Small Craft Advisory 842, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

TWO MAIN ISSUES ARE OF CONCERN TODAY FOR THE AREA. FIRST IS THE
STRONG STORM FORCE LOW JUST SOUTH OF UNALASKA AND THE ALASKA
PENINSULA. THE OTHER BIG ISSUE IS THE REMNANTS OF CHAMPI THAT IS
SOUTH OF THE WESTERN ALEUTIANS. THE MODELS HAVE A GOOD HANDLE ON
THE STORM JUST SOUTH OF THE ALASKA PENINSULA. EXPECT THIS LOW TO
MOVE EAST SOUTHEAST TO SOUTH OF KODIAK WHILE THE ASSOCIATED FRONT
ELONGATES AND WEAKEN ACROSS THE WESTERN GULF OF ALASKA THROUGH
KODIAK ISLAND. A SECOND LOW WILL FORM IN THE VICINITY OF THE
EASTERN ALEUTIANS MON NIGHT TO TUESDAY MORNING AND BECOME THE
MAIN CENTER THEREAFTER. THE OVERALL IMPACT TO THE MAINLAND IS
BROAD SOUTHERLY FLOW OVER SOUTHWEST ALASKA AND OVER THE RIDGE
ACROSS SOUTH CENTRAL ALASKA HOLDING THE REGION UNDER THE WORMER
CLOUDIER CONDITIONS FOR THE NEXT FEW DAYS.

THE REMNANTS OF CHAMPI ARE MORE PROBLEMATIC AS THE MODELS
CONTINUE TO STRUGGLE TO CONVERGE ON A SOLUTION EVEN IN THE NEXT 24
HOURS. SATELLITE IMAGERY ALONG WITH SHIP OBSERVATIONS TEND TO
SUPPORT THE ECMWF SOLUTION OF A STRONG LOW MOVING TOWARD THE
CENTRAL ALEUTIANS. THE LATEST ECMWF RUN RAPIDLY WEAKENS THIS LOW.
THE LATEST DETERMINISTIC GFS AND THE GFS ENSEMBLE MEAN HAVE COME
INTO AGREEMENT AND ARE BRINGING A STRONG STORM TO THE WESTERN
ALEUTIANS THEN RAPIDLY MERGING THIS STORM CENTER INTO THE MAIN LOW
CENTER SOUTHWEST OF THE WESTERN ALEUTIANS. THIS IS A HUGE AMOUNT
OF UNCERTAINTY FOR THE NEXT 24 TO 36 HOURS HOWEVER SINCE THE GFS
SEEMS TO BE WELL OFF THE MARK WE ARE MAKING SIGNIFICANT CHANGES TO
THE FORECAST FOR THE CENTRAL AND WESTERN ALEUTIANS TONIGHT AND
MONDAY TO ACCOUNT FOR THIS.

&&

.MODEL DISCUSSION...

THE MODELS AS STATED EARLIER ARE IN GOOD AGREEMENT WITH RESPECT TO
THE STORM SOUTH OF THE ALASKA PENINSULA AND EASTERN ALEUTIANS.
HOWEVER, THEY ARE HAVING GREAT DIFFICULTY RESOLVING HOW TO HANDLE
THE REMNANTS OF CHAMPI. THE DIFFERENCE IS NOTABLE WITHIN THE FIRST
24 HOURS RESULTING IN SOLUTIONS THAT DIVERGE BY 300 TO 500 NM AND
OVER 25 MB.

&&

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

GENERALLY CLEAR SKIES COVER SOUTHCENTRAL ALASKA THIS
EVENING...WITH HIGH PRESSURE IN PLACE OVER THE MAINLAND. THIS HIGH
PRESSURE SYSTEM WILL SUPPORT LIGHT DRAINAGE WINDS THROUGH LOCAL
GAPS...AND LOCAL PATCHY FOG IS POSSIBLE OVERNIGHT. INCREASING
CLOUDS ARE EXPECTED FOR SOUTHERN PORTIONS OF THE REGION AS A FRONT
SLOWLY DRIFTS NORTHWARD TOWARDS THE GULF OF ALASKA COAST MONDAY
INTO TUESDAY. IT IS NOT EXPECTED TO BE AN INTENSE FRONT...BUT
LOCALLY HEAVY RAIN COULD OCCUR ON KODIAK ISLAND MONDAY NIGHT.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE REGION WILL COME UNDER THE INFLUENCE OF THE LARGE LOW SOUTH
OF THE ALASKA PENINSULA OVER THE NEXT TWO DAYS WITH AN INCREASE IN
RAIN CHANCES AND WIND OVER THE REGION. OVERNIGHT...RAINFALL WILL
MAINLY BE LIMITED TO SHOWERS OVER THE SOUTHWEST COAST AS THE
REMNANTS OF THE PREVIOUS FRONT NOW LOCATED OVER THE EASTERN
BERING SEA SERVES AS A FOCUS FOR RAINFALL. AS THE FRONT ASSOCIATED
WITH THE LOW MOVES NORTHWARD MONDAY INTO TUESDAY...PRECIPITATION
COVERAGE WILL INCREASE OVER MUCH OF THE REGION WITH THE BEST
CHANCES FOR PRECIPITATION OVER THE SOUTHWEST COAST AND THE
BRISTOL BAY REGION WITH ONLY SCATTERED SHOWERS IN THE INLAND
AREAS. WINDS WILL BE ON THE INCREASE MONDAY EVENING ALONG THE
ALEUTIAN RANGE AND THE BRISTOL BAY COAST AS THE LOW BEGINS TO MOVE
NORTHWARD AND WEAKEN.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE 12Z MODEL RUNS WERE ONCE AGAIN SHIFTING FROM THEIR 00Z
RUNS WITH A WIDE SPREAD OF SOLUTIONS FOR THE INTERACTION AND
DEVELOPMENT OF EX-TYPHOON CHAMPI AND THE LOW NEAR KAMCHATKA. BASED
ON SATELLITE TRENDS THROUGH THIS MORNING...THE MORE EASTERN
SOLUTION OF THE EC/CANADIAN MODELS WERE CHOSEN FOR THE BASIS OF
THIS FORECAST PACKAGE FOR THE BERING SEA AND ALEUTIAN CHAIN. FROM
DUTCH HARBOR EASTWARD...MODELS WERE IN EXCELLENT AGREEMENT AND
THE FORECAST WAS CHANGED LITTLE IN THE SHORT TERM WITH THE LARGE
LOW SOUTH OF COLD BAY BEING THE OVERWHELMINGLY DOMINATE WEATHER
MAKER. WINDS AND SEAS WILL CONTINUE TO BE HIGH THIS EVENING WITH
STORM FORCE WINDS EXPECTED IN MARINE AREAS SOUTH OF THE ALASKA
PENINSULA TONIGHT. THESE WINDS ARE EXPECTED TO DECREASE OVERNIGHT
TO BELOW GALE FORCE BY TOMORROW AFTERNOON AS THE LOW BEGINS TO
WEAKEN.

OUT WEST...GALE FORCE WINDS ARE EXPECTED TO REMAIN OVER THE
WESTERN ALEUTIANS THROUGH TOMORROW ALONG THE STALLED FRONTAL
BOUNDARY. THE REMNANTS OF TYPHOON CHAMPI ARE EXPECTED TO MOVE TO
JUST SOUTHWEST OF ADAK BY TOMORROW AFTERNOON BRINGING A SMALL
SWATH OF GALE FORCE WINDS NEAR THE LOW CENTER. AS THE LOW MOVES TO
THE EAST AND HIGH PRESSURE SETS UP OVER THE WESTERN BERING
SEA...NORTHEASTERLY FLOW WILL DEVELOP BY MONDAY NIGHT...BRINGING A
LARGE AREA OF GALE TO NEAR STORM FORCE WINDS TO THE CENTRAL AND
WESTERN BERING SEA THROUGH TUESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE UPPER LEVEL LOWS CURRENTLY OVER THE NORTH PACIFIC AND JUST
SOUTH OF THE KAMCHATKA PENINSULA 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 MUCH OF THE 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 MIDWEEK. MODELS REMAIN IN
PRETTY GOOD AGREEMENT WITH A STRONG RIDGE ALOFT EXTENDING FROM THE
WESTERN US THROUGH BRITISH COLUMBIA...THE YUKON TERRITORY AND INTO
INTERIOR ALASKA. BY THE END OF THE WEEK...MODELS STRUGGLE WITH
TRACKING A SURFACE LOW MOVING FROM THE NORTH PACIFIC INTO THE
GULF. WPC WAS THE PREFERRED SOLUTION FOR THIS PART OF THE FORECAST
PACKAGE GIVEN THE DIFFERENCES IN THE MODELS AND THE WPC SOLUTION
TAKING MORE OF A MIDDLE GROUND.

NORTH TO NORTHEASTERLY GALES WILL PERSIST OVER THE BERING THROUGH
THURSDAY...THEN WEAKEN AS AN UPPER LEVEL RIDGE BUILD OVER MUCH OF
THE BERING AND ALEUTIAN CHAIN BY FRIDAY MORNING. 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...STORM WARNING 150 155 172.
 GALE WARNING 130 131 132 136 137 138 170 171 173 174 177 178 179
   180 185.

&&

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