Gale Warning 337, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
235 PM AKST TUE NOV 19 2013

.SHORT TERM...A LOW HAS DEVELOPED AND DEEPENED OVER THE NE GULF
TODAY. THIS IS CAUSING SNOW SHOWERS ALONG THE COAST WHICH ARE
BEING ENHANCED BY A LARGE TEMPERATURE DIFFERENCE BETWEEN THE SST
AND THE 850MB TEMPERATURE...ALSO KNOWN AS OCEAN EFFECT SHOWERS.
THE 850MB TEMPERATURE WAS ABOUT -14C FROM THE 12Z MORNING
SOUNDINGS WHILE THE OCEAN TEMPERATURE IS +8C...ONLY A 13 DEGREE
DIFFERENCE IS NEEDED FOR CONVECTION TO BEGIN. WHATS DIFFERENT
ABOUT TODAY THAN THE LAST COUPLE DAYS IS THAT MID AND UPPER LEVEL
FLOW HAS TURNED WESTERLY AND THAT IS HELPING TO PUSH THE SHOWERS
ONSHORE. TONIGHT THE LOW IN THE GULF WILL SLOWLY SHIFT SE OVER THE
SOUTHERN PANHANDLE AND WEAKEN SOME. THIS WILL CAUSE THE SNOW
SHOWERS TO PROGRESS EASTWARD INTO THE HYDER AREA. SNOW HAS ALREADY
BEEN FALLING AS FAR EAST AS WRANGELL AND KETCHIKAN THIS AFTERNOON.
THE COLD AND DRY AIR THAT IS IN PLACE IS CAUSING THE SNOW TO BE
SUGARY/POWDER WITH LOW RATIOS. THEREFORE ONLY EXPECT 1-3 INCHES OF
SNOW OVER THE SOUTH CENTRAL PANHANDLE TONIGHT...WITH MOST ALONG
WEST FACING MOUNTAIN SLOPES. THE JUNEAU AREA COULD SEE UP TO 2
INCHES IN SCATTERED SNOW SHOWERS BY MORNING.

THE LOW SHIFTING TO THE SOUTH WILL KEEP N-NELY WINDS BLOWING
THROUGH INTERIOR PASSES THIS EVENING...BUT WILL EASE SOME AS THE
LOW PRESSURE FILLS. STRONGEST WINDS THIS EVENING WILL BE OUT OF
CROSS SOUND WHERE 40 KT SUSTAINED WINDS HAVE BEEN OCCURRING DUE TO
THE LOW JUST OFFSHORE. HAVE INCLUDED A STRONG WIND HEADLINE FOR
ELFIN COVE AS GUSTS OF 40 MPH ARE LIKELY OVER LAND ALONG CROSS
SOUND THIS EVENING.

TOMORROW THERE WILL STILL BE A WEAK TROUGH OF LOW PRESSURE FROM
THE SOUTHERN PANHANDLE TO THE NE GULF. THIS WILL KEEP SCATTERED
SNOW SHOWERS ACROSS THE PANHANDLE DURING THE DAY. THE TROUGH WILL
MERGE WITH A FRONT MOVING IN FROM THE WEST IN THE AFTERNOON AND
START TO ENHANCE THE SNOW SHOWERS ALONG THE COASTAL AREAS. EXPECT
ABOUT 1 INCHES OF ADDITIONAL ACCUMULATION TOMORROW...BUT WEST
FACING MOUNTAIN SLOPES COULD SEE SLIGHTLY MORE.

MODELS DID POORLY WITH THE LOW IN THE GULF TODAY. NONE WERE DEEP
ENOUGH AS CURRENT CONDITIONS...BUT THE 12Z NAM WAS THE CLOSEST SO
THAT WAS USED FOR MOST CHANGES TODAY. FORECAST CONFIDENCE IS AVERAGE.
&&

.LONG TERM...
UPPER AIR TEMPS THIS MORNING WERE VERY COLD LIKE -44C AT 500 MB ON
THE 19/12Z YAKUTAT RAOB. ANOTHER WORRY ON ANALYSIS IS THAT THERE IS
TROPICAL MOISTURE ALONG 168W THAT IS ABOUT TO GET INTO THE
WESTERLIES. THIS MOISTURE WILL ARRIVE WED NIGHT. GOOD AGREEMENT WITH
19/12Z ECMWF AND AK-GFS-40 SO USED A MODEL BLEND ON THESE FOR THE
PACKAGE OUT TO DAY FOUR. THIS FIT IN WELL WITH THE LONG WAVE PATTERN
WHICH WAS REFLECTED IN WPC EXTENDED FORECASTS AND ACCEPTED. HIGH
CONFIDENCE ON A SNOW EVENT WED NIGHT ESPECIALLY NORTH PANHANDLE BUT
NOT SURE HOW LONG IT WILL LAST. WILL LET THIS BE REFINED IN LATER
SHIFTS FORECASTS ESPECIALLY AMOUNTS. COASTAL WIND EVENT LOOKS CERTAIN
ON FRIDAY AS THE WEATHER PATTERN CHANGES AND STORM FORCE WIND MOVES
UP TO THE COAST. UPPER JET LINES UP WITH THIS AND ANCHORAGE AGREES ON
THE BARRIER ACCELERATION. SEAS WILL BE IN THE 20S FOR THIS ONE
ESPECIALLY WITH A SOUTH FETCH BEHIND IT. COLD FRONT WILL COOL THINGS
OFF ON SAT TO MIX BACK PRECIP. VERY ACTIVE WEATHER FOR THE NEXT FEW
DAYS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-041>043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

FERRIN/JC

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