Small Craft Advisory 788, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
2 PM AKST THU DEC 1 2011

.SHORT TERM...SATELLITE IMAGERY THIS AFTERNOON SHOWING A FRONTAL
BAND ASSOCIATED WITH A LOW PRESSURE SYSTEM IN THE YUKON EXITING THE
REGION. THIS FRONT BROUGHT A MIX OF RAIN AND SNOW TO THE REGION
EVEN WITH DEW POINT TEMPERATURES IN THE MID 30S. WITH FRONTAL
PASSAGE PRECIP SWITCHED OVER THE RAIN...WITH THE EXCEPTION OF
HYDER. HEAVY SNOW IN HYDER WITH LAST REPORT OF 8 INCHES IN ABOUT 5
HOURS. PRECIP HAS TAPERED OFF BECOMING SCATTERED SHOWERS WHICH
WILL LAST OVER NIGHT. SHOULD SEE A MIX OF RAIN AND SNOW LATE
TONIGHT AND IN THE MORNING. NOW EXPECTING MUCH ACCUMULATION WITH
THE WARMER TEMPERATURES AND 1000MB-500MB THICKNESS NEARING
540...LESS THAN 1 INCH OF SNOW IN MOST PLACES WITH UP TO 2 INCHES
POSSIBLE. WINDS ALSO HAVE DIMINISHED SIGNIFICANTLY WITH THE
PASSING FRONT. THESE WESTERLY WINDS WILL BEGIN TO SHIFT TO THE
EAST OVERNIGHT AND INTO FRIDAY AFTERNOON AS RIDGE OF HIGH PRESSURE
CURRENTLY IN THE CENTRAL GULF CONTINUES ITS TRACK EAST MOVING OVER
THE PANHANDLE EARLY FRIDAY.

NEXT FRONTAL BAND MOVING INTO THE NORTHEAST GULF LATE TONIGHT IS
ASSOCIATED WITH SHORTWAVE TROUGH EXTENDING FROM A PARENT LOW IN
THE AK INTERIOR. THIS BAN WILL ENTER THE NORTHWEST PANHANDLE
TONIGHT MOVING SOUTH ACROSS THE ENTIRE REGION THROUGH FRIDAY.
EXPECTING MOSTLY RAIN FROM THIS SYSTEM WITH A MIX OF MORNING SNOW
OF AREAS NORTH OF SUMNER STRAIT. NO SIGNIFICANT QPF VALUES
EXPECTED THEREFORE NO HEAVY RAIN.

RIVER LEVELS DID RISE THROUGH THE DAY WITH SOME NEARING ACTION
STAGE BUT THEN SHOWING A DECREASING TREND AS PRECIP SUBSIDED
THROUGH THE DAY. NOT EXPECTING ANY OTHER SIGNIFICANT HYDRO ISSUES
BUT WILL CONTINUE TO SEE PONDING OF WATER ON ROADS AND IN PARKING
LOTS DUE TO ADDITIONAL RAIN AND SNOW MELT.

MODELS WERE IN GOOD AGREEMENT THIS MORNING WITH SOME SLIGHT
VARIATIONS. KEPT WITH A BLEND OF NAM/EC WITH INHERITED GRIDS WITH
OVERALL CHANGES BEING MINOR. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...
DEEP COLD MAJOR UPR LOW OVR SW BERING SEA THIS MORNING WITH A
RAPIDLY MOVING SHORT WAVE ALOFT MOVING ACROSS THE PANHANDLE. THIS
SETS UP A FLAT UPR RIDGE ALONG 140W AS PER ALL 01/12Z OPS MODELS AT
THE FRI AFTERNOON TRANSITION TO LONG TERM. NOTE THAT AN UPR LOW
CENTER DEVELOPS AROUND 35N 160W 00Z SAT WHICH THE MODELS HAVE BEEN
SAYING FOR DAYS. THIS FEATURE IS IMPORTANT IN THAT AS IT DEVELOPS
IT WILL DELAY THE UPPER RIDGE TO KICK OUT WHICH WILL MAKE FRI NITE
AND SAT MUCH LESS CHANCE OF PRECIP & A LITTLE COOLER. THIS SAME
FEATURE KICKS OUT LATE SAT FOR SOME PRECIP ON SUN WHILE MOVING THE
UPR RIDGE EAST. ALL OPS MODELS...ENSEMBLE MEANS AND EARLIER HPC
PROGS AGREE ON THIS SCENARIO.

ON MON ALL SE GETS A FETCH OF STRONG SW FLOW ALOFT FOR PRECIP AND
WIND...THEN THE PATTERN CHANGE PREVIOUSLY ADVERTISED BEGINS. EXPECT
ARCTIC HIGH PRESSURE TO BUILD TUE WED THU OF NEXT WEEK FOR STRONG
LOW LEVEL NORTHERLIES...DRY...VERY COLD TEMPERATURES...AND CLEAR
SKIES.

USED 01/12Z AK-GFS-40 FOR MOST OF THIS FORECAST WHICH WAS PREFERRED
IN THAT IT WAS SLOWER AND HAS A BETTER BLOCK THAN THE 01/00Z ECMWF.
HPC USED 12Z WED AND BEYOND DUE TO BLOCK HOLDING BETTER THAN GFS.
HPC USED 01/12Z ECMWF. TIMING IN THE PROGRESSION THRU SUN NIGHT CAN
ONLY BE MODERATE WITH RAPID MOVING SYSTEMS...BUT HAVE A STRONG
FEELING THAT A BLOCK WILL OCCUR NEXT WEEK AS PER HPC.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY TIL 4PM AKST THIS AFTERNOON
         AKZ029.
MARINE...GALE WARNING PKZ022.
         SMCR PKZ011>013-021-031>033-035-036-041>043-051-052.

&&

PRB / JC