043  
FXUS63 KILX 111112  
AFDILX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LINCOLN IL  
512 AM CST SUN DEC 11 2016  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 217 AM CST SUN DEC 11 2016  
 
CHALLENGING FORECAST THIS MORNING WITH RESPECT TO THERMAL PROFILE  
TODAY AND RESULTANT PRECIPITATION TYPE FORECAST.  
 
IN A LULL AT PRESENT ACROSS MOST OF FORECAST AREA AS AREA OF  
FRONTOGENESIS PUSHES NORTHEAST OF AREA ENDING PCPN TEMPORARILY.  
WEAK SHORTWAVE OVER ROCKIES WILL PUSH INTO THE PLAINS THIS MORNING  
WITH RESULTANT SURFACE LOW DEVELOPING ALONG THE CENTRAL HIGH PLAINS  
AND THEN TRACKING INTO THE MID-MISSISSIPPI VALLEY TODAY. TRACK OF  
SFC SYSTEM WILL HAVE A SIGNIFICANT IMPACT ON PRECIP TYPE FORECAST  
TODAY.  
 
STRONG WARM ADVECTION ALREADY OCCURING ACROSS AREA AHEAD OF SYSTEM.  
HOWEVER, DEW POINTS ARE STILL WELL BELOW FREEZING EVEN IN AREAS  
WHERE THE SURFACE TEMPERATURE HAS RISEN TO FREEZING OR ABOVE. AS  
PRECIPITATION MOVES BACK INTO THE AREA LATER THIS MORNING UNDER  
STRONG ISENTROPIC LIFT, TEMPERATURES WILL LIKELY FALL BACK BELOW  
FREEZING AS COLUMN SATURATES AND TEMP APPROACH WET BULB TEMPERATURE.  
AS WARM ADVECTION CONTINUES, PRECIPITATION SHOULD TRANSITION FROM A  
MIX TO MOSTLY RAIN FROM I-74 SOUTHWARD BY EARLY THIS AFTERNOON.  
CHANGEOVER IS EXPECTED TO STALL OVER NORTH CENTRAL ILLINOIS AS THE  
WEAK SHORTWAVE MOVES BY AND THE ASSOCIATED COLD FRONT MOVES ACROSS  
THE AREA. THE COLD AIR BEHIND THE FRONT MAY CHANGE THE PRECIPITATION  
BRIEFLY BACK TO SNOW BEFORE ENDING THIS EVENING IN AREAS THAT SAW  
RAIN THIS AFTERNOON.  
 
MODELS DIFFER ON HOW FAR NORTH THE CHANGEOVER WILL GET WITH NAM  
SUGGESTING THAT PEORIA AND BLOOMINGTON MAY BE THE NORTHERN EXTENT  
WITH THE HRRR BRINGING RAIN ALL THE WAY NORTH OF THE FORECAST AREA  
BY MID-AFTERNOON. PREVIOUS PACKAGE GENERAL SPLIT THE DIFFERENCE  
BETWEEN THE WARMER AND COLDER PROFILES AND WILL CONTINUE THAT  
APPROACH UNTIL THE TREND BECOMES MORE EVIDENT.  
 
IN THE AREA WHERE THE TRANSITION DOES NOT COMPLETELY CHANGEOVER,  
SNOW ACCUMULATION WILL BE CAPABLE OF REACHING SEVERAL INCHES AND  
GIVEN THE ADDED POTENTIAL FOR FREEZING RAIN/SLEET, THE LOCATION OF  
THE CURRENT ADVISORY IN STARK AND MARSHALL COUNTIES STILL LOOKS  
REASONABLE. WE WILL HAVE TO WATCH CLOSELY AREAS TO THE SOUTH WHERE A  
BRIEF PERIOD OF FREEZING PRECIPITATION MAY BE POSSIBLE AND MAY  
WARRENT AN ADVISORY FOR ICY ROADS. ANY QPF OF FREEZING RAIN WILL  
LIKELY BE QUITE LIGHT, BUT IT DOESN'T TAKE MUCH TO PRODUCE A THIN  
LAYER OF ICE AND IMPACT DRIVING CONDITIONS. GIVEN THE UNCERTAINTY OF  
THE EVOLUTION TODAY WILL HOLD OFF ON EXTENDING THE ADVISORY AT THIS  
TIME AND MONITOR CLOSELY.  
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 217 AM CST SUN DEC 11 2016  
 
MAIN FOCUS IN THIS PART OF THE FORECAST IS WITH THE NEXT SHOTS OF  
ARCTIC AIR, AS WELL AS PRECIPITATION TRENDS TOWARD THE LATTER PART  
OF THE WEEK.  
 
EXPANSIVE AREA OF ARCTIC AIR COVERS MOST OF CANADA EARLY THIS  
MORNING (850 MB TEMPERATURES GENERALLY BELOW -20C), AND LOBES OF  
THIS AIR WILL BE SHOVED SOUTHWARD THIS WEEK AS A STRONG 500 MB LOW  
DROPS SOUTH OUT OF THE HIGH CANADIAN LATITUDES. GREATEST THRUST OF  
THIS BITTER COLD FOR US WILL BE SWINGING THROUGH LATER WEDNESDAY  
WITH 850 MB TEMPS DOWN INTO THE -18C RANGE, ALTHOUGH A DEEPER  
THERMAL TROUGH WILL BE DIGGING SOUTHWARD ACROSS THE PLAINS NEXT  
WEEKEND. FAIRLY LARGE TEMPERATURE SPREAD EXPECTED OVER THE CWA ON  
TUESDAY, RANGING FROM THE TEENS OVER THE NORTHERN CWA TO THE MID 30S  
SOUTH OF I-70, BUT TEENS/20S WILL DOMINATE EVERYWHERE WEDNESDAY-  
THURSDAY.  
 
LATEST MODELS CONTINUE TO WEAKEN THE FAST-MOVING WAVE MID WEEK, WITH  
ONLY THE CANADIAN MODEL STILL SHOWING SOME SEMBLANCE OF THE  
PRECIPITATION STREAK. HAVE LOWERED POP'S DOWN TO 20% WEDNESDAY  
MORNING, BUT WOULD NOT BE SURPRISED TO SEE THEM DISAPPEAR IN THE  
NEXT PACKAGE. THUS, THE MAJOR FOCUS WILL BE WITH THE LATE WEEK  
SYSTEM.  
 
LATEST ECMWF/GFS DIG A TROUGH ALONG THE WEST COAST THURSDAY NIGHT  
AND EARLY FRIDAY, WHICH WILL SHIFT OUR FLOW OUT OF THE SOUTHWEST  
U.S. FOR A TIME. WHILE BOTH MODELS SPREAD PRECIPITATION OVER THE  
AREA ON FRIDAY, THE LOW TRACK FRIDAY NIGHT AND SATURDAY HAS SHIFTED  
MORE NORTHWEST, WHICH WOULD DRAW WARMER AIR NORTHWARD AND RESULT IN  
PRECIP TYPE ISSUES. NOT GOING TO GET CUTE THAT FAR OUT AND WILL  
LARGELY GO WITH SNOW FOR NOW, WITH A RAIN/SNOW MIX SOUTH OF I-70.  
SPEED DIFFERENCES IN THIS SYSTEM ARE RESULTING IN A WIDE TEMPERATURE  
RANGE AS WELL (ECMWF FOR SPRINGFIELD HAS A HIGH IN THE UPPER 20S ON  
SATURDAY, WHILE THE GFS IS CLOSE TO 50), WHICH IS ANOTHER REASON FOR  
REMAINING MORE ON THE CONSERVATIVE SIDE.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 502 AM CST SUN DEC 11 2016  
 
PRECIPITATION EXPECTED TO DEVELOP BY MID-MORNING ACROSS CENTRAL  
ILLINOIS TERMINALS. ALTHOUGH TEMPS ARE ABOVE FREEZING CURRENTLY AT  
KSPI AND KDEC, DEW POINT DEPRESSION REMAIN 10-15F IN THOSE AREAS  
AND WHEN PRECIPITATION BEGINS, TEMPERATURES WILL LIKELY FALL BELOW  
FREEZING. EXPECT PRECIP TO START OFF AS SNOW AT MOST LOCATIONS  
THIS MORNING AND THEN TRANSITION TO RAIN FROM SOUTH TO NORTH AS  
WARM ADVECTION ON SOUTH WINDS CONTINUE. ONCE PRECIP STOPS, IFR  
CIGS ARE LIKELY. WINDS SHOULD KEEP LOW-LEVEL MOISTURE IN THE FORM  
OF STRATUS RATHER THAN FOG.  
 
PROBABLY WILL BE A BRIEF PERIOD OF FREEZING PRECIP OR SLEET  
DURING THE TRANSITION AND WILL TRY TO COVER THAT WITH TEMPO  
GROUPS.  
 
WINDS WILL SHIFT AROUND TO NORTHWEST OVERNIGHT WITH GRADUAL  
CLEARING TOWARD THE END OF THE TAF TERMINAL PERIOD.  
 

 
   
ILX WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ILZ028-  
030.  
 

 
 

 
 
SHORT TERM...BARKER  
LONG TERM...GEELHART  
AVIATION...BARKER  
 
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