Small Craft Advisory 488, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1130 AM AKDT THU OCT 2 2008

.SHORT RANGE....SATELLITE IMAGERY THIS MORNING REVEALS A LARGE
MID LEVEL BAROCLINIC ZONE FROM THE CHARLOTTES EXTENDING NORTHWARD
ACROSS THE PANHANDLE WITH A DEEPENING 983 MB SURFACE LOW NOW NEAR
52N 134W. THE MIDDLE LEVEL TROUGH AXIS SOUTH OF THE CHARLOTTES
WILL CONTINUE TO TILT NEGATIVE THROUGH THE AFTERNOON AND THIS
WILL ALLOW CONTINUED DEEPENING OF THE SURFACE LOW TO 978 MB BY
EARLY EVENING. THIS LOW WILL MOVE NORTHWARD TONIGHT THROUGH THE
EASTERN GULF AND IT WILL MOVE INTO THE YUKON BY TOMORROW. HOWEVER
AS THE SURFACE LOW MOVES NORTHWARD ITS ASSOCIATED FRONT AND A 65
KNOT LLJ WILL HELP BRING WINDY CONDITIONS ACROSS THE ENTIRE
PANHANDLE THIS AFTERNOON THROUGH TOMORROW MORNING. KEPT TODAYS
PACKAGE AS IS AS BELIEVE IT HAS A GOOD HANDLE ON THE WINDS AND
ASSOCIATED SURFACE PRESSURE GRADIENT. DID ADJUST THE PRESSURE
FIELD WITH THE 12Z NAM12 EARLY ON AS THE DEEPENING SURFACE LOW IS
MOVING A LITTLE SLOWER THAN THE PREVIOUS MODEL GUIDANCE.

FOR TONIGHT RAINFALL WILL CONTINUE ACROSS THE PANHANDLE AS THE
MID LEVEL BAROCLINIC ZONE REMAINS OVER THE AREA. THE 977 MB GALE
FORCE LOW IN THE EASTERN GULF WILL MOVE NORTHWARD INTO THE YUKON
BY LATE TONIGHT. AS THE GALE FORCE LOW MOVES INTO THE YUKON A
VERY STRONG SOUTHERLY PRESSURE GRADIENT WILL FORM AND THIS WILL
ALLOW FOR WINDY CONDITIONS ACROSS THE PANHANDLE TO CONTINUE WITH
GUSTS TO 40 MPH AND SOUTHERLY GALES WITHIN THE INNER CHANNELS
TONIGHT. THESE WINDY CONDITIONS WILL BE ESPECIALLY PREVALENT IN
NORTHERN LYNN CANAL AND NEAR SKAGWAY WITH GUSTS TO 50 MPH BY LATE
TONIGHT. WINDS WILL DIMINISH LATE TONIGHT ACROSS THE SOUTHERN AND
CENTRAL PANHANDLE FROM SOUTH TO NORTH AS THE SURFACE PRESSURE
GRADIENT RELAXES.

FOR TOMORROW THE 977 MB SURFACE LOW IN THE YUKON WILL CONTINUE TO
MOVE NORTHWARD AND AS IT DOES THE SURFACE PRESSURE GRADIENT WILL
FINALLY RELAX NEAR TAIYA INLET AND NORTHERN LYNN CANAL...SO
EXPECT WINDY CONDITIONS TO DIMINISH NEAR SKAGWAY BY TOMORROW
AFTERNOON. ALSO COLD AIR AT MID LEVELS WILL HAVE ADVECTED OVER
THE ENTIRE PANHANDLE BY TOMORROW MORNING AND SO EXPECT A
CONVECTIVE ENVIRONMENT WITH WIDESPREAD SHOWERS ACROSS THE
PANHANDLE. THESE SHOWERS WILL BECOME SCATTERED TO ISOLATED INTO
THE AFTERNOON...ESPECIALLY NEAR THE CENTRAL OUTER COAST AS A WEAK
MID LEVEL RIDGE ADVECTS ACROSS THE EASTERN GULF AND THIS WILL
SUPPRESS SOME OF THE CONVECTIVE ACTIVITY.

.LONG TERM...
THE MONDO UPR RIDGE THAT HAS BLOCKED EASTERN PACIFIC SYSTEMS INTO
THE GULF HAS MOVED EAST TODAY...BUT 500HPA HGTS ARE STILL VERY
HIGH OVR THE ROCKIES. ZONAL JET AT 250 HPA FROM NORTHERN CHINA
ALMOST TO KSFO WITH 125 KT CORE S OF ADAK. 500 HPA TEMPS
INITIALIZED WELL AT 12Z ON AK-GFS-40 WITH -35C AT BARROW.
SECONDARY UPR LOW OVR SW AK.

00 AND 12Z THU GFS-ENSEMBLES INSIST THAT THIS BLOCK IS WEAKENING
AND HAS BEEN FORECASTING THIS FOR MANY RUNS...JUST TOO SOON. NOW
IS THE TIME TO BUY IT WHICH ALLOWS A NEG TILTED UPR TROF TO
DEVELOP OFF OUR COAST BY 00Z SAT ASSOCIATED WITH A MAJOR UPR LOW
CENTERD OVR NORTON SOUND. SOME COLD FALL AIR WILL MOVE INTO THE
MAJOR AND WILL ALLOW A DEEPR UPR TROF TO DIG ALONG 155W ON SUNDAY
WHICH GIVES US THE WET SW FLOW ALF THEN. NEW GFS 12Z OPS RUN
FORECASTS ANOTHER NEG TILT TO EMERGE FROM THIS DEVELOPMENT
DIGGING FURTHER OFF VNCVR ISL PUSHED ON BY -36C @500 HPA OVR
KODIAK. TENDANCY IS TO DRIVE SYSTEMS INLAND TO OUR SOUTH.

PLAN FOR FORECAST IS TO BLEND 12Z THU AK-GFS-40 THROUGH 12Z MON
THEN GO WITH HPC GRIDS. WILL KEEP TEMPS CLOSE TO CLIMATE AND KEEP
SE AK WET BY GUT FEELING WITH POPS LIKELY CATEGORY.
&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY ALL ZONES EXCEPT 17.
MARINE...GALES ALL WATERS EXCEPT PKZ052 AND PKZ053.

PSS / JC
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