Storm Warning 31, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
124 PM AKDT WED OCT 21 2009

.SHORT TERM...THE MOST SIGNIFICANT CHANGE IS FOR RAISING THE
WINDS IN THE COASTAL WATERS S OF CAPE FAIRWEATHER FOR THIS
EVENING. OTHER CHANGES ARE MINOR. FORECAST CONFIDENCE IN THIS
WIND ENHANCEMENT IS ONLY FAIR BECAUSE THE STRUCTURE OF THE SYSTEM
IS NOT THE MOST COMMON AND MUCH OF THE GUIDANCE HAS NOT DETECTED
THE SYSTEM AS SEPARATE FROM A PARENT LOW IN THE WESTERN GULF.

 THE COMPLEX OF LOWS IN THE GLFALSK INCLUDES A SMALL WARM-CORE
LOW ABT 250 NM SW OF PASI. THE UKMET, NAM, ECMWF, AND GFS ALL
DEPICT THE WARM CORE, BUT THIS FEATURE IS TOO SMALL TO BE TRACKED
ON THE CYCLONE PHASE EVOLUTION GUIDANCE. BASED ON GOES IMAGERY,
AND THE CLAIM TO BE USING CORRECT CONCEPTUAL MODELS, THE REGION OF
CYCLONIC FLOW CLOSEST TO THE LOW SEEMS BAROTROPIC, BUT THE REGION
MOVG TOWRD THE SRN PNHDL IS BAROCLINIC ENOUGH TO BE FRONTOGENETIC.

&&

.LONG TERM...MEDIUM RANGE MODELS ARE IN FAIR AGREEMENT THROUGH
THE WEEKEND WITH A SERIES OF SHORTWAVE TROUGHS MOVING EASTWARD
ACROSS THE FORECAST DOMAIN. THEN MODELS BEGIN TO DIVERGE THROUGH
THE MIDDLE OF NEXT WEEK AS A RIDGE BUILDING ACROSS THE GULF OF
ALASKA. THE NAM AND GFS ARE SIMILAR FOR THE EARLIER PORTIONS OF
THE LONG TERM AND BLENDED INTO THE INHERITED GRIDS. THE GFS AND
ECMWF SHOW A LITTLE DIFFERENCE ON TIMING OF BUILDING RIDGE EARLY
NEXT WEEK. THE INHERITED GRIDS DO NOT MATCH WELL WITH THE
CONSENSUS OF LATEST MODEL RUN. THUS OPTED THE GFS AND ECMWF
EQUALLY AS NEW GRIDS THROUGH THE END OF LONG TERM PERIOD.

 A COUPLE OF GALE FORCE LOWS WILL CONTINUE SWEEP ACROSS THE
OFFSHORE AND OUTSIDE COASTAL WATERS THROUGH THE WEEKEND WITH VERY
ROUGH SEAS REMAINING THROUGH EARLY NEXT WEEK. ADVISORY LEVEL WIND
GUSTS WILL CONTINUE ACROSS THE COASTAL SECTIONS FROM YAKUTAT TO
KETCHIKAN THROUGH THURSDAY EVENING OR NIGHT. MODERATE ONSHORE FLOW
WILL CONTINUE WITH A SERIES OF LOWS AND WET CONDITIONS WILL
PREVAIL ACROSS THE FORECAST DOMAIN THROUGH SUNDAY. AS THE TROUGH
FLATTENING ACROSS THE PANHANDLE AND A RIDGE BUILDING ACROSS THE
GULF...CONDITIONS WILL IMPROVE FROM THE NORTHWEST BEGINNING ON
SUNDAY NIGHT WITH INCREASING OFFSHORE FLOW...THEN SPREAD SOUTHEAST
ACROSS THE PANHANDLE THROUGH TUESDAY. POPS WILL BE LOWERED
DRAMATICALLY AS WELL FROM YAKUTAT AREA SUNDAY NIGHT THEN SPREAD
SOUTHEAST THROUGH TUESDAY.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM 6 PM TO 9 PM AKDT THIS EVENING FOR AKZ022.
         WIND ADVISORY UNTIL 9 PM AKDT THIS EVENING FOR AKZ023.
         WIND ADVISORY FROM MIDNIGHT TONIGHT TO 3 AM AKDT THURSDAY FOR
     AKZ017.
MARINE...GALE WARNING FOR PKZ022-036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-031>035.

&&

JBT/AHN