400
FXUS63 KLOT 021953
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
253 PM CDT Tue Jul 2 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 /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1254 PM CDT Tue Jul 2 2024

Key Aviation Messages:
- Gradual wind shift from SSE to SSW early this evening.
- SHRA with possibly some embedded TS late evening and early
  overnight.

A mid-level wave over central Kansas is expected to spread a
period of SHRA and perhaps some embedded TS across the area late
this evening into the early overnight hours. Confidence in
occurrence and associated coverage of TS at the Chicago
terminals remains low enough at this time to maintain a PROB30
mention roughly in the 06- 09Z window. However, have included a
short period (02-04Z) of VCTS at RFD where elevated instability
will be notably higher this evening.

Isolated to widely scattered -SHRA may persist to around
sunrise Wednesday ahead of an approaching cold front. A period
of post- frontal MVFR ceilings will follow through late morning
before ceilings SCT and lift into VFR levels through the
afternoon.

SE/SSE winds over 10 knots will begin to gust over 20 knots
this afternoon while gradually veering SSW through this evening.
Winds will begin to favor west of 180 degrees sometime in the
23-01Z window, especially with the development of a veering LLJ.
Winds will further veer SW overnight and WNW behind the cold
front after daybreak Wednesday.

Kluber

&&

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

&&

$$

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