPINNING OVER THE EASTERN GULF AND THE OTHER IS
SPINNING JUST NORTH OF BARROW. TO THE WEST...A STREAM OF MOISTURE
IS BEING PUMPED NORTH INTO THE BERING BETWEEN THE STRONG RIDGE
CENTERED SOUTH OF THE CENTRAL ALEUTIANS AND A CLOSED LOW SOUTH OF
THE KAMCHATKA PENINSULA. AT THE SURFACE...RAIN CONTINUES TO
DEVELOP ALONG A FRONTAL BOUNDARY THAT IS STRETCHED ALONG THE
NORTHERN WATERS OF THE BERING THROUGH THE SOUTHWEST COAST.
SOUTHCENTRAL AND THE MUCH OF THE GULF STAYED DRY OVERNIGHT WITH
NORTHERLY FLOW BEGINNING TO TAPER OFF THIS MORNING BEHIND THE
FRONT THAT MOVED THROUGH ON FRIDAY.

&&

.MODEL DISCUSSION...

MODELS ARE RELATIVELY IN GOOD AGREEMENT WITH THE SYNOPTIC PATTERN
FOR THE UPCOMING WEEKEND AND THEREFORE ONLY MINOR CHANGES WERE
MADE USING THE HIGHER RESOLUTION MODELS OF THE ECMWF...NAM AND
GEM. THE CHALLENGES FOR THE FORECAST THIS WEEKEND ARE GUSTY WINDS
AND OVERNIGHT LOW TEMPERATURES WHICH ARE DIFFICULT TO RESOLVE
SINCE MODELS HAVE SLIGHT VARIANCES IN THE TIMING OF SHORTWAVES AND
MOISTURE FIELDS. THE OVERALL TREND TODAY IS FOR THE FRONT ACROSS
THE CENTRAL BERING AND SOUTHWEST TO SLIDE SOUTH TO THE SOUTHERN
BERING AND WESTERN GULF AND THEN DISSIPATE THIS AFTERNOON. A COLD
DENSE AIR MASS ACROSS THE BERING STRAIT DIVES SOUTH LATE TODAY
BRINGING GUSTY WINDS BACK ACROSS THE SOUTHERN MAINLAND AND
SURROUNDING WATERS WITH GUSTS CONTINUING THROUGH SUNDAY BEFORE
TAPERING OFF. TO THE WEST...THE RIDGE STARTS TO LOOSE HOLD OVER
THE BERING AS THE ARCTIC LOW AND A LOW NEAR THE WESTERN ALEUTIANS
FORCE A PATTERN CHANGE.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE BIG STORY FOR SOUTHCENTRAL IS THAT THE COOL AND WINDY PATTERN
WILL PERSIST. A SERIES OF UPPER LEVEL SHORT-WAVES DROPPING OUT OF
THE ARCTIC WILL RATCHET WINDS BACK UP AREA-WIDE OVERNIGHT TONIGHT
INTO SUNDAY. WINDS WILL THEN INCREASE FURTHER SUNDAY NIGHT INTO
MONDAY AS AN UPPER LEVEL LOW FORMS AND DROPS THROUGH SOUTHCENTRAL
AND INTO THE GULF. ANOTHER POLAR JET STREAK WILL ENHANCE SUBSIDENCE
HELPING TO MIX DOWN STRONGER WINDS FROM ALOFT DOWN TO THE SURFACE.
THIS UPCOMING WINDSTORM DOES NOT LOOK QUITE AS STRONG AS THE ONE
WHICH JUST OCCURRED (THURSDAY THROUGH FRIDAY)...BUT IT WILL NOT
BE VERY FAR OFF.

A SURFACE LOW MOVING OVER TOP OF THE NORTH PACIFIC/BERING SEA
RIDGE WILL TRACK RIGHT ACROSS KODIAK ISLAND THIS MORNING. WITH
ABUNDANT TROPICAL MOISTURE EXPECT A DECENT RAIN ON THE WEST SIDE
OF THE ISLAND...WITH LOWER AMOUNTS ON THE EAST SIDE DUE TO
WESTERLY FLOW. DRIER CONDITIONS AND STRONG WINDS WILL THEN RETURN
BEHIND THIS. MEANWHILE...THE SHORT-WAVES TRACKING THROUGH
SOUTHCENTRAL THE NEXT COUPLE DAYS WILL ROTATE IN FROM THE WEST AS
THEY MOVE THROUGH. LIFT OUT AHEAD OF THESE COMBINED WITH
INCREASING INSTABILITY AS THE AIR ALOFT PROGRESSIVELY COOLS WILL
LEAD TO SOME SHOWERS...ESPECIALLY ALONG THE MOUNTAINS. SNOW LEVELS
WILL FLUCTUATE BUT WILL SHOW A GENERAL DOWNWARD TREND...SO CHANCES
ARE THE TOPS OF THE MOUNTAINS WILL BE COVERED WITH A LITTLE SNOW
BY EARLY NEXT WEEK.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 THROUGH 3)...
A FRONTAL SYSTEM AND SURFACE LOW TRACKING ALONG THE SOUTHWEST
ALASKA COAST WILL CONTINUE TO BRING RAIN TO MUCH OF SOUTHWEST
ALASKA THIS MORNING. THE SURFACE LOW WILL CROSS OVER THE ALEUTIAN
RANGE LATE MORNING WITH BREEZY NORTHWESTERLY WINDS PUSHING IN
BEHIND IT AND RAIN CHANGING OVER TO SCATTERED SHOWERS. A COLD
UPPER LEVEL LOW OVER INTERIOR ALASKA WITH A SERIES OF SHORTWAVES
SWINGING THROUGH WILL KEEP SOUTHWEST ALASKA WELL SUPPLIED WITH
COOL AIR THROUGH THE WEEKEND AND SCATTERED TO NUMEROUS SHOWERS
ALONG THE MOUNTAINS. SHOWERS IN SOUTHWEST ALASKA WILL TAPER OFF
MONDAY AS AN UPPER LEVEL RIDGE BUILDS OVER THE ALASKA PENINSULA
WHILE AN ALEUTIAN FRONTAL SYSTEM BEGINS TO GRADUALLY PUSH OVER THE
WESTERN PENINSULA MONDAY AND MONDAY NIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 THROUGH 3)...
THE UPPER LEVEL RIDGE OVER THE CENTRAL ALEUTIANS WILL GRADUALLY
FLATTEN AND SINK SOUTH TONIGHT AND SUNDAY ALLOWING THE FRONTAL
SYSTEM IN THE BERING TO SAG SOUTH OVER THE ALEUTIANS. A VERTICALLY
STACKED SURFACE LOW OFF OF THE KAMCHATKA PENINSULA WILL GRADUALLY
DRIFT TOWARDS SHEMYA THROUGH MONDAY. A LOW FROM THE NORTHERN
PACIFIC AND ASSOCIATED FRONTAL SYSTEM WILL LIFT NORTH OVER THE
CENTRAL AND EASTERN ALEUTIANS SUNDAY NIGHT THROUGH MONDAY NIGHT.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...MON THROUGH FRI)...MODELS
ARE IN FAIRLY GOOD AGREEMENT FOR THE EARLY PART OF NEXT WEEK. SO
FOR THE TIME BEING...FORECAST CONFIDENCE IS RELATIVELY HIGH. THE
HIGHLIGHT OF THIS PERIOD WILL BE THE TRANSITION FROM FAIRLY
STRONG...COOL NORTHWEST FLOW THROUGH MUCH OF SOUTH CENTRAL TO A
CALMER AND SLIGHTLY WARMER PATTERN. THE AREA OF THE LOW PRESSURE
IN THE NORTHEAST GULF WILL WORK IN COMBINATION WITH A DEVELOPING
HIGH OVER THE BRISTOL BAY AREA ON MONDAY TO KEEP THE PRESSURE
GRADIENT TIGHT. BUT AS THIS LOW PULLS FURTHER TO THE SOUTH AND
EAST ON TUESDAY...HIGHER PRESSURE WILL BUILD OVER SOUTHWEST
ALASKA. THIS WILL KEEP THINGS DRY ACROSS JUST ABOUT ALL OF THE
SOUTHERN HALF OF THE MAINLAND THROUGH TUESDAY. TEMPERATURES SHOULD
BE ABLE TO REBOUND TO A FEW DEGREES AS WELL WITH THE FLOW BECOMING
MORE WESTERLY AND 850 MB TEMPERATURES CLIMBING 5 TO 6 DEGREES
CELSIUS.

THE MORE ACTIVE WEATHER WILL BE OVER THE BERING SEA TO START THE
WEEK. THE REMNANTS OF TYPHOON ATSANI WILL CONTINUE TO DRIFT OVER
THE FAR WESTERN BERING. WHILE WINDS SHOULD ALL BE BELOW SMALL
CRAFT LEVEL...IT WILL KEEP A CHANCE FOR RAIN IN THE FORECAST. IT
WILL ALSO LEAVE A DECAYING WARM FRONT ALONG THE CENTRAL AND
EASTERN ALEUTIANS. A WEAK WAVE TRIES TO DEVELOP ALONG THIS
BOUNDARY AS WE GET TO WEDNESDAY. THIS IS WHERE MODELS START TO
DIFFER WITH THE GFS BEING RATHER AGGRESSIVE WITH THIS WAVE AND
SWINGING ANOTHER STORM THROUGH THE BERING STRAIT. MEANWHILE...THE
EC IS MUCH WEAKER AND ONLY BRINGS LIGHT RAIN TO THE SOUTHWEST.
BOTH GLOBAL MODELS SHOW SIGNS OF CYCLOGENESIS IN THE GULF BY THE
LATTER HALF OF THE WEEK WHICH WOULD MEAN A RETURN TO COOLER AND
WETTER WEATHER FOR MUCH OF THE MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 130 131 132 136 137 138 150 155 160 165.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...MO

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1235 PM AKDT SAT AUG 29 2015

AKZ152-312045-
LOWER KUSKOKWIM VALLEY-
1235 PM AKDT SAT AUG 29 2015

HEAVY RAINFALL THAT OCCURRED ALONG THE NORTHERN AND WESTERN SLOPES OF THE
ALASKA RANGE EARLIER THIS WEEK HAS PRODUCED A SURGE OF WATER THAT
IS PROGRESSING DOWN THE KUSKOKWIM RIVER. HIGH WATER WAS REPORTED
AT NIKOLAI ON THURSDAY MORNING (8/27). AT MCGRATH...WATER LEVELS
ROSE ALMOST 4 FEET SINCE THURSDAY MORNING AND ARE NOW ABOUT TO
CREST AT 14.50 FT.

THIS SURGE OF WATER IS PROGRESSING DOWNSTREAM AND WILL RESULT IN RISING WATER
ON THE KUSKOKWIM RIVER UPSTREAM OF ANIAK THROUGH MONDAY. AT THIS
TIME THE WATER IS NOT EXPECTED TO REACH FLOOD STAGE AT ANY
LOCATIONS. HOWEVER...THOSE WITH INTERESTS ALONG THE KUSKOKWIM
RIVER SHOULD PREPARE FOR A 1 TO 3 FOOT RISE IN WATER LEVELS OVER
THE NEXT FEW DAYS AND MOVE PERSONAL BELONGINGS AWAY FROM THE
WATERS EDGE.

THIS STATEMENT WILL BE UPDATED AS CONDITIONS WARRANT.

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