860 
fxus63 kilx 210157 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
857 PM CDT Sat Mar 20 2010 


Discussion... 
issued 857 PM CDT Sat Mar 20 2010 


Current forecast pretty much on track...as band of light precipitation 
continues to impact the western half of the kilx County Warning Area. Radar loops 
have shown a general decrease in areal coverage of precipitation this 
evening and think this trend will continue overnight as 850mb 
front weakens and shifts further northwest. Light snow is 
currently falling west of the Illinois River...but as warmer air 
advects in aloft...snow will eventually mix with rain. Not much 
additional accumulation is anticipated...perhaps around one half 
inch across Knox and Stark counties. Further east...a few light 
rain showers will occur along the I-55 corridor...with little or 
no rain across east-central and southeast Illinois. Will send a 
zone update to remove snow mention from I-55 zones...and to lower 
probability of precipitation across the E/se. 


Barnes 
&& 


Aviation... 
issued 651 PM CDT Sat Mar 20 2010 


Precipitation along and west of I-55 has been diminishing in coverage 
and intensity over the past couple of hours...and expect this 
trend to continue this evening. Will carry a tempo group for showers 
at both kspi and kbmi between 00z and 04z...followed by vcsh for 
the remainder of the night. Further west...will continue with 
predominant rasn at kpia...before dropping to just vcsh after 07z. 
Further east...no precipitation will impact either kdec or kcmi. After a 
lull in the precipitation Sunday morning...low pressure tracking into the 
Ohio River valley will spread low clouds and showers across the 
southern terminals after 21z. Winds will remain gusty out of the 
northeast through the entire 00z taf period. 


Barnes 
&& 


Previous discussion... 
issued 142 PM CDT Sat Mar 20 2010 


Main concern is precipitation type and amount of snow/ice that may 
accumulate tonight in our northwest County Warning Area. The 12z models are in relative 
agreement on the placement of the cold and warm layers above the 
ground...as well as the surface cold frontal progression out of 
our southeast County Warning Area. A complicated air pattern exists aloft...as the 850 mb 
front will be moving north and west across our County Warning Area at the same 
time the surface cold front moves southeast. This sets the stage 
for mixed precipitation overnight as warm air strengthens above 900 
mb...while cold air maintains then slowly erodes below 900 mb. 


Will go with a combo of NAM/GFS for the short term...then swing 
toward the European model (ecmwf) for the extended. 


Short term...tonight through Sunday. 


Radar trends indicate precipitation intensity has begun to weaken in the 
last hour...with another wave of heavier precipitation lifting north from 
Missouri toward our western County Warning Area. The models show the bulk of our 
precipitation coming this evening...with a let up beginning after 
midnight. Precipitation type will be a tough call. The rain snow line 
appears to have stopped advancing to the southeast...and has set up 
roughly along the Illinois River. Some sleet was reported earlier 
today northwest of the Illinois River...but has changed to snow for the most 
part. 


With the advancing warm air aloft...precipitation may change back to 
sleet at times due to melting aloft. Have gone with rain/snow for 
just south of the Illinois River...and snow and sleet for northwest of the Illinois 
River. I kept probability of precipitation the same after midnight...but conditions should 
improve toward Sunday morning. 


A break in the precipitation is indicated for much of the day 
Sunday...until the surface low lifts out of the south toward 
southern Illinois. By that time the air aloft will be warm enough for 
rain everywhere in our County Warning Area. We went with chance probability of precipitation in the southeast for 
Sunday afternoon...with slights elsewhere. Sunday night I went 
with categorical probability of precipitation for rain southeast of I-70...with likely 
probability of precipitation up to Shelbyville to Champaign. 


Long term...Monday through Saturday. 


Rain will likely linger Monday morning in the southeast...with 
decreasing chances of rain Monday afternoon. 


Dry conditions are expected for Monday night through Wednesday 
night...with low rain chances for Thursday through Friday as low 
pressure passes by to the south. Dry conditions return for Saturday. 


&& 


Ilx watches/warnings/advisories... 
none. 
&& 


$$