Gale Warning 349, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
350 PM AKST SUN NOV 18 2012

.SHORT TERM...A BROAD AREA OF LOW PRESSURE IN THE GULF OF ALASKA
WITH HIGH PRESSURE FIRMLY BUILDING OVER THE CANADIAN YUKON WILL
ACCELERATE WINDS TO GALE...AND EVEN STORM FORCE FOR LYNN
CANAL...OVER MUCH OF THE PANHANDLE TONIGHT AND MONDAY. IN
ADDITION...ANOTHER MOUNTAIN WAVE TAKU EVENT IS LIKELY DEVELOPING
LATE THIS EVENING FOR DOWNTOWN JUNEAU AND DOUGLAS....MORE ON THIS
LATER. MODELS NAM AND ECMWF HAVE THE GENERAL IDEA OF SHORTWAVE
SURFACE CIRCULATIONS ROTATING CLOCKWISE AROUND THE GULF OF ALASKA
THROUGH MONDAY...HOWEVER TIMING AND LOCATIONS OF INDIVIDUAL LOWS
ARE NOT CONCRETE BUT GENERAL. THE FIRST SHORTWAVE OF THE EVENING
IS CURRENTLY MOVING UP THE CENTRAL PANHANDLE COAST THIS AFTERNOON
AND SPREADING SNOW FROM NEAR JUNEAU TO NEAR PETERSBURG AND
WESTWARD. THE SNOW IS SPREADING NORTHWESTWARD AND THUS HAVE
CATEGORICAL POPS FOR MUCH OF THE AREA FROM NORTHERN CHATHAM
COAST-WARD THIS EVENING. OVERALL SHOWER ACTIVITY SHOULD DIMINISH
BY MIDNIGHT WITH POPS REDUCING MARKEDLY. WHILE INDIVIDUAL LOWS
ROTATING AROUND THE UPPER TROUGH IN THE GULF MAY BE HANDLED
SLIGHTLY DIFFERENTLY IN MODELS...THE OVERALL GRADIENT AND
ORIENTATION HAS REMAIN UNCHANGED FROM PREVIOUS FORECASTS...SO
LITTLE CHANGES TO THE WINDS OVER THE PANHANDLE. OVER THE OUTSIDE
WATERS...HAVE BUMPED WINDS BY 5 KT FOR TONIGHT AND MONDAY TIME
PERIOD. AS THE SHORTWAVE OF THIS EVENING EXITS TO SEA
OVERNIGHT...ANOTHER SHORTWAVE WILL MOVE INTO THE SOUTHERN ZONES
MONDAY MORNING AND SPREAD ANOTHER ROUND OF PRECIPITATION
NORTHWARD THROUGH THE PANHANDLE. HOWEVER...LYNN CANAL SHOULD
REMAIN DRY MONDAY AS OUTFLOW WILL TEND TO KEEP THEM DRY. IN
ADDITION...WITH VERY STRONG...PERSISTENT WINDS...COLD
TEMPERATURES...AND CHILLY WATER TEMPERATURES...EXPECT FREEZING
SPRAY OVER MUCH OF THE NORTH OVERNIGHT INTO MONDAY MORNING.

 NAM STRONGEST WITH MOUNTAIN WAVE TAKU EVENT FOR TONIGHT...WITH
INGREDIENTS OF INVERSION...REVERSE FLOW ABOVE CRITICAL LEVEL NEAR
500 MB...AND CROSS BARRIER FLOW ALL COMBINING FOR FAVORABLE
CONDITIONS TONIGHT. WRF WINDS HAVE ALSO HINTED FOR STRONGER WINDS
NEAR DOWNTOWN JUNEAU. WHILE WARNING ISSUED FOR 9 PM THIS SUNDAY
EVENING...TIME FOR WORST WINDS WILL BE POST MIDNIGHT INTO
MID-MONDAY MORNING. WINDS SHOULD SLOWLY DIMINISH BY LATE MONDAY
MORNING AS REVERSE FLOW RISES ABOVE 500 MB THUS REMOVING SOME
SUPPORT FOR EVENT. WINDS WILL REMAIN STRONG THROUGH THE
AFTERNOON...BUT WILL NOT QUALIFY AS THE ELEVATED CATEGORY OF
HIGH...THUS TO PREVENT CONFUSION DECIDED TO ELIMINATE HEADLINE
AFTER MUCH MORE SIGNIFICANT WARNING HEADLINE.

&&

.LONG TERM...MEDIUM RANGE MODELS ARE IN GENERAL AGREEMENT THROUGH
THE MID WEEK WITH AN UPPER LEVEL SHORTWAVE REMAINING OVER THE GULF
WITH AN EMBEDDED CLOSED UPPER LOW ROTATING WITHIN THE SHORTWAVE.
THE ASSOCIATED SURFACE LOW MOVES SOUTHEAST AND BECOMES NEAR
STATIONARY OVER THE FAR SOUTHEASTERN GULF THROUGH THE MID WEEK.
REFRESHED THE INHERITED FORECAST PACKAGE WITH THE ECMWF THROUGH
LATE WEDNESDAY NIGHT FOR ITS MOST PERSISTENT RUN-TO-RUN
PERFORMANCE AND BEST HANDLING OF THE SURFACE LOW. AN OCCLUDED
FRONTAL PASSAGE WILL MOVE SOUTHEAST WITH HIGHER POPS...LEAVING THE
NORTHERN AND CENTRAL PANHANDLE GENERALLY DRY. STRONG ARCTIC HIGH
WILL REMAIN OVER THE YUKON TERRITORY AND MAINTAIN STRONG NORTHERLY
PRESSURE GRADIENT. THEREFORE...STRONG OFFSHORE FLOW WILL CONTINUE
ACROSS THE FORECAST DOMAIN WITH STRONG WINDS HEADLINE FOR SKAGWAY
AREA EXTENDED INTO LATE MONDAY NIGHT. STORM FORCE WINDS WILL
CONTINUE THROUGH TUESDAY NIGHT OVER NORTHERN LYNN CANAL.

 MODEL DIFFERENCES BECOME LARGER FOR THE SECOND HALF OF THE WEEK
INTO THE WEEKEND AS THE UPPER LEVEL SHORTWAVE TROUGH MOVES EAST
AND AN UPPER HIGH BUILDS OVER THE WESTERN ALASKAN INTERIOR. WITH
GROWING UNCERTAINTY...LEANED OVER THE NEW HPC ENSEMBLE APPROACH
BLENDED INTO THE PREVIOUS GRIDS THROUGH THE END OF THE LONG TERM
PERIOD. MODEL CONSENSUS KEEPS HINTING ANOTHER STORM MAY MOVE INTO
THE FORECAST DOMAIN BUT THE UNCERTAINTY IS TOO BIG TO INVITE THE
SYSTEM INTO THE FORECAST PACKAGE. YET THE PERSISTING ARCTIC AIR
WILL HOLD SOUTHEAST ALASKA A COLDER SIDE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING FROM 9 PM THIS EVENING TO 3 PM AKST MONDAY FOR
     AKZ025.
         STRONG WIND THROUGH MONDAY AFTERNOON FOR AKZ019.
         STRONG WIND THROUGH LATE MONDAY NIGHT FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012-013.
         GALE WARNING FOR PKZ011-021-022-031-033>035-043-051.
         SMALL CRAFT ADVISORY FOR PKZ032-036-041-042-052-053.

&&

JWA/AHN