748  
FXUS63 KILX 211739  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
1139 AM CST TUE NOV 21 2017  
   
UPDATE
 
 
ISSUED AT 1058 AM CST TUE NOV 21 2017  
 
THE COLD FRONT HAS BEEN MORE ACTIVE THAN YESTERDAYS MODELS WERE  
INDICATING, WITH EVEN SOME SLEET REPORTS COMING IN FROM NW  
ILLINOIS. WHILE PRECIP MAY BE REACHING THE GROUND FROM TIME TO  
TIME AS THE COLD FRONT MOVES INTO INDIANA AROUND 6 PM, MEASURABLE  
RAIN OR MELTED PRECIP WILL BE ISOLATED. HAVE INCLUDED SOME  
CHANCE/SLIGHT CHANCE POPS FOR LIGHT PRECIP WITH THE FRONT, AND  
INCLUDED A RIBBON OF SNOW/SLEET ON THE BACK EDGE OF THE PRECIP  
SHIELD AS IT MOVES EAST. HRRR OUTPUT CONTINUES TO SHOW THE FRONTAL  
PRECIP DIMINISHING WITH TIME, BUT STILL HAS A FEW SPOTTY SHOWERS  
ALL THE WAY THROUGH 6 PM IN OUR FAR SE COUNTIES. FALLING TEMPS  
STILL LOOK ON TRACK FOR THIS AFTERNOON BEHIND THE COLD FRONT,  
ESPECIALLY FOR AREAS W OF I-55. CLEARING IS PROJECTED TO OCCUR  
RELATIVELY QUICKLY BEHIND THE PRECIP, SO MOSTLY CLEAR SKIES AND  
CHILLY NORTHWEST WINDS LOOK GOOD AS WELL.  
 
UPDATED FORECAST INFO IS ALREADY AVAILABLE.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 250 AM CST TUE NOV 21 2017  
 
08Z/2 AM SURFACE ANALYSIS SHOWS 984 MB LOW PRESSURE NEAR LAKE  
NIPIGON CANADA (JUST NORTH OF LAKE SUPERIOR) WITH ITS COLD FRONT  
EXTENDING THROUGH CENTRAL WI INTO EASTERN IA AND NW MO. BREEZY SSW  
WINDS AHEAD OF THE COLD FRONT OVER CENTRAL IL WITH WINDS GUSTING  
TO 20-30 MPH. THESE BREEZY SSW WINDS ALONG WITH SOME BANDS OF  
MID/HIGH CLOUDS KEEPING TEMPS UP TONIGHT, CURRENTLY RANGING FROM  
MID 30S IN FAR SOUTHEAST IL OVER LAWRENCE COUNTY, TO THE UPPER  
40S OVER WEST CENTRAL IL FROM MACOMB TO PITTSFIELD WEST. ALOFT A  
517 DM 500 MB LOW WAS NW OF LAKE SUPERIOR AND EMBEDDED IN A LARGER  
UPPER LEVEL TROF OVER THE MIDWEST AND EXTENDING SOUTHWARD ACROSS  
THE MS RIVER VALLEY.  
 
00Z FORECAST MODELS TAKE LOW PRESSURE EASTWARD TO THE SOUTHERN TIP  
OF JAMES BAY CANADA BY 18Z/NOON TODAY AND INTO NW QUEBEC BY 00Z/6  
PM AS IT WEAKENS TO 990 MB. THIS WILL PIVOT THE COLD FRONT SE  
ACROSS THE HEART OF CENTRAL IL BY NOON AND PASS THE WABASH RIVER  
BY LATE AFTERNOON. MOISTURE STILL APPEARS LIMITED WITH FRONTAL  
BOUNDARY, THOUGH SOME SHORT RANGE MODELS NOW SHOWING SOME PATCHES  
OVER QPF OVER NORTHERN CWA THIS AFTERNOON. ADDED SLIGHT CHANCES OF  
LIGHT RAIN SHOWERS MAINLY NE OF I-74 THIS AFTERNOON. HIGHS TODAY  
RANGE FROM MID 40S OVER THE IL RIVER VALLEY, TO MID 50S BY  
LAWRENCEVILLE. BRISK NW WINDS BEHIND THE COLD FRONT GUSTING 25-30  
MPH WILL DROP TEMPS TO THE LOWER 30S NORTHERN CWA BY 6 PM AND  
40-45F IN SOUTHEAST IL, SE OF I-70.  
 
1032 MB CANADIAN HIGH PRESSURE OVER CENTRAL ALBERTA CANADA WILL  
SETTLE INTO EASTERN KS OVERNIGHT AND RIDGE INTO IL BY SUNRISE  
WED. THIS WILL DECREASE CLOUDS AND WINDS AND BRING A MUCH COLDER  
NIGHT TONIGHT. LOWS TONIGHT WILL BE IN THE LOWER 20S OVER CENTRAL  
IL AND MID 20S IN SOUTHEAST IL. COULD EVEN DIP INTO UPPER TEENS NW  
OF IL RIVER OVER PARTS OF KNOX AND STARK COUNTIES.  
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 250 AM CST TUE NOV 21 2017  
 
HIGH PRESSURE RIDGES FROM TEXAS NE INTO THE OHIO RIVER VALLEY AT  
SUNSET WED AND TO BRING LIGHTER WINDS AND AMPLE SUNSHINE BUT COLD  
TEMPERATURES. HIGHS 35-40F WED WITH COLDEST READINGS FROM I-74 NE  
AND LOWS WED NIGHT IN THE MID TO UPPER 20S. HIGH PRESSURE SETTLES  
OVER THE MID ATLANTIC STATES THU WHILE A WEAK COLD FRONT WASHES  
OUT AS IT DROPS INTO NORTHERN IL DURING THURSDAY. NOT QUITE AS  
COLD ON THANKSGIVING DAY WITH HIGHS IN THE MID TO UPPER 40S.  
MILDER HIGHS IN THE 50S ON FRIDAY WITH BREEZY SSW WINDS, SIMILAR  
TO YESTERDAYS READINGS, WITH AREAS FROM SPRINGFIELD SW APPROACHING  
60F.  
 
MODELS TAKE A 980 MB SURFACE LOW PRESSURE EASTWARD ACROSS CENTRAL  
ONTARIO PROVINCE FRIDAY NIGHT AND PUSHES ANOTHER COLD FRONT SE  
ACROSS CWA. HAVE SLIGHT CHANCES OF LIGHT RAIN SHOWERS FROM I-74 NE  
FRIDAY EVENING. A DEEP UPPER LEVEL TROF DIGS OVER THE EASTERN  
STATES DURING THIS WEEKEND AND BRINGS IN COLDER AIR BACK TO THE  
AREA. HIGHS SAT RANGE FROM MID 40S NORTHERN CWA TO 50-55F SOUTHERN  
CWA, WITH TEMPS LIKELY SLIPPING DURING THE DAY. HIGHS SUNDAY ONLY  
IN THE UPPER 30S AND LOWER 40S DESPITE AMPLE SUNSHINE. UPPER LEVEL  
RIDGE BUILDS OVER THE GREAT PLAINS ON SUNDAY NIGHT AND MONDAY AND  
BRINGS IL FAIR WX WITH MODERATING TEMPERATURES. HIGHS MONDAY IN  
THE LOW TO MID 40S, AND IN THE UPPER 40S TO MID 50S NEXT TUESDAY.  
GFS AND ECMWF MODELS SIMILAR IN TAKING LOW PRESSURE EASTWARD  
ACROSS NORTHERN PARTS OF ND/MN AND LAKE SUPERIOR MONDAY NIGHT/TUE  
AND BRINGS A COLD FRONT THRU CENTRAL IL TUE AFTERNOON/EVENING WITH  
NEXT CHANCE OF SHOWERS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1139 AM CST TUE NOV 21 2017  
 
VFR CONDITIONS WILL PREVAIL THROUGH THE 18Z TAF PERIOD, DESPITE  
THE COLD FRONTAL PASSAGE THIS AFTERNOON. THE INITIALLY DRY AIR  
MASS IS LIMITING PRECIP POTENTIAL WITH THE FRONT, BUT SOME LIGHT  
RAIN/SLEET HAS BEEN REPORTED THIS MORNING. THE HRRR DOES SHOW THE  
FRONTAL CIRCULATION WEAKENING THIS AFTERNOON, BUT UNTIL THAT  
OCCURS, HAVE ADDED VCSH TO ALL THE TAFS FOR A FEW HOURS THIS  
AFTERNOON WITH FROPA. CLEARING SHOULD DEVELOP QUICKLY THIS  
EVENING, IF NOT LATE THIS AFTERNOON NW OF THE IL RIVER.  
 
WINDS HAVE SHIFTED TO W-SW AT 12G22KT, AND A SHIFT TO NW WILL  
OCCUR POST-FROPA. WIND SPEEDS ARE SLATED TO INCREASE TO 15G27KT  
THIS AFTERNOON FROM THE NW. WINDS WILL WEAKEN THIS EVENING, AND  
REMAIN LIGHT NW THROUGH THE MORNING TOMORROW UNDER MINIMAL CLOUD  
COVER.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
UPDATE...SHIMON  
SHORT TERM...07  
LONG TERM...07  
AVIATION...SHIMON  
 
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