581
FXUS63 KLOT 030554
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1254 AM CDT Wed Jul 3 2024

.KEY MESSAGES...

- Showers/storms expected to reach the I-39 corridor this
  evening, then decreasing in coverage and intensity as they
  attempt to move east toward/east of the I-55 corridor.

- Typical July warmth and humidity through the week with
  periodic chances for showers and storms late Wednesday night
  through Friday

&&

.DISCUSSION...
Issued at 253 PM CDT Tue Jul 2 2024

Through Wednesday:

After a persistent area of WAA-forced elevated showers north of
I-80 this morning, the last few showers should be lifting north
of the WI state line within the next hour. Otherwise, mostly
sunny skies are expected through sunset as temps rise into the
low to mid 80s for all areas except the northern tier of
counties.

A mid-level wave just west of Kansas City early this afternoon
will interact with a plume of higher theta-e air into central
and eastern Iowa late this afternoon, fostering quickly growing
convection into a generally linear MCS within the next few
hours. The resulting convection is expected to track into a
substantially less favorable environment around and east of the
Mississippi River this evening into the early overnight hours as
moisture decreases and mid-level lapse rates remain rather
marginal for sustained organized convection. Expectations are
for the convection to slow and weaken into a band of showers
with some embedded thunder as far east as the Chicago metro.
Poor low-level thermodynamics will limit the amount of surface-
based convection, but a narrow reservoir of 1000+ J/kg DCAPE
nosing northeastward ahead of the convection early this evening
could support a few strong wind gusts as far east as the I-39
corridor. Additionally, PWATs over 2" combined with weak
backward propagating vectors and deep layer shear vectors only
slightly oblique to the forcing may result in brief training and
subsequent localized rainfall amounts of 1-2" across the
western CWA.

After the early overnight hours, residual convection and
scattered showers will gradually drift southeastward as a cold
front approaches from the northwest late tonight into Wednesday
morning. The cold front should clear the southern CWA by late
afternoon, with a vast majority of the CWA in line for a partly
cloudy day with highs in the mid to upper 80s.

Kluber

Wednesday Night through Tuesday:

A surface frontal boundary is expected to settle across downstate
portions of IL and IN Wednesday night. This front is likely to
remain the focal point for convective activity Wednesday night,
especially south of our area. While our local weather looks rather
quiet Wednesday night, conditions will remain on the warm and
muggy side, with overnight lows only falling back into the mid to
upper 60s.

The remnants of some of Wednesday night`s convection will try
to shift northeastward into parts of the area Thursday morning
as a mid-level impulse tracks into the area. While a period of
showers does look to be a good bet, especially for areas south
of I-80 Thursday morning, poor lapse rates over our area will
likely curtail the threat of thunderstorms through the morning.
Following the morning activity, a low (~30%) chance for some
afternoon and evening thunderstorms exists. However, with the
surface frontal boundary looking to remain south of the area
until later Thursday evening and night, current thinking is that
there will be a good amount of dry time for any outdoor 4th of
July plans. Expect temperatures during the day to be in the low
to mid 80s.

The next mid-level trough will shift eastward across the Upper
Midwest late Thursday night into Friday morning. As it does, a
surface wave of low pressure will lift northward into the western
Great lakes while driving a surface cold frontal boundary
eastward across our area into Friday morning. While the timing of
this feature moving across our area will not be diurnally
favorable, we will have increasing chances for a period of
showers and thunderstorms late Thursday night into Friday morning.
Some showers, and possibly a few scattered storms may also linger
into Friday afternoon across far northern sections of IL into WI
as the central of the upper trough shifts overhead. Slightly
cooler temperatures are expected, with highs generally in the
upper 70s to low 80s.

The weather heading into the weekend overall does not look too
bad at this time. It appears that we could have a good deal of dry
time Saturday into Sunday before our chances for showers and
thunderstorms begin to increase again with the approach of the
next weather impulse late Sunday into Monday. Expect temperatures
to be in the low 80s Saturday, and into the mid 80s for Sunday.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1254 AM CDT Wed Jul 3 2024

Forecast concerns for the terminals...

- Showers and occasional thunderstorms to persist through the
  night

- Lowering ceilings overnight as showers end with MVFR
  conditions expected but pockets of IFR possible

- Ceilings improve Wednesday morning with VFR conditions through
  the rest of the period


An area of showers continues to pivot across northern IL this
evening as a cold front progresses over northern IA towards IL
and eventually IN. While there was some thunderstorms within
the area of showers earlier, the waning instability this evening
has allowed that threat to diminish and therefore felt
confident enough to remove formal TS from the TAFs. However,
there is a narrow plume of instability west-central IL that
could pool ahead of the front which may allow for a brief period
of more robust showers and/or thunderstorms towards daybreak.
Though, confidence on this new development occurring remains
too low for a formal mention at this time. Regardless, showers
should gradually taper from northwest to southeast after 09z
leaving dry conditions for Wednesday.

Ceilings will gradually lower in the wake of the showers
overnight allowing MVFR ceilings to develop over the terminals.
Though, there have been some pockets of IFR and even LIFR
ceilings across IA where higher moisture has been present. The
general thinking is that these IFR/LIFR ceilings should lift to
the MVFR category as they move into northern IL, but cannot
completely rule out a brief period of IFR conditions especially
at RFD. The lower ceilings are expected to persist into
Wednesday morning before scattering out between 15z-16z with VFR
conditions expected from that point forward.

Otherwise, expect south-southwest winds tonight to gradually
become westerly and eventually more northwesterly behind the
front Wednesday morning. Wind speeds may remain breezy at times
with any showers, but should generally remain in the 8-10 kt
range through Wednesday afternoon.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago