Gale Warning 425, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
404 PM AKST MON DEC 22 2014

.SHORT TERM...A STRENGTHENING LOW PRESSURE SYSTEM SEEN ON
SATELLITE IMAGERY THIS AFTERNOON NEAR 50N-140W WILL BE THE MAIN
WEATHER MAKER FOR SOUTHEAST ALASKA OVER THE NEXT 24 HOURS. THIS
SYSTEM WILL CONTINUE TO DEEPEN AND TRACK TO THE NORTHEAST REACHING
THE SOUTHERN PART OF PRINCE OF WALES ISLAND BY TUESDAY AFTERNOON.
MODEL GUIDANCE SUGGESTS THE SYSTEM WILL REACH A STRENGTH OF AROUND
976 MB BEFORE WEAKENING AS IT MAKES LANDFALL. THE TRACK WILL
RESULT IN THE GRADIENT SWITCHING TO THE NORTH OVER THE NORTHERN
PANHANDLE LATE THIS EVENING AND STRENGTHENING OVERNIGHT.

FOR THIS EVENING, LINGERING SHOWERS OVER THE NORTHERN PANHANDLE
WILL QUICKLY DIMINISH AS OFFSHORE FLOW INCREASES AHEAD OF THE
APPROACHING LOW. EXPECT THIS FLOW TO ALSO RESULT IN DECREASING
CLOUDS AS SOME DRIER AIR IS ADVECTED INTO THE AREA. DID INCLUDE
PATCHY FOG IN THE TONIGHT PERIOD FOR THE NORTHERN HALF AS BREAKS
IN THE CLOUD COVER INCREASE. ALSO, THERE WILL BE A LIGHTER PERIOD
OF WINDS AS THE GRADIENT SHIFTS FROM SOUTH TO NORTH WHICH WILL
PROMOTE FOG DEVELOPMENT. HOWEVER, DO EXPECT THAT INCREASING
NORTHEASTERLY FLOW WILL HELP TO DIMINISH FOG OVERNIGHT WHICH IS
WHY IT WAS NOT INCLUDED FOR TUESDAY MORNING. NORTHERLY SMALL
CRAFT TO GALE FORCE WINDS WILL OCCUR IN THE NORTHERN INNER
CHANNELS. THE PEAK OF THE WINDS ARE EXPECTED TO BE TUESDAY
MORNING BEFORE A SLOW DIMINISHING TREND TAKES PLACE IN THE
AFTERNOON WITH THE LOW TO THE SOUTH WEAKENING.

RAIN WILL MOVE INTO THE SOUTHERN PANHANDLE LATE THIS EVENING AND
INCREASE IN INTENSITY OVERNIGHT. EXPECT THAT RAIN WILL MAINLY STAY
FROM ANGOON SOUTHWARD AS EASTERLY FLOW INHIBITS FARTHER NORTHWARD
MOVEMENT OF PRECIP. HAVE ISSUED STRONG WIND HEADLINES FOR ZONES 27
AND 28 IN THE SOUTHERN PANHANDLE. ALTHOUGH IMPRESSIVE 925 MB WINDS
ARE SHOWN BY GUIDANCE, IT APPEARS GRADIENT ORIENTATION WON'T BE AS
FAVORABLE FOR THE WIND IN OUR SOUTHERN AREAS AS INDICATED BY THE
PREVIOUS SHIFT. THEREFORE HAVE ONLY GONE WITH GUSTS TO 40-45 MPH
FOR THESE AREAS THROUGH TUESDAY AFTERNOON. DID INCREASE WINDS OVER
THE SOUTHEAST GULF WITH A BAND OF STORM FORCE WINDS EXPECTED. THE
ONE CONCERN IS THE HI-RES GUIDANCE SHOWING A FASTER SOLUTION (BY 3
HOURS OR SO) OVER OTHER MODELS. THE 18Z NAM CAME IN WITH A FASTER
MOVING LOW AS WELL SO OPTED TO MAKE A FEW LATE CHANGES TO THE WIND
AND PRESSURE FIELD TO INCORPORATE A BIT FASTER SYSTEM.

USED THE 18Z NAM, 12Z EC ALONG WITH THE HIRES-ARW FOR UPDATES TO
THE INHERITED FORECAST. FORECAST CHANGES WERE MAINLY TO ACCOUNT
FOR SLIGHTLY FASTER MOVEMENT OF THE LOW IN THE SOUTHEAST GULF.
HOWEVER, THIS RESULTED IN MINIMAL CHANGES TO THE FORECAST GRAPHICS
AND TEXT. FORECAST CONFIDENCE IS ABOVE AVERAGE THROUGH THE NEXT 24
HOURS.

.LONG TERM...AS THE TIGHTLY WOUND LOW DISCUSSED ABOVE MAKES
LANDFALL AROUND THE ENTRANCE TO PORTLAND CANAL, DIMINISHING WINDS
FROM THE NORTHEAST WILL QUICKLY FLIP NORTHWEST AND RELAX EVEN
FURTHER. ALSO, RAIN WILL LESSEN THROUGH THE NIGHT. HYDER IS A
TOUGH CALL HERE, BUT FEEL THAT THICKNESSES WILL BE TOO MUCH FOR
ANY SHALLOW COLD AIR ADVECTION FROM BC. THE REST OF THE PANHANDLE
WILL DRY EVEN FURTHER FROM THE NORTHWEST. COOLER AIR WILL BEGIN
ENTERING THE PANHANDLE AT THIS TIME, WHICH IS KEY TO THE PIVOTAL
CHRISTMAS DAY FORECAST.

A WEAK TROUGH TRAVERSING THE NORTHERN GULF TUESDAY NIGHT MAY
INCITE SOME SCATTERED/ISOLATED SHOWER ACTIVITY ACROSS THE
PANHANDLE WEDNESDAY, BUT QPF IS PRETTY INSIGNIFICANT HERE. SHOWERS
WILL LIKELY BEGIN AS SNOW OVER THE NORTHERN PANHANDLE BUT
CHANGEOVER TO ALL RAIN ALONG THE COAST OR MIX OVER
GUSTAVUS/HOONAH. ANY ISOLATED SHOWER FOR JUNEAU WEDNESDAY
AFTERNOON WILL BE SNOW.

CHRISTMAS EVE A FRONT MOVES INTO THE GULF AND BEGINS WILL BE
POISED TO SPREAD PRECIPITATION ONSHORE BY CHRISTMAS MORNING. THERE
IS SOME MODEL DISAGREEMENT ON TIMING AND POSITION OF THE FRONT.
BUT IT LOOKS TO PROVIDE SOME LIGHT SNOW OVER MOST PORTIONS OF THE
NORTHERN PANHANDLE. ACCUMULATIONS WILL BE LESS THAN 3 INCHES BUT
MORE THAN LIKELY 1 TO 2, AS THIS SYSTEM WILL NOT CARRY A LOT OF
TROPICAL MOISTURE WITH IT, SINCE IT'S COMING FROM THE WEST. MODELS
ARE SUGGESTING THICKNESSES RISE ABOVE THE 1290 LINE THURSDAY
AFTERNOON THEREFORE SUPPORTING AT LEAST A MIX IF NOT A CHANGEOVER
TO RAIN FOR MUCH OF THE PANHANDLE. ALLOWED A MIX COAST-WARD AND
SOUTHWARD FROM JUNEAU BUT KEPT JUNEAU ALL SNOW AND SET THE
CHANGEOVER HERE FOR LATE THURSDAY NIGHT. HOWEVER, JUNEAU MAY SEE A
MIX AS EARLY AS THURSDAY AFTERNOON WITH A COMPLETE CHANGEOVER TO
RAIN THURSDAY NIGHT. IN ADDITION, WE NUDGED WINDS UPWARDS OVER THE
GULF ESPECIALLY CHRISTMAS EVE AND TO SOME EXTEND CHRISTMAS DAY.
WATCH FOR THESE WINDS TO RISE FURTHER IF THE MODELS KEEP THE
CURRENT ADVERTISED STRENGTH OF THE FRONT. SHOULD WE THINK MODELS
ARE CONVERGING A QUICK EXAMINATION OF THE 18Z GFS TEASES US
OTHERWISE AS IT TAKES THE LOW ON A SLIGHTLY MORE SOUTHERLY TRACK
AND ALLOWS OFFSHORE WINDS OVER THE NORTHERN PANHANDLE TO INHIBIT
SNOW DEVELOPMENT HERE, BUT COULD EFFECTIVELY PUSH THE RAIN/SNOW
LINE SOUTHWARD SHIFTING THE GREATEST SNOW FOR AREAS BETWEEN
PETERSBURG AND ANGOON. BUT THIS IS AN OUTLIER AT THIS POINT.

ONSHORE FLOW WILL KEEP PRECIPITATION IN THE FORECAST THROUGH
FRIDAY BEFORE A RIDGE GIVES SOUTHEAST A BREAK THIS WEEKEND.
FORECAST CONFIDENCE RISING FOR A WHITE CHRISTMAS, AND GOOD, BUT
NOT 100 PERCENT SOLID EITHER, AS THE GFS SO POIGNANTLY REMINDS US.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH TUESDAY MORNING
     FOR AKZ027.
         STRONG WIND FROM 3 AM AKST TUESDAY THROUGH TUESDAY AFTERNOON FOR
     AKZ028.
MARINE...STORM WARNING FOR PKZ041-042.
         GALE WARNING FOR PKZ012-013-036-043.
         SMALL CRAFT ADVISORY FOR PKZ011-021-022-031>035-051-052.

&&

TPS/JWA

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU