209  
FXUS63 KILX 210445  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
1145 PM CDT FRI SEP 20 2019  
   
SYNOPSIS
 
 
ISSUED AT 236 PM CDT FRI SEP 20 2019  
 
HEAVY RAINFALL IS FORECAST OVER CENTRAL ILLINOIS THIS WEEKEND DUE  
TO A SLOW MOVING COLD FRONTAL SYSTEM. THE HEAVIEST RAIN OF 2 TO 3  
INCHES WILL BE FOCUSED ACROSS THE ILLINOIS RIVER VALLEY...WITH  
AMOUNTS DECREASING TO AROUND 1 INCH FURTHER SOUTHEAST ALONG AND  
SOUTH OF I-70.  
 

 
   
UPDATE
 
 
ISSUED AT 901 PM CDT FRI SEP 20 2019  
 
CENTRAL ILLINOIS WILL REMAIN UNDER A WEAKLY FORCED HUMID AND  
UNSTABLE AIR MASS OVERNIGHT. MUCAPES OF 1500-2000 J/KG HAS BEEN  
ENOUGH TO ALLOW A FEW LINGERING CONVERGENT AREAS TO PRODUCE  
SHOWERS. THE PREDICTABILITY OF THE LOCATION OF THOSE SHOWERS THIS  
EVENING HAS BEEN AKIN TO THE WHACK-A-MOLE GAME. ISOLATED SHOWERS  
HAVE BEEN BUBBLING UP SPORADICALLY IN THE NORTH, SOUTHEAST AND  
EASTERN PORTIONS OF OUR FORECAST AREA SO FAR. LIGHTING THIS  
EVENING HAS BEEN MINIMAL IF AT ALL. CAMS ARE POINTING TOWARD MORE  
OF THE SAME THE REST OF THE NIGHT.  
 
A MORE WELL DEFINED FORCING MECHANISM IS PROJECTED TO APPROACH  
WESTERN ILLINOIS LATE TONIGHT, INCREASING RAIN AND STORM CHANCES  
WEST OF SPI TO PIA BY SUNRISE. THE CORRIDOR OF HIGHEST MOISTURE  
CONTENT TOMORROW LOOKS TO BE ON A SW TO NE AXIS ACROSS THE NW  
THIRD OF IL, WHERE OUR HIGHEST POPS AND FLASH FLOOD WATCH RESIDE.  
AS EVIDENCED WITH THIS EVENINGS SHOWERS, THERE WILL LIKELY BE  
ISOLATED TO SCATTERED SHOWERS EAST OF I-55 FROM TIME TO TIME AS  
WELL, DURING THE HEAT OF THE DAY ON SATURDAY.  
 
PERIODIC CLOUDS TONIGHT AND STEADY S-SE FLOW WILL KEEP LOW TEMPS  
VERY CLOSE TO 70 DEGREES, AS DEWPOINTS REMAIN IN THE UPPER 60S TO  
LOW 70S AS WELL. PATCHY FOG CAN NOT BE RULED OUT, BUT INCREASING  
CLOUD COVER IN WESTERN COUNTIES SHOULD PRECLUDE FOG FROM GETTING  
OUT OF HAND TOWARD BECOMING DENSE FOG.  
 
UPDATE THIS EVENING WAS TO THE POPS/WEATHER GRIDS PRIMARILY, TO  
CAPTURE THE CURRENT AND EXPECTED SHORT TERM TRENDS IN SHOWER/STORM  
COVERAGE. THE REMAINDER OF THE FORECAST APPEARED ON TRACK.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 246 PM CDT FRI SEP 20 2019  
 
MODELS CONTINUE SIMILAR TREND AS PAST OF BRINGING MAJOR UPPER TROF  
INTO REGION ON WEEKEND, WITH AMPLE MOIST AIR FLOWING IN AHEAD OF  
THE UPPER FEATURE. COLD FRONT ASSOCIATED WITH SYSTEM WILL APPROACH  
AREA EARLY SUNDAY MORNING AND CROSS AREA DURING DAY SUNDAY. STILL  
SOME MINOR DIFFERENCES ON FRONTAL TIMING, BUT THE RESULT WILL  
STILL BE MOST SIGNIFICANT RAINFALL AMOUNTS OVER THE NORTHWEST  
CWA(2-3 INCHES), WITH LESSER AMOUNTS TO THE EAST TO I-55. AS  
FRONT MOVES ACROSS REGION LATE SUNDAY, EXITING SYSTEM WILL PRODUCE  
NEAR 1 INCH AMOUNTS. 850MB MOISTURE TRANSPORT TODAY FOCUSING GOOD  
PLUME OF MOISTURE ADVECTION INTO THE KS-NE AREA AND EXPECT THIS  
SAME GOOD ADVECTION THROUGH DAY TOMORROW FURTHER TO THE EAST, SO  
AVAILABLE MOISTURE SHOULD NOT BE A PROBLEM WITH STRONG UPPER  
DYNAMICS. FOR THESE REASONS, HAVE SIMPLY MADE SOME MINOR  
ADJUSTMENTS TO MATCH COORDINATED POPS AND QPF WITH SURROUNDING  
OFFICES, USING BLEND OF WPC AND NBM AND COORDINATING WFO AMOUNTS.  
WILL ALSO KEEP THE CURRENT FLASH FLOOD WATCH GOING FOR THE WESTERN  
HALF OF CWA.  
   
LONG TERM
 
(MONDAY THROUGH FRIDAY)  
ISSUED AT 156 PM CDT FRI SEP 20 2019  
 
COLD FRONT THAT BRINGS THE HEAVY RAIN TO CENTRAL ILLINOIS OVER THE  
WEEKEND IS PROGGED TO DRIVE SOUTH OF THE OHIO RIVER VALLEY EARLY  
NEXT WEEK WHILE HIGH PRESSURE BUILDS ACROSS PORTIONS OF THE  
MIDWEST IN ITS WAKE. DRY WEATHER AND MORE SEASONABLE TEMPERATURES  
WILL BE IN PLACE BEHIND THE FRONT EARLY NEXT WEEK. EXPECT  
AFTERNOON HIGHS IN THE MID TO UPPER 70S WHILE OVERNIGHT LOWS WILL  
DIP INTO THE MID 50S MONDAY NIGHT INTO TUESDAY MORNING.  
 
THE LATTER HALF OF THE UPCOMING WEEK LOOKS TO BECOME MORE  
PROGRESSIVE AND ACTIVE AS A SERIES OF WAVES PUSH ACROSS THE  
REGION. AT THIS TIME, THERE REMAIN RATHER SIGNIFICANT DIFFERENCES  
BETWEEN THE MODELS, PARTICULARLY WITH HOW FAR NORTH THE BAROCLINIC  
ZONE LIFTS; HOWEVER, THERE IS A GENERAL THEME THAT THE LOCAL AREA  
WILL SEE A WAVE MIDWEEK AND ANOTHER LATE IN THE WEEK. WHILE THERE  
IS A DECENT LIKELIHOOD OF A COUPLE ROUNDS OF SHOWERS AND STORMS  
THROUGH THE LATTER HALF OF THE WEEK AS THESE WAVES TRANSIT THE  
REGION, TIMING WILL STILL NEED TO BE REFINED. HAVE FAIRLY LOW  
CONFIDENCE IN THE TEMPERATURES, THOUGH, GIVEN DIFFERENCES IN THE  
STORM TRACK AND LOCATION OF THE BAROCLINIC ZONE ON ANY GIVEN DAY.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1145 PM CDT FRI SEP 20 2019  
 
VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES IN THE FIRST 6 HRS  
OF THE 06Z TAF PERIOD, THEN MVFR CLOUDS WILL BEGIN TO ADVANCE  
INTO WESTERN ILLINOIS SATURDAY MORNING, ALONG WITH INCREASING  
CHANCES OF SHOWERS AND STORMS. PIA IS THE ONLY TAF WITH MVFR  
CLOUDS FORECAST IN THE MORNING FOR NOW. PIA AND SPI WILL SEE THE  
HIGHEST RAIN CHANCES BY LATER MORNING AND THROUGH THE AFTERNOON.  
THE PRIMARY FORCING FOR PRECIP WILL RESIDE WEST OF THE IL RIVER,  
BUT SCATTERED STORMS WILL DEVELOP IN THE HUMID AND UNSTABLE AIR  
MASS EAST OF THERE DURING THE DAY, MAINLY WEST OF I-57.  
 
WE DELAYED RAIN FOR DEC AND CMI UNTIL AFTER 00Z SAT EVENING.  
 
STEADY RAINS LOOK LIKELY OVERNIGHT SAT NIGHT, ESPECIALLY WEST OF  
I-55, WITH COVERAGE EXPANDING EASTWARD.  
 
WINDS LOOK TO INCREASE FROM SOUTH SAT MORNING, WITH AFTERNOON  
GUSTS CLIMBING TO 20-24KT AT TIMES. WIND GUSTS WILL DIMINISH WITH  
SUNSET, BUT SUSTAINED WINDS LOOK TO LINGER IN THE 10-12KT RANGE.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
FLASH FLOOD WATCH FROM SATURDAY EVENING THROUGH LATE SUNDAY  
NIGHT FOR ILZ027>031-036-037-040-041-047>050.  
 

 
 

 
 
UPDATE...SHIMON  
SYNOPSIS...GOETSCH  
SHORT TERM...GOETSCH  
LONG TERM...DEUBELBEISS  
AVIATION...SHIMON  
 
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