061  
FXUS63 KLSX 231311  
AFDLSX  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE SAINT LOUIS MO  
811 AM CDT SAT OCT 23 2021  
   
UPDATE
 
 
ISSUED AT 801 AM CDT SAT OCT 23 2021  
 
12Z REGIONAL SURFACE ANALYSIS DEPICTS A SUBTLE STATIONARY BOUNDARY  
ACROSS SOUTHWEST MISSOURI FORMED BY THE ONGOING CONVECTION THERE.  
THE HEAVIER DOWNPOURS AND THUNDERSTORMS THERE COULD CAUSE FLOODING  
CONCERNS AMIDST PRECIPITABLE WATER VALUES OVER 1.2" (ABOVE THE  
90TH CLIMATOLOGICAL PERCENTILE) IN THIS AREA. HOWEVER, THOSE  
HIGHER RAIN RATES ARE EXPECTED TO BE CONFINED TO THAT PORTION OF  
THE STATE AND NOT ENCROACH THE SOUTHERN COUNTIES OF OUR CWA.  
ADDITIONALLY, FLASH FLOOD GUIDANCE SUGGESTS THAT UPWARDS OF 2"/HR  
RAIN RATES WILL NEED TO BE REALIZED TO CAUSE CONCERN FOR US.  
WITHOUT CONVECTIVE ACTIVITY, THOSE RATES WILL LIKELY NOT BE  
REALIZED IN OUR AREA THIS MORNING.  
 
MRB  
 

 
   
SHORT TERM
 
(THROUGH LATE SUNDAY AFTERNOON)  
ISSUED AT 330 AM CDT SAT OCT 23 2021  
 
THE MAIN FOCUS FOR THIS PORTION OF THE PERIOD WILL BE SEVERAL ROUNDS  
OF CONVECTION, SOME CAPABLE OF HEAVY RAINFALL AND SEVERE WEATHER.  
 
CURRENTLY, A CLUSTER OF SHOWERS AND THUNDERSTORMS IS ONGOING OVER  
PORTIONS OF SOUTHWESTERN MISSOURI AT THE NOSE OF A LOW LEVEL JET.  
THIS JET IS EXPECTED TO VEER THROUGH THE MORNING INTO THE AFTERNOON,  
BRINGING THE FOCUS FOR THESE SHOWERS AND THUNDERSTORMS ACROSS  
PORTIONS OF SOUTHEASTERN MISSOURI AND SOUTHWESTERN ILLINOIS. AS THE  
JET WEAKENS THROUGH THE DAY, THE INTENSITY AND COVERAGE OF THIS  
CONVECTION IS EXPECTED TO WANE, MOSTLY EXITING THE CWA OR  
DISSIPATING DURING THE LATE AFTERNOON.  
 
OUR ATTENTION THEN TURNS TO TONIGHT AND EARLY SUNDAY MORNING. AT  
THAT TIME, A WARM FRONT WILL LIFT THROUGH THE CWA AS THE LOW LEVEL  
JET ONCE AGAIN RAMPS UP AND INTERACTS WITH THE BOUNDARY. THIS WILL  
RESULT IN A BAND OF SHOWERS AND THUNDERSTORMS ALONG THE BOUNDARY AS  
IT LIFTS NORTHWARD, EVENTUALLY SLOWING AND STALLING ACROSS  
NORTHEASTERN MISSOURI AND WEST-CENTRAL ILLINOIS. AT THAT TIME, THERE  
WILL BE TWO THREATS TO FOCUS ON: 1) THE POTENTIAL FOR TRAINING  
CONVECTION CAPABLE OF HEAVY RAINFALL, AND 2) SEVERE THUNDERSTORMS  
CAPABLE OF LARGE HAIL. AS FOR THE HEAVY RAIN THREAT, THE 00Z HREF  
MEAN HAS PRECIPITABLE WATER AROUND 1.5", AND WITH CONVECTION EXPECTED  
TO TRAIN ALONG THE FRONT, RAINFALL AMOUNTS OF 1-2" WITH LOCALIZED  
3"+ ARE POSSIBLE ACROSS NORTHEASTERN MISSOURI AND WEST-CENTRAL  
ILLINOIS THROUGH EARLY SUNDAY AFTERNOON. THE DURATION OVER WHICH  
THIS RAIN WILL FALL AS WELL AS DRIER SOILS IN THIS PORTION OF THE  
CWA ARE EXPECTED TO LIMIT FLOOD POTENTIAL. ALTHOUGH, I CAN'T  
COMPLETELY RULE OUT AN ISOLATED INSTANCE OF FLASH FLOODING OR A  
SMALLER TRIBUTARY OR TWO RISING TO AROUND FLOOD STAGE. WITH THE  
SATURDAY NIGHT/SUNDAY MORNING SEVERE THREAT, ELEVATED CONVECTION  
WITH THE FRONT WILL POSE A LARGE HAIL THREAT PRIMARILY ACROSS  
NORTHEASTERN MISSOURI AND WEST-CENTRAL ILLINOIS. HOWEVER, THE MAIN  
THREAT FOR SEVERE WEATHER WILL BE LATER IN THE DAY ON SUNDAY AS A  
SHORTWAVE EJECTS OUT OF THE GREAT PLAINS AND A SURFACE LOW DRAGS  
A COLD FRONT TOWARD THE CWA.  
 
THEN, THE ATMOSPHERE WILL BECOME RATHER UNSTABLE, WITH APPROXIMATELY  
1,500 TO JUST OVER 2,000 J/KG OF SBCAPE AHEAD OF THE FRONT. THE  
VERTICAL WIND PROFILE IS ALSO FORECAST TO BE SUPPORTIVE OF SEVERE  
STORMS, WITH ROUGHLY 40-50 KTS OF 0-6KM BULK SHEAR AND LONG, CURVED  
HODOGRAPHS PRESENT OVER THE CWA. BY MID AFTERNOON, THE FRONT IS  
EXPECTED TO BE IN WESTERN MISSOURI WITH A PRE-FRONTAL TROUGH OVER  
CENTRAL MISSOURI. SEVERAL CAMS HAVE DISCRETE CONVECTION ASSOCIATED  
WITH THIS TROUGH, WHICH WOULD BE SUPERCELLS CAPABLE OF ALL SEVERE  
HAZARDS. GIVEN LOW LCLS (<1,000 M), HIGH EFFECTIVE SRH (>300M2/S2),  
AND MLCAPE OF AROUND 1,500 J/KG, TORNADOES ARE OF PARTICULAR CONCERN  
WITH THESE EARLIER STORMS. AS THE FRONT ENTERS THE CWA DURING THE  
EVENING AND STORMS TRACK FURTHER INTO EASTERN MISSOURI AND WESTERN  
ILLINOIS, UPSCALE GROWTH INTO A LINEAR STORM MODE IS EXPECTED,  
WITH BOWING SEGMENTS CAPABLE OF PRIMARILY DAMAGING WIND GUSTS AND  
TORNADOES. THE SEVERE THREAT IS EXPECTED TO DIMINISH AS STORMS  
WEAKEN AND EXIT THE CWA SHORTLY AFTER MIDNIGHT ON MONDAY.  
 
ELMORE  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH FRIDAY)  
ISSUED AT 330 AM CDT SAT OCT 23 2021  
 
THE SHORTWAVE AND SURFACE LOW WILL CONTINUE PUSHING EASTWARD ON  
MONDAY. MOISTURE WRAPPING AROUND THE BACKSIDE OF THE LOW WILL  
SUSTAIN DENSE CLOUD COVER OVER THE CWA, AND WHEN PAIRED WITH LOW-  
LEVEL COLD AIR ADVECTION, WILL KEEP TEMPERATURES ON THE COOL SIDE  
OF CLIMATOLOGY FOR MOST LOCATIONS.  
 
THIS COOLER WEATHER WILL BE SHORT LIVED AS AN UPPER-LEVEL RIDGE  
BUILDS INTO THE MIDWEST LATE MONDAY INTO TUESDAY. IN TURN, LOW-LEVEL  
WINDS WILL SHIFT TO OUT OF THE SOUTH, USHERING IN WARMER AIR AND  
RETURNING TEMPERATURES TO NEAR NORMAL VALUES FOR TUESDAY AHEAD OF  
OUR NEXT SYSTEM ASSOCIATED WITH A DEEP, UPPER-LEVEL TROUGH.  
 
ENSEMBLE GUIDANCE STILL DIFFERS ON THE PHASING OF THIS TROUGH AND  
ITS ASSOCIATED SURFACE SYSTEM AS IT TRAVERSES THE CENTRAL PORTION OF  
THE CONUS. DESPITE THESE DIFFERENCES, CONFIDENCE IS HIGH THAT THE  
CWA WILL SEE ANOTHER ROUND OF RAIN LATE TUESDAY THROUGH POSSIBLY AS  
LONG AS FRIDAY. RAIN WILL NOT BE CONTINUOUS THROUGH THIS ENTIRE  
PORTION OF THE PERIOD, BUT A FROPA ON WEDNESDAY AND DEEPENING  
SURFACE LOW IN PROXIMITY TO THE CWA WILL LINGER THE CHANCE FOR  
SEVERAL ROUNDS OF SHOWERS FOR PORTIONS OF THE REGION.  
 
ELMORE  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)  
ISSUED AT 641 AM CDT SAT OCT 23 2021  
 
SEVERAL ROUNDS OF RAIN AND SUB-VFR FLIGHT CONDITIONS ARE EXPECTED TO  
IMPACT ALL LOCAL TERMINALS THROUGH THE PERIOD. THIS MORNING, AN AREA  
OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL SKIM PAST KCOU,  
KJEF, KSUS, KSTL, AND KCPS. WHILE THE BEST CHANCE FOR THIS  
CONVECTION WILL REMAIN SOUTH OF THESE TERMINALS, I CAN'T RULE OUT A  
SHOWER OR TWO PASSING NEAR THE TERMINALS LATER THIS MORNING INTO THE  
EARLY AFTERNOON. OF MORE IMPORTANT NOTE WITH THIS AREA OF SHOWERS IS  
ONSET OF LOW STRATUS FROM SOUTHWEST TO NORTHEAST ACROSS THE  
TERMINALS THROUGH THE LATE MORNING, FINALLY REACHING KUIN BY THIS  
EVENING. BY THAT POINT IN THE PERIOD, YET ANOTHER ROUND OF RAIN AND  
THUNDERSTORMS IS EXPECTED AT ALL LOCAL TERMINALS. THIS ROUND WILL  
HAVE POTENTIALLY GREATER IMPACT THAN THE EARLIER PERIOD SHOWERS, AS  
HEAVIER SHOWERS AND THUNDERSTORMS WILL LIKELY REDUCE VISIBILITIES TO  
MVFR AND POSSIBLY BRIEF IFR CONDITIONS. HOWEVER, GIVEN THE  
UNCERTAINTY IN THE PLACEMENT OF THESE HEAVIER CORES, I'VE LEFT  
VISIBILITIES VFR FOR NOW. IFR CEILINGS ARE EXPECTED AT KUIN, KCOU,  
AND KJEF LATER IN THE PERIOD, BUT CONFIDENCE IS CURRENTLY HIGH THAT  
CEILINGS WILL STAY MVFR AT THE OTHER LOCAL TERMINALS.  
 
ELMORE  
 

 
   
LSX WATCHES/WARNINGS/ADVISORIES
 
 
MO...NONE.  
IL...NONE.  

 
 

 
 
WFO LSX  
 
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