252  
FXAK67 PAJK 192250  
AFDAJK  
 
SOUTHEAST ALASKA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JUNEAU AK  
250 PM AKDT SUN AUG 19 2018  
   
SHORT TERM
 
OUR RIDGE OF HIGH PRESSURE OVER THE EASTERN GULF  
CONTINUES TO PROVIDE US WITH PLEASANT WEATHER TODAY. SKY  
CONDITIONS ARE CURRENTLY MOSTLY CLEAR THROUGHOUT ALL OF SE ALASKA,  
AND WITH TEMPERATURES IN THE MID TO UPPER 60S AND RELATIVELY  
LIGHT WINDS, OUTDOOR ACTIVITIES ARE HIGHLY ENCOURAGED TODAY.  
 
BY MONDAY, THIS PATTERN IS EXPECTED TO CHANGE FOR SOME LOCATIONS.  
THE DEEP UPPER LEVEL TROUGH OVER THE WESTERN GULF WILL BEGIN TO  
LIFT NORTHEAST, SHIFTING THE RIGHT JET REGION TO BE OVER THE NE  
GULF COAST, NAMELY YAKUTAT. THIS WILL AIM THE ADVECTED MOISTURE  
DIRECTLY OVER THE YAKUTAT AREA. WE'LL SEE RAIN CHANCES  
SUBSEQUENTLY INCREASE HERE. HOWEVER, DESPITE THE RIDGE WEAKENING  
AS THE LOW LIFTS, IT WILL BE SLOW TO PUSH OUT, LEAVING AN  
OPPORTUNITY FOR MOST OF THE PANHANDLE TO HAVE ANOTHER PLEASANT DAY  
IN STORE FOR TOMORROW. BASED ON 850 MB TEMPERATURE ANALYSIS, IT  
MAY EVEN BE A WARMER DAY FOR SOME AREAS DOWN SOUTH, WITH  
TEMPERATURES HOVERING AROUND THE 80 DEGREE MARK IN PLACES LIKE  
KETCHIKAN, HYDER, AND ANNETTE. MODELS DO SHOW THE MARINE LAYER  
MOVING INTO AREAS LIKE GUSTAVUS AND ELFIN COVE BY TOMORROW  
MORNING. CURRENT SATELLITE IMAGERY SHOWS THE MARINE LAYER JUST  
OFFSHORE THIS AFTERNOON, BUT FORECAST SOUNDINGS SHOW WIND VEERING  
TO BE OUT OF THE WEST-SOUTHWEST BY EARLY TOMORROW MORNING,  
INCREASING ONSHORE FLOW IN THESE AREAS.  
 
AS THE LOW CONTINUES TO WEAKEN AND LIFT NORTHEAST ON TUESDAY,  
HIGHER RAIN CHANCES WILL PIVOT TO NORTHERN AREAS IN THE  
PANHANDLE. PRECIPITATION AMOUNTS DO NOT APPEAR TO BE AS  
SUBSTANTIVE AS THE PREVIOUS DAY'S AMOUNTS OVER THE NE GULF COAST.  
AN ASSOCIATED WEATHER FRONT WILL ALSO MOVE EAST THROUGH THE  
EASTERN GULF THEN QUICKLY WEAKEN. THIS WILL ACT TO INCREASE WINDS,  
ALBEIT BRIEFLY, ALONG THE INNER CHANNELS AND INCREASE THE CLOUD  
COVER FOR MOST LOCATIONS. TEMPERATURES WILL BE COOLER ON TUESDAY  
DUE TO THIS INCREASED CLOUD COVER, PRECIPITATION, AND ONSHORE  
FLOW.  
   
LONG TERM.../TUESDAY THROUGH SATURDAY/
 
A SHARPLY DEFINED,  
NEGATIVELY TILTED UPPER LEVEL TROUGH WILL BE SITUATED OVER THE  
WESTERN GULF AT THE START OF THIS LONG RANGE FORECAST PERIOD. THE  
TROUGH WILL ROTATE NORTH AND THE TROUGH AXIS WILL PASS OVER  
SOUTHEAST ALASKA BY TUESDAY AFTERNOON. VERY STRONG UPPER LEVEL JET  
SUPPORT AND VIGOROUS MID LEVEL VORTICITY WILL STRENGTHEN A WEATHER  
FRONT THAT IS FORECAST TO BRING HEAVY RAIN TO THE NORTHEAST GULF  
COAST AREA TUESDAY AND TUESDAY NIGHT. CURRENT 24 HOUR RAINFALL  
TOTAL FOR THE NORTHEAST GULF COAST RANGES FROM 1.65 INCHES IN THE  
YAKUTAT AREA TO AS MUCH AS 3 INCHES WEST OF ICY BAY. RAIN WILL  
SPREAD SOUTH AND EAST THROUGH THE DAY AND NIGHT TUESDAY, BUT THE FRONT  
WILL WEAKEN RAPIDLY AS THE PARENT LOW WEAKENS OVER SOUTH CENTRAL  
ALASKA AND THE FRONT LOSES FAVORABLE JET SUPPORT. AS THE LOW  
WEAKENS AND FILLS AND THE FRONT MOVES OUT OF THE AREAS, HIGH  
PRESSURE WILL BUILD IN OVER THE GULF FROM THE SOUTH ON WEDNESDAY.  
MODELS ARE INDICATING THAT A SHORT WAVE TROUGH WILL RIDE UP OVER THE  
TOP OF THE RIDGE ON THURSDAY EVENING, MODE AGREEMENTS ON THIS FEATURE  
IS CURRENTLY VERY POOR WITH GFS BEING BY FAR THE MOST AGGRESSIVE  
IN TERMS OF POP. FOR NOW, HAVE LEFT THE FORECAST FOR THE LATTER  
HALF OF THE UPCOMING WEEK AS A VERY BROAD BRUSHED HIGH END CHANCE  
TO LOW END LIKELY FOR THE PROBABILITY OF RAIN.  
 
THE LOW ASSOCIATED WITH THE FRONT ON TUESDAY WILL BE WEAKENING AS  
IT APPROACHES FROM THE SOUTHWEST. THUS, HAVE ONLY SMALL CRAFT  
WINDS ASSOCIATED WITH THE FRONT OVER THE GULF. RESIDUAL RIDGING  
OVER THE PANHANDLE SHOULD RESULT IN VERY LITTLE WIND ON THE  
INSIDE AT FIRST. GRADIENT PINCHING AS THE FILLING LOW TRACKS  
INLAND AND OFF TO THE EAST WILL RESULT IN A STRONGER SOUTHERLY  
PRESSURE GRADIENT OVER THE FAR NORTHERN INNER CHANNELS. SMALL  
CRAFT WINDS ARE ANTICIPATED OVER LYNN CANAL TUESDAY NIGHT THROUGH  
WEDNESDAY AFTERNOON.  
 
DAYTIME HIGHS FOR THE WEEK ARE LOOKING TO BE SEASONABLE, RANGING  
FROM THE UPPER 50S TO MID 60S. OVERNIGHT LOWS WILL TREND A FEW  
DEGREES WARMER THAN NORMAL FOR LATE AUGUST OWING TO THE EXPECTED  
CLOUDINESS ASSOCIATED WITH FIRST THE FRONT AND THEN THE SHORT WAVE.  
 
USED A BLEND OF GFS AND ECMWF FOR UPDATES TO PRESSURE THROUGH  
TUESDAY NIGHT WITH GFS AS THE FOUNDATION FOR WIND SPEEDS. POP AND  
QPF FROM GFS FOR THE SAME TIMEFRAME. TEMPERATURES ADJUSTED USING  
GFS AND ENSEMBLE MOS. OVERALL FORECAST CONFIDENCE IS AVERAGE.  
 

 
   
AJK WATCHES/WARNINGS/ADVISORIES
 
 
PUBLIC...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-052.  
SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043-051-053.  
 

 
 

 
 
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