781 
fxus63 kilx 181749 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
1249 PM CDT Friday Jul 18 2008 


Discussion... 
issued 1026 am CDT Friday Jul 18 2008 
some middle and low level moisture spilling into the region from the 
northwest...off of dying convection from the overnight hours. Front still 
well off to the northwest and across WI..srn Minnesota and back into the northern 
plains. Ilx forecast area is in a bit of a transition zone between an exiting 
high pressure ridge...and an approaching front environment. Dewpoints 
and temperatures slowly increasing from yesterday to today...and should 
result in slightly more coverage of afternoon cumulus. Forecast has the 
situation rather well in hand. No updates anticipated at this point. 






&& 


Aviation... 
issued 1245 PM CDT Friday Jul 18 2008 
preferred model is keeping the precipitation out of the taf sites until 
after midnight...though knocking on the door of pia this 
afternoon. Have kept vc precipitation in to cover it for now. Moisture 
ribbon on Sat imagery is getting stretched out and thinned quite a 
bit in SW/NE flow ahead of the front in the upper Midwest. Looking 
at upper air maps...questioning the amount of available moisture 
enough to keep a vc/drier forecast. Best chances for precipitation 
towards the early morning hours from 08z-15z for most locations 
from west to east. Keeping thunder closer to the actual surface low in 
northern terminals...and just thunderstorms in the vicinity to the south. Cmi might just avoid 
it all as low pulls out to the NE before noon. 




Hjs 
&& 


Previous discussion... 
issued 330 am CDT Friday Jul 18 2008 


Forecast challenge is addressing convection chances next several 
days as several short waves over top of strong upper level ridge 
digs an upper level trough into the Great Lakes by Monday with frontal 
boundary meandering near Illinois. 00z short range models are not in 
good agreement like they had been. Leaned toward the NAM and European model (ecmwf) 
models with this package which appears to be a bit more consistent. 
GFS might be suffering from some convective feedback with stronger 
and quicker short waves moving across central/northern Illinois/in Sat. 


08z/3 am surface analysis shows 1019 mb high pressure across the 
Middle Atlantic States and ridging west into Illinois and Arkansas. Frontal 
boundary was draped from southern Ontario/Lake Superior into southeast 
Minnesota and northern Nebraska. Convection ahead of this front was over 
southeast Iowa and lifting NE and weakening. It produced an outflow 
boundary into far northwest Illinois. High clouds have spread into central Illinois 
where light south winds while southeast Illinois still clear with calm winds. 
Temperatures were in the upper 60s and lower 70s with dewpoints in 
the low to middle 60s...except upper 60s northwest of the Illinois River. Aloft a 
large upper level high pressure ridge was across the southern 
2/3rds of the country with upper level trough/low over Canadian and 
northern tier states with a short wave trough over Iowa into Kansas where 
there was more convection. 


Short term...today through Sunday night 


Have a chance of showers and thunderstorms this afternoon northwest of 
the Illinois River as daytime heating of very warm/humid air mass 
interacts with outflow boundary in northwest Illinois. Also have a short wave 
impulse ejecting NE from Kansas into southeast Iowa. More cloud cover over northwest 
Illinois to keep it a bit cooler with middle 80s by Galesburg. But mostly 
sunny and very warm over rest of central and southeast Illinois with highs in 
the upper 80s to near 90f and followed met/mav blend which has 
worked well this past week. Convection chances increase after 
midnight tonight to 30 to 50% northwest of the Illinois River with short waves 
moving into northwest Illinois and have a veering low level jet. Best chances 
of convection are closer to Iowa. Have likely chances of convection 
Sat north of Peoria and Storm Prediction Center has a slight risk of severe storms northwest 
of Peoria Sat. This due to short wave impulses moving across the 
northern half of Illinois and a weakening frontal boundary slipping 
south across central Illinois. Highs in the middle 80s far north to the 
lower 90s across southeast Illinois. 


Models have a strong short wave over the southern Canadian prairies 
moving into the Great Lakes Sunday with deepening low pressure 
moving east across the Great Lakes. Convection chances appear to 
be higher NE of central Illinois Sunday and hot yet with highs in the 
upper 80s and lower 90s with upper level ridge still in control. 


Long term...Monday through Thursday 


Upper level trough digs more into the Great Lakes Monday which drives 
another front south into Illinois. This front appears stronger and gets 
further south than saturdays front. Have chance of convection Monday 
with best chances shifting into southeast Illinois. Mex highs in the 90s 
appears too warm with Lawrenceville at 99f. Kept highs in the 
upper 80s north and lower 90s south. Lingered chances of 
convection Tuesday with frontal boundary SW of central Illinois but still 
close enough to keep a 20 to 30 pop. Weak high pressure moving 
into the Great Lakes to dry out NE Illinois where more sunshine possible. 
Temperatures appears to cool slightly Tuesday/Wednesday closer to normal 
values. 


Huettl 




&& 


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


$$