Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 161758
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1258 PM CDT Sat Sep 16 2017

.UPDATE...
Issued at 1051 AM CDT Sat Sep 16 2017

Updated the forecast to make minor changes to the high
temperatures and sky cover. Expecting to see more clouds in the
area as low level moisture gradually increases through the day.
Despite this, we should still high temperatures around 90 degrees
in most of central and eastern IL by early this afternoon.

The 12z ILX sounding, as well as upstream soundings, indicate
there is quite a bit of dry air in the mid levels of the
atmosphere. This will most likely delay the onset of any showers
or isolated t-storms until the daybreak hours, which the most
recent runs of the RAP and NAM point to.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 246 AM CDT Sat Sep 16 2017

As we remain on the periphery of an expansive high pressure area
over western New York, dry weather will continue through the
afternoon over our area. Another unseasonably warm day is on tap,
with temperatures pretty close to what was observed on Friday.
Went with highs near 90 degrees over most of the forecast area.

The frontal boundary to our west, currently stretching between
separate low pressure centers over Minnesota and northwest Kansas,
will start to make some headway later today. An upper low,
currently seen on water vapor imagery over northeast Idaho, will
lift northeast and give the front a shove. While a fairly
expansive line of showers and storms will form along the boundary
late afternoon and early evening, most of the synoptic and high-
resolution models significantly erode the rain as it crosses into
Illinois. As such, will only maintain the 20-30% PoP`s for late
tonight west of the Illinois River.

.LONG TERM...(Sunday through Friday)
ISSUED AT 246 AM CDT Sat Sep 16 2017

The cold front is expected to be through most of the forecast area
by early evening. While instability will build through the day,
with CAPE`s above 1000 J/kg, very weak bulk shear will prevent any
significant issues with severe weather. Have mainly kept PoP`s in
the 30-40% range as scattered showers and storms develop ahead of
the front.

Upper level patterns will favor a southwest flow for us through
much of the week, keeping the temperatures well above normal as we
wrap up the end of astronomical summer. The main storm track will
be across the northern tier of states, periodically dropping
fronts our way, though they won`t make much headway into the
higher 500 mb heights over us. As such, scattered convection will
be possible much of the week, at least until a significant
amplification of the upper ridge toward Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1256 PM CDT Sat Sep 16 2017

VFR conditions can be expected in eastern IL and most of central
IL during much of this TAF period.

This afternoon, mixing in the lower atmosphere will result in
periods of wind gusts over 15kts in parts of central IL, mainly
from PIA-BMI-CMI. The diurnally driven cumulus field will
primarily be scattered around 4500-6000 feet, but a few clusters
of broken cloud cover are possibly - primarily early this
afternoon.

The 12z ILX sounding indicated some increasing low level
moisture, but a very dry layer aloft. This will play a role later
tonight in delaying the onset of scattered showers in central IL
until just after daybreak. Thus, held off on MVFR visibility and
VCSH until 14z or later along and west of the I-55 corridor.
Scattered showers and a few t-storms should hold off in the rest
of central and eastern IL until 18Z or later Sunday.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Miller
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Miller



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