Small Craft Advisory 651, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
219 PM AKST MON NOV 5 2012

.SHORT TERM...A HIGH PRESSURE RIDGE OVER SE AK WILL DRIFT E OF
THE AREA TONIGHT. A WEAK LOW WILL DEVELOP S OF THE GULF AND MOVE
NE TO THE SE GULF TUE. A LOW OVER THE NW GULF WILL DRIFT SLOWLY S
TO THE SW GULF BY TUE AFTERNOON. LEADING EDGE OF ARCTIC AIRMASS
OVER THE YUKON WILL BE SPREADING SWD INTO THE FAR N LATE TUE
AFTERNOON. USED THE 12Z ECMWF AS IT HAD BEST FIT TO THE MAIN
SYSTEMS THAT WILL AFFECT THE AREA THE NEXT 24 HRS.

 MAIN FORECAST ISSUES WILL BE WINDS AND PRECIP POTENTIAL. RIGHT
NOW...A FAIRLY STRONG S PRESSURE GRADIENT IS OVER THE INNER
CHANNELS WITH FAIRLY WIDESPREAD SCA LEVEL WINDS...WITH GALES OVER
NRN LYNN CANAL. DO EXPECT THESE WINDS TO SLOWLY DECREASE TONIGHT
AS THE GRADIENT RELAXES...WITH ONLY SCA LEVEL WINDS LEFT OVER THE
FAR SERN INNER CHANNEL AREA BY LATE TONIGHT. WILL KEEP PAGY IN A
STRONG WIND HEADLINE UNTIL 06Z THIS EVENING. THE GRADIENT
ORIENTATION WILL GRADUALLY SHIFT TO FAVOR MORE ELY WINDS BY LATE
TONIGHT AS WELL. AS LOW MOVES TOWARD THE SE GULF TUE...THE
GRADIENT ORIENTATION WILL SHIFT FURTHER TO FAVOR MORE NE
FLOW...WITH A TIGHTER N GRADIENT DEVELOPING OVER THE FAR N LATE
TUE AS LEADING EDGE OF ARCTIC AIRMASS MOVES IN. SCA LEVEL SE
WINDS SHOULD CONTINUE OVER THE FAR SE INNER CHANNELS WITH NRN
LYNN CANAL COMING UP TO SCA NLY WIND LATE TUE AFTERNOON. OVER THE
GULF...THE SCA LEVEL SW FLOW WILL GRADUALLY WEAKEN AND START
BACKING TO A MORE S-SE DIRECTION LATER TONIGHT BUT SEAS WILL
REMAIN ABOVE 8 FT SO SCA WILL CONTINUE DUE TO SEAS THRU TUE.

 AS FOR PRECIP...MUCH OF THE AREA HAS TRANSITIONED TO SHOWERS.
ONLY EXCEPTION IS AROUND THE PAYA AREA WWD...AND THEY SHOULD
TRANSITION TO SHOWERS BY EARLY EVENING. RADAR SHOWS FAIRLY GOOD
SHOWER COVERAGE SO WILL KEEP POPS ON THE HIGH SIDE...EXCEPT WILL
LIMIT PAGY TO CHANCE LEVELS. THE PAYA AREA WILL SEE THEIR SHOWERS
DIMINISH LATER TUE AS LOW LEVEL FLOW BECOMES MORE ELY. AS LOW
MOVES IN FOR TUE...PRECIP CHARACTER MAY TRY TO BECOME MORE STEADY
STATE BUT MODEL SOUNDINGS SHOW 50-100 J/KG OF POSITIVE CAPE
VALUES... SUGGESTING THAT SHOWERS WOULD BE EMBEDDED WITHIN A
LARGER PRECIP SHIELD SO WILL MAINTAIN SHOWER TERMINOLOGY TUE FOR
SIMPLICITY.

&&

.LONG TERM...ANOTHER COOL DOWN IS IN THE WORKS FOR THE LONG TERM
ONCE THE SHOWERS OVER THE PANHANDLE DIMINISH AS ANOTHER STRONG COLD
HIGH BUILDS IN THE YUKON ON TUES NIGHT. THERE WILL STILL BE SOME
SHOWERS AROUND THE AREA TUES NIGHT AND EARLY WED AS THE LOW IN THE
GULF SLOWLY MAKES ITS WAY TO THE SE. SHOWERS WILL END AS THE LOW
EVENTUALLY BECOMING AN INVERTED TROUGH BY WED EVENING SETTING UP
OFFSHORE FLOW OVER THE WHOLE AREA. COLD OUTFLOW WINDS WILL START
UP OVER THE NORTHERN PANHANDLE TUES NIGHT AS A 1035 MB HIGH BUILDS
IN THE YUKON. I AM EXPECTING GALES FOR LYNN CANAL AND SMALL CRAFT
WINDS FOR MOST OF THE OTHER NORTHERN INNER CHANNELS WED INTO THURS
NIGHT AS THE HIGH SPREADS ITS INFLUENCE OVER THE AREA. WITH THESE
WINDS AND THE COLD AIR FREEZING SPRAY IS POSSIBLE FOR LYNN CANAL
AND GLACIER BAY AT THE SAME TIME.

ALSO A POSSIBILITY IS A MOUNTAIN WAVE EVENT FOR DOWNTOWN JUNEAU
AND DOUGLAS TUES EVENING INTO THURS AFTERNOON. CROSS BARRIER FLOW
IS EXPECTED TO BE IN THE 30 TO 35 KT RANGE WITH A GOOD INVERSION
AND A DECENT LOOKING CRITICAL LEVEL. I AM EXPECTING WIND GUSTS
POSSIBLY UP INTO STRONG WIND CRITERIA DURING THAT TIME.

THIS COLDER CLEARER DRYER WEATHER WILL NOT LAST VERY LONG HOWEVER.
CLOUDS WILL START ENCROACHING INTO THE AREA BY SAT AS THE NEXT
FRONT BEGINS ITS ADVANCE ON THE AREA. STILL SOME MODEL
DISAGREEMENT ON HOW TO HANDLE IT THOUGH. EC HAS BEEN FLIP FLOPPING
ON WHERE TO TAKE MOST OF THE ENERGY. 0Z RUN HAD THE ENERGY DIVING
SOUTH AND UNDERCUTTING THE AREA. NEW 12Z RUN HAS GONE TOWARD THE
GFS WITH THE LOW WANDERING AROUND JUST OFFSHORE OF THE NORTHERN
PANHANDLE SUNDAY. DECIDED ON GOING TOWARD THE 0Z EC AS THAT WAS
MORE IN LINE WITH THE ENSEMBLES AND HPC. IN ANY CASE SNOW AND RAIN
AND SOME SOUTHERLY WINDS WILL BE COMING BACK INTO THE FORECAST BY
SAT NIGHT AND SUN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 9 PM AKST THIS EVENING FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ013-021-022-031>036-041>043-051-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

RWT/EAL