425
FXUS63 KLOT 201959
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
259 PM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Spotty shower chances Sunday through Tuesday with greatest
  potential for showers and thunderstorms on Wednesday.

- Near to slightly below normal temperatures through next week

&&

.DISCUSSION...
Issued at 259 PM CDT Sat Jul 20 2024

Through Sunday Night:

A surface high continues to reside across the mid-Mississippi
Valley and southern Great Lakes keeping tranquil weather
conditions in place for the rest of the weekend. Winds beneath
the high will remain light and generally out of a westerly
direction though another lake breeze Sunday afternoon will turn
winds east-northeasterly for areas near the lake shore. Never
the less, these wind directions will limit the moisture return
into northern IL and northwest IN which will keep humidity
values low (for mid-July). Therefore, expect comfortable
humidity and near average temperatures to persist through the
weekend with highs in the low to mid-80s.

However, there is a baggy upper trough over southern WI and
northeast IA which is forecast to pivot over northern IL and
southern Lake Michigan on Sunday. While forecast soundings do
show some modest instability developing across the area Sunday
afternoon, the aforementioned limited low-level moisture should
keep coverage of any precipitation low. If any precipitation
does materialize Sunday afternoon the bulk of it should stay
near and north of the IL-WI line and be primarily in the form of
light showers. Though, a few showers could develop along the
lake breeze so I did expand the slight chances (20%) POPs
eastward to the lake for this potential. Regardless, most areas
should remain dry with just a mix of sun and clouds for our
Sunday.


Monday through Saturday:

The aforementioned surface high and baggy upper trough will
continue to reside overhead for Monday and Tuesday keeping a
slight (around 20 to 25%) chance for showers and storms in
play, especially on Tuesday. Though, many dry hours are expected
too. Temperatures on Monday and Tuesday will be similar to
Sunday with highs in the mid-80s, but a lake breeze on Monday
may keep readings a touch cooler along the lake shore.

Heading into Wednesday, the baggy trough will be forced east as
a more organized trough digs into the Great Lakes from Canada.
At the surface, winds will become more southwesterly overnight
Tuesday night into Wednesday which should allow dew points to
increase back into the mid to upper 60s prior to the trough`s
arrival. Therefore, instability should increase with diurnal
heating on Wednesday and give way to widespread showers and
thunderstorms Wednesday afternoon. While guidance does show a
modest 30 to 35 kt jet streak with the trough, most guidance
shows the effective shear to be rather limited in the 20 to 30
kt range. So while a stronger storm cannot be completely ruled
out, the threat for widespread severe weather looks low at this
point.

Shower and thunderstorm chances should gradually diminish
Wednesday evening as the core of the trough pivot into northern
IN and lower Michigan. However, rain chances may persist into
Thursday (mainly east of I-57) as residual upper waves pivot
overhead behind the main trough. High pressure is expected to
move into the area on Thursday and remain in place through the
end of next week and into at least the start of next weekend.
Therefore, rain chances for the end of next week look limited
with near to slightly below normal temperatures as well.

Looking beyond next weekend, ensemble guidance continues to hint
that a return to a more active pattern may materialize for the
end of July into early August. Obviously details at this range
are very fluid on timing and coverage of any potential storms,
but will be a period to keep an eye on going forward.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1228 PM CDT Sat Jul 20 2024

Concerns:

- Lake breeze boundary turning winds easterly at ORD/MDW this
  afternoon.

High pressure over the region is keeping VFR conditions in place
with generally light and variable winds. A lake breeze boundary
has developed, turning winds north to northeast at KGYY and
pushing inland across Chicago. Based on latest trends, have sped
up the arrival at KMDW to 1830z and arrival at KORD may be a bit
before the 20z time in the TAF. Speeds behind the boundary
should range from 8-10 kt. Light and variable to even calm winds
will return this evening and become light north to northeast
Sunday.

MDB

&&

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

&&

$$

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