312 
fxus63 kilx 240201 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
901 PM CDT Wednesday Jul 23 2008 


Discussion... 
issued 900 PM CDT Wednesday Jul 23 2008 


Main concern for the update is how to handle the approaching 
showers from across Iowa. There appears to be some persistence to 
them that is not being picked up by the models. A few sprinkles 
reached the ground from 11k feet based on a few surface observation across 
Iowa. However...not too convinced that any locations had more than 
a trace so far. The drier air in place across our County Warning Area has ME leaning 
toward keeping a dry forecast the rest of the night. Feel like virga 
will be the primary result of the middle level upward vertical velocity and moisture that 
reaches central Illinois. Will increase cloud cover in the grids 
the rest of the night. Low temperatures are on track...based on our surface 
dewpoints and the amount of time left before middle and high clouds 
thicken over the area. 


The strongest signal for possible severe weather remains Thursday 
night...as a complex rolls out of Iowa into the area. 


Shimon 
&& 


Aviation... 
issued 635 PM CDT Wednesday Jul 23 2008...for the 00z tafs 


A few diurnal cumulus clouds in eastern Illinois are dissipating this 
evening. Middle and high clouds rolling over the upper ridge in the 
plains are affecting western Illinois already. Rain bands are in west 
Iowa...but we should be dry the rest of the night. Thursday 
morning...we may see a few showers close by to Schuyler 
County...but the pia and spi should remain dry until middle to late 
morning. I added a thunderstorms in the vicinity for that time period...and went with 
prevailing thunderstorms and rain after 21z for pia and spi. I put thunderstorms in the vicinity for the 
remainder of the taf sites for later afternoon. 


Based on the instability params for afternoon...we may see a watch 
box that includes spi before middle afternoon on Thursday. Did not 
hit them too hard just yet...but the potential exists for the LIFR 
ceilings and/or visible in strong storms before evening. 


Shimon 
&& 


Previous discussion... 
issued 306 PM CDT Wednesday Jul 23 2008 


Short term...tonight through Saturday... 
high pressure ridge across Illinois will move slowly across the 
region tonight and Thursday. The cold front that previously moved 
through Illinois is now located from central Kansas to near 
Memphis...however the frontal surface gets quite shallow from 
central Missouri into southern Illinois. Another thunderstorm 
cluster is expected to fire up tonight over the Dakotas...then ride 
southeastward along the northwesterly mean upper flow. This activity 
is timed to remain to our west through 12z Thursday...but remnants 
may make headway into the western half of the state by 18z Thursday and 
continue to spread eastward from there. Will have some chance probability of precipitation 
in the extreme west 12z-18z Friday...then likelys in the afternoon. 
Further east will indicate a dry morning with chance/slight chance 
probability of precipitation in the afternoon. 


The cold front to our south will move north as a warm front Thursday 
night...with thunderstorms becoming more numerous along and north of 
the front. Will put in some likely probability of precipitation for then...but hold them in 
the chance category on Friday since there remains some question on 
how far north the front will come. Front should be lingering just to 
our south on Saturday which could support precipitation over the 
south and west. Will just have slight chance probability of precipitation for then. 


04 


Long term...Sunday through Wednesday... 
an amplifying upper level weather pattern is expected to take hold 
through most of the extended period with a building ridge across The 
Rockies and digging trough across the eastern US. This will leave 
most of the region in northwesterly flow through most of the extended 
period with a few weak shortwave troughs propagating southeastward 
along with the flow. The best chances for any precipitation in the 
extended period will likely be on Sunday as warm air again advects 
northward back into the region. A stalled out frontal boundary will 
likely be lingering across the region which will have to watched for 
any northward movement that could usher in warmer air from the south. 


&& 


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


$$