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000
FXAK67 PAJK 221418
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
618 AM AKDT WED MAY 22 2013

.SHORT TERM...THE NORTHERN, CENTRAL, AND SOUTHWESTERN PANHANDLE
ALL ENJOYED CLEAR SKIES OVERNIGHT. HOWEVER, AN UPPER LEVEL LOW
CENTERED OVER WASHINGTON STATE HAS BEEN DIRECTING SOME BACK-DOOR
MOISTURE INTO CENTRAL AND NORTHERN BC OVERNIGHT. AND SOME OF THIS
MOISTURE HAS MANAGED TO PENETRATE THE INTERIOR PARTS OF THE
PANHANDLE IN THE FORM OF MID TO HIGH LEVEL CLOUDS. WEBCAMS
CONFIRM THAT THERE ARE MORE CLOUDS IN THE SOUTHEASTERN PANHANDLE,
BUT SKAGWAY AND EVEN HAINES ARE SEEING SOME CLOUDS AT THIS HOUR
AS WELL. ALL MODELS AGREE THAT YESTERDAY`S BEAUTIFUL SUNNY SKIES
AND THE CLEAR ONES OVERNIGHT HAVE RESULTED FROM DRY NORTHWESTERLY
FLOW ALOFT. BUT IN BC, THE FLOW IS MORE SOUTHERLY, AND THEREFORE,
THERE IS A BAND OF DEFORMATION ACROSS THE INTERIOR PANHANDLE THAT
WILL ACT AS A WALL TO PREVENT CLOUDS FROM ENCROACHING MUCH TO THE
WEST. THIS DEFORMATION ZONE DEVELOPS SOME SPIN INTO THE AFTERNOON
AS A RIDGE ALOFT PUSHES IT TO THE NORTHEAST. THIS WILL DEFLECT
ANY SHOWER ACTIVITY AWAY FROM US. HOWEVER, A FEW OUTER LOCATIONS
MAY NOT ESCAPE THE MOISTURE COMPLETELY AS BOTH HYDER AND WHITE
PASS MAY EXPERIENCE AN ISOLATED SHOWER TODAY. A FEW CANADIAN
STATIONS IN INTERIOR BC REPORTED RAIN OVERNIGHT, AND PRINCE
RUPERT HAS SEEN RAIN EARLY THIS MORNING. SO SHOWERS ARE NOT OUT
OF THE QUESTION.

 AS THIS UPPER LEVEL SPIN ZONE IS PUSHED NORTH AND EAST, THE
RIDGE ALOFT PROGRESSING EASTWARD ACROSS THE GULF WILL ALLOW THE
NORTHWESTERLY FLOW TO VEER TO MORE ONSHORE. THIS WILL WEAKEN THE
SURFACE HIGH OVER THE GULF, FLATTENING IT A BIT, AGAIN TO DIRECT
WINDS SLIGHTLY FROM NORTHWEST...MISSING THE SHORE...TO A BIT MORE
WEST. THIS COMBINED WITH DAYTIME HEATING IN THE 60S OVER MOST
PARTS OF THE PANHANDLE WILL BEGIN THE CHANGEOVER THIS AFTERNOON.
CHANGEOVER TO WHAT? WHILE NOT EVIDENCED ON YESTERDAY EVENING`S
VISIBLE, STILL THINK SOME STRATUS WILL DEVELOP OVER THE GULF AND
MOVE INTO OUR COASTAL COMMUNITIES LIKE YAKUTAT, PELICAN, SITKA,
AND CRAIG LATE TONIGHT...EVEN MOVING INTO ICY STRAIT CORRIDOR.
HOONAH AND GUSTAVUS COULD SEE A FEW STRATOCUMULUS LATE. THUS
RAISED OVERNIGHT LOW TEMPERATURES IN THIS REGION A BIT.

 THIS UPPER LEVEL DEFORMATION ROTATING INTO A VORTICITY LOW ALOFT
THIS AFTERNOON WILL IN TURN WEAKEN HIGH PRESSURE OVER NORTHWEST
CANADA. WITH WEAKENING HIGH PRESSURE OVER CANADA AND WEAKENING
HIGH PRESSURE OVER THE GULF, THE GRADIENTS AROUND A THERMAL
TROUGH EXTENDING NORTHWEST OVER THE PANHANDLE FROM CENTRAL BC
WILL SLACKEN QUICKLY THROUGH THE REST OF TODAY. OUTFLOW WINDS,
ALTHOUGH DEVELOPED AT SHEEP MOUNTAIN, NEVER REACHED THE SURFACE
AT DOWNTOWN JUNEAU OVERNIGHT, JUST LIKE THE PREVIOUS NIGHT. BUT
WINDS IN NORTHERN LYNN CANAL, AND MOST RECENTLY AT SKAGWAY HAVE
BEEN SCA STRONG FROM THE NORTH. THE WEAKENING TREND FROM THE
SYNOPTIC GRADIENT WILL ALLOW MESOSCALE SEA BREEZES TO ASSUME
CONTROL OF LOCAL WIND PATTERNS THIS AFTERNOON. SO EXPECT SOME
TYPICAL CHANNEL BREEZES TO BEGIN DEVELOPING LATE THIS MORNING AND
AFTERNOON IN SPOTS.

 IT IS A DEFINITE LUXURY TO SWEAT OVER PARTLY CLOUDY OR SUNNY SKY
ON A FORECAST SHIFT. BUT WHILE I WANTED TO FUDGE SKIES
TODAY...ESPECIALLY OVER THE INTERIOR PANHANDLE TO MOSTLY SUNNY OR
PARTLY CLOUDY IN SOME CASES, LONG TERM PARTNER CONVINCED ME THAT
FORECASTERS LOOK UP AND PEOPLE LOOK DOWN. IF PEOPLE SEE A SHADOW
IN SOUTHEAST ALASKA, IT MEANS A SUNNY DAY. SO TO A FORECASTER SKY
COVER MAY READ AS OPTIMISTIC, BUT TO THE PUBLIC, HOPEFULLY IT
WORKS JUST RIGHT. TO BE CLEAR I WILL STATE THAT THERE WILL BE
SOME ALTO-CUMULUS AND CIRRUS CLOUDS PASSING ACROSS THE SOUTHERN
AND INTERIOR PANHANDLE TO ADD TEXTURE TO TODAY`S SUNSHINE.

 FIRE WEATHER...RELATIVE HUMIDITIES BOTTOMED OUT IN THE TEENS
YESTERDAY AFTERNOON AND EARLY EVENING IN SKAGWAY ALONG DRYING
NORTHEAST WINDS. AS FUELS WERE ALREADY DRY, THIS ALL SUPPORTED A
RED FLAG WARNING BEING ISSUED YESTERDAY AFTERNOON. FEEL THAT
WEAKENING WINDS THROUGH THE REST OF TODAY AND POSSIBLY A
SWITCHOVER TO SOUTH LATE THIS AFTERNOON MAY KEEP RH`S FROM
DROPPING AS LOW AS YESTERDAY. BUT THIS WILL BE WATCHED.

 HYDROLOGY...THERE WILL BE NO ISSUES WITH HYDROLOGY FOR WEDNESDAY
AND WEDNESDAY NIGHT. DID EMPLOY ECMWF WITH SOME NAM AND RFC QPE
FOR QPF ACROSS THE FORECAST AREA AND WATERSHEDS OVER BC. MADE FEW
CHANGES.

 MODEL OF CHOICE WAS THE NAM, WITH A LITTLE ECMWF THROWN IN FOR
POP AND QPF. BUT CHANGES WERE MAINLY LOCAL IN NATURE AND WERE
SMALL. CONFIDENCE IN FORECAST GOOD OVERALL.

 &&

.LONG TERM.../THU THROUGH TUES/ THE CHALLENGE WITH THE LONG TERM
FORECAST IS DETERMINING WHEN THE CURRENT WARM AND DRY WEATHER WILL
END. IT NOW APPEARS TEMPS WILL REMAIN AT OR ABOVE MORMAL FOR MUCH
OF THE PANHANDLE THROUGH THE WEEKEND. BUT SOME LIGHT RAIN MAY
AFFECT THE REGION...ESPECIALLY THE SOUTHERN PANHANDLE...AS SOON AS
FRI. FORECAST CONFIDENCE IN THIS TRANSITION IS WEAK AS MODELS ARE
SHOWING DIFFERENT SOLUTIONS.

 IN GENERAL SE AK IS UNDER THE INFLUENCE OF A SUMMER TIME WEATHER
PATTERN WITH HIGH PRESSURE...SURFACE AND ALOFT...TO THE WEST OVER
THE GULF AND LOWER PRESSURE EAST OF THE COASTAL MOUNTAINS.
SATELLITE IMAGERY THIS MORNING SHOWS A MOIST SE FLOW ALOFT OVER
BRITISH COLUMBIA ASSOCIATED WITH AN UNSEASONABLY COLD AND
UNSTABLE UPPER LOW OVER THE PAC NW. BY FRI THIS UPPER LOW IS
FORECAST BY THE GFS TO WEAKEN BUT DRIFT NORTH AND WEST AND
POSSIBLY STEER A BAND OF SHOWERS INTO THE SOUTHERN
PANHANDLE...ESPECIALLY NEAR THE COASTAL MOUNTAINS. MODEL RAINFALL
AMOUNTS DONT LOOK VERY HEAVY BUT CANADIAN RAOBS ARE ALREADY
SOMEWHAT MOIST AND STABILITY WILL BE DECREASING AS COOL AIR MOVES
IN ALOFT.

 THIS CHANGE WILL ALSO FLATTEN THE OFFSHORE RIDGE SLIGHTLY AND
RESULT IN A BIT STRONGER WESTERLY ONSHORE FLOW. LOW MARINE
STRATUS CLOUDS ARE CURRENTLY OVER THE CENTRAL GULF UNDER THE
SURFACE RIDGE AXIS. THE NAM INCREASES LOW LEVEL BOUNDARY LAYER RH
ALONG THE COAST AS SOON AS THUR BUT THE RIDGE AXIS IS FORECAST TO
REMAIN OFFSHORE. THAT SUGGESTS THE LOW CLOUDS WONT MOVE INTO THE
INNER CHANNELS VERY QUICKLY. MOS GUIDANCE CONTINUES TO PREDICT AT
OR ABOVE AVERAGE TEMPS NEXT WEEK. MY GUT FEELING IS THAT THE
UPPER LEVEL LOW DRFTING NORTH AND SLOW BUT STEADILY INCREASING
ONSHORE FLOW WILL GRADUALLY INCREASE CLOUD COVER FRI AND SAT AND
EVENTUALLY LEAD TO WIDESPREAD CLOUDS AND CHANCES OF LIGHT RAIN
OVER THE PANHANDLE BY SUNDAY AND MONDAY.

 &&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-031-034-036-041>043.

&&

$$

JWA/TA