Small Craft Advisory 836, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
431 PM AKDT FRI OCT 23 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW CENTERED OVER THE SOUTHEASTERN BERING
SEA. AN ASSOCIATED FRONT IS OVER THE NORTHERN GULF AND IS IN THE
PROCESS OF INTENSIFYING. THERE IS ANOTHER UPPER LOW TO THE WEST OF
THE WESTERN ALEUTIANS WHICH IS RAPIDLY MOVING EASTWARD. THIS
SYSTEM IS ASSOCIATED WITH THE POLAR JET. A SYSTEM THAT CONTAINS
THE REMNANTS OF A FORMER TROPICAL DEPRESSION IS SITUATED WELL
SOUTH OF THE CENTRAL ALEUTIANS...AND IS ASSOCIATED WITH THE
SUBTROPICAL JET. THE POLAR AND SUBTROPICAL JET STREAMS ARE RUNNING
PARALLEL WITH THE POLAR JET JUST SOUTH OF THE ALEUTIANS AND THE
SUBTROPICAL JET JUST SOUTH OF 40 DEGREES NORTH LATITUDE. THESE
JETS ARE CLOSE ENOUGH FOR INTERACTION BETWEEN THEM.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM
PORTION OF THE FORECAST...WITH SOME DIFFERENCES DEVELOPING BY SUNDAY
AFTERNOON. THERE ARE TWO FAIRLY STRONG LOWS ON SUNDAY FOR WHICH
THE MODELS BEGIN TO DIFFER IN THEIR SOLUTIONS. ONE WILL BE WELL
SOUTH OF THE ALASKA PENINSULA AND THE OTHER WELL SOUTH OF THE
WESTERN ALEUTIANS. THE PRACTICAL (ACTUAL WEATHER) IMPACTS OF
THESE DIFFERENCES ARE MINOR...AND ONLY BEGIN TO BRING UNCERTAINTY
INTO THE FORECAST FOR THE LONG TERM PORTION OF THE FORECAST.
FORECAST CONFIDENCE IS THUS ABOVE NORMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A FRONT ACROSS THE GULF OF ALASKA IS ALREADY BEGINNING TO IMPACT
SOUTHERN PORTIONS OF THE SOUTHCENTRAL MAINLAND THIS AFTERNOON.
GUSTY WINDS ARE EXPECTED OUT OF MANY OF THE COASTAL GAPS LATE THIS
EVENING INTO SATURDAY AFTERNOON AS THE FRONT PUSHES NORTHWARD. IN
ADDITION...MODERATE TO HEAVY RAIN IS EXPECTED TO SPREAD NORTHWARD
FROM THE KENAI PENINSULA THIS EVENING. HOWEVER...STRONG DOWNSLOPE
WINDS SHOULD RESULT IN LOWER RAINFALL IN ANCHORAGE AND THE WESTERN
KENAI PENINSULA UNTIL SATURDAY AFTERNOON.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONTAL SYSTEM THAT HAD BEEN OVER THE BERING SEA IS NOW MOVING
THROUGH BRISTOL BAY...WHICH WILL BRING RAIN SHOWERS AND GUSTY
EASTERLY WINDS (ESPECIALLY ALONG THE ALEUTIAN RANGE) THROUGH
TONIGHT. THIS FRONT WILL THEN SPREAD INTO THE KUSKOKWIM
VALLEY/DELTA BY LATE TONIGHT BRINGING WIDESPREAD RAIN TO THOSE
AREAS. THIS RAIN MAY ALSO BEGIN TO MIX WITH SNOW OVERNIGHT IN
INTERIOR LOCATIONS...HOWEVER WITH OVERNIGHT LOW TEMPERATURES
EXPECTED AT OR SLIGHTLY ABOVE FREEZING ANY ACCUMULATIONS WILL BE MINOR.
RAIN SHOWERS WILL THEN PERSIST THROUGHOUT THE AREA ON SATURDAY
BEHIND THE FRONT AS AN UPPER LEVEL LOW REMAINS OVER THE EASTERN
BERING...PROVING A SERIES OF SHORTWAVES THAT WILL MOVE OVER THE
AREA WITH MOIST ONSHORE FLOW. THIS ONSHORE FLOW WILL ALSO LIKELY
BRING PATCHY FOG INTO THE AREA FOR SATURDAY NIGHT/SUNDAY
MORNING...ESPECIALLY ALONG THE BRISTOL BAY COAST. SKIES AND
PRECIPITATION WILL THEN BEGIN TO CLEAR ON SUNDAY AS WEAK RIDGING
MOVES OVERHEAD...PROVING MOST AREAS WITH PARTLY CLOUDY
SKIES...LIGHT WINDS...AND SEASONABLE TEMPERATURES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A WEAKENING GALE FORCE LOW OVER THE EASTERN BERING WILL CONTINUE
TO MOVE TOWARDS THE KUSKOKWIM DELTA COAST BY SATURDAY
MORNING...WHICH WILL ALLOW FOR GUSTY NORTHWESTERLY WINDS AND RAIN
SHOWERS FROM THE PRIBILOFS INTO THE EASTERN ALEUTIANS TO DIMINISH.
AS THIS LOW DISSIPATES...A NEW AND MUCH DEEPER LOW WILL APPROACH
THE AKPEN BY SATURDAY NIGHT...HOWEVER THERE IS NOW GOOD CONFIDENCE
THAT THIS LOW WILL REMAIN WELL SOUTH OF THE CHAIN. AS A RESULT THE
ONLY IMPACTS EXPECTED FROM THIS SYSTEM ARE STRONG WINDS AND RAIN
TO THE EASTERN ALEUTIAN/AKPEN FROM SATURDAY NIGHT INTO SUNDAY.

OVER THE WESTERN BERING...A COLD UPPER LEVEL LOW WILL CONTINUE TO
BRING RAIN SHOWERS...MAINLY TO AREAS WEST OF THE DATELINE. THERE
IS ENOUGH COLD AIR ALOFT ASSOCIATED WITH THIS SYSTEM THIS
AFTERNOON TO CREATE A FEW LIGHTNING STRIKES WEST OF SHEMYA WHICH
WILL MOVE EASTWARD AND MAY GIVE A FEW ISOLATED LIGHTNING STRIKES
TO THE WESTERN BERING/ALEUTIANS THIS EVENING. SHOWERS OVER THE
AREA WILL THEN DIMINISH SATURDAY AS WEAK RIDGING APPROACHES...GIVING
CLEARING SKIES AND LIGHT WINDS TO THE AREA FOR SUNDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
A DEEP LOW PRESSURE SYSTEM CONTAINING REMNANT TROPICAL MOISTURE
WILL BE CENTERED AROUND 45N BY SUNDAY AFTERNOON...AND SLOWLY
WEAKEN AS IT TRACKS EASTWARD TOWARD THE SOUTHWESTERN COAST OF
BRITISH COLUMBIA. THE ASSOCIATED FRONTAL SYSTEM WILL REMAIN
MAINLY SOUTH OF THE FORECAST AREA BUT BRUSH CLOSE ENOUGH TO SPREAD
SOME RAIN AND GUSTY WINDS TO THE ALASKA PENINSULA AND EASTERN
ALEUTIANS...AS WELL AS THE COASTAL WATERS SOUTH OF THESE
AREAS. IN RESPONSE TO THIS DEEP LOW...A RIDGE OF HIGH PRESSURE
WILL AMPLIFY OVER THE CENTRAL AND EASTERN GULF SUNDAY THEN BUILD
NORTH INTO SOUTH CENTRAL ALASKA BY MONDAY MORNING...TAPERING OFF
ANY LINGERING SHOWERS IN THAT AREA. THE NEXT STRONG FRONTAL SYSTEM
WILL PUSH INTO THE WESTERN ALEUTIANS SUNDAY AFTERNOON AND BRING
THE POTENTIAL FOR STORM FORCE WINDS AS IT SWINGS THROUGH SUNDAY
NIGHT INTO MONDAY MORNING.

THE REMNANTS OF TYPHOON CHAMPI WILL MERGE WITH A LARGE LOW NEAR
THE SOUTHERN TIP OF KAMCHATKA ON MONDAY...AND SLOWLY PROGRESS
EASTWARD JUST SOUTH OF THE WESTERN ALEUTIANS BY TUESDAY MORNING.
MODELS ARE STILL STRUGGLING WITH THE DETAILS OF THESE SYSTEMS.
REGARDLESS OF HOW THE MODELS RESOLVE THESE LOWS...THEY WILL LIKELY
BRING RAINFALL AND STRONG WINDS TO THE WESTERN ALEUTIANS AND
WESTERN BERING SEA EARLY NEXT WEEK. IT IS LIKELY THAT THE CHAMPI
REMNANTS WILL QUICKLY WEAKEN INTO A LARGE ELONGATED UPPER LEVEL
TROUGH SOUTH OF THE ALASKA PENINSULA BY MID WEEK. FRONTAL WAVES
WILL BEGIN SWINGING FURTHER NORTH INTO THE WESTERN GULF BRINGING
RAINY AND WINDY CONDITIONS TO COASTAL AREAS TUESDAY AND THEN
SPREADING PRECIPITATION FURTHER INLAND WEDNESDAY. BY THURSDAY AND
INTO FRIDAY...A LARGE UPPER LEVEL LOW WILL MIGRATE INTO THE GULF
OF ALASKA WITH A COLD UPPER TROUGH SETTLING OVER NORTHERN AND
INTERIOR ALASKA...BRINGING ANOTHER ROUND OF WET AND WINDY WEATHER
TO PARTS OF SOUTHCENTRAL. CONFIDENCE IN THIS FEATURE REMAINS BELOW
AVERAGE DUE TO MODEL DIFFERENCES REGARDING THE PLACEMENT OF THE
SYSTEM IN THE GULF.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 119 120 125 130 131 139 155 172 174.

&&

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