Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 202309

Area Forecast Discussion
National Weather Service Lincoln IL
609 PM CDT Sun Jul 20 2014

ISSUED 327 PM CDT Sun Jul 20 2014

SHORT TERM...Tonight through Wednesday

Scattered cumulus covers much of Illinois again this afternoon,
generally based around 4000 to 6000 feet. 24 hour change in
temperatures and dewpoint generally up a few degrees since
yesterday as expected with a warm high pressure ridge building
into the region. Overnight, some fog is possible again as clear
skies combine with increased low-level moisture. West of I-57
pressure gradients start to increase overnight indicating some
light wind which will likely prevent any substantial fog, however
from around I-57 east have placed patchy fog in the forecast
again from around midnight to 7 a.m.

Monday into Tuesday a strong 500 mb ridge will continue to develop
over the West and extend into the Midwest. This will bring a warm
and stable air mass over Illinois. Southerly low level flow will
bring an increase in moisture yielding dewpoints over 70 by Monday
and Tuesday and heat index values approaching 100 by Tuesday

An upper level trough will move over the top of the ridge and
southeastward through the Midwest Tuesday night, along with a
surface cold front. Most model solutions feature fairly similar
timing of a progressive system moving into northwest Illinois
Tuesday evening and exiting Illinois Wednesday afternoon. Have
only slightly increased probability of precipitation with this
feature to bring likely category (60% or greater) to most of the
central IL forecast area at some point as the feature moves
through. Not expecting a significant severe threat given the
arrival time at night, but don`t think the possibility can be
ruled out at this point given uncertainty with the timing and
CAPE/shear values expected to accompany the system. Some lingering
showers/storms will continue through Wednesday across the
southeast CWA, but areas I-72 north will likely be dry by
afternoon as high pressure begins to build from the north.

LONG TERM...Thursday through Sunday

Cooler conditions are expected Thursday and Friday as cool dry
northerly flow pushes into the region following the Tuesday night
shortwave. Past there, focus shifts to potential MCS activity
Friday night sliding down the upper ridge, which will be re-
establishing itself along and west of the Rockies. For Sunday, a
deep trough is progged by both the GFS and European models over
the Midwest, hence cooler than climatological temperatures and a
chance for precipitation are in the forecast.



ISSUED 605 PM CDT Sun Jul 20 2014

Elevated smoke layer from fires over western Canada continues to
drift southeast into our region, as has been the case over the
past several days. Latest visible satellite loop showing probably
the thickest band of smoke now over central IL and continuing to
drift south-southeast with the upper wind flow. As far as general
aviation concerns this forecast period, other than some MVFR vsbys
in fog again towards Monday morning (roughly in the 09z-12z time
frame), no real forecast concerns in our area as high pressure at
the surface and aloft prevails. Cumulus should develop again by
16z Monday and then quickly dissipate towards 00z Tuesday. Surface
winds will be light south to southeast tonight and then southerly
on Monday with speeds around 10 kts by late morning/early



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