699
FXUS63 KLOT 051128
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
628 AM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Shower chances return this afternoon north of I-80 with a
  slight chance of thunderstorms

- Mostly dry conditions for the weekend, but there will be
  increasing rain chances late Sunday through Monday.

- Seasonable temperatures will continue through next week.

&&

.DISCUSSION...
Issued at 319 AM CDT Fri Jul 5 2024

Through Saturday:

An upper level trough over Southern Minnesota will swing over
Wisconsin and head toward the mitten of Michigan on Friday. A line
of showers and thunderstorms has been passing over northern
Illinois this evening ahead of the trough. But at the time this
discussion is published, the southern periphery is starting to
erode as it moves into Lee and La Salle counties, while the bulk
of the thunder is drifting toward the better instability in
Wisconsin focusing the strongest cells along the state line.
This line will continue to move east over the next couple hours
but gradually diminish into day break.

Friday morning will have a brief break in the rain chances,
before the next lobe of vorticity wraps around the upper level
trough and passes over Illinois to provide enough forcing to
allow for shower chances to return in the afternoon. While
slight chance PoPs were extended down to the I-80 corridor, the
better chances for showers will be north of I-88 and once again
closer to the Wisconsin border. Instability does not look
terribly robust with lower ELs on model soundings, so thunder
mentions in the forecast were clipped to just a slight chance
(less than 25 percent). Shower chances diminish into Friday
night as the diurnal component of falls off.

Temperatures on Saturday will be in the upper 70s and low 80s
once again. Dew points will still be in the 60s on Saturday, so
maybe with enough heating a stray shower might develop which is
probably why the blend of models was trying to add some low end
PoPs Saturday afternoon. But with the trough exiting to the
east and better height rises over the area PoPs were kept in the
unmentionable range (5 to 14 percent) and keeping the forecast
dry with decreasing cloud cover.

DK


Saturday Night through Thursday:

Conditions are expected to remain quiet and seasonably mild
across our area Saturday night. However, attention will turn to
the possibility for the development of a complex of storms to our
west-northwest (northern MO northward into southern MN) as a
short-wave impulse tracks northeastward into the Upper Midwest.
Should this complex develop, the weakening remnants would be
likely to track east-northeastward towards the Mississippi river
by daybreak Sunday, before potentially shifting into parts of
northwestern IL and WI during the morning on Sunday. Some
potential also exists for renewed scattered afternoon thunderstorm
development as a weakly capped airmass destabilizes. However,
this would be most favored to occur to the northwest of I-55 in
the vicinity of any remnant outflow boundary`s. Rising heights and
an overall less favorable thermodynamic environment farther to
the southeast should largely curtail the threat of storms on
Sunday.

The threat and coverage of showers and thunderstorms should
increase from northwest to southeast across the area Sunday night
through Monday night. This as a slow eastward moving cold front
shifts into the area beneath a series of small scale mid-level
perturbations streaming over the area in the southwest flow
aloft. The highest chances for showers and storms will remain
northwest of I-55 Sunday night into Monday morning, before chances
ramp up farther east later Monday into Monday night. The main
threat we will have to keep an eye on with these storms is the
possibility for some locally heavy rainfall given the potential
for some northeastward training along the slow moving cold front.

The surface cold front should begin to shift east of the area into
Tuesday morning as the main mid-level trough axis makes steady
eastward progress into the Western Great Lakes. However, in spite
of the early frontal passage, chances for scattered showers and
storms will continue into Tuesday as relatively cool mid-level
temps under the upper trough shift over a still warm and humid
post frontal airmass. Accordingly, we continue to carry 30-40%
PoPs. The threat of these showers and storms should come to a
quick end later in the afternoon, however.

The threat of organized showers and thunderstorms looks to become
rather low for a period around midweek owing to upper level
height rises and overall parched air aloft. However, later in
next week our local weather could become influenced by the
remnants of Beryl, depending upon where it tracks. Accordingly,
we will have to keep a close eye on its post tropical evolution
and track late in the period. Otherwise, expect seasonably mild
temperatures in the 80s for much of the period, with some
instances of cooler onshore flow along the lakeshore.

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 628 AM CDT Fri Jul 5 2024

Forecast concerns include...

- A period of MVFR CIGs expected across the area early this
  morning, and possible again tonight.
- Small chance for a few widely scattered showers this
  afternoon.

A couple hour period of MVFR CIGs (possibly as low as IFR near
RFD) are likely across the area this morning, before diurnal
mixing results in a quick return to VFR conditions through the
morning. Otherwise, aside from a small chance for some isolated
to widely scattered afternoon showers and some breezy westerly
winds, the weather will remain quiet today.


KJB

&&

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

&&

$$

Visit us at weather.gov/chicago