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fxus63 kilx 182000 
afdilx 


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


Discussion... 
issued 300 PM CDT Friday Jul 18 2008 


Another warm and increasingly muggy day unfolding across forecast 
area today. High pressure centered over the Middle Atlantic States 
has continued to pull east...allowing better low level warm/moist 
flow ahead of main front/baroclinic zones...from the Central Plains 
into the upper Great Lakes...to sink closer to the region. 
Aloft...main belt of the westerlies remains mostly zonal across 
the northern tier of the United States...but there are numerous... 
potentially significant...impulses embedded in the flow for 
central/southeast Illinois. Main concern over the next several 
days revolves around coming ripples in the westerlies and where 
they push the low level baroclinic zone. Precipitation chances 
over the next few days will modulated by how/where these shifts 
take place. 


12z models in reasonable agreement with features expected to impact 
the forecast area over the next few days. However...as is usually 
the case during the warm months...the local scale nature of the 
convection will not be perfectly depicted by any of the models. 


Short term...tonight through Monday... 


Tonight and Saturday...a couple distinct upper impulses may impact at 
least northern sections of the forecast area tonight. The first is 
centered just northwest of Kansas City...while the second is 
moving along the Nebraska/South Dakota border. Showers are 
beginning to expand to the east of these waves...which are 
expected to impact mainly northern Illinois tonight. However...a 
few showers are starting to bubble over northwest sections of the 
forecast area...in the vicinity of an outflow boundary from last 
night/S mesoscale convective system. So...have bumped up shower/storm chances in the north 
to account for the expected nearby passage of the above mentioned 
waves and outflow boundary. The precipitation with these features 
may linger into Saturday. How much additional development occurs in 
the afternoon along new boundaries is pretty tough to call at this 
time. 


Saturday night and Sunday...convection chances will be somewhat 
lower during the period. Stronger energy...currently moving across 
the northern rockies and British Columbia...will pull the main 
front/baroclinic zone further north...along with the high 
precipitation risk. 


Sunday night through Tuesday...the front will push into and 
eventually through the the forecast area during the period as The 
Rockies/British Columbia waves dig over the Great Lakes. The passage of the 
front and the upper energy will raise the risk for showers/storms 
once again. The probability of precipitation will probably need to be raised above the 
chance mention currently in the grids/zones...but the local scale 
details still make the specifics very difficult to Pin Point at 
this time. 




Long term...Tuesday night through Friday...models/ensembles in 
reasonable agreement and trending toward at least a few days of 
northwest flow aloft in wake of the early week system. This 
pattern would provide at least some relief from the heat/humidity. 
The precipitation risk should be reduced as well as long as the 
low level front/baroclinic zone does not stall out too close to 
the region. 


Bak 
&& 


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 
&& 


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


$$