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517
FXAK67 PAJK 231320
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
520 AM AKDT WED APR 23 2014

.SHORT TERM...UPPER TROF OVER SRN SE AK WILL DRIFT N INTO THE
CENTRAL AREA TONIGHT. VORT MAX OVER THE NRN PANHANDLE WILL DRIFT
WNW INTO THE NE GULF BY LATE THIS AFTERNOON. SFC LOW OVER NRN SE
AK WILL REACH THE FAR NE GULF BY LATE THIS AFTERNOON. INVERTED
TROF WILL DEVELOP NW INTO THE SRN PANHANDLE TONIGHT. USED MAINLY
THE 00Z ECMWF AS IT HAD BEST HANDLE ON THESE FEATURES.

MAIN FORECAST ISSUES WILL BE PRECIP POTENTIAL/CHARACTER AND HOW
QUICKLY ANY CLEARING WILL OCCUR. RIGHT NOW WITH SHORTWAVE OVER THE
NRN PANHANDLE...BROKEN AREA OF PRECIP IS OCCURRING FROM PAGN NWD
TO PAHN. THINK THIS AREA OF PRECIP WILL SHIFT WNW WITH THE
SHORTWAVE WITH A DIMINISHING TREND FROM THE E-SE LATER THIS
AFTERNOON AND TONIGHT. THINK SOME PRECIP WILL REACH THE PAYA AREA
BY LATE THIS AFTERNOON OR EARLY THIS EVENING AS VORT MAX MOVES
INTO THAT AREA. MODEL SOUNDINGS SHOW A WEAK FRONTAL LAYER IN THE
MID-LEVELS OVER THE NRN HALF OF THE AREA...SO WENT WITH PERIODS OF
RAIN THERE. WILL PROBABLY TRANSITION TO SCT SHOWERS TONIGHT BUT
FOR NOW JUST INDICATED DIMINISHING TREND IN STEADIER PRECIP FOR
SIMPLICITY. OVER THE S...WITH COLDER AIR ALOFT...THINK SOME
SHOWERS WILL POP UP WITH THE DAYTIME HEATING OVER AND NEAR THE
MTNS...SO GENERALLY GOING WITH ISO/SCT SHOWERS OVER THE S...WITH
THE BEST THREAT IN ZONE 26. THESE SHOWERS SHOULD DIMINISH THIS
EVENING WITH LOSS OF DAYTIME HEATING.

AS UPPER TROF SHIFTS NWD AND LOW LEVEL N-NW FLOW INCREASES WITH
THE DEVELOPING INVERTED TROF...THINK SRN AREA WILL SEE DECENT
AMOUNT OF CLEARING ESPECIALLY TONIGHT. THERE MAY BE LARGER BREAKS
IN THE CLOUDS THIS AFTERNOON OVER THE FAR SRN AREA HOWEVER. THIS
PART OF THE FORECAST IS TRICKY THOUGH DUE TO SOME MODEL
UNCERTAINTY HANDLING SMALL SCALE FEATURES IN LOW LEVELS THERE.

OTHERWISE...WITH FAIRLY WEAK PRESSURE GRADIENTS WINDS WILL BE
RATHER LIGHT...GENERALLY UP TO 15 KT. THERE ARE SOME LOCAL
ENHANCEMENTS TO THE WINDS ALONG THE OUTER COAST WITH WEAK TIP JETS
THERE BUT THIS WILL WEAKEN TODAY. A SYSTEM CURRENTLY WELL TO THE
SW OF THE AREA WILL SEND IN INCREASING SWLY SWELLS INTO THE ERN
GULF THRU TONIGHT...BUT CURRENTLY EXPECT THEM TO REMAIN BELOW SCA
LEVELS FOR THE GULF COASTAL WATERS.

&&

.LONG TERM...A COMPACT MIDLEVEL SHORTWAVE TROUGH WILL BE THE
PRIMARY WEATHER MAKER AT THE START OF THE LONG TERM PERIOD. THIS
FEATURE WILL BE LOCATED OVER THE NRN CWA THU AFTERNOON...AND THEN
DEPART NWD INTO THE YUKON TERRITORY BY FRI MORNING. THE UPPER
DISTURBANCE WILL YIELD CLOUDY SKIES AND SHOWERS FOR NRN
AREAS...WHILE SKIES ARE EXPECTED TO BEGIN CLEARING OVER THE SRN
PANHANDLE. AFTERNOON SUNSHINE COMBINED WITH WARMING 850 MB
TEMPERATURES SHOULD AID IN BOOSTING THU HIGHS INTO THE MID TO
UPPER 50S FROM ROUGHLY JUNEAU SWD. DRY MIDLEVEL AIR WILL THEN
SPREAD NWD INTO THE CNTRL/NRN PANHANDLE ON FRI. THIS WILL SUPPORT
PLEASANT AFTERNOON CONDITIONS...WITH TEMPERATURES IN THE LOW TO
MID 50S...AND A WEAK PRESSURE GRADIENT RESULTING IN LIGHT WINDS.
THE LIGHT PRESSURE GRADIENT AND MILD TEMPERATURES MAY ALSO SUPPORT
SEA BREEZE DEVELOPMENT FOR LOCATIONS SUCH AS
JUNEAU...HAINES/SKAGWAY...AND GUSTAVUS.

MEANWHILE...A WEAK UPPER DISTURBANCE LOCATED NEAR COASTAL B.C. WILL
BE ENTRAINED NWD INTO A BROAD AREA OF TROUGHING OCCURRING OVER THE
WRN/CNTRL GULF FRI NIGHT. THIS WILL HERALD THE RETURN OF CLOUDS AND
PRECIPITATION FOR SE AK BEGINNING THIS WEEKEND THROUGH THE
REMAINDER OF THE LONG TERM PERIOD. IN ADDITION...SURFACE LOW
PRESSURE WILL DEEPEN OVER THE GULF...WHICH WILL LEAD TO A
TIGHTENING GRADIENT OVER THE OUTER WATERS BY SAT...INCREASING
ESELY WINDS...AND BUILDING SEAS.

THE 00Z/23 MODEL GUIDANCE WAS IN GENERAL AGREEMENT THROUGH THE
WEEKEND...WITH FORECAST CONFIDENCE ABOVE AVERAGE. MODEL SPREAD
THEN INCREASES WITH THE EVOLUTION OF THE GULF CYCLONE MON THROUGH
WED...AND FORECAST CONFIDENCE SUBSEQUENTLY DECREASES. MINOR
ADJUSTMENTS TO PRESSURE/WINDS /USING 00Z ECMWF BLENDED IN WITH
PREVIOUS FORECAST/...TEMPERATURES...AND POP/QPF WERE MADE THROUGH
SUN...WITH VERY LITTLE CHANGE INTRODUCED TO THE FORECAST FOR MON
AND BEYOND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.

&&

$$

RWT/GARNER







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