224  
FXUS64 KMRX 242047  
AFDMRX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MORRISTOWN TN  
347 PM EST WED FEB 24 2021  
   
SHORT TERM...(TONIGHT AND THURSDAY)
 
 
IMPRESSIVE WAA OVER THE EASTERN TENNESSEE VALLEY AND SOUTHERN  
APPALACHIANS THIS AFTERNOON AS STRONG SOUTHWEST WINDS OF 15 TO 20  
MPH WITH GUSTS TO AROUND 35 MPH HAVE WARMED TEMPERATURES INTO THE  
UPPER 60S TO LOWER 70S. RELATIVE HUMIDLY VALUES HAVE DROPPED TO  
20 TO 25 PERCENT AND LOCAL AREAS ARE AS LOW AS 15 TO 20 PERCENT.  
 
HIGH PRESSURE AT THE SURFACE IS BEGINNING TO SHIFT EAST THIS  
AFTERNOON WITH NEARLY ZONAL FLOW ALOFT BEING INTERRUPTED BY A  
WEAK UPPER TROUGH AND ASSOCIATED COLD FRONT MOVING INTO THE OHIO  
VALLEY AND GREAT LAKES. CLOUDS WERE INCREASING ACROSS WEST  
TENNESSEE AND NORTHERN AND WESTERN KENTUCKY AHEAD OF THE FRONT  
THIS AFTERNOON.  
 
SKIES WILL START CLEAR EARLY THIS EVENING THEN CLOUDS INCREASE  
AFTER SUNSET AS COLD FRONT APPROACHES. THIS WEAK SYSTEM WILL BRING  
JUST A FEW LIGHT RAIN SHOWERS TO NORTHERN SECTIONS OF THE  
FORECAST AREA...MAINLY SOUTHWEST VIRGINIA AND NORTHEAST TENNESSEE  
LATE TONIGHT AND EARLY THURSDAY ALONG AND JUST AHEAD OF THE FRONT.  
RAINFALL AMOUNTS WILL BE LESS THAN 0.10 INCHES. BY ABOUT 12Z  
THURSDAY THE FAST MOVING FRONT WILL BE SOUTH OF THE TENNESSEE  
BORDER AND OVER THE CAROLINAS AND GEORGIA. SKIES WILL CLEAR WITH  
MOSTLY SUNNY SKIES RETURNING THURSDAY MORNING. TEMPERATURES WILL  
BE SIGNIFICANTLY COOLER BEHIND THIS FRONT WITH HIGHS THURSDAY ONLY  
LOWER 50S TO LOWER 60S.  
 
TD  
   
LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
 
 
KEY MESSAGES:  
 
1. SHOWERS DEVELOP THURS NIGHT INTO SAT, BUT THERE WILL BE DRY  
PERIODS BETWEEN SHOWERS WITH LIGHT TO MODERATE RAINFALL AMOUNTS.  
 
2. PERIODS OF HEAVY RAIN WITH EVEN A FEW THUNDERSTORMS SAT NIGHT  
INTO MON WILL ELEVATE FLOODING CONCERNS LATER THIS WEEKEND INTO  
EARLY NEXT WEEK.  
 
3. LOW CONFIDENCE ON HOW MUCH ADDITIONAL RAINFALL MON THROUGH WED  
DUE TO MAJOR MODEL DIFFERENCES, BUT PERIODS OF SHOWERS REMAIN  
POSSIBLE WITH COOLER TEMPS.  
 
DISCUSSION:  
 
THURSDAY NIGHT AND FRIDAY...  
 
THIS WILL BE THE BEGINNING OF A VERY WET PERIOD AS A LEAD MID/UPPER  
SHORTWAVE DEAMPLIFIES AND TRACKS THROUGH THE ZONAL FLOW FROM THE S  
PLAINS ACROSS THE MS AND TN VALLEYS. INCREASING WARM, MOIST  
ADVECTION AND LIFT FROM THE RIGHT ENTRANCE REGION OF A 150-160+ KT  
300 MB JET STREAK OVER THE OH VALLEY WILL SUPPORT AN EXPANDING  
SHIELD OF SHOWERS AS ISENTROPIC LIFT ALSO INCREASES AHEAD OF A  
NORTHWARD ADVANCING WARM FRONT. THIS FRONT AND THE BEST MOISTURE  
AXIS WILL REMAIN NEAR THE S PLATEAU AND SE TN/SW NC THROUGH FRI  
MORNING, SO HAVE THE HIGHEST POPS DOWN THERE EXPANDING ACROSS THE  
REST OF THE REGION FRI AFTERNOON AS THE FRONT LIFTS A BIT FARTHER N.  
QPF FROM THIS FIRST WAVE OF SHOWERS LOOKS TO BE VERY MANAGEABLE IN  
THE 0.25 TO JUST OVER 0.50 INCH RANGE, WITH THE GREATEST AMOUNTS IN  
THE AFOREMENTIONED SOUTHERN AREAS, SO DO NOT EXPECT FLOODING AT THIS  
TIME. HIGHS N OF THE WARM FRONT FRI WILL BE HELD IN THE UPPER  
40'S/LOW 50'S.  
 
FRIDAY NIGHT AND SATURDAY...  
 
THE LEAD MID/UPPER SHORTWAVE WILL QUICKLY EXIT E FRI NIGHT, BUT A  
MUCH STRONGER AND BROADER MID/UPPER TROUGH WILL DIVE INTO THE  
ROCKIES AND N/CENTRAL PLAINS FRI NIGHT INTO SAT WITH QUASI-ZONAL  
FLOW CONTINUING DOWNSTREAM ACROSS THE TN VALLEY PARALLEL TO A QUASI-  
STATIONARY FRONT/SLOWLY RETREATING WARM FRONT. MUCH OF FRI NIGHT AND  
SAT SHOULD SEE A BREAK FROM THE MORE WIDESPREAD SHOWERS AS WE WILL  
BE BETWEEN SHORTWAVES AND ASSOCIATED FORCING, BUT WITH THE FRONTAL  
BOUNDARY LAYING ACROSS THE AREA AND CONTINUED SOUTHERLY  
FLOW/ISENTROPIC LIFT N OF IT, KEPT CHANCE POPS FOR SHOWERS. HIGHS  
SAT WILL WARM INTO THE UPPER 50'S/LOW 60'S AS THE FRONT SLOWLY  
RETREATS N AS A WARM FRONT.  
 
SATURDAY NIGHT THROUGH MONDAY...  
 
AS THE AFOREMENTIONED PLAINS AND ROCKIES BROAD MID/UPPER TROUGH  
BEGINS TO MOVE E SAT NIGHT AND SUN, DEEP SW FLOW WILL DEVELOP ACROSS  
THE TN VALLEY AND MUCH OF THE SE CONUS WITH THE WARM FRONT LIFTING  
JUST N OF OUR REGION IN RESPONSE. THIS FRONT WILL THEN BECOME QUASI-  
STATIONARY AGAIN WITH SUBTLE N AND S MOVEMENTS UNTIL AT LEAST MON.  
THE TN VALLEY AND S APPALACHIANS POSITIONED IN THE FAVORABLE RIGHT  
ENTRANCE REGION OF A 150-170 KT 300 MB JET ACROSS THE OH VALLEY,  
STRONG WARM, MOIST ADVECTION FROM A WIDE OPEN GULF ADVECTING IN  
ANOMALOUS PWAT VALUES, ISENTROPIC ASCENT, AND THE FRONT ORIENTED  
PARALLEL TO THE WSW MID/UPPER FLOW ALL SUPPORT PERIODS OF HEAVY  
RAIN. NAEFS TABLES SUGGEST PWATS OF 1 TO 1.4 INCHES OR GREATER SAT  
NIGHT INTO MON WHICH IS AT OR ABOVE THE MAXIMUM DAILY CLIMATOLOGICAL  
VALUE. IT IS A LITTLE EARLY TO DIVE INTO DETAILED SOUNDING ANALYSIS,  
BUT PATTERN RECOGNITION ALSO SUPPORTS A DEEP WARM CLOUD LAYER WITH  
WARM RAIN PROCESSES. WITH ALL OF THIS SAID, CONFIDENCE IS INCREASING  
THAT PERIODS OF HEAVY RAIN WILL OCCUR SAT NIGHT INTO MON WITH  
FLOODING BECOMING INCREASINGLY LIKELY LATER THIS WEEKEND INTO EARLY  
NEXT WEEK. TOTAL QPF FROM FRIDAY THROUGH MON COULD AVERAGE 3 TO 5  
INCHES WITH THE MAJORITY FALLING SAT NIGHT THROUGH MON. FOLLOWED WPC  
QPF WHICH IS IN GOOD OVERALL AGREEMENT WITH THE GEFS, EURO, AND  
CANADIAN ENSEMBLE MEANS. A STRONG LLJ SAT NIGHT AND SUN WILL ALSO  
LEAD TO A FEW HUNDRED JOULES OF CAPE (MOSTLY ELEVATED), SO ADDED  
THUNDER DURING THIS TIME. ANY CONVECTION WILL LEAD TO LOCALLY HIGHER  
RAINFALL TOTALS. DETERMINISTIC AND ENSEMBLE GUIDANCE STARTS TO  
DIVERGE MON AFTERNOON WITH HOW THE BROAD MID/UPPER SHORTWAVE TROUGH  
WILL EJECT E, WHICH AFFECTS WHEN THE COLD FRONT WILL SWEEP E AND  
BRING COOLER, DRIER CONDITIONS. AT THIS TIME, KEPT LIKELY POPS  
THROUGH MON. HIGHS SUN WILL WARM WELL INTO THE MID/UPPER 60'S  
COOLING INTO THE MID/UPPER 50'S MON.  
 
MONDAY NIGHT THROUGH WEDNESDAY...  
 
THIS IS A LOW CONFIDENCE PERIOD IN TERMS OF HOW FAR S THE ACTIVE  
FRONTAL BOUNDARY WILL CLEAR, WHICH AFFECTS ADDITIONAL RAINFALL  
CHANCES THAT COULD AGGRAVATE ANY ONGOING FLOODING. THE GFS AND TO AN  
EXTENT, ITS ENSEMBLE MEANS, MOVE THE WHOLE MID/UPPER TROUGH AXIS  
EASTWARD EARLY NEXT WEEK MERGING WITH NORTHERN STREAM ENERGY NEAR  
THE GREAT LAKES, LEADING TO COOLER, DRIER NW FLOW OVER THE EASTERN  
CONUS MON NIGHT THROUGH WED. THE DETERMINISTIC ECWMF AND ITS  
ENSEMBLE MEANS KEEP THE FLOW MORE ZONAL WITH ADDITIONAL MID/UPPER  
SHORTWAVE TROUGHS PROGRESSING FROM THE ROCKIES INTO THE TN VALLEY  
DURING THIS TIME WHICH LIFT THE FRONT QUICKLY BACK N INTO OUR REGION  
WITH ADDITIONAL WAVES OF RAINFALL. KEPT CHANCE POPS THROUGH THIS  
PERIOD WITH TEMPS NEAR TO SLIGHTLY ABOVE NORMAL.  
 
GARUCKAS  
 

 
   
AVIATION
 
 
18Z TAF DISCUSSION.  
 
GUSTY SOUTHWEST WINDS WILL CONTINUE THIS AFTERNOON. TONIGHT,  
WINDS WILL DECREASE AND CLOUDS INCREASE FROM THE NORTH AHEAD OF  
AN APPROACHING COLD FRONT. CHANCES FOR LIGHT RAIN WITH THE  
FRONTAL PASSAGE STILL LOOKS GOOD AT KTRI SO ARE KEEPING THE PROB30  
GROUP. AT KTYS AND KCHA RAIN CHANCES NOT HIGH ENOUGH TO INCLUDE A  
PROB GROUP. MVFR CONDITIONS FOR A FEW HOURS THURSDAY MORNING AT  
KTYS AND KTRI BEFORE BECOMING VFR BY THE LAST FEW HOURS.  
 
TD  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
CHATTANOOGA AIRPORT, TN 45 64 40 52 46 / 10 0 40 70 60  
KNOXVILLE MCGHEE TYSON AIRPORT, TN 43 57 38 50 45 / 20 10 30 60 60  
OAK RIDGE, TN 42 58 38 50 44 / 20 10 20 60 60  
TRI CITIES AIRPORT, TN 39 55 34 49 39 / 30 10 20 60 60  
 

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

 
 

 
 
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