High Wind in Alaska, September 29 to 30, 2011

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
212 PM AKDT THU SEP 29 2011

.SHORT TERM...STRONG WINDS AND SOME ISOLATED THUNDERSTORM
ACTIVITY ARE THE MAIN FEATURES OF THE SHORT TERM FORECAST THROUGH
FRIDAY AFTERNOON. A 991 MB GALE FORCE LOW IMMEDIATELY WEST OF
HAIDA GWAII IS TRACKING RAPIDLY TO THE NORTH AND IS FORECAST TO
MAKE LANDFALL LATE THIS EVENING VICINITY CAPE DECISION.
ASSOCIATED WINDS ARE ALREADY RAMPING UP OVER THE SOUTHERN PUBLIC
ZONES AS WELL AS THE INNER CHANNELS AND SOUTHERN COASTAL MARINE
ZONES. UPSTREAM SYNOPTIC DATA HAS SHOWN THIS STORM CAPABLE OF
SUSTAINED 40 KTS OF WIND. BELIEVE IT WILL CONTINUE TO STRENGTHEN,
ALBEIT ONLY FOR A SHORT WHILE LONGER, IN THE LEFT DIVERGENT
QUADRANT OF A 140 KT JET MAXIMA, SO HAVE FORECAST A MAXIMUM OF
50 KTS OVER WATER TONIGHT OVER THE SOUTHERN ENTRANCE REGION OF
CLARENCE STRAIT. DO NOT FEEL THE LOW HAS GOT QUITE ENOUGH
STRENGTH TO PRODUCE HIGH WIND GUSTS, SO HAVE NOT ISSUED ANY HIGH
WIND WARNINGS WITH THE AFTERNOON FORECAST. 850 MB LOW LEVEL JET
IS MAXING OUT AT AROUND 65 KTS EARLY TONIGHT, SO AM EXPECTING
AROUND 50 MPH GUSTS OVER LAND, WHICH ACCOUNTS FOR THE CIRCULATION
AROUND THE STORM AS WELL AS THE SPEED OF ADVANCE OF THE LOW
ITSELF. STRONGEST WINDS WILL BE IN THE RIGHT FORWARD QUADRANT AND
WILL HIT PUBLIC ZONE 27 THE HARDEST, FOLLOWED BY ZONE 28. WINDS
WILL CHANGE DIRECTION RAPIDLY TONIGHT, AS THEY HAVE WITH SIMILAR
COMPACT, FAST MOVING SYSTEMS WE HAVE SEEN OVER THE PAST FEW
WEEKS. EXPECT STRONGEST WINDS OUT OF THE SOUTHEAST THROUGH LATE
THIS EVENING FOLLOWED BY A BRIEF LULL, AND THEN AN INCREASE OUT
OF THE SOUTHWEST AS THE STORM TRACKS OVERLAND. WINDS WILL
DIMINISH RAPIDLY LATE TONIGHT AS THE STORM WEAKENS AND TRACKS
INTO CANADA.

 HAVE RAIN TONIGHT FOLLOWED BY SHOWERS TOMORROW. SOME COLD AIR
AND SIGNIFICANT INSTABILITY BEHIND THE LOW HAVE PROMPTED THE
INCLUSION OF ISOLATED THUNDERSTORMS FOR THE SOUTHERN COASTAL
MARINE ZONES AS WELL AS PORTIONS OF THE SOUTHERN INNER CHANNELS
AND EASTERN PORTIONS OF THE DIXON ENTRANCE FOR TOMORROW. STOPPED
SHORT OF INCLUDING THUNDERSTORMS FOR OVERLAND ZONE 26 TOMORROW
AFTERNOON, SINCE RARELY DOES SUCH CONVECTION MAKE IT THAT FAR
INLAND BUT THAT WILL BE A PLACE TO WATCH CLOSELY.

 SMALL CRAFT ADVISORIES DUE TO WIND, GALES, AND STORM WARNINGS
LIMITED TO SOUTHERN WATERS FROM CAPE EDGECUMBE SOUTH ON THE
OUTSIDE, AND SOUTHERN CHATHAM, SUMNER, AND CLARENCE STRAIT IN THE
INSIDE. DO NOT FEEL THE PRESSURE GRADIENT WILL BE STRONG ENOUGH
ON THE WESTERN SIDE OF THE STORM TO PRODUCE SMALL CRAFT WINDS
OVER FREDERICK SOUND. FARTHER NORTH, NORTHERN LYNN CANAL IS
ALREADY RESPONDING TO THE NORTHERLY PRESSURE GRADIENT AND AS OF
THIS AFTERNOON, HAVE 20 KTS THERE. HAVE NOT INCLUDED A SMALL
CRAFT ADVISORY FOR NORTHERN LYNN FOR THIS EVENING. ONCE THE LOW
HAS PASSED AND THE SURFACE RIDGE BUILDS IN TOMORROW, EXPECT WINDS
TO SHIFT OVER THE NORTHERN INNER CHANNELS AND LOOK FOR SMALL
CRAFT SOUTHERLIES OVER NORTHERN LYNN CANAL BY TOMORROW AFTERNOON.

 USED A BLEND OF ECMWF AND GFS FOR PRESSURE AND WINDS. FELT NAM
WAS TRACKING THE SYSTEM TOO FAST AD TOO FAR EAST. BLENDED GFS AND
NAM TO EXISTING POP FIELD AND HAVE INCLUDED AN AREA OF HEAVY RAIN
FOR TONIGHT. FORECAST CONFIDENCE IS ABOVE AVERAGE.

 &&

 .LONG TERM...LONG RANGE FORECAST IS LOOKING RATHER QUIET INTO
EARLY NEXT WEEK. A BUILDING RIDGE FRIDAY NIGHT OVER THE PANHANDLE
WILL BE THE MAIN CULPRIT AS IT KEEPS MOST OF THE ADVANCING STORMS
OUT OVER THE WESTERN AND CENTRAL GULF. WHAT WE'RE LEFT WITH IS
SOME ISOLATED SHOWERS LINGERING INTO SAT PARTICULARLY ALONG THE
COAST MOUNTAINS AS WEAK ONSHORE FLOW CONTINUES. BY EARLY SUNDAY
THAT FLOW SWITCHES AROUND TO AN E OR SE FLOW AND WILL HELP TO DRY
OUT AND PARTLY CLEAR OUT THE PANHANDLE FOR SUN INTO EARLY MONDAY.

 WITH THE CLEARING SKIES SUNDAY AND THE LENGTHENING NIGHTS OF
FALL, SUNDAY MORNING AND SUNDAY NIGHT ARE LOOKING LIKE THEY MIGHT
GET SOMEWHAT COLD PARTICULARLY IN AREAS AWAY FROM THE WARM WATERS
OF THE CHANNELS. FROST MIGHT BE A POSSIBILITY IN SOME NORTHERN
PANHANDLE AREAS AND FOG MIGHT ALSO BE A POSSIBILITY WITH THE
LINGERING LOW LEVEL MOISTURE STILL IN THE AREA.

 BY MONDAY, CLOUDS AND RAIN START MOVING NORTH INTO THE SOUTHERN
PANHANDLE AS A NEW SYSTEM MOVES NORTHWARD OUT OF THE EAST
PACIFIC. IT IS HERE THAT THE MODEL AGREEMENT STARTS BREAKING DOWN
AS THEY CAN'T QUITE DECIDE WHAT TO DO WITH THAT SYSTEM. THEY ALL
GENERALLY KEEP IT SOUTH OF THE AREA WITH RAIN BANDS AFFECTING
MOST OF THE PANHANDLE WITH THE EXCEPTION OF THE FAR NORTHERN
AREAS AND YAKUTAT, BUT THAT IS ABOUT ALL THEY AGREE ON. THE EC IS
FAVORING MERGING THE SYSTEM WITH A BROADER AREA OF LOW PRESSURE
BY TUES WHILE THE GFS MOSTLY RETAINS THE IDENTITY OF THE SYSTEM
AS OTHER SHORT WAVES MOVE AROUND IT TO THE SOUTH. NEXT THURSDAY
THERE APPEARS TO BE ANOTHER RIDGE MOVING IN AS WE GET ANOTHER
BRIEF DRY SPELL.

 MODEL AGREEMENT IS DECENT THROUGH SUN THEN STARTS BREAKING
APART. FROM THAT POINT ON IT LOOKS LIKE THE NAM IS A BIT OF AN
OUTLIER. DECIDED TO UPDATE THE FORECAST WITH A NAM/EC BLEND UP TO
THE POINT THAT THE MODEL DIVERGE ON SUN, THEN CONTINUE ON WITH
GFS/EC INCORPORATING HPC INTO THE MIX FARTHER OUT. FORECAST
CONFIDENCE IS ABOVE AVERAGE OUT TO SUN THEN BECOMES AVERAGE TO
SLIGHTLY BELOW AVERAGE AFTER SUN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH LATE TONIGHT FOR AKZ027.
         STRONG WIND UNTIL 1 AM AKDT FRIDAY FOR AKZ028.
         STRONG WIND UNTIL 7 PM AKDT THIS EVENING FOR AKZ029.
MARINE...STORM WARNING FOR PKZ036.
         GALE WARNING FOR PKZ041-042.
         SMALL CRAFT ADVISORY FOR PKZ012-033-035-043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051-052.

&&

FRITSCH/EAL