321
FXUS63 KLOT 121131
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
631 AM CDT Thu Jun 12 2025

.KEY MESSAGES...

- Today will be very warm and more humid inland of Lake
  Michigan, though it will be much cooler near the lake.

- Shower and thunderstorm chances will continue to remain muted
  locally through tonight. Greatest shower and storm coverage
  expected Friday and Saturday.

- Seasonable temperatures expected through the weekend, but with
  notably cooler conditions near Lake Michigan. Temperatures to
  warm again next week with a return for periods of showers and
  storms too.

&&

.DISCUSSION...
Issued at 305 AM CDT Thu Jun 12 2025

Through Friday:

A weak west-to-east oriented cold frontal boundary sagging
southward across far northeastern IL early this morning will
stall near the I-80 corridor during the day today. North of the
boundary, persistent onshore cool northeasterly winds are
expected through the day across the southern shores of Lake
Michigan. Accordingly, this will foster much cooler temperatures
today (a good 15-20F degrees cooler than yesterday),
particularly at and near the Lake Michigan shore. Conversely,
far interior sectors of northern IL and points south of the
frontal boundary will experience another warm early summer day,
as highs in these areas look to again top out in the mid to
upper 80s. Unlike yesterday, however, more higher level
cloudiness will be streaming across our area through the day,
thus resulting in partly sunny conditions.

The primary focus for showers and thunderstorms early this
morning will continue to reside north and northwest of the area
across northern IA into southern WI. While this is the case, we
certainly cannot rule out a few remnant non impactful showers
drifting into parts of the far northern IL counties (areas near
the WI state line) over the next few hours this morning before
dissipating. Otherwise, we are looking to experience mainly dry
conditions through the morning.

The threat of showers and thunderstorms will also remain low in
our area this afternoon (<20%), owing to continued poor mid-
level column moisture and weak flow overhead within a split mid-
level flow regime across the central CONUS. However, while
largely unfavorable for many storms, we cannot rule out the
potential for a couple of isolated storms developing this
afternoon (3 to 6 pm). This low potential (~20%) would largely
be confined to the vicinity of the surface frontal boundary
across the western 1/3 of the CWA where locally higher surface
dewpoints pooling along the front during peak heating could
contribute to their development. If any storms do develop, weak
low to mid-level flow should limit their organization and
duration, thus greatly curtailing threat for any severe weather.
Any isolated slow moving showers/storms out over the western
1/3 CWA this afternoon will quickly dissipate early this
evening.

Late tonight, some isolated showers may push into the far
southern CWA on the northeastern fringes of closed mid-upper
level low pressure moving into the Ozarks. Mid-level overcast
will keep overnight temps propped up again, with most spots in
the low- mid 60s by early Friday, except upper 50s in far
northeast IL farther north of the front.

The threat for showers and some thunderstorms will increase
into our area during the day Friday. This will particularly be
the case for areas along and south of I-80 as the mid and upper-
level low tracks into over the Lower Missouri Valley. Severe
weather is not expected with this activity, though rather slow
storm motions and increasing column moisture could support some
locally heavy downpours late in the day into Friday night. More
cloud cover and some better chances for rain should result in
cooler temperatures areawide on Friday, with highs once again
expected to be the coolest (in the low to mid 70s) along the
Lake Michigan shore due to continued onshore flow. Farther
inland, expect readings to generally be around 80.

KJB


Friday Night through Wednesday:

The upper low currently over eastern TX is expected to be
moving into the Ohio River Valley Friday night broadening into
an elongated trough as it does so. At the same time, a frontal
boundary will be slowly starting to advance southward as a cold
front. While scattered showers (and perhaps an isolated storm or
two) are expected to be ongoing in association with these two
features Friday night, the coverage of showers should be
gradually waning from northwest to southeast heading into
Saturday as the front progresses through the area. That said,
still looks as if a fair coverage of showers and occasional
storms will materialize along and east of I-55 for Saturday with
lesser coverage to the north and west. Outside of the rain,
temperatures on Saturday are forecast to be in the seasonable
range with highs in the lower 80s inland but only in the 60s to
lower 70s near the lake due to onshore winds.

The cold front and the upper trough are expected to move east
of the area by Sunday morning which will allow rain to come to a
close across northern IL and northwest IN as a surface high
moves into the western Great Lakes. However, winds will remain
east-northeast behind the front which will continue to support
60s and lower 70 degree readings along the lakeshore while those
inland once again warm into the lower 80s. A broad upper ridge
is expected to develop across the southwest and central CONUS
Sunday into Monday which will gradually begin to advect warmer
and more humid air into the Great Lakes from Monday onward.
Therefore, expect temperatures to warm through next week with
highs back solidly into the 80s (possible even nearing 90s at
times) including near the lake. Though, lingering onshore winds
on Monday will offer one more day of cooler conditions near the
lake with highs in the 70s (mid-80s inland).

With the building warmth and humidity will also come more
chances for showers and thunderstorms particularly towards the
later half of next week as the upper ridge gets moved into the
Gulf Coast and a more zonal oriented pattern sets up over the
rest of the CONUS with several shortwaves progged to traverse
the pattern. Given the high degree of uncertainty with the
timing and track of each shortwave, the forecast for next week
carries daily chances for showers and thunderstorms. However,
suspect that many dry hours will still be seen in between the
waves so stay tuned as details get refined in the coming days.

Yack

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 631 AM CDT Thu Jun 12 2025

Forecast concerns for the terminals...

- 15-20% chance for isolated showers and/or thunderstorms this
  afternoon mainly south and west of the terminals.

- Another period of scattered showers Friday.


The frontal boundary that moved through the terminals last night
will stall across portions of northern IL and northwest IN
today. While this will cause little impact to the TAF sites, the
boundary may serve as the focus for some isolated showers and/or
thunderstorms this afternoon (15-20% chance) mainly south and
west of a RPJ to JOT line. Since any showers/storms should
remain away from the TAF sites have maintained dry forecasts,
but will watch trends closely. Winds will remain east-northeast
today but will increase slightly this afternoon with occasional
gusts in the 15-18 kt range before easing again this evening.
Otherwise, VFR conditions are expected through tonight.

The upper low over eastern TX will begin to move into the
Mississippi and Ohio River Valleys Friday morning bringing with
it another period of scattered showers and perhaps
thunderstorms. Due to some lingering uncertainty with the exact
arrival timing of the showers, have opted to introduce a PROB30
into the 30-hour TAFs for -SHRA but suspect further adjustments
with future updates. That said, confidence in storm coverage is
somewhat low due to modest instability so have foregone a formal
mention at this time. Otherwise, expect mainly VFR conditions
outside of the showers (potential for MVFR ceilings with
showers) with winds becoming more southeasterly around 10 kts.

Yack

&&

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

&&

$$

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