Small Craft Advisory 613, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
556 AM AKST TUE NOV 11 2008

.SHORT TERM...SATELLITE THIS MORNING REVEALS A GALE FORCE FRONT
ADVECTING NORTHWARD ACROSS THE PANHANDLE. TWO MID LEVEL VORTICITY
CENTERS ARE ALSO ADVECTING NORTHWARD, ONE TOWARDS CORDOVA, THE
OTHER ACROSS THE CENTRAL PANHANDLE. THESE TWO MID LEVEL VORTICITY
CENTERS ARE NOT ALLOWING THE SYSTEM TO REMAIN STRONG, BUT ARE
CAUSING THE GALE FRONT TO SHEAR APART AS THE FRONT MOVES
NORTHWARD. WINDS ARE QUICKLY DIMINISHING OFFSHORE AND EXPECT THIS
TREND TO CONTINUE ACROSS THE SOUTHERN PANHANDLE EARLY THIS
MORNING AS WIND ADVY GUSTS WILL QUICKLY DIMINISH. ELSEWHERE RAIN
CONTINUES TO PUSH NORTHWARD BUT AMOUNTS REMAIN LIGHT AS THE
EASTERLY WINDS ARE ADVECTING IN DRIER AIR NEAR THE SURFACE. THE
RAIN/SNOW LINE REMAINS AROUND ICY STRAIT AND THIS LINE WILL SHIFT
NORTHWARD DURING THE DAY AS THE SOUTHEASTERLY WINDS PICK UP
BEHIND THE 850 MB FRONT WHICH WILL PUSH THROUGH JUNEAU LATE IN
THE MORNING. WITH THE SOUTHEASTERLY MID LEVEL PARCEL TRAJECTORIES
AND LOW LEVEL WINDS OUT OF THE NORTHWEST COULD SEE HEAVY SNOW
NEAR AND ALONG THE HAINES HIGHWAY THROUGH EARLY THIS AFTERNOON
BEFORE THE WARMER AIR ADVECT NORTHWARD AND MIXES OUT THE LOW
LEVEL COLD AIR NORTHWEST OF HAINES. USED THE LOCAL 06Z WRF MODEL
FOR THIS MORNINGS WINDS AS IT HAD A GOOD HANDLE ON THE TIMING FOR
THE SURFACE AND 850 MB FRONT AS IT PROGRESSES NORTHWARD. THEN
TONIGHT USED THE 00Z UKMET MODEL AS IT HAS BEEN THE MOST
CONSISTENT MODEL FOR THE NEXT APPROACHING GALE FORCE LOW TONIGHT.

 FOR TONIGHT THE 200 KNOT 300MB JET ACROSS THE NORTHERN PACIFIC
WILL CONTINUE TO ALLOW FOR ANOTHER GALE FORCE LOW TO STRENGTHEN
AND MOVE INTO THE SOUTHEASTERN GULF BY LATE TONIGHT. GALE FORCE
WINDS WILL PICK UP LATE TONIGHT AS A 60 TO 65 KNOT 850 MB LLJ
MOVES OVER THE SOUTHERN PANHANDLE. EXPECT WIND ADVY GUSTS AGAIN
LATE TONIGHT ALONG PRINCE OF WALES ISLAND WITH GALES ALONG THE
ASSOCIATED COASTAL WATERS AND WITHIN CLARENCE STRAIT. SOUTHERLY
SMCR WINDS LATE THIS AFTERNOON AND EVENING ACROSS THE NORTHERN
INNER CHANNELS WILL QUICKLY DIMINISH AND BECOME NORTHERLY LATE
TONIGHT AS THE NEW APPROACHING GALE FORCE LOW WILL INDUCE A
NORTHERLY SURFACE PRESSURE GRADIENT. EXPECT LOCALLY BREEZY
CONDITIONS OUT OF INTERIOR PASSES TONIGHT AS THE SURFACE PRESSURE
GRADIENT AGAIN INCREASES. WITH THE 200 KNOT 300 MB JET LEFT EXIT
REGION OVER THE SOUTHERN PANHANDLE AND THE INCREASED DIVERGENCE
ALOFT EXPECT LOCALLY HEAVY RAINFALL AT TIMES LATE TONIGHT NEAR
KETCHIKAN AND ANNETTE. ELSEWHERE RAINFALL AMOUNTS WILL BE LIGHT
AS THE NORTHERLY TO NORTHEASTERLY SURFACE PRESSURE GRADIENT AND
NORTHERLY 850 MB WIND FLOW WILL BRING DRIER AIR ACROSS THE
NORTHERN PANHANDLE. AS THE FIRST FRONT ADVECTS NORTHWARD TODAY IT
SHOULD HELP RAISE THE SNOW LEVEL AND THEREFORE TONIGHT ONLY
EXPECT SNOW ALONG AND NEAR THE PASSES WITH AMOUNTS BEING LIGHT.

.LONG TERM...MODEL AGREEMENT AT THE BEGINNING OF THE LONG RANGE
PERIOD IS GOOD WITH THE 06Z GFS NOW MORE IN LINE WITH...BUT STILL
DEEPER THAN...THE EC AND UKMET SOLUTIONS. USED EC AT THE VERY
BEGINNING OF THE LONG RANGE PERIOD AND THEN TRANSITIONED TO
UKMET/EC BLEND THROUGH WEDNESDAY. FAIRLY BENIGN PATTERN FOR
THURSDAY WITH HIGH PRESSURE RIDGING OVER THE PANHANDLE FROM THE
SOUTH. MODEL DIVERGENCE BECOMES AN ISSUE AGAIN THURSDAY NIGHT. EC
AND GFS BOTH DEPICTING A STRONG LOW IN THE SOUTH CENTRAL GULF AND
ARE SIMILAR TO YESTERDAYS HPC FORECAST...THOUGH SIGNIFICANTLY
DEEPER. ACCORDINGLY...DID A UK/GFS BLEND FOR THURSDAY NIGHT AND A
GFS/EC/HPC BLEND FOR FRIDAY MORNING TO WEAKEN THE GFS LOW AND
CORRECT FOR THE EC LOW BEING TOO FAR SOUTHWEST. FOR FRIDAY EVENING
AND SATURDAY MORNING...BLENDED EC AND GFS...WHICH WERE BOTH CLOSE
IN LOCATION BUT DIVERGED ON DEPTH. THIS IN EFFECT PROVIDED A
MIDDLE GROUND SOLUTION ON INTENSITY OF THIS SYSTEM. ADDED HPC TO
THE BLEND FOR FRIDAY MID-DAY. AFTER THIS TIME FRAME...MODEL
DIVERGENCE WAS TOO GREAT WITH GFS DEVELOPING A LOW IN THE
NORTHWEST GULF AND EC DEVELOPING A VERY SIGNIFICANT LOW IN THE
NORTH PACIFIC THAT IT TRACKS INTO THE SOUTHEAST GULF ON MONDAY
MORNING...SO MADE NO CHANGES SATURDAY AFTERNOON THROUGH TUESDAY
MORNING. FILLED IN DAY 8 WITH A BLEND OF EC...GFS...AND HPC.

WINDS ASSOCIATED WITH THE GALE FORCE LOW APPROACHING THE PANHANDLE
FROM THE SOUTHWEST TONIGHT WILL WINDS DOWN ON WEDNESDAY. ONSHORE
FLOW WILL KEEP POP IN MOST LOCATIONS AT LIKELY OR BETTER THROUGH
THURSDAY NIGHT. THE NEXT LOW WILL ENTER THE SOUTH CENTRAL GULF
THURSDAY NIGHT AND HAS THE POTENTIAL FOR BEING A STORM FORCE
SYSTEM. WAS NOT COMPLETELY CONVINCED OF THIS JUST YET...SO LIMITED
WINDS TO MAX GALE FOR THE TIME BEING. POSSIBILITY FOR ANOTHER
ROUND OF WIND ADVISORIES FOR THE CENTRAL AND SOUTHERN OUTER COAST
AS THIS SYSTEM APPROACHES THE COAST FRIDAY NIGHT INTO SATURDAY
MORNING. FRONTAL PRECIPITATION SHOULD ARRIVE OVER THE SOUTHERN
ZONES BY FRIDAY MORNING. THE SYSTEM WILL BE PUSHING AN UPPER
RIDGE AHEAD OF IT...SO ZONE 26 AND THE SOUTHERN THREE SHOULD SEE
ALL RAIN WITH MIXED PRECIP TO THE NORTH. CURRENT TRAJECTORY IS NOT
IDEAL FOR A SIGNIFICANT SNOWFALL...BUT IF THE TRACK OF THIS LOW
CHANGES TO ALLOW FOR A MORE SOUTHERLY LANDFALL...LOCATIONS NORTH
OF A LINE FROM CROSS SOUND TO FIVE FINGERS MAY SEE FROM 2 TO 5
INCHES OF SNOW LATE FRIDAY NIGHT INTO SATURDAY MORNING.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING UNTIL 3 PM AKST THIS AFTERNOON FOR
 AKZ019.
MARINE...GALE WARNING FOR PKZ022-031-033>036-041>043-051-052.
 SMALL CRAFT ADVISORY FOR PKZ011>013-021-032.

&&

PSS/FRITSCH