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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Monday
• 
• High: 73 °
• Low: 48 °
• Partly Cloudy

• Tuesday
• 
• High: 75 °
• Low: 50 °
• Clear

• Wednesday
• 
• High: 82 °
• Low: 59 °
• Partly Cloudy

• Thursday
• 
• High: 88 °
• Low: 70 °
• Clear

• Friday
• 
• High: 91 °
• Low: 72 °
• Partly Cloudy

Area forecast discussion 
National Weather Service Lincoln Illinois 
1202 PM CDT Monday may 21 2012 


Discussion... 
issued 953 am CDT Monday may 21 2012 


Main concern for today is with cloud cover. Have been seeing an 
expanding area of stratocumulus coming in from the northeast... 
mainly north of I-74 but have seen some recent development as far 
southwest as Springfield. Latest 925-850 mb humidity layer off the 
rap model indicates very little further westward spread...with the 
current Wing of clouds filling in areas east of I-55 but breaking 
up somewhat early this afternoon. Have made some tweaks to the 
hourly sky grids to account for this. Also made some slight 
adjustments to the hourly temperatures and winds...but none of 
these changes required a zone update at this time. 


Geelhart 


&& 


Aviation... 
issued 1201 PM CDT Monday may 21 2012 


Area of stratocumulus continues along and east of a kbmi-kspi line 
at midday. Cloud heights over far east central Illinois are still 
in the MVFR range around 2000 feet...but will rise at kcmi into 
VFR range by around 20z per latest forecast soundings. At the 
other sites...the clouds have risen above 3000 feet or will do so 
very shortly...and will diminish in coverage through the 
afternoon. Northerly winds will gust to around 20 knots at times 
through middle afternoon...before diminishing. After 00z...expect 
clear skies the remainder of the forecast period...as high 
pressure settles over Illinois. 


Geelhart 


&& 


Previous discussion... 
issued 258 am CDT Monday may 21 2012 


06z surface map placed cold front and leading edge of drier air just 
east of the I-55 corridor. Northwest wind behind the front were 
bringing in low 40s dewpoint air into western Illinois. Pre- frontal 
convergence band and associated showers and thunderstorms already 
pushed well east into Indiana early this morning. Aloft...W/v 
imagery indicated middle level trough tracking through the upper 
Mississippi River valley and broad west-northwest flow behind this feature 
extending back into the northern rockies. A quiet weather pattern 
will set up across the Midwest through middle week...while more 
active weather may develop to our northwest late this week. Below 
normal temperatures to start off the week will transition to well 
above normal towards the end of the week and next weekend. 


Short term...today through Tuesday 


Cold air advection will be in full force today courtesy of 20 knots 
northerly flow surface-700 mb and low/middle level cold pool rotating 
south across the County Warning Area. These conditions and a moist layer near 850 
mb should lead to a fairly extensive cumulus field for the eastern 
half to 2/3 of the area. Highs will return to near/slightly below 
normal levels...or 15-20 degrees cooler than the past two days. 
Clearing skies overnight and lighter winds as surface ridge builds 
east towards the area by Tuesday morning will lead to good 
radiational cooling. Have adjusted mins down a couple degrees into 
the upper 40s. Excellent weather looks to be on tap for Tuesday as 
the ridge slides across the area for light winds and seasonable 
temperatures with low humidity. 


Long term...Wednesday through Sunday 


Warming trend will commence on Wednesday as return flow kicks in 
on the back side of the ridge. The remainder of the extended 
period will feature a more active storm track to our 
northwest...ahead of a broad trough digging into The Rockies. This 
will initially allow strong southwest flow in the low/middle levels 
to develop and help push temperatures well above normal for 
Thursday and Friday. Questions remain if any of the shortwaves 
passing to our north will be strong enough to drive a cold front 
south towards central Illinois. 00z GFS/European model (ecmwf) runs suggest this may 
occur late Friday or early Saturday. However during this time 
strong middle level ridging is forecast to develop and move north 
from the lower Mississippi Valley. This will introduce very 
warm air aloft and act to suppress thunderstorm activity. 
Additional energy diving into the western trough should help send 
that front back north into the upper Midwest this weekend along 
with precipitation chances. If the projected strength of the middle level 
ridge advertised by the 00z medium range models verifies...highs 
in the lower 90s would be widespread for Saturday and Sunday. 


25 




&& 


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


$$