181  
FXUS63 KILX 210846  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
346 AM CDT FRI JUL 21 2017  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 325 AM CDT FRI JUL 21 2017  
 
WEAK BOUNDARY DRAPED ACROSS THE REGION, NOT EXACTLY A TRADITIONAL  
REPRESENTATION OF A FRONT, IS THE BOUNDARY BETWEEN AN AREA OF MORE  
ACTIVE CONVECTION, AND A DOME OF HOT AIR THAT IS DOMINATING THE  
MID MISSISSIPPI RIVER VALLEY THIS MORNING. IN FACT, THE SOUTHERN  
TIER OF THE COUNTRY IS DOMINATED BY AN UPPER RIDGE AND PLENTY OF  
HOT AIR THAT HAS MOVED INTO PLACE ALOFT OVER THE PAST FEW DAYS.  
FRIDAY LANDS ILX RIGHT IN THE MIDDLE OF AN EXTENDED PERIOD OF HEAT  
AND THE APPROPRIATE WARNINGS AND ADVISORIES. VERY LITTLE IN THE  
FORECAST HAS CHANGED, INCLUDING THE NEARBY CONVECTION SHUNTED OFF  
MOSTLY TO THE NORTHWEST THROUGH NORTHEAST, AS WAVES MOVE ALONG A  
MORE ACTIVE FLOW/TIGHTER HEIGHT GRADIENT ALOFT. MODELS HAVE  
CONTINUED TO STRUGGLE WITH THE EVOLUTION OF THE MCS/STORMS IN THE  
PAST WEEK, AS MUCH AS HANDLING THE BOUNDARY LAYER RH AND AS A  
RESULT, CONVECTIVE PARAMETERIZATION IS UNDERSTANDABLY OFF. MUCH  
OF THE SHORTER TERM IS A BLEND OF BEST MODEL OUTPUT AND  
PERSISTENCE. UNTIL THE UPPER RIDGE BREAKS DOWN CONSIDERABLY, OR A  
LARGER TROF MOVES INTO THE UPPER MIDWEST LATER IN THE WEEKEND, THE  
TREND WILL CONTINUE OF HOT, HUMID, AND BEST CHANCES FOR SHOWERS/TS  
CONFINED TO AREAS NORTH OF INTERSTATE 74 FROM THE OUTFLOW OF THE  
NORTHERN STORMS AND THE PERIMETER OF THAT CONVECTION.  
 
TODAY WILL REMAIN HOT...WITH H85 TEMPS SUCCESSFULLY REACHING 23C +  
BY THE 00Z SOUNDING...AND ANY CONVECTION MAY MAKE SMALL IMPACTS  
TO LOCALLY REDUCE MAX TEMPS...BUT CONFIDENCE IN EXPANSIVE COVERAGE  
IS NOT HIGH ENOUGH TO REDUCE GOING FORECAST HIGHS...AND HEAT  
INDICES WILL REMAIN IN THE 100-110F RANGE. LATE IN THE  
AFTERNOON/EVENING, MODELS SHOW SOME CONSISTENCE IN PASSING THROUGH  
SOME SHOWER/TS CHANCES A LITTLE FURTHER SOUTH.  
TONIGHT...REMAINING HOT AND MUGGY WITH THE OVERNIGHT LOWS IN THE  
MID TO UPPER 70S.  
 

 
   
LONG TERM
 
(SATURDAY THROUGH THURSDAY)  
ISSUED AT 325 AM CDT FRI JUL 21 2017  
 
SAME DISCUSSION APPLIES FOR SATURDAY...HOT AND HUMID, AND BETTER  
CHANCES FOR MORE THUNDERSTORMS PASSING TO THE NORTH. THE STRENGTH  
OF THE UPPER RIDGE IS HOLDING THE BULK OF THE STORMS TO THE  
NORTH...BUT LOCAL OUTFLOWS AND MESOSCALE INFLUENCES RESULT IN AT  
LEAST A SLIGHT CHANCE OF STORMS NORTH OF INTERSTATE 74. SATURDAY  
NIGHT, THE FRONT/BOUNDARY THAT HAS BEEN DEVELOPING FOR THE LAST  
FEW DAYS FINALLY MAKES ITS WAY TO THE SOUTH WITH A WAVE MOVING  
INTO THE GREAT LAKES ALOFT. SAID WAVE IS STARTING TO DIG OUT A  
TROF ALOFT AND PUSH THROUGH A SLIGHTLY DIFFERENT AIRMASS. WITH THE  
MOVEMENT OF THE BOUNDARY, PRECIP CHANCES SPREAD THROUGH THE  
STATE. SLIGHTLY COOLER TEMPS ON THE BACK SIDE OF IT FOR SUNDAY.  
FORECAST EXPECTED TO BE DRY FOR THE START OF NEXT WEEK, WITH  
TEMPERATURES FAR MORE MODERATE IN THE LOW TO MID 80S. IT SHOULD  
ALSO BE MENTIONED THAT THE PREVIOUSLY DRY MON-WED PERIOD IS  
STARTING TO PICK UP SOME MAJOR DIFFERENCES IN THE GFS/ECMWF  
SOLUTIONS. EXPECT SOME CHANGES TO THE FORECAST ON THE OTHER SIDE  
OF THE WEEKEND IN SUBSEQUENT FORECASTS.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)  
ISSUED AT 102 AM CDT FRI JUL 21 2017  
 
PREDOMINANTLY A LIGHT AND VARIABLE WIND OVERNIGHT, WITH BKN  
CIRRUS. HOWEVER, CONVECTION PASSING TO THE NORTH AND NORTHEAST  
WILL KEEP A VCSH IN PIA AND VCTS IN BMI AT THE VERY LEAST.  
ANOTHER ROUND OF SHOWERS/TS POSSIBLE FOR THE AFTERNOON HOURS AGAIN  
IN THE NORTH CLOSER TO THE STALLED FRONTAL BOUNDARY.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
EXCESSIVE HEAT WARNING UNTIL 8 PM CDT SATURDAY FOR ILZ027>029-  
036-037-040>042-047>054-061-062-066>068-071>073.  
 
HEAT ADVISORY UNTIL 8 PM CDT SATURDAY FOR ILZ030-031-038-043>046-  
055>057-063.  
 

 
 

 
 
SHORT TERM...HJS  
LONG TERM...HJS  
AVIATION...HJS  
 
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