Small Craft Advisory 565, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM AKDT FRI JUL 18 2008

.ANALYSIS AND UPPER LEVELS...MAJOR UPPER LEVEL CLOSED LOW THAT HAS
BROUGHT RAIN TO MUCH OF THE STATE THE PAST COUPLE DAYS IS SLOWLY
TRANSITIONING EASTWARD FROM SOUTHWEST ALASKA TO SOUTHCENTRAL ALASKA.
THERE ARE MULTIPLE UPPER LEVEL CENTERS AND VORTICITY MAXIMUMS
EMBEDDED WITHIN THE LARGER CYCLONIC CIRCULATION...RESULTING IN SLOW
AND VARIABLE MOVEMENT OF SHOWERS ACROSS MAINLAND ALASKA. THERE ARE
ALSO TWO WEAK SURFACE CENTERS...THE ORIGINAL PARENT LOW OFF THE
KUSKOKWIM DELTA COAST AS WELL AS A REMNANT TRIPLE POINT LOW EAST
OF SEWARD. THESE LOWS ARE BOTH DISSIPATING. RADAR IMAGERY SHOWS
SHOWER ACTIVITY DIMINISHING ACROSS THE SOUTHERN MAINLAND. MUCH OF
SOUTHCENTRAL RECEIVED OVER ONE INCH OF RAIN. THE COMBINATION OF
RAIN AND SNOWMELT HAS RESULTED IN HIGH RUNNING RIVERS AND STREAMS
IN THE WESTERN SUSITNA VALLEY. A FLOOD WARNING HAS BEEN ISSUED FOR
THE YENTNA RIVER AT LONG CREEK AND SURROUNDING TRIBUTARIES. WATER
LEVELS HAVE NEARLY REACHED BANKFULL IN THIS AREA AND WILL CONTINUE
TO CREST THROUGH TONIGHT OR SATURDAY MORNING...RESULTING IN MINOR
FLOODING.

THE UPPER JET IS NEARLY ZONAL...RUNNING ALONG THE ALEUTIANS AND
ACROSS THE SOUTHERN GULF TO SOUTHEAST ALASKA. A WEAK SURFACE LOW
SOUTH OF THE WESTERN ALEUTIANS IS BEING DRIVEN QUICKLY
EASTWARD...JUST BRINING SOME RAIN TO THE ALEUTIANS.

.MODEL DISCUSSION...MODELS INITIALIZED REASONABLY WELL AND ARE
IN GOOD AGREEMENT THROUGH THE WEEKEND. SOLUTIONS HAVE COME INTO
AGREEMENT WITH THE ARCTIC FRONT DROPPING DOWN INTO WESTERN ALASKA
SUNDAY NIGHT AND MONDAY. THERE HAS BEEN A TREND TOWARD A SLOWER
SOLUTION...WHICH THE ECMWF HAS BEEN INDICATING...SO THIS WILL BE
ADOPTED INTO THE FORECAST. THE DETAILS BECOME QUESTIONABLE HEADING
THROUGH THE BEGINNING OF NEXT WEEK DUE TO COMPLEXITIES INHERENT IN
CLOSED UPPER LEVEL LOWS...BUT LARGE SCALE IMPLICATIONS ARE HANDLED
WELL BY THE CURRENT FORECAST.

.SHORT TERM FORECAST...THE UPPER LEVEL LOW COMPLEX WILL MOVE
OVERHEAD OF SOUTHCENTRAL SATURDAY AND THEN CONTINUE EASTWARD INTO
CANADA SUNDAY INTO MONDAY. SHOWERS WILL GRADUALLY END ACROSS
SOUTHWEST ALASKA TONIGHT AND DIMINISH A BIT OVER SOUTHCENTRAL
SATURDAY. SHOWERS WILL GENERALLY BE SLOW MOVING...SO RAINFALL
AMOUNTS WILL BE QUITE VARIABLE. THERE WILL BE LITTLE OR NO BREAK
BEFORE ANOTHER UPPER LEVEL CLOSED LOW DROPS DOWN OUT OF THE
ARCTIC...PUSHING AN ARCTIC FRONT ACROSS SOUTHWEST ALASKA SUNDAY AND
INTO SOUTHCENTRAL MONDAY. SOUTHWEST ALASKA MAY SEE A LITTLE SUN
SATURDAY...BUT SOUTHCENTRAL WILL REMAIN MOSTLY CLOUDY WITH A FEW
SHOWERS UNTIL THE IMPACTS OF THE NEXT SYSTEM ARE FELT SUNDAY NIGHT.
SIMILAR TO THE SYSTEM FROM THE PAST COUPLE DAYS...SIGNIFICANT
RAINFALL CAN BE EXPECTED ONCE AGAIN. WILL HAVE TO KEEP AN EYE ON THE
FLOODING POTENTIAL SINCE SOME RIVERS AND STREAMS ARE NOW RUNNING
HIGH.

HIGH PRESSURE WILL BUILD OVER THE ALEUTIANS SATURDAY AS A WEAK
SURFACE LOW TRACKS AWAY FROM THE AREA. THIS WILL HOLD UNTIL EARLY
NEXT WEEK AS A LOW APPROACHES THE WESTERN ALEUTIANS.

.LONG TERM FORECAST...A MEAN TROUGH WILL REMAIN OVER MAINLAND ALASKA
THROUGH NEXT WEEK...SO COOL AND WET WEATHER WILL PERSIST.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...ASHFALL ADVISORY ZONE 185.
         FLOOD WARNING ZONE 145 FOR YENTNA RIVER AT LAKE CREEK.
MARINE...ASHFALL ADVISORY ZONE 170.
FIRE WEATHER...NONE.

SEB JUL 08