692  
FXUS64 KMRX 191934  
AFDMRX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MORRISTOWN TN  
334 PM EDT FRI JUL 19 2019  
   
SHORT TERM...(TONIGHT AND SATURDAY)
 
 
MAIN WEATHER STORY FOR THE SHORT TERM PERIOD WILL BE THE HOT AND HUMID  
CONDITIONS THROUGH SATURDAY. CURRENTLY ACROSS THE AREA, SKIES  
WERE PARTLY TO MOSTLY CLOUDY WITH TEMPERATURES IN THE MID TO UPPER  
80S ATOP DEWPOINTS IN THE LOW TO MID 70S. LATEST RADAR IMAGERY  
DEPICTS AN AREA OF SHOWERS AND THUNDERSTORMS MAINLY WEST OF I-75  
AND SOUTH OF I-40. WATER VAPOR IMAGERY IS INDICATING DRIER AIR  
ALOFT ADVECTING FROM THE NORTH THAT HAS LIKELY KEPT MOST AREAS  
DRY TODAY. THE UPPER LEVELS FEATURE RIDGING ALOFT THROUGH MUCH OF  
THE REGION WHICH IS HELPING TO KEEP CONDITIONS WARM. WITH HIGHS  
EXPECTED IN THE UPPER 80S TO LOW 90S AND DEWPOINTS NEAR THE LOW  
70S, THIS WILL CREATE VERY HUMID CONDITIONS WITH HEAT INDICES IN  
THE UPPER 90S TO NEAR 100. NOT ANTICIPATING NEEDING ANY HEAT  
ADVISORIES FOR THIS AFTERNOON AS MOST LOCATIONS SHOULD STAY BELOW  
ADVISORY CRITERIA.  
 
THE CURRENT CONVECTION SHOULD DISSIPATE AFTER SUNSET AS THE BOUNDARY  
LAYER BEGINS TO STABILIZE. WARM AND HUMID CONDITIONS WILL PERSIST  
INTO TONIGHT AS THE RIDGE HOLDS OVER THE AREA. LOWS TONIGHT  
SHOULD BOTTOM OUT INTO THE LOW TO MID 70S. SATURDAY SHOULD  
CONTINUE TO BE WARM AND HUMID AS TEMPERATURES QUICKLY INCREASE  
UNDER RIDGING ALOFT. GUIDANCE SUGGESTS MOST LOCATIONS WILL REACH  
OR SURPASS THE 90 DEGREE MARK, ESPECIALLY ACROSS THE VALLEY. THIS  
SEEMS PLAUSIBLE AS 925MB TEMPERATURES INCREASE UPWARDS OF 28-30  
DEGREE C.THIS COMBINED WITH A MOIST AIRMASS WITH DEWPOINTS NEAR  
70-75 DEGREES WILL PRODUCE HEAT INDEX VALUES INTO THE UPPER 90S  
TO LOW 100S. DECIDED TO HOLD OFF ON ISSUING ANY HEAT ADVISORIES  
FOR SATURDAY AS CONFIDENCE ON HOW MUCH OF THE AREA REACHES  
ADVISORY CRITERIA REMAINS LOW. NONETHELESS, THE DANGEROUS HEAT  
INDEX VALUES WILL PERSIST AND SHOULD CONTINUE TO BE MONITORED.  
INSTABILITY WILL INCREASE ON SATURDAY WITH CAPE VALUES IN THE  
2,000-3,000 J/KG RANGE. AS A RESULT, CONVECTION IS EXPECTED  
MAINLY DURING THE AFTERNOON HOURS. COVERAGE IS EXPECTED TO BE  
GREATER THAN TODAY AS THERE ARE SOME INDICATIONS THAT THE RIDGE  
BEGINS TO BREAK DOWN. DCAPES OF 800-1200 J/KG MEANS THAT ANY OF  
THE STRONGER STORMS COULD PRODUCE STRONG/GUSTY WINDS. PW VALUES  
NEAR 2.0 INCHES SUGGEST THAT LOCALLY HEAVY RAINFALL WILL ALSO BE  
POSSIBLE.  
   
LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
 
 
GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT THROUGH THE EXTENDED WITH  
THE MAIN STORY BEING A SIGNIFICANT PATTERN CHANGE ACROSS THE REGION  
EARLY THIS UPCOMING WEEK.  
 
THE EXTENDED BEGINS WITH A SHORTWAVE TROUGH DIVING SOUTHEASTWARD  
ACROSS THE NORTHERN GREAT PLAINS AND UPPER MISSISSIPPI VALLEY LATE  
SUNDAY INTO SUNDAY NIGHT. THIS WILL BRING HEIGHT FALLS ACROSS THE  
REGION WITH INCREASING POPS FOR SCATTERED CONVECTION ON SUNDAY AND  
MONDAY. MLCAPE EACH AFTERNOON WILL BE IN THE 1000 TO 2000 J/KG RANGE  
ACROSS THE AREA WITH EFFECTIVE DEEP LAYER SHEAR GENERALLY BETWEEN 10  
TO 20 KT AND INCREASING TO 20 TO 25 KT LATE MONDAY AS STRONGER  
DYNAMICS ASSOCIATED WITH THE UPPER TROUGH APPROACHES THE REGION.  
WHILE WIDESPREAD SEVERE WEATHER IS NOT FORECAST WITH THIS SYSTEM,  
THE SETUP FAVORS THE POTENTIAL FOR A FEW STRONG TO POSSIBLY SEVERE  
THUNDERSTORMS, ESPECIALLY LATER MONDAY AS THE FRONT APPROACHES AND  
MID-LEVEL LAPSE RATES INCREASE WITH PVA ACROSS THE AREA.  
 
THE SHORTWAVE WILL AMPLIFY LONGWAVE TROUGHING ACROSS THE EASTERN  
CONUS MONDAY NIGHT WITH AN ASSOCIATED SURFACE COLD FRONT MOVING  
THROUGH THE REGION. LIKELY WIDESPREAD CONVECTION WILL BE ASSOCIATED  
WITH THIS FRONT, AND WITH STRONG BOUNDARY LAYER FORCING AND PW  
BETWEEN 1.8 AND 2.0 INCHES, EXPECT SOME HEAVY RAINFALL AT TIMES.  
 
THE COLD FRONT SHIFTS EAST ON TUESDAY WITH A FEW LINGERING SHOWERS  
OR ISOLATED THUNDERSTORMS ACROSS THE FAR EASTERN MOUNTAINS CLOSER TO  
THE FRONT AND WHERE SOME WEAK OROGRAPHIC LIFT MAY ENHANCE SHOWERY  
COVERAGE. HOWEVER, EXPECT OROGRAPHIC LIFT TO BE MINIMAL WITH WINDS  
FROM THE N/NNE BEHIND THE FRONT WHICH IS NOT NORMAL TO THE AVERAGE  
TERRAIN AXIS. SURFACE HIGH PRESSURE BUILDS IN WITH MUCH LOWER  
DEWPOINT IN THE MID 50S TO LOWER 60S BY WEDNESDAY MORNING. IN FACT,  
BOTH NAEFS AND ECMWF OUTPUT SHOW 850MB TEMPERATURES BEING BETWEEN  
THE 3RD AND 10TH PERCENTILE COMPARED TO CLIMATOLOGY. IN ADDITION,  
CIPS ANALOG DATA SHOWS HIGH PROBABILITIES OF BELOW NORMAL  
TEMPERATURES WITH SURFACE TEMPERATURES BEING ABOUT 10 DEGREES BELOW  
NORMAL. THIS ANOMALOUS COLD AND DRY AIRMASS WILL RESULT IN MUCH  
COOLER TEMPERATURES WITH AN ALMOST FALL-LIKE FEEL MID TO LATE WEEK  
WITH VERY LOW TO NO CHANCES OF PRECIPITATION IN THE FORECAST.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
CHATTANOOGA AIRPORT, TN 75 91 74 89 / 30 60 40 60  
KNOXVILLE MCGHEE TYSON AIRPORT, TN 74 92 72 88 / 20 40 30 50  
OAK RIDGE, TN 74 92 73 88 / 20 30 30 50  
TRI CITIES AIRPORT, TN 70 92 70 87 / 20 20 30 60  
 

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

 
 

 
 
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