Gale Warning 225, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
1215 PM ADT WED SEP 19 2007

.SYNOPSIS...
.SHORT RANGE...A STRONG WARM FRONT EXTENDING FROM NEAR YAKUTAT
OUT INTO THE COASTAL MARINE ZONES THIS MORNING IS MOVING RAPIDLY
TO THE EAST. SURFACE PRESSURE FALLS ARE AS STRONG AS
2.5 TO 3 MB PER HOUR BETWEEN YAKUTAT AND CAPE EDGECUMBE. THE
PRESSURE GRADIENT BETWEEN SKAGWAY AND JUNEAU HAS ALREADY BEEN AS
HIGH AT 8 MB THIS MORNING. THIS HAS PROMPTED WIND ADVISORIES FOR
THE SKAGWAY...HAINES...JUNEAU...AND SITKA ZONES AS WELL AS
UPGRADING SMALL CRAFT TO GALE WARNINGS IN NORTHERN LYNN CANAL AND
COASTAL MARINE ZONE 42. CURRENTLY ALL STATIONS IN THE PANHANDLE
EXCEPT SKAGWAY ARE REPORTING RAIN AND WINDS ARE JUST NOW
BEGINNING TO SHIFT IN YAKUTAT AND SATELLITE IMAGERY IS SHOWING
THE TRAILING EDGE OF THE FRONTAL CLOUD MASS OVER THEM RIGHT NOW
SO BELIEVE THE FRONT WILL BE THROUGH THERE SHORTLY.

MAIN FORECAST PROBLEM TODAY WILL BE HOW LONG AND HOW STRONG WINDS
WILL BLOW. GALE WARNINGS IN COASTAL ZONES 43...51...AND 52
ALREADY VERIFYING. CURRENTLY FEEL CONFIDENT THAT WIND ADVISORIES
FOR ZONES 23 AND 25 UNTIL 6PM WILL BE SUFFICIENT. WIND ADVISORY
UNTIL NOON FOR ZONES 18 AND 19 WAS UPDATED AND EXTENDED THROUGH
6PM ALSO. CONSIDERED A WIND ADVISORY FOR ZONE 27 FOR LATER
TODAY BUT THE ORIENTATION OF THE WIND IS MORE SOUTHERLY THAN THE
USUAL SOUTHEASTERLY WINDS NECESSARY TO GENERATE WIND ADVISORY
CONDITIONS THERE. REGARDLESS...WILL KEEP A CLOSE WATCH ON
CONDITIONS DOWN THERE. ANOTHER WIND CONCERN TODAY IS CLARENCE
STRAIT. APART FROM THE GALE WARNING IN NORTHERN LYNN CANAL...ALL
INNER CHANNELS ARE CURRENTLY COVERED BY STRONG SMALL CRAFT WINDS
IN THE FORECAST. BOUNDARY LAYER PRESSURE GRADIENTS ON BOTH NAM
AND GFS INDICATE THE POTENTIAL FOR A SOUTHEAST GALE IN CLARENCE
AS WELL THIS AFTERNOON. NEW LINCOLN ROCK OB RISING TWD 30KTS
SUSTAINED AT NOON. FOR NOW WILL KEEP THAT MARINE ZONE AS HIGH END
SCA.

SOME SIGNIFICANT TEMPERATURE FALLS IN THE UPPER LEVELS BEHIND THE
FRONT OVER THE PANHANDLE BY TONIGHT BUT NOT COLD ENOUGH TO
TRIGGER ANY SIGNIFICANT CONVECTION. CAPE AND LIFTED INDICES
SUPPORT THIS IDEA AND SO HAVE NO POST FRONTAL THUNDERSTORMS IN
THE FORECAST.

CONDITIONS IN TERMS OF WINDS WILL IMPROVE QUICKLY FROM NORTH TO
SOUTH AFTER FRONTAL PASSAGE AND SO BY TONIGHT THE FRONT WILL HAVE
CLEARED THE PANHANDLE TO THE SOUTH. WESTERLY WINDS AROUND 20 KTS
IN THE COASTAL ZONES THROUGH TOMORROW WITH SCATTERED SHOWERS OVER
THE INNER CHANNELS AS A SHORT LIVED SURFACE RIDGE BUILDS OVER THE
EASTERN GULF TONIGHT AND THEN MOVES OVER THE PANHANDLE ON
THURSDAY IN ADVANCE OF THE NEXT SYSTEM DISCUSSED BELOW.

.LONG RANGE...BY FRI MORNING A DEVELOPING WAVE ALONG THE TRAILING
FRONT...CURRENTLY AT 45N 180...WILL DEEPEN TO AROUND 995 MB AS IT
MOVES TO ABOUT DIXON ENTRANCE. ENSEMBLE VARIABILITY WITH THIS
SYSTEM IS MOSTLY ABOUT STORM DEPTH BUT THERE IS ALSO A RANGE OF
TRACKS THIS LOW WILL TAKE. 12Z NAM AND GFS RUNS ARE DEEPER THAN
EURO RUNS AND UKMET TAKES LOW FARTHER SOUTH INTO CHARLOTTES. WILL
KEEP DIXON ENT AS TARGET IN GRIDS AND MAY DEEPEN PRESSURES IN
THAT AREA A BIT. SOME GALE FORCE GUSTS POSSIBLE S OF CAPE
DECISION AND OUT OF INTERIOR PASSES AHEAD OF THE FRONT THU NIGHT
AND FRI MORNING BUT STRONGEST WINDS WILL BE FORECAST FARTHER
SOUTH. RAIN AMOUNTS WILL BE HEAVIEST SRN PANHANDLE WITH THIS
SYSTEM.

BRIEF TRANSITORY RIDGING BEHIND THIS SYSTEM ALLOWS FOR BREAK IN
STEADY PRECIP FRI NIGHT AND SAT. ONSHORE FLOW AND COOLING ALOFT
WILL KEEP ENVIRONMENT RIPE FOR SHOWERS. 1000-500 MB THICKNESS
LOWERS INTO 538-540 DM RANGE OVER NORTHERN PANHANDLE SAT WHICH
MEANS MORE SNOW ON MTNS ABOVE 3000 FT MSL N OF JNU-CAPE SPENCER
LINE.

NEXT MAJOR LOW IS FORECAST TO MOVE INTO THE SOUTH CENTRAL GULF
EARLY SUNDAY THEN DRIFTS EAST INTO THE SE GULF MONDAY. ASSOCIATED
OCCLUDED FRONT WILL SPREAD PRECIP FROM S TO N SATURDAY NIGHT
AND EARLY SUNDAY. CURRENT FCSTS HAVE PAYA-PAGY AS CHANCE OF
PRECIP AS WINDS EXPECTED TO BE ELY. BEYOND SUNDAY FCSTR
CONFIDENCE DIMINISHES ON THE DETAILS. NCEP DISCUSSIONS DESCRIBE
SIGNIFICANT MODEL SPREAD. LONG WAVE PATTERN EARLY NEXT WEEK HAS
ANCHOR LOW OVER WRN BERING OR EVEN KAMCHATKA AND STRONG BUT
DIFFLUENT WLY FLOW ACROSS GULF. WILL LEAN TOWARD CLIMO FOR TEMPS
/40S AND 50S/ AND PROBILITY OF PRECIP /60 PERCENT RANGE/.  TA

.AJK...WATCHES/WARNINGS/ADVISORIES
PUBLIC...WIND ADVISORY AKZ018-019-023-025
MARINE...GALE PKZ012-042>043-051>052 SMALL CRAFT ALL REMAINING
MARINE ZONES