Small Craft Advisory 841, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
542 AM AKDT SUN OCT 25 2015

.ANALYSIS AND UPPER LEVELS...

THE LARGEST FEATURE AFFECTING THE AOR THIS MORNING IS A RAPIDLY
DEEPENING LOW CENTERED SOUTH OF THE EASTERN ALEUTIANS. IR
SATELLITE IMAGERY SHOWS POLAR AIR RAPIDLY PUSHING SOUTHWARD AROUND
THE WEST SIDE OF THE LOW...COINCIDENT WITH A DEEPENING TROUGH OVER
THE CENTRAL ALEUTIANS. EAST OF THE LOW...STRONG SOUTHEASTERLY
WINDS ARE TAPPING ABUNDANT PACIFIC MOISTURE. THE LATEST ASCAT
PASSES INTO THIS REGION OF THE LOW SHOWS A BROAD AREA OF 40-45 KT
WINDS SOUTH OF THE ALASKA PENINSULA ASSOCIATED WITH THE WARM
CONVEYOR BELT WRAPPING AROUND THE EAST AND NORTH SIDES OF THE LOW. THE
BAROCLINICITY BETWEEN THESE TWO AIR MASSES IS ONE OF THE PRIMARY
FACTORS CONTRIBUTING TO THE RAPID INTENSIFICATION OF THE
LOW...IN ADDITION TO VERY STRONG UPPER LEVEL DIVERGENCE ASSOCIATED WITH
A NEGATIVELY-TILTED TROUGH AND ALSO THE LOW DEEPENING IN THE
FAVORABLE LEFT EXIT REGION OF A STRONG 155 KT JET. IT REALLY
SHOULD NOT BE UNDERSTATED...THE FORECAST DEEPENING OF THE LOW IS
EXPECTED TO BE ON THE ORDER OF 30 MB IN 12 HOURS WHICH IS A VERY
IMPRESSIVE RATE OF DEEPENING...CONSIDERING THE DEFINITION OF BOMB
CYCLOGENESIS IS A RATE OF 24 MB IN 24 HOURS.

ACROSS MAINLAND ALASKA...MANY AREAS ARE STILL DEALING WITH THE
REMNANTS OF THE PREVIOUS LOW TO MOVE INTO THE GULF. BY NOW THE LOW
HAS DISSIPATED...WITH REMAINING SCATTERED LIGHT SHOWER ACTIVITY
PRIMARILY BEING DRIVEN BY A WEAKENING UPPER-LEVEL FRONT...MARKING
THE LEADING EDGE OF UPPER LEVEL RIDGING BUILDING NORTHWARD EAST OF
THE ALEUTIAN LOW. THE UPPER LEVEL FRONT IS MOVING NORTHWARD INTO
INTERIOR ALASKA. A MUCH WEAKER LOW CENTERED NEAR NUNIVAK ISLAND IS
ALSO DISSIPATING...THOUGH IS KEEPING CONDITIONS UNSETTLED AROUND
THE KUSKOKWIM DELTA.

WELL OUT WEST...A PAIR OF DEEP LOWS...THE NORTHERN AND STRONGER
NEAR THE SOUTHERN TIP OF THE KAMCHATKA PENINSULA...AND THE
SOUTHERN ONE THE REMNANTS OF TYPHOON CHAMPI...WILL BE WATCHED FOR
FUTURE IMPACTS TO THE WESTERN BERING AND ALEUTIANS IN THE COMING
DAYS.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN VERY GOOD AGREEMENT WITH THE GENERAL LARGE SCALE
SYNOPTIC PATTERN THROUGH TUESDAY OF NEXT WEEK. THEY ARE NOW ALSO
IN VERY GOOD AGREEMENT WITH THE POWERFUL BOMB CYCLONE SOUTH OF THE
ALASKA PENINSULA. HOWEVER...THEY REMAIN IN HORRIFIC AGREEMENT WITH
THE REMNANTS OF FORMER TYPHOON CHAMPI MOVING INTO THE WESTERN
BERING. IN FACT...THE MODEL DIVERGENCE AS CLOSE AS 36 HOURS OUT
IS THE LARGEST I HAVE EVER SEEN...WITH THE 00Z CANADIAN GLOBAL AND
06Z GFS AS FAR AS 900 MILES APART. EVEN 18 HOURS OUT...THE MODELS
DIVERGE DRAMATICALLY AS SOME SOLUTIONS TRY AND PHASE THE TROPICAL
ENERGY WITH THE POWERFUL KAMCHATKA LOW WHILE OTHERS TRACK THE LOW
EAST...EVENTUALLY INTERACTING WITH THE POWERFUL NORTH PACIFIC LOW
WHICH RESULTS IN RAPID WEAKENING OF THE AFOREMENTIONED LOW WELL
BEFORE IT REACHES THE BERING. MOREOVER...NONE OF THE MAJOR
MODELING CENTERS ARE PARTICULARLY CONSISTENT...WITH ALL OF THEM
MAKING LARGE CHANGES RUN BY RUN. AND AS OF 10Z THIS MORNING...THE
SPREAD IN THE MODELS IS NOT YET LARGE ENOUGH TO DETECT A
DIFFERENCE THAT COULD BE USED TO DETERMINE WHICH IS VERIFYING THE
BEST AGAINST SATELLITE OR OBSERVATIONS. THUS...A BLEND TO THE
ECMWF WAS FAVORED...WHICH ONCE AGAIN SHIFTED WESTWARD AND STRONGER
INTO THE BERING AFTER IT HAD DONE THE OPPOSITE ON THE MORNING 12Z
CYCLE. MOREOVER...THE LATEST GFS...NAM...AND 06Z CANADIAN REGIONAL
HAVE ALL ONCE AGAIN SHIFTED DRAMATICALLY WEST AND STRONGER.
FORECAST CONFIDENCE IS VERY HIGH EVERYWHERE EXCEPT THE WESTERN
BERING WHERE CONFIDENCE ON THE TRACK OF CHAMPI IS RATHER LOW. WITH
THAT SAID...THE MAIN IMPACT WILL BE THE DIFFERENCE BETWEEN HIGH
END GALE FORCE WINDS TO MINIMUM HURRICANE FORCE WINDS OVER THE FAR
WESTERN PORTION OF MARINE ZONE 178.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

GENERALLY THE LAST LINGERING SHOWERS ACROSS THE SOUTH CENTRAL
MAINLAND PUSHES EAST TODAY AS A WEAK UPPER RIDGE BUILDS ACROSS THE
MAINLAND. THIS WILL BRING AN END TO SHOWERS AND ALLOW FOR PATCHY
FOG DEVELOPMENT TONIGHT OVER INLAND AREAS. A NORTH ADVANCING
OCCLUDED FRONT...ASSOCIATED WITH A STRONG NORTH PACIFIC LOW...
BRINGS ANOTHER BOUT OF RAIN AND VERY WINDY CONDITIONS TO THE GULF
TONIGHT AND MON. RAIN ASSOCIATED WITH THIS FEATURE SHOULD SPREAD
TO KODIAK BY MON AFTERNOON. THE BRUNT OF THE RAIN THROUGH MON
NIGHT SHOULD REMAIN IN CENTRAL AND WESTERN GULF...THOUGH
INCREASING EASTERLY FLOW WILL BRING INCREASED CHANCES OF RAIN TO
THE EASTERN KENAI PEN MON NIGHT. WIDESPREAD GALES ARE EXPECTED
ALONG AND IN ADVANCE OF THE FRONTAL BOUNDARY AS IT HEADS NORTH
TONIGHT AND MON. BRISK GAP FLOWS ARE ALSO EXPECTED TO DEVELOP
ACROSS THE TURNAGAIN ARM/PORTAGE VALLEY AND MAT VALLEY MON
AFTERNOON AND NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SUN AND
MON)...

THE SOUTHWEST WILL REMAIN RELATIVELY QUIET OVER THE NEXT
COUPLE OF DAYS. AN EXTENSION OF THE RIDGE FROM THE NORTH PACIFIC
IS MOVING THROUGH THIS MORNING AND HELPING TO DRY THINGS OUT SOME
WHILE ALLOWING FOR SOME FOG DEVELOPMENT. TODAY SHOULD BE DRY FOR
MOST AREAS. ENERGY IS BEING CONSOLIDATED SOUTH OF THE ALASKA
PENINSULA AS A STORM-FORCE LOW RAPIDLY INTENSIFIES THERE. THIS
CENTER OF THIS LOW WILL REMAIN WELL SOUTH OF THE AREA BUT IT WILL
SWING SOME RAIN...WARMER AIR...AND GUSTY SOUTHEAST WINDS THROUGH
THE SOUTHWEST. THE FIRST BOUT OF THIS LOOKS TO BE MONDAY MORNING.
BUT EVEN STILL...NONE OF THE PRECIPITATION WILL BE HEAVY AND THE
WARMER AIR WILL KEEP IT ALL RAIN. EAST TO SOUTHEAST WINDS WILL BE
ON THE INCREASE THROUGHOUT BRISTOL BAY MON AS THE OCCLUDED FRONT
SLIDES NORTH AND EAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SUN AND
MON)...

TWO MAJOR LOWS WILL IMPACT THIS AREA OVER THE NEXT 36 HOURS. THE
FIRST IS TAKING SHAPE SOUTH OF COLD BAY THIS MORNING AND IS VERY
IMPRESSIVE ON SATELLITE. SHIP REPORTS HAVE ALREADY COME THROUGH
WITH SUSTAINED 50 KT WINDS ON THE NORTH SIDE OF THE LOW. THERE IS
FAIRLY SOLID MODEL AGREEMENT WITH THIS SYSTEM NOW AND SO
CONFIDENCE CONTINUES TO BE QUITE HIGH. THE WARM OCCLUSION WILL
CAUSE THE RAIN AND WIND TO INCREASE THROUGH THE ALASKA PENINSULA
WHILE A DEFORMATION BAND WILL BRING DETERIORATING CONDITIONS TO
FROM ATKA TO DUTCH HARBOR. DUTCH WILL LIKELY SEE SOME OF THE WORST
OF THIS STORM AS THE NORTHEASTERLY FLOW FAVORS STRONGER
GUSTS...HEAVIER RAIN...AND HIGHER SEAS INTO THE HARBOR. THE LOW
ITSELF WILL BE SLOW TO MOVE TOWARD THE GULF ON MONDAY...SO
CONDITIONS WILL BE SLOW TO IMPROVE.

FURTHER WEST THE THEME IS LOW CONFIDENCE AS MODELS CONTINUE TO BE
VERY ERRATIC. THE GENERAL IDEA IS THAT SOME OF THE REMNANTS OF
FORMER TYPHOON CHAMPI WILL MAKE IT INTO THE VERY WESTERN ALEUTIANS
BY MONDAY AFTERNOON. THIS WILL BRING AN INCREASE IN WINDS AND
PERIODS OF HEAVY RAINFALL. HOWEVER...THERE IS STILL UNCERTAINTY IN
HOW STRONG THESE WINDS WILL BE AND WHERE THE CORE WILL GO.
TYPICALLY THE MODELS WILL BECOME MORE CONSISTENT WITH THEIR
SOLUTION BY THIS POINT...SO THIS MUCH DISPARITY THIS LATE IN THE
GAME IS QUITE UNUSUAL. THIS FORECAST PACKAGE INCREASE THE WINDS
SOME THROUGH THE AREA...BUT DID NOT GO TO HURRICANE FORCE (AS SOME
OF THE LATEST MODELS ARE ADVERTISING). INTERESTED PARTIES SHOULD
KEEP A CLOSE EYE ON THE FORECAST AS IT REMAINS POSSIBLE THAT A
HIGH WIND WARNING WILL BE NEEDED MON. THE OTHER FEATURE OF NOTE IS
HOW MUCH CONVECTION IS FIRING OVER THE NORTHWEST PACIFIC WITH VERY
COLD AIR ALOFT AND PLENTY OF SUB-TROPICAL MOISTURE BEING PULLED
NORTH. WE DID ADD SOME ISOLATED THUNDERSTORMS INTO THE FORECAST
FOR MON AFTERNOON.

&&

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

AS THE DEEP SURFACE LOWS BECOME VERTICALLY STACKED AS THEY
WEAKEN...THE UPPER LEVEL LOWS WILL MERGE INTO A RATHER LARGE
ELONGATED TROUGH STRETCHING FROM SOUTHWEST OF THE FAR WESTERN
ALEUTIANS TO SOUTH OF THE CENTRAL GULF. THIS BROAD TROUGH WILL
ENCOMPASS THE NORTH PACIFIC...ALEUTIANS...ALASKA PENINSULA...SOUTHERN
BERING AND SOUTHWESTERN GULF WITH A VARIETY OF SURFACE LOW CENTERS
SPINNING AROUND WITHIN IT BRINGING GENERALLY WET WEATHER TO THESE
AREAS THROUGH MIDWEEK.

A STRONG RIDGE ALOFT EXTENDING FROM THE WESTERN US THROUGH
BRITISH COLUMBIA...THE YUKON TERRITORY AND INTO INTERIOR ALASKA
WILL HELP KEEP THE MAINLAND PRECIPITATION CONFINED TO SOUTHWEST
ALASKA AND COASTAL PORTIONS OF SOUTH CENTRAL ALASKA TUESDAY AND
TUESDAY NIGHT. THE NEXT SURFACE LOW WILL SPIN UP INTO GULF ON
WEDNESDAY PUSHING A FRONTAL SYSTEM TO THE NORTHERN GULF COAST AND
PRECIPITATION A BIT FURTHER INLAND. A STRONGER RAPIDLY DEEPENING
LOW WILL ENTER THE GULF THURSDAY PUSHING A STRONG FRONTAL SYSTEM
TO GULF COAST THURSDAY NIGHT AND INLAND ON FRIDAY.

NORTH TO NORTHEASTERLY GALES WILL PERSIST OVER THE BERING THROUGH
WEDNESDAY AND THEN WEAKEN AS AN UPPER LEVEL RIDGE BUILD OVER THE
WESTERN ALEUTIANS AND BERING WEDNESDAY NIGHT AND THURSDAY AND THEN
SHIFTS EAST THROUGH THE END OF THE WEEK. THE NEXT STRONG FRONTAL
SYSTEM WILL SWING OFF OF THE KAMCHATKA PENINSULA FRIDAY NIGHT THEN
RAPIDLY SWEEP ACROSS THE ALEUTIANS AND BERING SATURDAY...PUSHING
INTO SOUTHWEST ALASKA ON SUNDAY WITH A FAIR BIT OF COLD AIR
FOLLOWING IN THE ACCOMPANYING UPPER LEVEL TROUGH.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 130 131 132 136 137 138 150 170 171 174 176.
         STORM WARNING 155 172 173 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...JA/JW
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JR