788  
FXUS64 KMRX 140725  
AFDMRX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MORRISTOWN TN  
325 AM EDT FRI AUG 14 2020  
   
SHORT TERM...(TODAY AND TONIGHT)
 
 
UPPER TROUGH REMAINS ACROSS THE TENNESSEE VALLEY AND SOUTHERN  
APPALACHIANS. THIS IS PRODUCING SW FLOW ACROSS THE REGION WITH A  
VERY MOIST AIRMASS IN PLACE. A 300MB 40KT JET WILL PRODUCE UPPER-  
LEVEL DIVERGENCE ACROSS THE FORECAST AREA DURING THE AFTERNOON AND  
ASSIST WITH WEAK SYNOPTIC ASCENT. IN RESPONSE, A WEAK SURFACE LOW  
IS FORECAST TO FORM ACROSS NORTHERN AL WITH BOUNDARY LAYER  
CONVERGENCE ACROSS SOUTHEAST TN. WHILE SCATTERED SHOWERS AND  
THUNDERSTORMS ARE FORECAST ACROSS THE ENTIRE AREA ON FRIDAY, MOST  
WIDESPREAD COVERAGE IS FORECAST ACROSS THE HIGHER ELEVATIONS AS  
WELL AS SOUTHEAST TN.  
 
THE RISK OF SEVERE WEATHER WILL BE LOW ON FRIDAY WITH RAP FORECAST  
SOUNDINGS INDICATING VERY SATURATED THERMODYNAMIC PROFILES.  
INSTABILITY IS EXPECTED TO BE MARGINAL WITH MLCAPE BETWEEN 1000  
TO 2000 J/KG, BUT WITH THE VERY MOIST ATMOSPHERE AND HIGH FREEZING  
LEVELS, RISKS OF DAMAGING WINDS AND HAIL WILL BE LOW. THE MAIN  
RISK WITH THUNDERSTORMS ON FRIDAY WILL BE HEAVY RAINFALL AND  
LOCALIZED FLOODING. THE 0Z SOUNDING AT OHX OBSERVED PW NEAR 1.9  
INCHES, AND MODEL CONSENSUS IS PLACING PW VALUES OF 1.9 TO 2.1  
INCHES ACROSS THE REGION ON FRIDAY AFTERNOON. THESE PW VALUES WILL  
BE NEAR THE MAXIMA OF CLIMATOLOGY, AND WHEN COMBINED WITH THE  
FAVORABLE SYNOPTIC LIFT, DEEP WARM CLOUD LAYER OF 12K TO 14K FT,  
AND NEAR UNIDIRECTIONAL FLOW, SOME TRAINING AND FLASH FLOODING  
WILL BE POSSIBLE.  
 
CONVECTIVE ACTIVITY WILL DECREASE IN COVERAGE FRIDAY NIGHT, BUT  
SOME SCATTERED SHOWERS OR THUNDERSTORMS WILL CONTINUE WITH LOCALLY  
HEAVY RAINFALL, PRIMARILY EAST OF INTERSTATE 75. IN AREAS THAT  
HAVE A CLEARING SKY, WINDS WILL BE LIGHT AND FOG DEVELOPMENT WILL  
BE LIKELY.  
 
JB  
   
LONG TERM...(SATURDAY THROUGH THURSDAY)
 
 
MODELS IN DECENT AGREEMENT THAT THE AXIS OF A MID/UPPER LEVEL  
TROUGH WILL BE TRAVERSING THE AREA ON SATURDAY WITH A COLD FRONT  
PUSHING ACROSS AT THE SURFACE. WHILE SOME UNCERTAINTY ABOUT THE  
EXACT POSITIONING OF THESE FEATURES AT THE START OF THE PERIOD, IT  
DOES APPEAR BETTER CHANCES FOR PRECIP WILL BE EAST SO WILL CARRY  
CHANCE POPS WEST AND LIKELY TO EVEN CATEGORICAL NORTH AND EAST.  
WHILE A FEW STRONGER STORMS WITH STRONG GUSTY WINDS CANNOT BE  
RULED OUT SATURDAY, THE MAIN THREAT SHOULD BE LOCALLY HEAVY  
RAINFALL WHICH MAY LEAD TO FLOODING. WILL KEEP THIS IN THE HWO.  
 
BY MONDAY THE TROUGH AXIS AND INITIAL FRONT WILL BE TO OUR EAST, WITH  
DRYER AIR OVER OUR AREA. HOWEVER, MODELS HINT AT ANOTHER WEAKENING  
FRONTAL BOUNDARY THAT WILL BE PUSHING THROUGH, SO DESPITE THE DRYING  
WILL KEEP LOW POPS FOR CONVECTION MONDAY AS WELL. THE DRIER AIR WILL  
REMAIN IN PLACE ON TUESDAY, ALTHOUGH MODELS SHOW ANOTHER MID/UPPER  
LEVEL SHORT WAVE TROUGH APPROACHING, SO AGAIN WILL CARRY LOW POPS  
FOR CONVECTION. THE TROUGH AXIS ALOFT WILL BE SET UP TO OUR WEST FOR  
THE LATTER PART OF THE PERIOD. BETTER CHANCES FOR CONVECTION CAN BE  
EXPECTED BOTH WEDNESDAY AND THURSDAY AS FLOW GAINS A MORE SOUTHERLY  
COMPONENT AND MOISTURE INCREASES. TEMPERATURES DURING THE LONG TERM  
PERIOD WILL GENERALLY BE NEAR TO SLIGHTLY BELOW SEASONAL NORMALS.  
 
LW  
 

 
   
AVIATION
 
 
06Z TAF DISCUSSION.  
 
SHOWERS AND THUNDERSTORMS NEAR CHA WILL PERSIST FOR THE NEXT FEW  
HOURS WITH VCTS AND TEMPO REDUCTIONS IN VIS WITH SHRA. SOME FOG IS  
EXPECTED ACROSS THE AREA WHERE CLOUD COVER IS LOWER, AND AT THIS  
TIME, HIGHEST CONFIDENCE IN LOW FOG IS NEAR RIVER VALLEYS ACROSS  
THE NORTHERN AND EASTERN PORTIONS OF THE CWA NEAR TRI, AND  
POSSIBLY TYS. WIDESPREAD SCATTERED SHOWERS AND THUNDERSTORMS ARE  
EXPECTED LATE FRIDAY AFTERNOON AND FRIDAY EVENING ASSOCIATED WITH  
AN UPPER LOW IMPACTING EACH TAF SITE. AS CONVECTION DECREASES IN  
COVERAGE FRIDAY NIGHT, PATCHY FOG IS ONCE AGAIN EXPECTED TO  
DEVELOP WITH CALM WINDS AND A CLEARING SKY.  
 
JB  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
CHATTANOOGA AIRPORT, TN 87 73 87 70 90 / 80 70 40 10 20  
KNOXVILLE MCGHEE TYSON AIRPORT, TN 86 71 84 69 87 / 70 60 70 10 20  
OAK RIDGE, TN 85 71 85 68 88 / 70 60 60 10 20  
TRI CITIES AIRPORT, TN 84 69 82 65 83 / 70 50 70 30 20  
 

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

 
 

 
 
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