488  
FXUS63 KILX 011751  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
1151 AM CST SUN FEB 1 2015  
   
UPDATE
 
 
ISSUED AT 1054 AM CST SUN FEB 1 2015  
 
LATEST SURFACE MAP SHOWING LOW PRESSURE CENTER OVER SOUTH CENTRAL  
MISSOURI LATE THIS MORNING. THE WARMER AIR CONTINUES OVER THE  
ENTIRE CWA AND TEMPERATURES ARE ABOVE FREEZING EVERYWHERE, BUT  
SURFACE REPORTS INDICATING THE PRECIPITATION HAS REMAINED LARGELY  
SNOW NORTH OF I-72. STEADIER RAIN ACROSS SOUTHEAST ILLINOIS HAS  
MOVED OFF INTO INDIANA, WITH A DRY SLOT COMING THROUGH, BUT  
ANOTHER SURGE OF SNOW IS COMING BACK INTO SPRINGFIELD. HAVE ADDED  
SOME RAIN/SNOW MIXTURE AS FAR NORTH AS I-72 FOR THIS AFTERNOON AS  
TEMPERATURES WON'T BE GOING ANYWHERE FOR A FEW MORE HOURS, AND  
WE ARE NOW GETTING REPORTS OF MIXED RAIN/SNOW ON THE WEST SIDE OF  
SPRINGFIELD.  
 
THE HRRR TRACKS THE LOW UP ALONG THE I-70 CORRIDOR THIS AFTERNOON  
AND WON'T EXIT UNTIL AROUND MID AFTERNOON, SO HAVE UPDATED THE  
WIND TRENDS ACROSS THE EASTERN CWA TO HOLD BACK THE RAMPING UP OF  
THE WINDS UNTIL EVENING. THE ONGOING QUESTION THROUGH THE DAY  
THOUGH WILL BE WITH THE EXTENT OF THE DEFORMATION ZONE CURRENTLY  
EXTENDING FROM EASTERN NEBRASKA/NORTHWEST MISSOURI EASTWARD ACROSS  
THE MIDWEST. LATEST RAP FOCUSES THE EXTENT OF IT MORE ACROSS THE  
NORTHERN THIRD OF THE CWA THIS AFTERNOON, WHILE THE NAM AND THE  
HRRR IS FURTHER SOUTH NEAR . THE RAP TRACK MAY BE A BIT TOO FAR  
NORTH BASED ON WHERE IT ANALYZED THE LOW AT THE START OF THE 15Z  
RUN, SO WILL FAVOR THE HRRR/NAM SOLUTION. HAVE NOT MADE A LOT OF  
CHANGES TO THE SNOW TOTALS ACROSS THE NORTH, BUT SHARPENED THEM  
DOWNWARD FURTHER SOUTH DUE TO THE MIXTURE. NO CHANGES TO THE  
HEADLINES AT THE MOMENT, BUT SOME ADJUSTMENTS ON THE SOUTH END MAY  
BE REQUIRED SOON, SPECIFICALLY WITH THE ADVISORY.  
 

 
   
SHORT TERM
 
(TODAY)  
ISSUED AT 331 AM CST SUN FEB 1 2015  
 
MUCH AS ANTICIPATED YESTERDAY, IT HAS BEEN A STRUGGLE TO GET  
SIGNIFICANT SNOW ACCUMULATION GOING THUS FAR ACROSS THE FORECAST  
AREA GIVEN MARGINAL SURFACE TEMPERATURES AND LOW LEVEL THERMAL  
PROFILES. WAVES OF PRECIPITATION HAVE SPREAD MAINLY ACROSS THE  
NORTHWEST HALF FORECAST AREA (MAINLY NORTH OF A SPRINGFIELD TO  
DANVILLE LINE) SINCE LAST NIGHT. PREDOMINANTLY DRY CONDITIONS HAVE  
BEEN SEEN ACROSS THE SOUTHEAST HALF OF THE AREA.  
 
FOR THE MOMENT, SURFACE OBSERVATIONS SUGGEST MOST OF THE  
PRECIPITATION IN THE AREA HAS CHANGED OVER TO SNOW, ALTHOUGH AREAS  
CLOSER TO THE I-72 CORRIDOR ARE STILL SEEING A MIX. STRONG  
WAA/ISENTROPIC LIFT IS EXPECTED TO PERSIST THROUGH THE MORNING,  
ALONG WITH GOOD UPPER DIVERGENCE COURTESY OF JET COUPLING. THIS WILL  
RESULT IN WIDESPREAD PRECIPITATION TO START THE DAY ACROSS MOST OF  
THE FORECAST AREA. SOME OF THE MORE RECENT MODEL GUIDANCE IS  
SUGGESTING A WARMER LOW LEVEL THERMAL PROFILE ACROSS MUCH OF THE  
FORECAST AREA THIS MORNING WHICH SHOULD BE ABLE TO KEEP A RAIN,  
SNOW, OR SLEET MIX GOING BETWEEN THE I-72 AND I-70 CORRIDORS, WITH  
RAIN EXPECTED SOUTH OF THE I-70 CORRIDOR. THE FURTHER NORTH AND  
LONGER LASTING MIX WILL CUT SNOW TOTALS SOME ACROSS THE ADVISORY  
AREA, AS WELL AS AT LEAST CHAMPAIGN AND VERMILION COUNTIES IN THE  
WARNING AREA. SINCE UNCERTAINTY STILL EXISTS REGARDING THE ULTIMATE  
STORM TOTAL SNOW AMOUNTS, DO NOT PLAN TO ALTER CURRENT HEADLINES AT  
THIS TIME. HOWEVER, IT IS LOOKING INCREASINGLY LIKELY THAT TOTALS  
WILL BE LIGHTER THAN EXPECTED SOUTH OF A RUSHVILLE TO BLOOMINGTON  
LINE, SINCE LITTLE IF ANY ACCUMULATION HAS OCCURRED IN THIS AREA  
THUS FAR.  
 
TEMPERATURES AND THE LOW LEVEL THERMAL PROFILE WILL FINALLY COOL  
STARTING THIS AFTERNOON AS THE SURFACE LOW PUSHES OFF TO THE EAST.  
THE LOW IS CURRENTLY CENTERED OVER EASTERN KANSAS, AND IT IS  
EXPECTED TO REACH CENTRAL INDIANA BY THIS EVENING. THIS COOLING WILL  
EVENTUALLY RESULT IN PRECIPITATION CHANGING OVER TO SNOW OVER MOST  
OF THE AREA BY LATE AFTERNOON, WITH THE MAIN EXCEPTION BEING SOME OF  
OUR COUNTIES SOUTH OF I-70. HOWEVER, THE BEST FORCING WILL ALREADY  
BE EAST OF THE AREA BY THIS AFTERNOON, AND PRECIPITATION INTENSITY  
MUCH LOWER. IN FACT, IT IS LOOKING INCREASINGLY LIKELY THAT A DRY  
SLOT WRAPPING AROUND THE SYSTEM WILL PUSH INTO THE EASTERN 2/3 OF  
THE FORECAST AREA DURING THE AFTERNOON WHICH WOULD GREATLY CURTAIL  
OR EVEN END PRECIPITATION CHANCES FOR A TIME. FORCING WITHIN THE  
DEFORMATION ZONE BEHIND THE DRY SLOT IS NOT VERY ROBUST AND SHOULD  
NOT BE A PROLIFIC SNOW PRODUCER AS IT CROSSES THE AREA STARTING LATE  
THIS AFTERNOON INTO TONIGHT.  
 

 
   
LONG TERM
 
(TONIGHT THROUGH SATURDAY)  
ISSUED AT 331 AM CST SUN FEB 1 2015  
 
LATER THIS EVENING, NORTHERN TIER OF THE STATE STILL EXPERIENCING  
SOME LIGHT SNOW AS THE SYSTEM PULLS AWAY TO THE EAST. BOTH THE GFS  
AND THE ECMWF SLOWER WITH THE PROGRESSION OF THE SYSTEM AND LINGERS  
THE ACCUMULATING SNOWFALL AFTER 00Z. AS THE SFC LOW MOVES EASTWARD,  
THE TIGHTENING PRESSURE GRADIENT IN THE WAKE WILL RESULT IN GUSTY  
WINDS GOING INTO THE OVERNIGHT HOURS. NORTHERLY WINDS UP TO 20-25  
MPH AND GUSTING TO 30...AND IN EXCESS OF 30 MPH EARLY IN THE  
EVENING...WILL CREATE A POTENTIAL FOR BLOWING SNOW. WILL KEEP THE  
BLOWING SNOW MENTION AS THE LAST PORTIONS OF SNOWFALL MAY BE A LOT  
FLUFFIER AFTER 00Z. BUT THE BULK OF THE SNOW IN THIS EVENT WILL BE  
HEAVY AND WET, SO BLOWING SNOW MAY BE LIMITED. COLD AIR MOVING INTO  
THE REGION BEHIND THIS SYSTEM WILL DROP THE HIGHS FOR MONDAY DOWN  
INTO THE TEENS AND 20S...ALBEIT BRIEFLY. AFTER A QUICK CLIPPER  
SYSTEM BRINGING SOME LIGHT SNOW TO THE NORTHERN THIRD OF ILLINOIS  
MONDAY NIGHT, ANOTHER ABRUPT CHANGE TO THE PATTERN SETS UP A WARMER  
TUESDAY. SOUTHERLY WINDS, A SWITCH TO WAA BRINGS THE HIGHS UP 24  
HRS LATER ON TUESDAY INTO THE 30S. TUESDAY NIGHT MODELS AGAIN HINT  
AT ANOTHER QUICK CLIPPER, THOUGH THE WAVE IS NOT AS WELL REPRESENTED  
IN THE MODELS AND CONSISTENCY IS LACKING. NOT WILLING TO GO TOO  
HIGH ABOVE LOW CHANCE AT THIS POINT.  
 
REMAINING FORECAST IS RELATIVELY DRY WITH TEMPS DROPPING AGAIN FOR  
WED AND THUR WITH THE PULSES MOVING INTO THE SYNOPTIC TROF ALOFT  
DEEPENING THE COLD AIR. THEN WARMING BACK UP AS THE SFC RIDGE SHIFTS  
EAST AND SOUTHERLY WINDS AND WAA PICK BACK UP AGAIN. ALL IN ALL, A  
RATHER PROGRESSIVE AND ACTIVE PATTERN. ANOTHER SYSTEM STARTING TO  
DEVELOP FOR SAT NIGHT NEXT WEEKEND, BUT MODELS HAVE PLENTY OF  
DISAGREEMENT SO FAR IN THE TRACK.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1151 AM CST SUN FEB 1 2015  
 
DRY SLOT HAS EXITED THE TAF SITES, AND THE NEXT BAND OF  
PRECIPITATION IS ABOUT TO COME INTO KCMI. HAVE SEEN VISIBILITIES  
LOWER TO AROUND 1/2SM OR SO WITH THE HEAVIER SNOW BANDS, ALTHOUGH  
SOME MIXED RAIN/SNOW WILL BE OCCURRING EARLY THIS AFTERNOON FROM  
KSPI-KCMI. AS LOW PRESSURE MOVES THROUGH CENTRAL ILLINOIS EARLY  
THIS AFTERNOON, SOUTHEAST WINDS WILL BE TRENDING MORE NORTHEAST TO  
NORTH. RAPID INCREASE IN WINDS IS EXPECTED DUE TO THE STRENGTH OF  
THE CURRENT SYSTEM, AND GUSTS OVER 20 KNOTS WILL BE AFFECTING KPIA  
BY MID AFTERNOON AND SPREADING OVER THE REMAINING SITES THROUGH  
00Z. GUSTS OF 25-30 KNOTS ARE LIKELY MUCH OF THE NIGHT, AND WITH  
LINGERING LIGHT SNOW THROUGH THE EVENING, SOME BLOWING SNOW WILL  
BE POSSIBLE. HAVE ONLY ADDED THIS TO KPIA/KBMI, AS THE LOCATIONS  
FURTHER SOUTH HAVE HAD LESS SNOW AND WHAT HAS FALLEN IS VERY WET.  
WINDS AND CLOUDS WILL DIMINISH MONDAY MORNING, ALTHOUGH MVFR  
CONDITIONS WILL LIKELY LINGER AT KDEC/KCMI THE REMAINDER OF THE  
MORNING.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR ILZ027>031-  
036>038-040>048.  
 
WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR  
ILZ049>057-061.  
 

 
 

 
 
UPDATE...GEELHART  
SHORT TERM...BAK  
LONG TERM...HJS  
AVIATION...GEELHART  
 
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