634  
FXUS64 KMRX 251124 AAA  
AFDMRX  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE MORRISTOWN TN  
724 AM EDT MON OCT 25 2021  
   
UPDATE
 
 
FOR 12Z AVIATION.  
 

 
   
SHORT TERM (TODAY AND TONIGHT)
 
 
 
KEY MESSAGES:  
 
1. A LINE OF SHOWERS WITH SOME EMBEDDED THUNDERSTORMS WILL CROSS THE  
AREA FROM LATE MORNING THROUGH MID AFTERNOON. STRONG TO SEVERE WIND  
GUSTS ARE POSSIBLE.  
 
DISCUSSION:  
 
CAMS SEEM TO HAVE A GOOD HANDLE ON THE CURRENT POSITION OF  
CONVECTION ACROSS WESTERN KY AND NW TN. THERE IS GOOD AGREEMENT THAT  
THIS LINE WILL REACH OUR PLATEAU COUNTIES AROUND 9-10 AM. THE LINE  
IS EXPECTED TO WEAKEN, AS SHOWN BY THE HREF MAX REFLECTIVITY  
PROBABILITY AND THE UPDRAFT VERTICAL VELOCITY DROPPING OFF QUICKLY  
AS IT NEARS THE PLATEAU. AS USUAL WITH EVENTS LIKE THESE THIS TIME  
OF YEAR, CAPE WILL BE THE LIMITING FACTOR FOR SEVERE POTENTIAL.  
HOWEVER, WITH GOOD UPPER DIVERGENCE IN THE LEFT EXIT REGION OF THE  
JET AND MIDLEVEL WINDS OF 50-60 KTS, SOME STRONG TO MARGINALLY  
SEVERE WIND GUSTS CAN'T BE RULED OUT WITH DEEPER EMBEDDED CELLS. NE  
TN/SW VA WILL HAVE THE BEST CHANCE OF THIS SINCE THERE WILL BE A  
WINDOW OF SURFACE HEATING THIS MORNING FOR SLIGHTLY MORE  
DESTABILIZATION. TORNADO POTENTIAL APPEARS LOW AS IT WILL BE  
DIFFICULT TO GET SURFACE WINDS BACKED ENOUGH IN THE NORTHERN VALLEY  
IN THE LEE OF THE MOUNTAINS, AND WE DO NOT HAVE A BOUNDARY IN PLACE  
TO AID LOW LEVEL HELICITY. THE MAIN CONVECTIVE LINE SHOULD BE  
EXITING OUR AREA BETWEEN 19-21Z.  
 
FRONTAL PASSAGE WILL TRAIL CONVECTION BY A FEW HOURS, LIKELY  
OCCURRING IN THE 22-02Z TIME FRAME. GUSTY WEST WINDS MAY ACCOMPANY  
THE FROPA. COLD ADVECTION TONIGHT WILL BRING AN INCREASE IN CLOUD  
COVER AFTER SUNSET, AND AN UPSLOPE FLOW COULD KEEP SOME LIGHT  
SHOWERS GOING IN HIGHER ELEVATIONS.  
 
DGS  
   
LONG TERM (TUESDAY THROUGH SUNDAY)
 
 
KEY MESSAGES:  
 
1. DRYING OUT TUES AND WED WITH BELOW NORMAL TEMPS TUES WARMING TO  
AROUND NORMAL WED. PATCHY FROST POSSIBLE IN NE AREAS EARLY WED.  
 
2. WIDESPREAD SHOWERS AND THE POTENTIAL FOR PERIODS OF HEAVY RAIN  
MOVE IN WED NIGHT AND THURS WITH MUCH COOLER TEMPS AND SHOWERS  
LINGERING FRI AND SAT.  
 
3. DRYING OUT BY SUN, BUT TEMPS STILL A FEW DEGREES BELOW NORMAL.  
 
DISCUSSION:  
 
TUESDAY THROUGH WEDNESDAY...  
 
DEEP SURFACE LOW PRESSURE WILL REALLY BOMB OUT TO 974-978 MB AND  
REMAIN NEARLY STATIONARY OFFSHORE OF CT AND RI TUES WITH DEEP  
MID/UPPER TROUGHING OVER THE EASTERN CONUS BEHIND THIS SYSTEM. THIS  
WILL BRING A MUCH COOLER AND DRIER NW FLOW TO THE S APPALACHIANS.  
SOME LINGERING MOISTURE AND UPSLOPING WILL KEEP A FEW SCATTERED  
SHOWERS GOING FROM SW VA THROUGH THE EASTERN MOUNTAINS TUES BEFORE  
STRONG SURFACE HIGH PRESSURE BUILDS S FROM THE OH VALLEY TUES NIGHT  
AND WED WITH THE ASSOCIATED DRY AIR AND SUBSIDENCE BRINGING DRY  
CONDITIONS. THE MID/UPPER TROUGH AXIS WILL SHIFT INTO THE NE CONUS  
BY WED WITH SHORTWAVE RIDGING BUILDING ACROSS THE TN AND OH VALLEYS  
AHEAD OF THE NEXT DEEP MID/UPPER TROUGH PROGRESSING INTO THE PLAINS.  
THIS WILL LEAD TO MODERATING TEMPS WED. HIGHS TUES WILL STRUGGLE TO  
CLIMB OUT OF THE UPPER 50'S BUT WILL REBOUND INTO THE MID 60'S WED.  
STRONG RADIATIONAL COOLING TUES NIGHT WILL LEAD TO LOWS IN THE UPPER  
30'S/LOW 40'S, SO PATCHY FROST IS POSSIBLE FROM THE N PLATEAU  
THROUGH NE TN AND SW VA.  
 
WEDNESDAY NIGHT THROUGH FRIDAY...  
 
THIS WILL BE THE START OF A COOL, WET, UNSETTLED PERIOD AS THE  
AFOREMENTIONED DEEP PLAINS MID/UPPER TROUGH SHIFTS INTO THE MS  
VALLEY WED NIGHT AND THURS AND EVOLVES INTO A CLOSED LOW OVER THE  
LOWER OH AND TN VALLEYS BY FRI. THE DETERMINISTIC ECMWF, GFS, AND  
CMC ARE ALL IN SOLID OVERALL AGREEMENT ON THIS PATTERN EVOLUTION  
WITH JUST SMALL DIFFERENCES ON THE PLACEMENT OF THE CENTER OF THE  
VERTICALLY STACKED LOW BY FRI. FOR WED NIGHT AND THURS, THE DEEP  
MID/UPPER TROUGH SWINGING INTO THE MS VALLEY AND BECOMING NEGATIVELY  
TILTED WILL SUPPORT A DEEPENING SURFACE LOW AROUND SE MO AND WESTERN  
KY AIDED BY THE LEFT EXIT OF A 110 KT H3 JET STREAK OVER THE DEEP  
SOUTH. AN ASSOCIATED 30-50 KT SOUTHERLY LOW-LEVEL JET DEVELOPING  
AHEAD OF THIS LOW OVER THE S APPALACHIANS WILL ADVECT COPIOUS  
AMOUNTS OF MOISTURE INTO THE REGION WED NIGHT AND THURS, AS WELL AS  
CAUSE POSSIBLE MOUNTAIN WAVE HIGH WINDS IN THE SMOKIES. A LOOK AT  
THE NAEFS MEAN INTEGRATED WV TRANSPORT SHOWS VALUES NEARING THE 90TH  
PERCENTILE INDICATING THAT MOISTURE FLUX COULD BE ANOMALOUS OVER OR  
JUST E OF THE REGION DURING THIS TIME. THUS, EXPECT SHOWERS TO MOVE  
IN FROM W TO E WED NIGHT WITH PERIODS OF HEAVY RAIN POSSIBLE THURS.  
AT THIS TIME, INSTABILITY LOOKS VERY WEAK GIVEN CLOUDS AND  
RELATIVELY COOL CONDITIONS, SO KEPT THUNDER OUT OF THE FORECAST. AS  
THE SURFACE LOW PULLS A BIT FARTHER N INTO THE LOWER OH VALLEY THURS  
NIGHT INTO FRI, A COLD FRONT WILL PUSH THROUGH THE REGION. H85 TEMPS  
FALLING TO 1-3 C AND DEEP WRAPAROUND MOISTURE AS THE SYSTEM CLOSES  
OFF AND BECOMES VERTICALLY STACKED WILL LEAD TO MUCH COOLER TEMPS  
AND FREQUENT SHOWERS LINGERING THROUGH FRI, BUT PROBABLY NOT AS  
HEAVY AS THE RAIN THURS. HIGHS THURS WILL BE IN THE LOW/MID 60'S  
WITH ONLY MID/UPPER 50'S FRI. LOWS BOTH WED AND THURS NIGHTS WILL  
BE IN THE UPPER 40'S/LOW 50'S.  
 
FRIDAY NIGHT THROUGH SUNDAY...  
 
DETERMINISTIC AND ENSEMBLE GUIDANCE IS IN OVERALL AGREEMENT THAT THE  
CLOSED LOW WILL GRADUALLY LIFT OUT SAT WITH QUASI-ZONAL FLOW ACROSS  
THE CONUS BY SUN AND A SURFACE HIGH BUILDING E FROM THE MID SECTION  
OF THE COUNTRY. THUS, STAYED WITH NBM POPS WHICH HAS LINGERING  
SHOWERS SCATTERED AROUND FRI NIGHT AND SAT BECOMING MOSTLY DRY BY  
SUN EXCEPT FOR A FEW ISOLATED SHOWERS FROM NE TN INTO SW VA.  
WELL BELOW NORMAL TEMPS CONTINUING SAT WILL MODERATE A BIT SUN.  
 
GARUCKAS  
 

 
   
AVIATION
 
 
12Z TAF DISCUSSION.  
 
SHOWERS ARE APPROACHING THE AREA FROM THE WEST AND WILL MOVE  
THROUGH THE TAF SITES BETWEEN 14-19Z. MVFR VIS AND CIGS WILL  
ACCOMPLANY THE SHOWERS, WITH THE POSSIBILITY OF A SHORT-LIVED TS.  
A COLD FRONT MOVES THROUGH SHORTLY AFTER THAT IN THE LATE  
AFTERNOON, WHICH WILL SHIFT WINDS TO W-NW WITH GUSTS AT TIMES.  
MVFR CIGS ARE EXPECTED TONIGHT IN THE COOLER AIR MASS BEHIND THE  
FRONT.  
 
DGS  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
CHATTANOOGA AIRPORT, TN 73 49 65 46 68 / 70 10 0 0 0  
KNOXVILLE MCGHEE TYSON AIRPORT, TN 70 48 60 42 66 / 90 10 10 0 0  
OAK RIDGE, TN 69 48 60 42 66 / 90 10 0 0 0  
TRI CITIES AIRPORT, TN 68 46 56 38 64 / 90 20 10 0 0  
 

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

 
 

 
 
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