872  
FXUS63 KDVN 222000  
AFDDVN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE QUAD CITIES IA IL  
300 PM CDT FRI SEP 22 2023  
   
SHORT TERM  
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 259 PM CDT FRI SEP 22 2023  
 
KEY MESSAGES:  
 
1. SHOWERS AND STORMS TONIGHT, ESPECIALLY ACROSS PORTIONS OF E IOWA  
AND NW ILLINOIS.  
 
2. LOCALIZED HEAVY RAIN AND FLASH FLOOD THREAT.  
 
3. LOW POTENTIAL FOR NEAR SURFACE BASED STORM THREAT LATE AFTERNOON  
THROUGH EARLY EVENING MAINLY ACROSS PORTIONS OF E IOWA.  
 
A SURFACE WARM FRONT IS POSITIONED ACROSS SE IOWA AND WC ILLINOIS  
EARLY THIS AFTERNOON. ALONG AND TO THE SOUTH VERY WARM CONDITIONS  
ARE PRESENT WITH TEMPERATURES IN THE RANGE OF 80 TO 85 BENEATH  
AMPLE SUNSHINE. TO THE NORTH, BOUTS OF SHOWERS AND SOME STORMS AND  
CONSIDERABLE CLOUDINESS WITH PATCHY DRIZZLE IN THE WARM ADVECTION,  
WHICH HAS LIMITED HIGHS TO THE UPPER 60S AND 70S. A MESOSCALE  
CONVECTIVE VORTEX (MCV) WAS LIFTING ACROSS WESTERN IOWA EARLY THIS  
AFTERNOON. THIS IS EXPECTED TO LIFT NORTHEASTWARD THROUGH TONIGHT.  
VORTICITY ADVECTION AND ISENTROPIC ASCENT SHOULD CONTINUE TO FOSTER  
SHOWERS AND STORMS ESPECIALLY ACROSS PORTIONS OF OUR NORTHERN AND  
WESTERN SERVICE AREA, MOST NUMEROUS POTENTIALLY ACROSS PORTIONS OF  
NE/EC IOWA. OBSERVED AND FORECAST SOUNDINGS SUPPORT AN ENVIRONMENT  
CONDUCIVE FOR HEAVY RAIN WITH WARM CLOUD DEPTHS ABOVE 10KFT AGL,  
MAX PWATS AROUND 1.5 INCHES (90TH PERCENTILE OF CLIMATOLOGY) AND  
RATHER TALL, THIN ELEVATED CAPE PROFILES (AT OR BELOW 1000 J/KG).  
WE'VE SEEN IN RECENT DAYS IN PARTS OF THE MIDWEST THIS SIMILAR  
ENVIRONMENT HAS PRODUCED POCKETS OF LOCALLY HEAVY TO VERY HEAVY RAIN  
3+ INCHES AND A CORRESPONDING LOCALIZED FLASH FLOOD THREAT, AND  
THIS LOOKS TO AGAIN BE THE PRIMARY CONCERN IN THE SHORT TERM.  
THE 12Z HREF LOCALIZED PROBABILITY MATCHED MEAN (LPMM) FOR 24 HOURS  
ENDING 12Z SATURDAY, SUPPORTS THIS PATTERN RECOGNITION OF HEAVY RAIN  
POTENTIAL DEPICTING AN AREA OF 3+ INCH RAINFALL ACROSS PORTIONS OF  
NORTHEAST IOWA. THIS HAS BEEN A TREND FOR THE PAST COUPLE OF RUNS, AND  
SUPPORTS THE NOTION OF THE SIGNAL FOR AT LEAST LOCALIZED HEAVY TO  
VERY HEAVY RAIN. FORTUNATELY, WE CAN USE THE RAIN AND FLASH FLOOD  
GUIDANCE (FFG) IS FAIRLY HIGH AT AROUND 3-3.5 INCHES IN 3 HOURS.  
A STRENGTHENING LOW LEVEL JET SHOULD KEEP CONVECTIVE ELEMENTS MOVING  
SUFFICIENTLY, WITH MOTIONS GENERALLY AROUND 20 KTS. THIS SHOULD AID  
IN KEEPING ANY FLASH FLOODING FAIRLY LOCALIZED, AND SO MONITORING  
RAINFALL RATES WITH THESE EFFICIENT WARM RAIN PROCESSES AND THE  
POTENTIAL FOR REPEATED ACTIVITY WITH A SOUTHWESTERLY LOW LEVEL JET  
WILL BE IMPORTANT.  
 
LOW LEVEL INSTABILITY WILL FURTHER INCREASE IN THE WARM SECTOR SOUTH  
OF THE FRONT THIS AFTERNOON. THIS COULD BE IN CLOSE ENOUGH PROXIMITY  
TO YIELD AT LEAST SOME LOW POTENTIAL FOR A NEAR SURFACE BASED STORM  
WITH MAINLY STRONG GUSTY WINDS ACROSS PORTIONS OF NORTHEAST IOWA.  
A LOW POTENTIAL FOR A BRIEF TORNADO COULD ALSO EVOLVE FOR A FEW  
HOURS LATE AFTERNOON INTO VERY EARLY EVENING, WITH FURTHER INCREASE  
OF 0-3KM CAPE SUPPORTIVE OF THE POTENTIAL FOR MORE ROBUST UPDRAFTS  
IN THE PRESENCE OF BACKED LOW LEVEL SURFACE WIND ENHANCING 0-3KM SRH.  
 
THE PRECIPITATION LOOKS TO DIMINISH OVERNIGHT WITH THE PASSAGE OF  
THE MCV TO OUR NORTH. ISENTROPIC ASCENT WILL BE PERSISTENT INTO  
SATURDAY, BUT WEAKER AND WITHOUT MUCH FOCUS IT WOULD APPEAR AS  
THOUGH ANY PRECIPITATION WOULD BE FAIRLY ISOLATED IF AT ALL DURING  
THIS TIMEFRAME LATE TONIGHT THROUGH MUCH OF THE DAY ON SATURDAY.  
 
THERE IS A SIGNAL IN A FEW OF THE CAMS ON POSSIBILITY OF SOME  
CONVECTION SUSTENANCE AND/OR DEVELOPMENT LATE SATURDAY AFTERNOON  
INTO PORTIONS OF E IOWA LIKELY ATTRIBUTED TO POTENTIAL OUTFLOW AND ALSO  
A WEAK LEAD WAVE EJECTING OUT. THIS IS FAIRLY LOW CONFIDENCE, BUT  
SOMETHING TO MONITOR AS THE INSTABILITY GRADIENT MAY BE NEARBY AND  
DEEP LAYER SHEAR (25-30 KTS 0-6KM) POTENTIALLY SUFFICIENT FOR STRONGER  
STORMS.  
   
LONG TERM  
(SATURDAY NIGHT THROUGH FRIDAY)  
ISSUED AT 259 PM CDT FRI SEP 22 2023  
 
KEY MESSAGES:  
 
1. SHOWERS AND STORMS SATURDAY NIGHT, WITH A FEW STRONG TO ISOLATED  
SEVERE STORMS POSSIBLE SATURDAY EVENING INTO PORTIONS OF E IOWA  
AND NE MISSOURI.  
 
2. SLOW MOVING SYSTEM MAY KEEP SOME CHANCE FOR PRECIPITATION  
AROUND LONGER NEXT WEEK THAN CURRENTLY HAVE FORECASTED.  
 
DISCUSSION:  
 
THE PRIMARY FOCUS WILL BE WITH AN APPROACHING FRONT AND ACCOMPANYING  
SHOWERS AND STORMS SATURDAY EVENING INTO EARLY SUNDAY. THE  
PREPONDERANCE OF THE GUIDANCE SUITE IS SUPPORTIVE OF A WEAKENING IN  
THE FORCING, INSTABILITY AND SHEAR IN TIME AFTER DARK SATURDAY NIGHT  
INTO SUNDAY. THUS, CONFIDENCE IS LOW ON SEVERE WEATHER AND THE  
MARGINAL RISK OR LEVEL 1 OUT OF 5 FOR PORTIONS OF EASTERN IOWA AND  
NORTHEAST MISSOURI SEEMS REASONABLE, IN THE EVENT THAT THIS WANING  
PROCESS SLOWS TO WHEREBY A RISK FOR ISOLATED SEVERE STORMS COULD OCCUR  
FROM CEDAR RAPIDS TO KEOKUK, IOWA ON WESTWARD. THINK WINDS ARE THE  
PRIMARY CONCERN.  
 
THE MAIN UPPER LEVEL LOW, WHICH HAS BEEN SLOW MOVING ALREADY, IS  
LIKELY TO SLOW DOWN EVEN FURTHER WITH AID OF THE NEWLY FORMED  
TROPICAL STORM OPHELIA OFF THE SE COAST, AS IT MOVES UP THE  
EASTERN SEABOARD AND BLOCKS THE EASTWARD PROGRESSION OF THE LOW.  
THIS WILL IN TURN SLOW THE FRONT AND KEEP PRECIPITATION CHANCES  
LINGERING THROUGH SUNDAY. THESE PRECIPITATION CHANCES COULD EXTEND  
BEYOND THROUGH THE MIDDLE OF NEXT WEEK AT LEAST, AS THE TEMPORARY  
BLOCKING BY OPHELIA COULD KEEP THE UPPER LOW STAGNANT ACROSS THE  
MIDWEST FOR SEVERAL DAYS AND POSSIBLY THROUGH MIDWEEK.  
 
 
   
AVIATION  
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1254 PM CDT FRI SEP 22 2023  
 
A MOIST AND CHAOTIC WEATHER PATTERN WILL CONTINUE TO BRING  
VARIABLY LOW CEILINGS AND BOUTS OF HEAVY RAIN SHOWERS AND A FEW  
THUNDERSTORMS THROUGH TONIGHT. WHILE ONE BAND OF HEAVY SHOWERS  
WILL MOVING NORTH OUT OF THE AREA THROUGH 19Z ALONG HIGHWAY 20,  
ADDITIONAL SHOWERS/STORMS COULD FORM THIS AFTERNOON, AND  
ESPECIALLY THIS EVENING, AS A WAVE OF ENERGY ARRIVES FROM  
MISSOURI. THIS NEXT ROUND COULD PRODUCE STORMS THROUGH TONIGHT,  
AND WHILE STRONG WINDS ARE NOT EXPECTED, THEY COULD PRODUCE LOW  
VISIBILITY IN HEAVY RAIN, AND MINIMUM CONDITIONS AT TIMES.  
 
RIGHT NOW, THERE'S ENOUGH CONFIDENCE TO A TEMPORARY THUNDERSTORM  
TO MOST LOCATIONS THIS EVENING, THEN REVERT BACK TO A MVFR RAIN.  
OTHERWISE, AN IMPROVEMENT TO A BREEZY VFR IS EXPECTED FOR MID  
MORNING SATURDAY AS A WARM FRONT LIFTS NORTH OF THE AREA.  
 
 
   
DVN WATCHES/WARNINGS/ADVISORIES  
 
IA...NONE.  
IL...NONE.  
MO...NONE.  
 
 
 
 
SHORT TERM...MCCLURE  
LONG TERM...MCCLURE  
AVIATION...ERVIN  
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