Weather

686 
fxus63 kilx 061950 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
250 PM CDT Monday Oct 6 2008 


Discussion... 
issued 250 PM CDT Monday Oct 6 2008 


Main concerns in the short-term package will be onset and ending 
of precipitation with next system moving through the area tomorrow and 
Wednesday. In the long term...the concern is when the next chance of 
precipitation will be. 


GFS and NAM-WRF seem very similar through next 42hrs...Tuesday 
night...but then show some differences in the speed of the front 
as it pulls away from the area on Wednesday. Appears a blend of 
the models is best. 


In the long- term...big differences on what the overall pattern 
and surface pattern will look like through the period. Here...the 
ensemble mean/blend is probably the best way to go since there is 
very low confidence in what the operational models area 
forecasting at this time. 


Short term...tonight through Thursday night 


One more dry night before precipitation arrives in the area. Frontal system 
is still in the plains but showers and thunderstorms are located 
out ahead of the front in eastern Kansas and parts of western MO. This 
frontal system will approach the area overnight with precipitation expected 
not to start until tomorrow morning. As the system and dynamics 
move into the region precipitation will continue across the area Tuesday 
and into Tuesday night. 12z model runs have precipitation ending little sooner 
than first thought so have pulled probability of precipitation for areas along and northwest of 
I-55 for Wednesday...and have kept chance probability of precipitation in the east. Have system 
pushes east later Wednesday and into Wednesday night high prss will build 
into the region bringing dry weather and normal temperatures for Thursday. 


Clouds and precipitation will keep temperatures below normal (lower 70s) tomorrow 
and Wednesday...except in the southeast where precipitation will take longer to 
reach. Then normal temperatures return for Thursday. Guidance looks 
pretty good today. 


Long term...Friday through Monday 


Long wave pattern flattens out for most of the extended time 
period and becomes somewhat zonal. Then next weekend and long wave 
trough builds in the west and County Warning Area returns to southwesterly flow. 
After being dry in the area for several days...a frontal system 
could enter the region and bring the return of precipitation to Illinois for 
Sunday night and possibly first part of next week. However with 
models differing lots with how this will evolve confidence is low. 
So will just follow ensemble blend for now and have precipitation Sunday 
night and leave out chances of precipitation for Monday until models get 
better handle on things. 


Temperatures will warm back to above normal for the extended period. Guidance 
looks fine with temperatures until the weekend...which is too cool given 
expected pattern. So have raised temperatures for Sat through Monday to 
better match current thinking. 


Auten 
&& 


Aviation... 
issued 1251 PM CDT Monday Oct 6 2008 


The latest water vapor satellite loop indicated that upper level 
ridging which has resulted in quiet VFR conditions the past few 
days will depart the area. An upper level trough from the Southern 
Plains is expected to rotate northeastward toward the Midwest 
reaching western Illinois late Tuesday morning according to the 
distance speed tool. Low and middle level warm advection ahead of 
this trough will result in widespread altocumulus clouds around 
7000 feet after 06z tonight. 


The NAM and GFS models are in fairly good agreement on bringing 
MVFR conditions and showers into west central Illinois...including pia 
and spi. As a result...added MVFR ceilings and visibilities with showers 
to those two taf sites...but will leave out of the rest as there 
is uncertainty as to the timing of the rainfall in eastern Illinois. 


Miller 
&& 


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


$$