Gale Warning 238, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1259 PM AKDT WED OCT 1 2008

.SHORT TERM...PERIODS OF RAIN CONTINUE TO SPREAD NORTHWARD
ACROSS THE PANHANDLE THIS MORNING AS THE RIGHT ENTRANCE REGION OF
AN UPPER LEVEL JET STREAK IS ENHANCING THE UPPER LEVEL DIVERGENCE
AND THIS COMBINED WITH WEAK ONSHORE LOW LEVEL FLOW AND A MID
LEVEL BAROCLINIC ZONE WILL CONTINUE THE PERIODS OF RAIN INTO THE
AFTERNOON. ON SATELLITE, HOWEVER, THE UPPER LEVEL CLOUD FEATURES
ARE BECOMING MORE ANTICYCLONIC AND SHEARING APART WHICH IS
LEADING TO A DECREASE IN THE INTENSITY OF RAINFALL AS WELL AS A
FEW BREAKS IN THE CLOUD COVER...ESPECIALLY ALONG THE SOUTHERN
PANHANDLE. YAKUTAT REMAINS WEST OF THE MID LEVEL BAROCLINIC ZONE
AND WILL CONTINUE TO SEE MOSTLY CLOUDY SKIES WITH A FEW ISOLATED
SHOWERS INTO THE AFTERNOON AND EVENING BEFORE THE RAINFALL
SPREADS NORTHWARD THERE. ELSEWHERE THE RAINFALL RATES HAVE
DECREASE SIGNIFICANTLY IN THE SKAGWAY AREA AND WITH THE TAIYA
RIVER CRESTING NEAR 16.90 FEET RIGHT NOW WILL DROP THE FLOOD
ADVISORY BY EARLY AFTERNOON. WINDS ACROSS THE PANHANDLE THIS
MORNING CONTINUE TO DIMINISH AS THE SURFACE PRESSURE GRADIENT
RELAXES AND THE STRONGEST WINDS REMAIN IN NORTHERN LYNN CANAL AND
TAIYA INLET WITH GUSTS TO 25 KNOTS...HOWEVER THESE WINDS WILL
DIMINISH INTO THE AFTERNOON. MODEL OF CHOICE FOR TODAYS PACKAGE
WAS THE ECMWF AS IT INITIALIZED THE BEST WITH THE UPPER LEVEL LOW
AND DEVELOPING SURFACE WAVE IN THE NORTHEASTERN PACIFIC. HOWEVER,
THE 12Z GFS WAS USED TO THE NUDGE THE ECMWF SOLUTION A LITTLE
FURTHER WESTWARD AS HAS BEEN THE TENDENCY IN EVERY MODEL RUN FROM
YESTERDAYS SOLUTIONS TO TODAYS SOLUTIONS.

 FOR TONIGHT THE MID LEVEL BAROCLINIC ZONE WILL REMAIN OVER THE
PANHANDLE AND WITH THE UPPER LEVEL JET SUPPORT THIS WILL HELP TO
INDUCE SEVERAL WEAK SURFACE LOWS TO MOVE NORTHWARD IN THE EASTERN
GULF. THESE WEAK SURFACE LOWS WILL HELP TO INCREASE THE SURFACE
PRESSURE GRADIENT TONIGHT ACROSS THE PANHANDLE BRINGING LOCALLY
BREEZY CONDITIONS TO THE SOUTHERN PANHANDLE BY LATE TONIGHT.
PERIODS OF RAIN WILL CONTINUE TONIGHT AS THE MID LEVEL BAROCLINIC
ZONE REMAINS ACROSS THE PANHANDLE BUT WITH THE UPPER LEVEL FLOW
CONTINUING TO BE ANTICYCLONIC AND SOUTHEASTERLY MID LEVEL PARCEL
TRAJECTORIES EXPECT THE HEAVIEST RAINFALL TO BE ALONG THE
SOUTHERN PANHANDLE.

 FOR TOMORROW THE MID LEVEL TROUGH AS A WHOLE WILL ADVECT
NORTHWARD AND PUSH INTO THE NORTHEASTERN GULF BY THE AFTERNOON
AND THIS WILL INDUCE A MODERATELY STRONG 980 MB SURFACE LOW IN
THE EASTERN GULF. THE SURFACE PRESSURE GRADIENT WILL AGAIN
TIGHTEN ACROSS THE PANHANDLE AND WITH AN 850 MB LLJ OF 60 KNOTS
EXPECT GALES IN NORTHERN CLARENCE STRAIT AND NEAR WIND ADVY GUSTS
ALONG PRINCE OF WALES ISLAND TOMORROW AFTERNOON. AS THE SURFACE
LOW AND FRONTAL BAND ADVECT NORTHWARD TOMORROW AFTERNOON EXPECT
LOCALLY BREEZY CONDITIONS TO MOVE INTO THE CENTRAL PANHANDLE WITH
MODERATE TO HEAVY RAINFALL. TEMPERATURES WILL BE ABOVE NORMAL
AGAIN TOMORROW ACROSS THE CENTRAL AND SOUTHERN PANHANDLE AS
850 MB TEMPERATURES RISE TO NEAR 8 C.

.AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...AREAL FLOOD ADVISORY
UNTIL 5 PM AKDT THIS AFTERNOON FOR AKZ018. MARINE...SMALL CRAFT
ADVISORY FOR PKZ012-033-035-036-041>043-051.

.LONG TERM...MODELS ARE IN BETTER AGREEMENT NOW BUT PREVIOUS GFS
AND ECMWF HAD MAJOR DIFFERENCES BY MONDAY OF NEXT WEEK. IN THE
UPPER LEVELS THE GENERAL TREND IS CONSISTENT. THE LONGWAVE TROUGH
IN THE NORTHEAST PACIFIC ALONG 140W IS EXPECTED TO MOVE SLOWLY
EASTWARD AND WEAKEN WHILE A COLD LOW DROPS SOUTHWARD FROM THE
WESTERN ALASKAN INTERIOR THROUGH THE WEEKEND...REACHING THE
NORTHWEST GULF BY MONDAY.

AT THE SURFACE...MODELS ARE SIMILAR IN THE POSITION AND DEPTH OF A
MODERATE LOW THAT MOVES ONSHORE OVER SOUTHERN B.C. EARLY SATURDAY.
BY MONDAY THE GFS DEVELOPED A SIGNIFICANT STORM IN THE GULF OF
ALASKA WHERE THE OLD ECMWF HAD ONLY VERY WEAK GRADIENTS. THIS
MORNINGS ECMWF RUN HAS SHIFTED CLOSER TO THE GFS AND NOW BOTH
MODELS DEEPEN THE LOW TO AROUND 965 MB IN THE EASTERN GULF EARLY
MONDAY. HOWEVER THE ENSEMBLE SPREAD FOR THIS SYSTEM IS STILL
FAIRLY LARGE WITH A MEAN DEPTH OF AROUND 990 MB. SINCE THERE IS
STILL CONSIDERABLE FLIP-FLOPPING BETWEEN CYCLES THE PREFERENCE
WAS TO GO WITH AN ENSEMBLE MEAN SOLUTION WHICH IS NOT AS STRONG
AS GFS BUT DOES BRING A LOW INTO THE GULF. WITH COLDER AIR IN THE
INTERIOR POISED TO INJECT INTO THIS FEATURE IT IS NOT UNREASONABLE
TO EXPECT SOME DEVELOPMENT TO OCCUR.

PRECIPITATION SHOULD DIMINISH OVER THE WEEKEND WITH WINDS
BECOMING MORE NORTHERLY AS THE FIRST LOW MOVES ONSHORE SOUTH OF
THE PANHANDLE. RAIN AND SOUTHEASTERLY WINDS WILL THEN INCREASE
LATE SUNDAY WITH THE APPROACH OF THE NEXT LOW IN THE GULF.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...AREAL FLOOD ADVISORY UNTIL 5 PM AKDT THIS AFTERNOON FOR AKZ018.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-033-035-036-041>043-051.

PSS/CFD