256  
FXUS64 KMRX 190709  
AFDMRX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MORRISTOWN TN  
254 AM EDT THU SEP 19 2019  
   
SHORT TERM...(TODAY AND TONIGHT)
 
 
A BACKDOOR COLD FRONT IS SLIDING THROUGH THE AREA, AND APPEARS TO  
BE LOCATED BETWEEN TYS AND CHA AT THE MOMENT. AS IT CONTINUES TO  
PUSH WESTWARD, BROKEN TO OVERCAST CLOUD COVER WILL EXPAND WESTWARD  
AS WELL, SO THAT MUCH OF THE AREA MAY START THE DAY WITH MOSTLY  
CLOUDY SKIES. HOWEVER, MODELS INDICATE THAT THIS CLOUD LAYER IS  
FAIRLY THIN, AND WE WILL HAVE DRIER AIR PUSHING IN FROM THE NE AT  
850 MB THIS AFTERNOON. SO THE EXPECTATION IS THAT WE WILL SEE  
CLOUDS ERODING THROUGH THE AFTERNOON. THIS WILL MAKE FOR A TRICKY  
TEMPERATURE FORECAST, BUT THE BOTTOM LINE IS THAT BEHIND THE  
FRONT, TEMPERATURES WILL BE QUITE A BIT COOLER THAN WE HAVE SEEN  
OVER THE PAST FEW DAYS, WITH HIGHS IN THE UPPER 70S TO LOWER 80S  
IN MOST SPOTS. DEWPOINTS WILL DROP AS WELL, ALLOWING OVERNIGHT  
LOWS IN THE 50S IN THE VALLEY.  
   
LONG TERM...(FRIDAY THROUGH WEDNESDAY)
 
 
THE NICE BREAK FROM THE HIGH HEAT AND HUMIDITY WILL UNFORTUNATELY  
COME TO AN END FRIDAY THROUGH THE WEEKEND AS LONGWAVE TROUGHING  
AMPLIFYING OVER THE WESTERN U.S. RESULTS IN A STRONG AMPLIFYING  
RIDGE OVER THE TN AND OH VALLEYS. H5 HEIGHTS WILL EXCEED 592 DAM  
CENTERED OVER THE SOUTHEAST STATES BY SATURDAY AND SUNDAY. AT THE  
SURFACE, HIGH PRESSURE OVER THE SOUTHERN APPALACHIANS FRIDAY WILL  
SLOWLY MOVE TO THE MID ATLANTIC COAST BY SUNDAY RESULTING IN  
STRENGTHENING SOUTHWESTERLY WAA. SUBSIDENCE FROM THE ABOVE  
MENTIONED SURFACE AND UPPER LEVEL RIDGING WILL KEEP ALL AREAS DRY  
THROUGH THE WEEKEND WITH HIGH TEMPS INCREASING A FEW DEGREES EACH  
DAY. WENT SLIGHTLY ABOVE GUIDANCE FOR HIGHS AND SLIGHTLY BELOW  
GUIDANCE FOR LOWS AS THE DRY CONDITIONS WILL LEAD TO LOWER OVERALL  
TD'S. SUSPECT THAT TD'S WILL STRUGGLE TO RISE ABOVE THE UPPER  
50'S DESPITE THE DEEP LAYER WAA UNTIL THE NEXT SHORTWAVE AND COLD  
FRONT APPROACHES MONDAY. THIS HOT AND RELATIVELY DRY AIRMASS WILL  
START TO INCREASE FIRE DANGER THIS WEEKEND.  
 
BY MONDAY A SHORTWAVE TROUGH AND ATTENDANT COLD FRONT WILL BE MOVING  
ACROSS THE GREAT LAKES AND OH VALLEY. THE ECMWF CONTINUES TO BE  
SOMEWHAT MORE AMPLIFIED WITH THIS SYSTEM THAN THE GFS, BUT EITHER  
WAY, THE STRONG SOUTHEAST RIDGE WILL BE FLATTENING, AND THIS WILL  
ALLOW THE COLD FRONT TO SETTLE TO AT LEAST NORTHEAST TN AND  
SOUTHWEST VA BY MONDAY EVENING. THERE IS NOT STRONG MOISTURE  
TRANSPORT FROM THE GULF AHEAD OF THIS FRONT, SO WITH THE DROUGHT  
CONDITIONS IN PLACE, HAVE CONTINUED TO KEEP POPS IN THE SLIGHT  
CHANCE RANGE MONDAY AND MONDAY NIGHT WITH ANOTHER HOT DAY EXPECTED.  
 
MODEL SPREAD INCREASES TUESDAY THROUGH WEDNESDAY WITH THE GFS  
LINGERING THE OLD FRONT IN THE VICINITY OF THE SOUTHERN APPALACHIANS  
AS A SECOND AND STRONGER MID LEVEL SHORTWAVE DIVES INTO OUR REGION  
FROM THE MISSISSIPPI VALLEY, WHILE THE ECMWF MAINTAINS ITS MORE  
AMPLIFIED SOLUTION OF BROAD LONGWAVE TROUGHING DEVELOPING OVER THE  
EASTERN U.S. TUESDAY AND WEDNESDAY CAUSING THE FRONT TO PUSH WELL  
SOUTH AND SURFACE HIGH PRESSURE TO SETTLE INTO THE TN VALLEY. HAVE  
SLIGHT CHANCE POPS TUESDAY AND WEDNESDAY FOR VERY LIGHT SHOWERS OR  
SPRINKLES TO ACCOUNT FOR THIS UNCERTAINTY, BUT ANYTHING WILL REMAIN  
WIDELY SCATTERED DUE TO FEEDBACK OF THE DRY GROUND. TEMPS WILL BE  
COOLER TUESDAY AND WEDNESDAY, BUT STILL ABOVE THE NORMAL LATE  
SEPTEMBER VALUES.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
CHATTANOOGA AIRPORT, TN 83 60 87 59 / 0 0 0 0  
KNOXVILLE MCGHEE TYSON AIRPORT, TN 81 58 87 59 / 10 0 0 0  
OAK RIDGE, TN 83 59 87 58 / 0 0 0 0  
TRI CITIES AIRPORT, TN 79 51 84 54 / 10 0 0 0  
 

 
   
MRX WATCHES/WARNINGS/ADVISORIES
 
 
NC...NONE.  
TN...NONE.  
VA...NONE.  

 
 

 
 
DGS/RG  
 
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