145  
FXUS63 KDMX 220448  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
1148 PM CDT THU SEP 21 2017  
   
SHORT TERM
 
/TONIGHT THROUGH FRIDAY/  
ISSUED AT 315 PM CDT THU SEP 21 2017  
 
WARM FRONT MAKING NICE PROGRESS ACROSS IOWA. EARLY AFTERNOON HAD  
THE BOUNDARY JUST NORTH OF HIGHWAY 20. THE FRONT WILL MOVE INTO  
SOUTHERN MN THIS EVENING PUTTING ALL OF THE FORECAST AREA IN STRONG  
WARM ADVECTION. LOWS TONIGHT WILL BE AROUND WHAT NORMAL HIGHS ARE  
FOR THIS TIME OF YEAR WITH READINGS IN THE LOW TO MID 70'S. EXPECT A  
SOUTHERLY WIND TO MAINTAIN THROUGH THE NIGHT AT 10 TO 15 MPH.  
 
ON FRIDAY WE WILL MIX TO AT LEAST 850MB SO WINDS WILL BE PRETTY  
STRONG AND GUSTY...IN THE 20 TO 30 MPH RANGE. THE GOOD MIXING WILL  
ALSO MEAN THAT TEMPS WILL WARM UP QUITE A BIT. I NUDGED HIGHS AT  
LEAST 2 TO 3 DEGREES ABOVE GUIDANCE AND THIS MAY NOT BE WARM ENOUGH.  
HEAT INDICES IN THE MID AFTERNOON HOURS WILL LIKELY HIT 100 OR SO IN  
A FEW PLACES. THE WIND WILL HELP BUT IT WILL BE A HOT DAY.  
 
AS FAR AS THE OVERALL PATTERN...WE WILL REMAIN STAGNANT WITH A LOW  
AND FRONT PARKED OUT WEST IN SOUTH DAKOTA AND NEBRASKA BRINGING  
RAINFALL TO THOSE AREAS WHILE OVER IOWA WE WILL BE IN BETWEEN THE  
LOW TO THE WEST AND THE HIGH TO THE EAST, WHILE UNDER THE INFLUENCE  
OF AN UPPER RIDGE. WE WILL REMAIN HOT AND BREEZY GOING INTO THE  
WEEKEND WITH LITTLE THREAT OF RAIN.  
   
LONG TERM
 
/FRIDAY NIGHT THROUGH THURSDAY/  
ISSUED AT 315 PM CDT THU SEP 21 2017  
 
HIGHLY AMPLIFIED PATTERN WILL BE IN PLACE AT THE START OF LONGER  
TERM WITH DEEP SOUTHERLY FLOW ACROSS THE MIDWEST. FRONTAL BOUNDARY  
WILL BE LOCATED IN THE PLAINS WITH UPPER FLOW NEARLY PARALLEL  
WITH THE FRONT. THEREFORE, NOT MUCH MOVEMENT/OR ONLY SLOW MOVEMENT  
IS EXPECTED WITH THE FRONT FOR SEVERAL DAYS LEAVING IOWA IN THE  
WARM SECTOR DURING THE WEEKEND. 850MB TEMPERATURES WILL BE  
APPROACHING +20C OVER THE WEEKEND AND WITH GOOD MIXING, SHOULD  
LEAD TO SURFACE TEMPERATURES OF AROUND 90 DEGREES IN MOST  
LOCATIONS THROUGH SUNDAY. THE COMBINATION OF THESE WARM  
TEMPERATURES AND DEWPOINTS APPROACHING 70 WILL HAVE HEAT INDEX  
VALUES IN THE UPPER 90S TO NEARLY 100 DURING THE AFTERNOON  
TIMEFRAME. HIGHS WILL ALSO BE NEAR RECORD LEVELS, ESPECIALLY ON  
SUNDAY WHERE READINGS AROUND AROUND 90 ACROSS THE AREA.  
 
FRONTAL BOUNDARY BEGINS TO APPROACH ON MONDAY AS UPPER LOW ACROSS  
THE WESTERN UNITED STATES SLOWLY MOVES EAST. LIFT WILL INCREASE  
WITH THE APPROACH OF THE TROF WITH SHOWERS AND THUNDERSTORMS  
BECOMING MORE LIKELY BY LATE MONDAY INTO TUESDAY AS THE FRONT  
PROVIDES SUFFICIENT CONVERGENCE FOR DEVELOPMENT. HOWEVER, SYSTEM  
OVERALL IS WEAKENING THROUGH THE EARLY PART OF THE WEAK AND WIND  
FIELDS/LIFT WILL BECOME LESS WITH TIME. THEREFORE, COVERAGE AND  
INTENSITY MAY NOT BE QUITE A GOOD AS PREVIOUS FORECAST, BUT MOST  
LOCATIONS WILL LIKELY SEE AT LEAST A LITTLE RAINFALL. MUCH COOLER  
TEMPERATURES ARE EXPECTED BY THE END OF THE PERIOD AS CANADIAN AIR  
MOVES INTO THE MIDWEST BEHIND THE SYSTEM.  
 

 
   
AVIATION
 
/FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT/  
ISSUED AT 1148 PM CDT THU SEP 21 2017  
 
VFR CONDITIONS WILL CONTINUE THROUGH THE FORECAST PERIOD. THE WIND  
WILL BECOME GUSTY AGAIN ON FRIDAY BEFORE DIMINISHING BY THE  
EVENING. LOW LEVEL WIND SHEAR IS POSSIBLE THROUGH 12Z.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...FAB  
LONG TERM...COGIL  
AVIATION...DONAVON  
 
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