Gale Warning 405, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
336 PM AKST SAT NOV 21 2015

.SHORT TERM...WINDS AND PRECIPITATION HAVE WORKED OUT AS PLANNED.
SKAGWAY'S WINDS GUSTED TO 66 MPH THIS MORNING WITH OTHER GUSTS TO
60 MPH THROUGH THE MORNING. HOWEVER, AS A SHORT-WAVE CAUSES SOME
PRESSURE FALLS ACROSS THE NORTHERN PANHANDLE...GRADIENTS THROUGH
THE CANAL WILL ALSO LOWER A LITTLE. THEREFORE, STRONG WINDS WILL
CONTINUE THROUGH SKAGWAY OVERNIGHT, BUT GUSTS WILL STAY BELOW THE
60 MPH WARNING CRITERIA. WESTERLIES THROUGH CROSS SOUND HAVE
GUSTED TO 77 MPH...EASILY VERIFYING STORM FORCE WINDS. POINT
RETREAT AND PORTLAND ISLAND EASILY VERIFIED GALES WITH SOUTHWEST
GUSTS TO 50 MPH. IN ADDITION...STRONG GUSTS WERE REPORTED IN
JUNEAU AND YAKUTAT AS WELL AS BREEZY CONDITIONS IN GUSTAVUS,
HOONAH, AND SITKA. SOME BREEZY CONDITIONS ALSO WERE REPORTED TO
THE SOUTH AROUND FRONTAL PASSAGE TIME, BUT THESE HAVE RELAXED THIS
AFTERNOON. AS 925 MB WESTERLY WINDS FALL OVERNIGHT, AND GRADIENTS
RELAX ACROSS THE PANHANDLE, WINDS WILL DIMINISH THROUGH THE NIGHT.
AS A LOW DEVELOPS OVER THE NORTHERN GULF TONIGHT AND DROPS INTO
THE NORTHERN PANHANDLE...HIGH PRESSURE BUILDS TO THE
NORTH...THEREFORE, CAUSING SOUTHERLIES TO FLIP TO NORTHWESTERLIES
OVER MUCH OF THE NORTH. HEAVY RAIN ALSO FELL AHEAD OF THE FRONT
OVERNIGHT WITH 1 TO 3 INCHES ACROSS THE PANHANDLE WITH LCL HIGHER
AMOUNTS. PELICAN CAME IN WITH 5.5 INCHES WITH SNETTISHAM TOPPING 7
INCHES.

NOW THE BIG CHANGE FOR THE FORECAST WAS TO LOOK AT TEMPERATURES.
1000 TO 850 MB THICKNESSES WILL DECREASE RAPIDLY TONIGHT ACROSS
THE NORTHERN PANHANDLE AND CONTINUE DECREASING OVER THE CENTRAL
AND SOUTHERN PANHANDLE ON SUNDAY. HOWEVER, THE WESTERLY TRAJECTORY
OF THE MID-LEVELS TAKES IT ACROSS THE GULF WHERE MOISTURE FLUX
WILL KEEP THE LOWER LEVELS WARMER THAN ATMOSPHERIC COLUMN
THICKNESSES WOULD SUGGEST. THUS, WE HAVE SLOWED THE COOLING ACROSS
THE PANHANDLE TONIGHT AND INTO SUNDAY MORNING. THIS HAS
NEGATIVELY AFFECTED SNOW ACCUMULATION ESTIMATES. BLENDED HEAVILY
TO THE ECMWF TEMPERATURES AND RELIED ON MOS FOR TIMING FOR
TEMPERATURES BETWEEN SYNOPTIC HOURS. THIS RESULTED IN LOW
TEMPERATURES IN THE MID-MORNING SUNDAY MORNING WITH WEAK DIURNAL
RISES IF AT ALL INTO SUNDAY AFTERNOON. HAINES, SKAGWAY, AND
YAKUTAT THOUGH SHOULD SEE DROPS.

FINALLY...WE TRIMMED POPS AND QPF THROUGH THE AFTERNOON BEGINNING
FROM THE NORTHWEST INTO THE NORTHERN PANHANDLE TOMORROW AFTERNOON.
THUS WHEN THE ATMOSPHERE IS BY AND LARGE THE COLDEST...IT WILL
ALSO BE DRIER AS WELL.

USED NAMDNG AND GFS22 FOR POPS/QPF. MADE MINOR TWEAKS FOR WIND
LOCAL EFFECTS. ECMWF HELPED AND VARIOUS MOS PRODUCTS HELPED WITH
TEMPERATURES.

.LONG TERM...ON SUNDAY EVENING SHOWERS WILL BE DIMINISHING FROM
NORTH TO SOUTH ACROSS THE PANHANDLE. A STRENGTHENING AREA OF HIGH
PRESSURE WILL BE SLIDING ACROSS THE YUKON AND INTO BRITISH
COLUMBIA LATE SUNDAY NIGHT AND MONDAY. THIS WILL BRIEFLY
STRENGTHEN THE NORTHERLY GRADIENT OVER THE NORTHERN PANHANDLE WITH
WINDS INCREASING TO GALE IN NORTHERN LYNN CANAL. 850 MB
TEMPERATURES WILL FALL TO AROUND -10 TO -12 C ON MONDAY BUT THE
COLDEST AIR ASSOCIATED WITH THIS HIGH WILL STAY ON THE OTHER SIDE
OF THE MOUNTAINS IN CANADA. THE LOWEST TEMPERATURES WILL BE FELT
ON MONDAY NIGHT WITH TEMPERATURES FALLING INTO THE TEENS AND 20S.
AS THE HIGH DOES SLIDE INTO BRITISH COLUMBIA THE POTENTIAL FOR
GUSTY WINDS IN OUTFLOW LOCATIONS ALONG THE COAST MOUNTAINS WILL
INCREASE INCLUDING NEAR DOWNTOWN JUNEAU AND DOUGLAS. THIS WILL NOT
BE A LONG LIVED EVENT BUT GUSTS OF 25 TO 35 MPH COULD OCCUR.

AS WE HEAD INTO MID WEEK A SHARPENING UPPER LEVEL RIDGE OVER THE
GULF WILL BECOME THE DOMINANT WEATHER FEATURE FOR SOUTHEAST
ALASKA. THIS RIDGE COMBINED WITH AN UPPER LOW CUTTING OFF SOUTH OF
THE ALEUTIANS AND AN UPPER LOW OVER THE WESTERN US WILL HELP TO
INDUCE AN OMEGA BLOCK OVER THE AREA. THE OMEGA BLOCK WILL SLOW THE
WESTERN PROGRESSION OF SYSTEMS MOVING ACROSS THE GULF. IT ALSO
WILL ADVECT VERY WARM AIR ALOFT BEGINNING ON TUESDAY. BOTH THE
12Z GFS AND ECMWF INDICATE 850 MB TEMPERATURES AROUND +5 TO 6 C
OVER THE SOUTHERN PANHANDLE WEDNESDAY NIGHT AND +1 TO +2 C IN THE
VICINITY OF JUNEAU. THE PRESENCE OF THIS WARM AIR ALOFT COMBINED
WITH WEAK FLOW ESPECIALLY OVER THE SOUTHERN HALF OF THE PANHANDLE
COULD RESULT IN A PERIOD OF WIDESPREAD FOG AND/OR DRIZZLE MID
WEEK. THIS IS A CONCERN DUE TO THE INCREASED AMOUNT OF TRAVEL
EXPECTED OVER SOUTHEAST ALASKA AROUND THANKSGIVING. BASED UPON
THIS AS WELL AS THE RIDGE AXIS SHIFTING EAST OF THE PANHANDLE HAVE
BUMPED UP SKY COVER TO MOSTLY CLOUDY DURING THIS TIME PERIOD.

A FRONT WILL SLOWLY MOVE ACROSS THE GULF AGAINST THE BACK SIDE OF
THE RIDGE NEXT WEEK REACHING YAKUTAT WEDNESDAY/THURSDAY. LATEST
MODEL GUIDANCE INDICATES THIS FRONT WON'T REACH THE REMAINDER OF
THE AREA UNTIL THURSDAY NIGHT AT THE EARLIEST. PRECIPITATION
CHANCES WILL INCREASE BY THE WEEKEND HOWEVER. SOUTHERLY FLOW AND
WARM AIR ALOFT IN PLACE WOULD KEEP SNOW CONFINED TO THE HIGHER
ELEVATIONS.

USED THE 12Z NAM AND ECMWF FOR UPDATES TO THE FORECAST THROUGH
DAY 4. THEN USED THE LATEST WPC GUIDANCE FOR THE REMAINDER OF THE
EXTENDED PERIOD.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 9 PM AKST THIS EVENING FOR AKZ017-022.
         STRONG WIND UNTIL 3 AM AKST SUNDAY FOR AKZ018.
MARINE...STORM WARNING FOR PKZ022.
         GALE WARNING FOR PKZ012-013-021-043-051>053.
         SMALL CRAFT ADVISORY FOR PKZ011-031>035-041-042.

&&

JWA/TPS

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