066 
fxus63 kilx 051149 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
649 am CDT Sat Jul 5 2008 


Discussion... 
issued 229 am CDT Sat Jul 5 2008 


Early morning surface analysis indicated broad area of high pressure 
stretching from the eastern Great Lakes back into the middle 
Mississippi Valley. This feature was producing mostly clear/calm/cool 
conditions over central and southeast Illinois this morning. Some light 
fog has developed in areas that saw more substantial rainfall the 
last couple days...with 2 to 5 sm visibilities common east of I-55. Aloft...a 
middle level ridge stretched from the desert SW north along The East 
Slope of The Rockies...with downstream northwest flow prevailing 
across the Midwest. Main forecast issue is a period of unsettled 
weather to start the work week. 


Short term...Saturday through Sunday... 
high pressure ridge over the lower Great Lakes will provide pleasant 
conditions today with light winds and low humidity levels. Expect 
some afternoon cumulus development especially over the eastern half of 
the County Warning Area where higher surface moisture could lead to periods of at 
least scattered cumulus this afternoon. Temperatures will remain a few degrees below 
normal...reaching into the lower 80s. Ridge axis departs to the 
east on Sunday as next shortwave and front take shape in the 
plains. This will cause southerly flow to develop by afternoon and 
start transporting warmer and more humid air in from the Gulf. 
Deeper mixing and approaching thermal ridge from the west should 
lead to highs into the upper 80s for the western County Warning Area...with middle 
80s farther east. Short range models showing possible low level jet/warm 
front interaction to spawn mesoscale convective system over Iowa on Sunday night. This 
activity should generally track east/southeast and may affect the northern County Warning Area 
into early Monday morning...in a decaying fashion. 


Long term...Monday through Friday... 
after morning mesoscale convective system dissipates...broad warm air advection pattern should boost 
highs near 90 along with dewpoints into the upper 60s. This will 
create cape values above 2k j/kg by afternoon...and with any 
boundaries drifting around from early mesoscale convective system...scattered thunderstorm 
development cannot be ruled out. Lack of wind shear should 
preclude much organized severe development even with high 
instability. The shortwave and surface low are prognosticated to track across 
the Great Lakes on Tuesday...with the cold front trailing 
southwest into the Mississippi Valley. Chance probability of precipitation will continue in 
the forecast through Tuesday night as the front slowly slips southeast 
through the state. By Wednesday...the front should be moving 
through the southern third of the state as high pressure builds 
into the upper Midwest. Latest run of medium range models suggest 
this high will be strong enough to push the front south of the 
Ohio Valley. This could potentially produce another stretch of 
drier and somewhat cooler/less humid conditions into the end of 
the week...but will just start trending grids this way and await 
better continuity. 


Schaffer 


&& 


Aviation... 
issued 649 am CDT Sat Jul 5 2008...for the 12z tafs 


A subsidence inversion has allow for some patchy fog to affect spi 
and Dec early this morning. Visible dropped to LIFR for a short time 
earlier. However...conditions have improved since sunrise. This 
trend should continue with visible improving to p6sm by 15z. After 
that...a broken SC deck may form in the heat of the day per cumulus 
rule output from the NAM/GFS and RUC. Satellite trends show a 
layer of moisture drifting into central Illinois from Indiana...and 
early information from our 12z balloon launch shows a moist layer around 
5k feet as well. I went with a broken VFR cloud deck at all taf 
sites for much of the day as a result. 


Skies will clear out this evening...and areas of fog will be 
possible for Dec and spi again Sunday morning. I added a tempo for 
MVFR visible for now after 09z. 




Shimon 
&& 


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


$$