564
FXUS63 KILX 201101
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
601 AM CDT Sun Apr 20 2025

.KEY MESSAGES...

- There is a level 2 of 5 (slight) risk for severe weather today.
  All severe hazards are in play (tornadoes, damaging winds, large
  hail). Most likely timing would be 6pm to midnight.

- Thunderstorms this evening may also produce torrential rain. If
  there is training of storms, localized flash flooding may
  occur. The greatest risk will be near and west of roughly I-55.

- Above normal temperatures are expected this week beginning on Tuesday.
  Highs will be in the 70s to near 80 and lows in the 50s to low
  60s.

&&

.DISCUSSION...
Issued at 257 AM CDT Sun Apr 20 2025

Today a low pressure system is going to be lifting from the southern
Plains northeastward into the Great Lakes. The cold front that
sagged through yesterday will lift back north this morning as a warm
front. By late afternoon, the associated cold front will push
eastward across Illinois. These frontal passages will bring
additional showers and thunderstorms (some potentially severe) to
central and southeastern IL. By Monday afternoon, a high pressure
system will set up over the Midwest, giving us a short break from
the wet weather. Several pushes of shortwave energy will allow the
rainy/stormy weather to return to the area for the latter half of
the week. There is a slight risk (level 2 of 5) today for our
southwest counties. The marginal risk (level 1 of 5) stretches as
far east as the I-57 corridor.

The warm front will begin to lift over the area this morning after
12z. This will return the chances for some scattered showers and
thunderstorms through 20z. A couple hundred J/kg and 50-60 knots of
0-6km bulk shear in the region of the warm front may allow for some
of the storms to be on the stronger side of things, if they can
break through the weak cap in place. However, the healthier CAPE
values are found in the warm sector. If storms are able to fire
along any outflow boundaries of existing thunderstorms in this
region, we could see some severe storms develop. The closer these
storms are to the warm front, the more tornadic potential they will
have, with 0-3km SRH of 600-700 m^2/s^2. This first round of severe
potential is focused mainly east of the I-57 corridor.

The main show of the day comes later in the evening, starting at
about 00z Monday (7pm tonight). The cold front will push east over
the area, bringing a line of showers and embedded thunderstorms
along with it. We are mostly concerned with this line having
damaging winds and marginally severe hail, but the isolated tornado
cannot be completely ruled out. Some forecast soundings are showing
an inverted V signature for mid afternoon into early evening,
supporting strong winds. Long, skinny CAPE profiles and PWATs of
around 1.5 can also be seen on these forecast soundings, which can
support heavy (maybe even torrential) rainfall in these storms.
There is a localized flash flooding risk where the heavier rainfall
occurs. As this line moves east, it will move into a less favorable
environment and will gradually decay as it exits into Indiana.

Behind the front, some gusty south winds will push through Monday
afternoon. Wind gusts as high as 35-40 mph at times. By 00z Tuesday,
winds will have shifted out of the west and will begin to calm down
as the high pressure settles in.

Several more rounds of rain for the second half of the week are
possible, resulting from some disturbances passing overhead.
Temperatures will remain above normal for much of the week with
highs on Tuesday (and beyond) will be in the 70s to near 80 and lows
in the 50s to low 60s.

Copple

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 601 AM CDT Sun Apr 20 2025

The 12z TAF are a bit messy as a lot is going on today. ESE winds
will pick up this morning, gusting to 25kts much of the day. By
the end of the period, the winds will have shifted out of the SW.
There will be a period of LLWS (170 @ 50kt) as the cold front
moves through this evening, but SPI and PIA should miss out on
this.

Showers and thunderstorms will make their way through today. THis
morning mainly showers will impact each site in some way. This
evening into the overnight hours, a line of strong thunderstorms
are expected to move through along the cold front. Starting at the
western sites by 00z and exiting the eastern sites by 06z.

Ceilings are going to bounce around today between the
showers/t`storms and boundary passages. We will be VFR to start
but then drop down to MVFR later this morning. The ceilings will
rebound to VFR by early afternoon ahead of the line of storms.
During thunderstorm activity, ceilings may drop to MVFR.
Otherwise, will be VFR until becoming MVFR (again) after 06z for
the eastern sites (BMI/CMI/DEC).

Copple

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$