400  
FXUS63 KDMX 291828  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
128 PM CDT THU JUL 29 2021  
   
..UPDATED FOR 18Z AVIATION DISCUSSION
 
 
   
DISCUSSION
 
/TODAY THROUGH WEDNESDAY/  
ISSUED AT 345 AM CDT THU JUL 29 2021  
 
FORECAST HIGHLIGHTS  
-HOT/HUMID SOUTH TODAY  
-STORM POTENTIAL LATE TONIGHT INTO EARLY SATURDAY  
-COOLER TEMPS AND DRY WEATHER SUNDAY INTO NEXT WEEK  
 
TODAY INTO TONIGHT...EARLY THIS MORNING, WEAK CONVECTION HAS  
DEVELOPED ALONG A BOUNDARY SAGGING SOUTHWARD IN NORTHERN PARTS OF  
THE FORECAST AREA. COVERAGE REMAINS FAIRLY ISOLATED AND  
SUSTAINABILITY LOOKS TO BE ONLY A FEW HOURS THIS MORNING AS DEEP  
SHEAR IS LOW IN THE VICINITY OF THIS CONVECTION AT ABOUT 25 KT.  
ENOUGH MOISTURE CONVERGENCE AND CERTAINLY PLENTY OF INSTABILITY  
PRESENT, BUT THERE IS ALSO PLENTY OF CIN. STILL, WITH DCAPE  
VALUES AT ~1500 J/KG AND HIGH LCLS, IF A STORM DOES BREAK THROUGH  
THE CAP, COULD PRODUCE SOME ISOLATED STRONG WIND GUSTS. MOST OF  
THE HIRES MODELS DISSIPATE THIS WEAK CONVECTION BY 15Z AT THE  
LATEST, IF IT DOES SUGGEST CONVECTION. HRRR IS THE MOST  
AGGRESSIVE, BUT CONFIDENT ENOUGH TO KEEP SOME POPS GOING THROUGH  
THE AFOREMENTIONED TIME.  
 
HEAT AND HUMIDITY REMAIN A FACTOR ACROSS THE SOUTH TODAY WITH THE  
BOUNDARY GRADUALLY STALLING OR SLOWING DOWN OVER CENTRAL IOWA.  
SHOULD BE ENOUGH TIME FOR HIGHS TO REACH THE LOWER 90S, ESPECIALLY  
WITH TEMPERATURES REMAINING IN THE MIDDLE 70S OVERNIGHT. PLUS,  
DEWPOINTS CONTINUE TO BE SULTRY AS THEY RANGE IN THE LOWER TO  
MIDDLE 70S AND THUS EXPANDED THE HEAT ADVISORY A ROW OF COUNTIES  
NORTH TODAY WITH HEAT INDEX VALUES NEARING 105. WITH THE BOUNDARY  
IN THIS VICINITY, THIS WILL BRING SOME CONVECTION POTENTIAL LATE  
THIS AFTERNOON INTO TONIGHT BUT SHOULD BE SHORT-LIVED AS MOST  
HIRES MODELS QUICKLY PUSH THE CONVECTION INTO NORTHERN MISSOURI.  
 
FRIDAY INTO SATURDAY...SURFACE LOW PRESSURE OVER EASTERN ROCKIES  
DEEPENS A BIT THROUGH THE DAY FRIDAY INTO FRIDAY NIGHT AND PUSHES  
EAST INTO WESTERN KANSAS. MID-LEVEL SHORTWAVE CUTS ACROSS SD/NE  
ALONG THE PRESSURE GRADIENT B/T THE SURFACE LOW OVER CO AND THE HIGH  
PRESSURE TO THE NORTHEAST. HEAVY RAIN THREAT SEEMS VIABLE WITH  
PRECIPITABLE WATER VALUES OVER 2 INCHES, WARM-LAYER CLOUD DEPTHS OF  
4000 METERS, AND CORFIDI VECTORS LINING UP WITH THE MEAN STORM  
MOTION. THE GREATEST THREAT LOOKS TO BE CENTRAL TO SOUTHWEST  
PORTIONS OF THE IOWA FRIDAY AFTERNOON INTO EARLY SATURDAY MORNING  
AND THE WPC DY2 EXCESSIVE RAINFALL OUTLOOK HIGHLIGHTS THIS SETUP  
WELL.  
 
SUNDAY INTO NEXT WEEK...SURFACE HIGH PRESSURE BUILDS INTO THE STATE  
SUNDAY AND REMAINS THE STALWART THROUGH AT LEAST WEDNESDAY. THERE  
ARE SIGNS OF THE RIDGE BREAKING DOWN BY THURSDAY INTO FRIDAY OF NEXT  
WEEK, BUT CONFIDENT TO KEEP FORECAST DRY ATTM WITH MODELS IN  
DISARRAY.  
 

 
   
AVIATION
 
/FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON/  
ISSUED AT 128 PM CDT THU JUL 29 2021  
 
MAIN CONCERN THIS PERIOD ARE CEILINGS THIS AFTERNOON AND SURFACE  
VISIBILITY REDUCTION DUE TO SMOKE FROM CANADIAN WILDFIRES LATER  
THIS AFTERNOON THROUGH THE END OF THE PERIOD. SITES HAVE BEEN  
BOUNCING BETWEEN VFR AND MVFR WITH SCT/BKN DECK AND SHOULD GO TO  
PREVAILING VFR AS BOUNDARY LAYER DEPTH GROWS THIS AFTERNOON.  
HOWEVER, SMOKE FROM CANADIAN WILDFIRES WILL SINK SOUTHWARD THIS  
AFTERNOON INTO TONIGHT AND BEGIN TO IMPACT VISIBILITY. CONFIDENCE  
IS HIGH IN SMOKE, BUT TO WHAT DEGREE THE VISIBILITY IS REDUCED IS  
LOWER CONFIDENCE. FOR NOW, HAVE SMOKE ARRIVING TO THE NORTHERN  
TERMINALS THIS AFTERNOON OR EARLY EVENING WITH 5SM FU, WHICH  
CONTINUES INTO TONIGHT. BASED ON UPSTREAM OBS, RESTRICTIONS COULD  
FALL INTO IFR, BUT WAS NOT CONFIDENT TO INCLUDE ANYTHING BEYOND  
HIGH END MVFR AT THIS TIME. FU OR HZ MAY EXPAND INTO DSM AND OTM  
LATER IN THIS PERIOD, BUT WILL ALLOW FUTURE TAFS TO EVALUATE.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR IAZ070>075-081>086-  
092>097.  
 

 
 

 
 
DISCUSSION...PODRAZIK  
AVIATION...ANSORGE  
 
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