514  
FXUS63 KJKL 211439  
AFDJKL  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE JACKSON KY  
1039 AM EDT MON AUG 21 2017  
   
UPDATE
 
 
ISSUED AT 1039 AM EDT MON AUG 21 2017  
 
UPDATED NDFD FOR LATEST OBSERVATIONAL TRENDS. THERE WAS VERY  
LITTLE CHANGE IN THE ONGOING FORECAST. SKY COVER STILL LOOKS TO  
BE MINIMAL DURING THE EASTERN KY PARTIAL ECLIPSE THIS AFTERNOON.  
SOME THIN CIRRUS WILL MOVE ACROSS THE AREA FROM THE THUNDERSTORMS  
OVER IL, BUT IT APPEARS THAT THE THICKER CIRRUS WILL REMAIN NORTH  
OF OUR AREA.  
 
UPDATE ISSUED AT 745 AM EDT MON AUG 21 2017  
 
FRESHENED UP THE HOURLY TEMPERATURES, DEW POINTS, AND SKY COVER  
THROUGH THIS MORNING. PATCHY FOG WILL BURN OFF BY AROUND 9 AM,  
WITH SOME THIN CIRRUS MOVING IN FROM THE NORTHWEST OUT AHEAD OF A  
WEAKENING THUNDERSTORM COMPLEX LOCATED ACROSS THE MIDWEST.  
 

 
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 358 AM EDT MON AUG 21 2017  
 
SURFACE HIGH PRESSURE IS CENTERED NEAR THE MID-ATLANTIC, WITH A  
QUASI-STATIONARY BOUNDARY ALIGNED FROM THE GREAT LAKES TO THE  
CENTRAL PLAINS, WITH A SECONDARY WARM FRONT EXTENDING SOUTHEAST  
INTO THE OHIO VALLEY. ALOFT, AN UPPER LEVEL RIDGE RULES ACROSS THE  
SOUTHEAST CONUS, WITH FLATTER FLOW ACROSS THE MAJORITY OF THE  
MISSISSIPPI VALLEY. A MORE VIGOROUS SHORT WAVE TROUGH IS MOVING  
SOUTHEAST OUT OF THE SOUTHWEST CANADA, CURRENTLY MOVING THROUGH  
THE BRITISH COLUMBIA/ALBERTA BORDER.  
 
EASTERN KENTUCKY IS ENJOYING ANOTHER MOST CLEAR NIGHT, WITH AREAS  
OF VALLEY FOG. SOME DEBRIS HIGH CLOUDS HAVE BEEN MAKING IT INTO  
THE AREA FROM THE WEST, BUT THESE REMAIN PRETTY THIN. THE NEXT 24  
HOURS WILL REMAIN DRY, AS THE UPPER LEVEL RIDGE TO OUR SOUTHEAST  
REMAINS IN CONTROL. TODAY STILL LOOKS LIKE AN OVERALL GOOD VIEWING  
DAY FOR THE FULL ECLIPSE. HIGHS WILL PEAK IN THE UPPER 80S TO NEAR  
90, WITH SOME CUMULUS AND THINNER HIGH CLOUDS TO CONTEND WITH  
DURING THE DAY, BUT NOTHING EXTENSIVE.  
 
TONIGHT, SKIES WILL REMAIN MOSTLY CLEAR INITIALLY, AS AFTERNOON  
CUMULUS DRIES UP. MEANWHILE, THE CANADIAN SHORT WAVE TROUGH WILL  
DEEPEN AND CONTINUE TO MOVE SOUTHEAST, REACHING THE GREAT LAKES  
REGION BY DAWN TUESDAY. SOME HIGH CLOUDS WILL MOVE IN BY EARLY  
TUESDAY MORNING, KEEPING FOG A BIT LESS EXTENSIVE. LOWS WILL  
GENERALLY RANGE FROM 65 TO 70 DEGREES.  
 
AS THE SHORT WAVE TROUGH CONTINUES TO AMPLIFY ACROSS THE  
U.S./CANADIAN BORDER ON TUESDAY, LOW PRESSURE WILL ORGANIZE AND  
DEEPEN RAPIDLY ALONG THE SURFACE BOUNDARY TO THE EAST. THE COLD  
FRONT WILL MOVE SOUTHEAST ACROSS THE OHIO VALLEY TUESDAY  
AFTERNOON, WITH SHOWERS AND THUNDERSTORMS BREAKING OUT ALONG AND  
AHEAD OF THE BOUNDARY. THE BLENDED POPS YIELDED LIKELY VALUES FROM  
THE NORTHWEST DURING THE AFTERNOON, AND GIVEN THE FORCING AND  
INSTABILITY, THIS SEEMS REASONABLE. ADDITIONALLY, STRONGER 0-6KM  
BULK SHEAR VALUES THAN WE HAVE SEEN IN A WHILE WILL BE ON TAP,  
SUPPORTING A SEVERE THUNDERSTORM THREAT, ESPECIALLY ACROSS THE  
NORTHWEST HALF OF THE AREA. WILL HIGHLIGHT THIS THREAT IN THE HWO.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 358 AM EDT MON AUG 21 2017  
 
FORECAST WILL START OUT WITH A COLD FRONT APPROACHING THE REGION  
TUESDAY EVENING, AND TRAVERSING FROM NW TO SE TUESDAY NIGHT AND  
DURING THE FIRST HALF OF THE DAY WEDNESDAY. SHOWERS AND  
THUNDERSTORMS WILL BE POSSIBLE THROUGHOUT THE NIGHT, BUT WILL PEAK  
DURING THE DAY WEDNESDAY JUST AHEAD OF THE FRONTAL PASSAGE. THAT  
BEING SAID, ONCE THE FRONT PASSES, WINDS WILL QUICKLY SHIFT TO A  
MORE NORTHERLY DIRECTION AND INSTABILITY WILL DROP OFF. LINGERING  
PRECIP ON THE BACK SIDE OF THE FRONTAL PASSAGE THROUGH THE DAY  
WEDNESDAY WILL THEREFORE LIKELY BE IN THE FORM OF RAIN, AND SHOULD  
COME TO AN END BY WEDNESDAY EVENING AS THE FRONTAL BOUNDARY SHIFTS  
SOUTHEAST OF THE STATE.  
 
A LARGE AREA OF HIGH PRESSURE WILL TAKE HOLD WEDNESDAY NIGHT AND  
THROUGH THE REST OF THE WORK WEEK. A STRONG TROUGHING PATTERN WILL  
STILL BE IN PLACE ALOFT, PROMOTING NW FLOW ACROSS THE STATE. THIS,  
IN CONJUNCTION WITH NORTHERLY WINDS AT THE SURFACE, WILL HELP TO KEEP  
TEMPERATURES WELL BELOW NORMAL. HIGHS WILL GENERALLY BE IN THE UPPER  
70S WITH LOW HUMIDITY THROUGH FRIDAY.  
 
BY SATURDAY AND SUNDAY, MODELS ARE STILL IN FAIR AGREEMENT SHOWING  
THE UPPER LEVEL TROUGHING MOVING EAST OF THE REGION BUT SOME  
SHORTWAVES DEVELOPING AND MOVING INTO THE OHIO VALLEY UNDER  
CONTINUED NW FLOW. THAT BEING SAID, THEY ARE NOT IN GOOD AGREEMENT  
AS FAR AS THE EXACT TIMING AND MAGNITUDE OF THESE WAVES ACROSS THE  
STATE. SURFACE WINDS ALSO SUGGEST A WEAK SURFACE LOW PASSING ACROSS  
THE REGION DURING THE DAY SUNDAY. HOWEVER, NOT CONFIDENT ON THE  
EXACT LOCATION AND TIMING GIVEN THE UNCERTAINTY IN MODELS ALOFT.  
REGARDLESS, THERE IS THE POSSIBILITY FOR SOME UNSETTLED WEATHER  
DURING THE WEEKEND. RIGHT NOW MODEL CONSENSUS IS FOR MAINLY  
DIURNALLY DRIVEN ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS,  
WITH BEST COVERAGE DURING THE DAY SUNDAY. SURPRISINGLY BOTH THE GFS  
AND ECMWF ARE BOTH PUTTING SIMILAR AREAS OF COVERAGE ACROSS FAR SE  
KY DURING THE DAY SUNDAY AS OF NOW, SO CONFIDENCE WAS A BIT HIGHER  
HERE. BUT EXPECT THIS FORECAST TO CONTINUE EVOLVING OVER THE NEXT  
FEW DAYS.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 745 AM EDT MON AUG 21 2017  
 
IFR OR WORSE FOG WILL BURN OFF THROUGH 13Z. SOME CUMULUS AT 5-6K  
FEET AGL WILL DEVELOP DURING THE DAY, ALONG WITH SOME PASSING HIGH  
CLOUDS. PATCHY FOG WILL DEVELOP ONCE AGAIN AFTER 06Z, MAINLY ALONG  
THE DEEPER RIVER VALLEYS. WINDS WILL AVERAGE LESS THAN 5 KTS  
THROUGH THE PERIOD.  
 

 
   
JKL WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...SBH  
SHORT TERM...GEOGERIAN  
LONG TERM...JMW  
AVIATION...GEOGERIAN  
 
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