Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 300125

Area Forecast Discussion
825 PM CDT Wed Oct 29 2014


Backedge of clouds now just east of Champaign and should gradually
exit the state by 03z. Meanwhile, high pressure centered over west
central Illinois has brought about the clearing trend early this
evening accompanied by a very light wind, resulting in temperatures
dropping off rather quickly over the past few hours. A few sites
have already dropped into the upper 30s with low to mid 40s being
reported over eastern Illinois where the clouds linger.

Latest satellite loop indicating some mid and high level clouds
streaking east-southeast across northwest Iowa early this evening
and based on the present movement, will get into west central
Illinois by 08 or 09z, effectively putting an end to the temp
decline in that area. Have made some adjustments to the early and
mid evening temperature trends in the grids with the coldest
readings thru about 07z-09z out west and 09z-11z east. Most of the
area will see some patchy frost with the main emphasis across the
east where the skies will be clear the longest. Other than the
temp adjustments this evening, no other changes made to the grids.
Should have an update out by 900 pm.


.SHORT TERM...(Tonight)

Surface high continues to build into the region this evening.
Despite the quiet weather, a wave moving into the upper trof will
usher some moisture into ILX in the form of clouds.  Time heights
showing arrival of cirrus and a slow transition to more mid clouds
as the early morning hours progress.  Light and variable winds will
assist in efficient radiational  cooling under the clearer skies.
Frost threat is better in the eastern half of the state under the
ridge axis in the early morning hours. The winds slowly pick up a
more southerly component a few hours before dawn in the western
half, pushing slightly warmer air into the area and keeping the
temps from bottoming out.


.LONG TERM...(Thursday through Wednesday)

An extended period of below normal temperatures is on tap across
central and southeast Illinois for the next several days. The
coldest period will extend from Friday to Sunday, with a hard freeze
likely early Saturday and Sunday mornings. Do not plan to go with a
Freeze Watch at this time since the freezing conditions are more
than 48 hours out in time, but will continue to highlight the risk
in the Hazardous Weather Outlook and Weather Story Graphics. While
this will be the first hard freeze across the forecast area, it is
"normal" (or late in many areas) for a first freeze to occur in late
October. Halloween Trick or Treat conditions will be less than ideal
with actual temperatures in the upper 30s or lower 40s and Wind
Chill values around 30 degrees.

Other than the chilly temperatures, the main forecast concerns
revolve around rainfall chances tomorrow with a weak wave, as well
as with a stronger system for the beginning of the next work week.
For tomorrow, a short wave, currently digging southeast out of the
northern Rockies, is progged to pass just southwest of the forecast
area. A quick shot of WAA/isentropic ascent ahead of the wave,
mainly Thursday afternoon/early evening, should be able to squeeze
out some light showers. However, the rainfall is not expected to be
significant. A much stronger wave, currently diving into
Saskatchewan and Manitoba, will track across the Great Lakes/Midwest
on Friday. While this system is potent, it will be moisture starved,
with most of the associated precipitation expected to fall
north/east of the forecast area as it passes through. However, this
system will be accompanied by gusty winds and will help usher in the
airmass that will provide our hard freeze for the weekend.

Upper level ridging will begin to build into the area by late in the
weekend into early next week. The ridge will break down by later
Monday into Tuesday as a strong disturbance of Pacific origin pushes
east toward the area. The frontal system driven by this wave will be
accompanied by showers. The risk of showers may be prolonged since
the front will become nearly parallel to the upper level flow and be
a slow mover. However, the model guidance is still not in good
agreement (or with great run-to-run consistency) regarding how quick
the front will ultimately be. So, how long the rainfall risk will
linger beyond Tuesday is still subject to debate.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)

VFR conditions are expected thru this forecast period. Backedge
of stratocu deck pushing east of AAA and BMI and should be east
of CMI by 02z with a clear sky expected thru 09z before cirrus
and altocumulus clouds advance into west central IL in the 10z-
12z time frame. A weak wave of low pressure will push to our
southwest late tomorrow with clouds gradually lowering and
thickening to low VFR by the end of this forecast period. We
may see some scattered light showers develop during the afternoon
as well but coverage still looks to at this time will
add a VCSH to PIA and SPI in the 18z-21z time frame with rain
chances spreading further east by evening. With high pressure
over the forecast area tonight, look for light and variable winds
most of the night to turn more southeasterly on Thursday with
speeds increasing to 7 to 12 kts by afternoon.




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