325  
FXUS63 KILX 050409  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
1109 PM CDT TUE AUG 4 2015  
   
UPDATE
 
 
ISSUED AT 835 PM CDT TUE AUG 4 2015  
 
FRONTAL BOUNDARY OVER FAR SOUTHERN ILLINOIS WILL CONTINUE TO BE  
THE FOCUS FOR PERIODIC SHOWERS AND THUNDERSTORMS OVER THE NEXT  
24 TO 36 HOURS WITH A GRADUAL SHIFT NORTHEAST INTO OUR FORECAST  
AREA ON WEDNESDAY AS A WEAK SURFACE WAVE APPROACHES FROM THE  
WEST. MOST OF THE SHORT TERM FORECAST SOLUTIONS FOR THE OVERNIGHT  
HOURS KEEP THE BULK OF THE SHOWER ACTIVITY OVER SOUTHERN IL WITH  
QUITE A BIT OF MID AND HIGH LEVEL CLOUD COVER EXPECTED TO ITS  
NORTH OVER THE REMAINDER OF OUR FORECAST AREA. HIGHER POPS WILL  
CONTINUE TO BE LOCATED OVER THE SOUTHERN AREAS WITH PROGRESSIVELY  
LOWER POPS AS YOU HEAD NORTH. UPDATED ZONES SHOULD BE OUT BY 900  
PM.  
 

 
   
SHORT TERM
 
(TONIGHT)  
ISSUED AT 303 PM CDT TUE AUG 4 2015  
 
A STATIONARY FRONTAL BOUNDARY WILL LINGER ACROSS SOUTHERN IL  
TONIGHT, WHERE BETTER CHANCES OF SHOWERS AND STORMS SHOULD START OUT  
THE EVENING. NORTH OF THE BOUNDARY INTO OUR SOUTHERN COUNTIES, WEAK  
ISENTROPIC LIFT AND MID LEVEL CONVERGENCE WILL WORK TO TRIGGER  
SHOWERS AND A FEW STORMS TOWARD SPRINGFIELD TO MATTOON TONIGHT. THIS  
AFTERNOON, SHOWERS/STORMS DEVELOPED WELL NORTH OF WHERE THE HRRR AND  
RAP MODELS INDICATED, SO THE FACT THAT THEY CONTINUE TO SHOW DRY  
CONDITIONS OVERNIGHT FOR OUR COUNTIES DOES NOT PRECLUDE THAT SHOWERS  
REACH AS FAR NORTH AS LINCOLN TO MATTOON AGAIN OVERNIGHT. ONGOING  
SHOWERS/STORMS LATE THIS AFTERNOON FROM SPRINGFIELD TO SHELBYVILLE  
ARE EXPECTED TO DISSIPATE AS THEY PROGRESS EASTWARD. THEREFORE  
WILL START OUT THE EVENING GRIDS WILL MAINLY SLIGHT CHANCE IN OUR  
SOUTHERN COUNTIES, BUT MAY ADJUST POPS UP AS LATE AFTERNOON  
CONDITIONS WARRANT. DESPITE THE DRY HIGH RESOLUTION MODELS  
TONIGHT, THE CONSENSUS OF THE GFS, NAM, ECMWF AND CANADIAN  
INDICATES ENOUGH FORCING FOR PRECIP REDEVELOPING ACROSS OUR  
SOUTHERN COUNTIES. THEREFORE, HAVE NOT STRAYED FAR FROM THE  
CURRENT FORECAST OF CHANCE POPS EXPANDING NORTH TO AREAS SOUTHWEST  
OF A LINE FROM CANTON TO LINCOLN TO MATTOON.  
 
LOW TEMPS TONIGHT WILL VARY BASED ON THE AMOUNT OF CLEARING THAT  
DEVELOPS UNDER LIGHT ENE FLOW. AFTERNOON DEWPOINTS HAVE POINTED  
TOWARD LOWS TONIGHT GENERALLY IN THE LOWER 60S NORTH OF I-74, WITH  
UPPER 60S IN SOUTH OF I-70, WHERE CLOUDS MAY BE MORE PREVALENT LATER  
TONIGHT.  
   
LONG TERM
 
(WEDNESDAY THROUGH TUESDAY)  
ISSUED AT 303 PM CDT TUE AUG 4 2015  
 
WEDNESDAY COULD START OUT WILL A LULL IN THE SHOWERS AS THE  
ENERGY FROM THE OVERNIGHT CONVECTION SHIFTS EAST INTO INDIANA. THE  
NEXT WAVE OF PRECIP LOOKS TO BE TIED TO THE ADVANCEMENT OF A LOW  
PRESSURE SYSTEM FROM THE CENTRAL PLAINS ACROSS SOUTH CENTRAL IL.  
THE 12Z MODELS HAVE CONTINUED WITH THE SOUTHWARD TREND OF TRACKING  
THE LOW ACROSS IL WEDNESDAY NIGHT INTO THURSDAY. HOWEVER, THEY  
ALSO CONTINUE TO PROJECT OVERRUNNING SHOWERS/STORMS DEVELOPING  
AHEAD OF THE LOW WED AFTERNOON ACROSS OUR SOUTHERN COUNTIES.  
WEDNESDAY NIGHT, PRECIP CHANCES ALONG AND SOUTH OF I-72 WILL RAMP  
UP TO LIKELY, WITH CATEGORICAL POPS SOUTH OF I-70 AS THE LOW  
PASSES JUST SOUTH OF STATE HWY 50. HEAVY PRECIP REMAINS POSSIBLE  
WED NIGHT INTO THURSDAY MORNING SOUTH OF I-70, AS PRECIPITABLE  
WATER VALUES CLIMB TO 1.8". WILL MONITOR FOR POSSIBLE FLASH FLOOD  
WATCH, BUT DRY CONDITIONS RECENTLY MAY HELP PREVENT FLASH  
FLOODING. ALSO, A DRIER TREND IN THE 12Z MODELS HAS LOWERED  
CONFIDENCE IN VERY HEAVY RAINFALL IN OUR SOUTHERN COUNTIES.  
 
THURSDAY SHOULD SEE DRY CONDITIONS RETURN BY AFTERNOON AS THE LOW  
PULLS AWAY TO THE EAST AND HIGH PRESSURE GAINS CONTROL OF THE LOCAL  
WEATHER. RIDGING ALOFT WILL REACH WESTERN IL, WITH HEIGHT RISES  
HELPING HIGHS REACH THE LOW 80S.  
 
LOW PRESSURE TRACKING FROM THE DAKOTAS THURSDAY AFTERNOON TO EASTERN  
LAKE SUPERIOR SATURDAY MORNING COULD DRAG A WEAKENING COLD FRONT  
INTO NORTHERN IL LATE FRIDAY INTO FRI EVENING. WE ONLY ACKNOWLEDGED  
THAT FEATURE WITH SLIGHT CHANCE POPS WEST OF I-55 FOR NOW.  
 
THERE ARE INDICATIONS IN THE EXTENDED MODELS THAT AN MCS COULD  
DEVELOP IN NEBRASKA ON SATURDAY, THEN PROGRESS EASTWARD INTO CENTRAL  
IL SAT NIGHT-SUNDAY. THE CANADIAN IS THE NORTHERN OUTLIER WITH THE  
TRACK OF THE SYSTEM, KEEPING IT GENERALLY NORTH OF OUR COUNTIES,  
WHILE THE GFS/ECMWF BOTH PUSH THE WAVE INTO CENTRAL IL. WILL KEEP  
CHANCE POPS FOR THE ENTIRE FORECAST AREA SUNDAY INTO SUNDAY NIGHT,  
WITH DECREASING CHANCES FROM WEST TO EAST ON MONDAY. DRY  
CONDITIONS ARE EXPECTED FOR TUESDAY AS AN UPPER TROUGH BUILDS INTO  
THE AREA.  
 
HEAT AND HUMIDITY ARE PROJECTED TO INCREASE SATURDAY AND CONTINUE  
INTO MONDAY, WITH HIGHS IN THE MID 80S AND HEAT INDICES IN THE LOWER  
90S.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 1102 PM CDT TUE AUG 4 2015  
 
FORECAST CONCERN WILL BE COVERAGE OF SHOWERS AND THUNDERSTORMS  
LATE TONIGHT INTO WEDNESDAY AND THEIR AFFECT ON CIGS...ESPECIALLY  
AT KSPI AND KDEC...AS A WEATHER SYSTEM DRIFTS ACROSS SOUTHERN  
ILLINOIS. WIDELY SCATTERED SHOWERS AND STORMS WERE NOTED OVER  
PARTS OF CENTRAL MISSOURI LATE THIS EVENING AND THOSE ARE EXPECTED  
TO DRIFT EAST TOWARDS THE MISSISSIPPI RIVER OVER THE NEXT SEVERAL  
HOURS. THE AIR MASS IN OUR AREA LATE THIS EVENING WAS QUITE STABLE  
SO IT APPEARS AT LEAST THE INTENSITY WILL WEAKEN AS THEY DRIFT  
EAST BUT CONFIDENCE ON COVERAGE OF THE RAIN OVER WESTERN IL LATE  
TONIGHT IS NOT VERY HIGH AS MODELS CONTINUE TO SUGGEST A DECREASE  
IN COVERAGE AS THEY MOVE INTO THE MORE STABLE ENVIRONMENT. AS A  
RESULT...UNLESS WE SEE AN INCREASE IN COVERAGE TO OUR WEST OVER  
THE NEXT HOUR OR SO...WILL ONLY INCLUDE A VCTS AT KSPI IN THE 06Z  
TO 09Z TIME FRAME.  
 
AS THE WEAK SURFACE WAVE MOVES ALONG THE STALLED FRONTAL BOUNDARY  
TO OUR SOUTH ON WEDNESDAY...THE HIGHER THREAT FOR SHOWERS AND  
STORMS WILL BE ROUGHLY FROM SPRINGFIELD TO DECATUR AND SOUTH.  
STILL THINKING MAINLY SOME SCATTERED TO BKN MID CLOUDS WITH SOME  
HIGHER OVERCAST FURTHER NORTH...WITH LOWER VFR CIGS AT KSPI AND  
KDEC. SURFACE WINDS WILL REMAIN LIGHT AND VARIABLE OVERNIGHT AND  
BECOME LIGHT EASTERLY ON WEDNESDAY WITH SPEEDS OF 10 KTS OR LESS.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...SMITH  
SHORT TERM...SHIMON  
LONG TERM...SHIMON  
AVIATION...SMITH  
 
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