249 
fxus63 kilx 071151 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
651 am CDT Tuesday Oct 7 2008 


Discussion... 
issued 128 am CDT Tuesday Oct 7 2008 


A period of wet weather is expected across central Illinois today 
and tonight...before a return to warm and dry conditions through 
the upcoming weekend. 


06z surface analysis shows sprawling area of high pressure 
extending from the eastern Great Lakes southward into 
Florida...providing a dry east/southeast flow across the kilx County Warning Area. 
Meanwhile...an area of low pressure is noted over northeast 
Kansas...with scattered showers and thunderstorms along and west 
of the Mississippi River. Aloft...high amplitude pattern noted 
across the Continental U.S....with the main feature of interest being a 
trough currently situated over the plains states. 


Short term...today through Thursday 


As plains upper trough and associated surface low slowly move 
eastward today...rain will gradually spread across central 
Illinois from southwest to northeast. 00z kilx and kdvn upper air 
soundings both showed quite a bit of dry air at middle and 
low-levels...so precipitation will likely be slow to get started. Initial 
short-wave and band of light showers is already crossing the 
Mississippi River into southwest Illinois and may begin impacting 
areas along and west of I-55 before dawn. Any precipitation that occurs 
before 12z will be very light...probably only sprinkles at best. 
Once the atmospheric column slowly moistens...additional showers 
developing ahead of the approaching system will move into the area 
later this morning. Models in good agreement with timing of 
precipitation...generally keeping east-central Illinois along and east of 
I-57 largely dry until afternoon. Based on continued dry east/southeast 
flow...will only carry chance probability of precipitation across the eastern zones during 
the morning hours...rising to categorical probability of precipitation along and west of 
I-55. Will increase probability of precipitation to categorical across the board by 
afternoon as system approaches the Mississippi River. Instability 
will be rather meager today...with the most unstable air prognosticated 
to remain further south across the lower Mississippi River valley. 
Despite lack of instability...upper dynamics associated with wave 
will likely be enough to set off isolated thunderstorms. Due to 
all the cloud cover and precipitation...high temperatures will be held down 
quite a bit...particularly across the west. High temperatures will range 
from the upper 60s along and west of I-55...to the lower to middle 
70s along the Indiana border. 


Primary rainfall event will occur between noon today and midnight 
tonight...with most locations picking up between one half and one 
inch of rain. Slightly higher amounts over one inch will be 
possible along and south of I-70. Will continue with categorical 
probability of precipitation into tonight...as weakening surface low moves right through 
central Illinois. Models continue to advertise a rather quick exit 
to the system on Wednesday...with the GFS being the slowest to 
eject the precipitation. Will use a blend of the slower GFS and the 
faster NAM-WRF...and will continue to carry low chance probability of precipitation across 
the east/southeast Wednesday morning...before going dry everywhere by 
afternoon. 


Once system moves off to the east...high pressure will begin to 
build in from the plains states Wednesday night into 
Thursday...allowing skies to clear and temperatures to climb back into 
the 70s on Thursday. 


Long term...Friday through Monday 


Medium range models in somewhat better agreement tonight...with 
the GFS and Canadian coming more into line with previous and 
current run of the European model (ecmwf). Bottom line will be digging trough 
across The Rockies this weekend...resulting in rising heights and 
warming temperatures across the Midwest. Still some question as to the 
exact evolution of the trough and the timing of its associated 
cold front...but model consensus keeps it west of Illinois at 
least through Sunday. Will therefore keep things dry for the 
upcoming weekend...with high temperatures both Saturday and Sunday 
approaching the 80 degree mark. 


Barnes 
&& 


Aviation... 
issued 651 am CDT Tuesday Oct 7 2008 


Ceilings starting to lower across the central Illinois terminals... 
with rains beginning to spread in from the southwest. This trend 
will continue through the morning hours...with all taf sites 
expected to have MVFR ceilings/visibilities and showers by midday. An 
isolated thunderstorm can not be ruled out through early 
evening...but the chances are too low at any one terminal to go 
above a cumulonimbus mention in the tafs. The precipitation is expected to 
taper off to drizzle this evening as a cold front pushes into the 
region. Expect ceilings to lower into the IFR category as rains taper 
off with the approach/passage of front. Once they arrive...IFR 
conditions will prevail through the remainder of the 12z taf 
period. 


Bak 
&& 


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


$$