Storm Warning 38, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
350 PM AKST THU NOV 12 2009

.SHORT TERM...ACTIVE WEATHER DAY AGAIN AS POWERFUL COLD FRONT
CONTINUES TO PUSH THROUGH THE PANHANDLE. FRONT IS ALONG A TAKU
INLET TO PAGN LINE AND CONTINUES TO MOVES EAST AND SOUTHEAST.
AHEAD OF THE FRONT STRONG SOUTHEAST WINDS CONTINUE WITH ADVISORY
LEVEL GUSTS IN ZONES 26 27 28 AND EXPOSED LOCATIONS IN ZONE 29.
CLARENCE STRAIT CURRENTLY AT STORM FORCE WINDS WITH 50KTS
SUSTAINED AND GUSTS TO 66 KT. RAIN...HEAVY AT TIMES CONTINUES
AHEAD OF THE FRONT AND IS MIXING WITH SNOW AT TIMES IN PAPG.

BEHIND THE FRONT WINDS QUICKLY DIMINISH AND TURN TO WEST OR
NORTHWEST AND THERE IS A RAPID TRANSITION TO SHOWER ACTIVITY. ICE
PELLETS MIXING IN SHOWERS AS NOTED IN PASI OB AS WELL AS JUNEAU
WFO OFFICE. CIGS AND VIS HAVE JUMPED BETWEEN IFR AND MVFR WITH
PASSING SHOWERS OF RAIN AND RAIN AND SNOW AND SNOW AFTER THE
FRONT. MAX SCA FORCE WINDS STILL IN THE OUTSIDE WATERS WITH STRONG
GRADIENT. CAPE SPENSER STILL GUSTING TO 55KTS ATTM.

WINDS WILL CONTINUE TO DIMINISH THROUGH THE EVENING IN THE
SOUTHERN ZONES AS FRONT CONTINUES TO MOVE INTO CANADA. A TROUGH
MOVING THROUGH THE CENTRAL GULF ATTM WILL CONTINUE TO MOVE EAST
SOUTHEAST INCREASING COVERAGE AND INTENSITY OF RAIN AND SNOW
SHOWERS EVIDENT ON RADAR IN THE GULF. ATMOS IS SUFFICIENTLY
UNSTABLE WITH VERY CHILLY AIR ALOFT AND WITH VORTICITY ASSOCIATED
WITH TROUGH...CAN NOT RULE OUT LIGHTNING THIS AFTERNOON AND
EVENING IN THE OFFSHORE WATERS AND OUTSIDE WATERS. WINDS ALSO
INCREASE TOMORROW A 850 MB WIND MAX APPROACHING 50 KTS PUSHES
ONSHORE FROM THE SOUTHWEST. ATTM GRIDS FALL SHORT OF ADVISORY
LEVEL WINDS FOR BULLSEYE ZONES 23 AND 25.

MODEL GUIDANCE WAS CONSISTENT TODAY WITH PREVIOUS MODEL RUNS AND
DIFFERED MINIMALLY IN BETWEEN MODEL FAMILIES IN THE SHORT TERM
PERIOD. OPTED TO UPDATE OFFICIAL GRIDS WITH A BLEND OF 12Z NAM12
AND 12Z GFS. FORECAST CONFIDENCE IS ABOVE AVERAGE THROUGH THE
SHORT TERM.

.LONG TERM...THE EXPLOSIVE CYCLOGENESIS EVENT TRACKING NE INTO THE CNTRL
GLFALSK IS STILL TO OCCUR DURG 00Z SAT TO 12Z FRI. THE INFLECTION
OF THE POLAR FRONT WILL RAPIDLY OCCLUDE SHORTLY BEFORE LANDFALL
DURING THE SAME PERIOD.  ABT 00Z MON THE CDFNT WILL EXTEND NE
TO SW OVER CWZV.  NOTE THE DISCUSSION OF STRONG COLD ADVECTION
THAT IS GIVEN BLO.

THE EXPLOSIVE CYCLOGENESIS HAS A PRIOR WAVE MOVING NE ALONG THE
AK PEN.  THIS WAVE AS WELL AS THE EARLY CYCLONE WAVE EVOLUTION
IS GIVEN A MORE REALISTIC TREATMENT BY THE GFS THAN THE ECMWF.
WHILE THIS VIEW IS REACHED BASED ON EXPERIENCE AND IS THEREFORE
SUBJECTIVE, THE SAME CONLUSION WAS INDEPENDANTLY REACHED BY THIS
OFFICE AND PAFC.

LANDFALL OF THE NEWLY FORMED OCFNT SHOULD OCCUR FM PASI N BY
12Z SAT. MODEST DIFFERENCES IN FRONTAL TIMING ARE GIVEN IN THE
MODELS, FOR SAT 12Z ONWARD, BUT THIS FAR IN THE FUTURE
THE AGREEMENT IS GOOD.

STRONG AND LONG COLD ADJECTION WILL OCCCUR AFTER FROPA. FOR EXAMPLE
INVOG PAKT: THE 1000-500 MB THICKNESS DROPS FM 540 DAM 18Z SAT
TO 519 DAM 18Z SUN. THIS STRONG COLD ADVECTION WILL ALSO
OCCUR OVER ALL THE INNER CHANNELS THAT CAN RETAIN MUCH OF
THE PRIOR WARM AMS IN THE LOWER BNDRY LAYER. POST FROPA
CONVECTION WILL CHANGE MOST OF THE PRECIP TO SNOW SHOWERS
ESPECIALLY N OF FREDERICK SOUND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING FOR
     AKZ022-023-027-028.
         WIND ADVISORY UNTIL 6 PM AKST THIS EVENING FOR AKZ018-028-029.
         HIGH WIND WATCH SATURDAY MORNING FOR AKZ029.
MARINE...STORM WARNING FOR PKZ041.
         GALE WARNING FOR PKZ011>013-021-022-031>036-042-043-051-052.

&&

CCC/JBT