985 
fxus63 kilx 202000 
afdilx 


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


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. 


Shimon 
&& 


Aviation... 
issued 1250 PM CDT Sat Mar 20 2010 


Band of precipitation currently over the Illinois River valley will 
remain in place for the balance of the afternoon into the evening 
hours. Meanwhile...an upper-level wave tracking northeastward out 
of Missouri will help spread showers as far east as the I-55 
corridor. Based on radar timing tools...will introduce light rain 
at kspi between 18z and 22z and further north at kbmi between 19z 
and 23z. Further east...dry conditions will likely continue at 
the eastern terminals...so have only included a vcsh at both kdec 
and kcmi. Meanwhile...light snow with ceilings around 1000ft will 
persist at kpia. As warmer air is advected in aloft tonight...the 
snow will gradually mix with and change to rain at kpia. Once the 
upper wave lifts out of the area...models are indicating a gradual 
end to to the precipitation after midnight. Winds through the entire 18z 
taf period will remain gusty out of the northeast. 


Barnes 
&& 


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


$$