635
FXUS63 KLOT 120146
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
846 PM CDT Wed Jun 11 2025

.KEY MESSAGES...

- Thursday 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.

&&

.UPDATE...
Issued at 846 PM CDT Wed Jun 11 2025

We find a complex of strong to severe thunderstorms pushing
across northeast and east-central IA this evening. These storms
formed beneath an upper shortwave and along a quasi-stationary
front oriented west-east across north-central IA and right
along the IL/WI state line. This activity had been expanding
southward into the open warm sector with the help of some
outflow forcing, but this trend has really slowed down as of
late. A number of convective-allowing models had been resolving
such a trend, and a large majority of them suggest that the
southern extent of the activity will actually retreat back north
as diurnal cooling depletes instability and high pressure to
our south further impedes on the better thunder environment
closer to and east of the Mississippi. So while recent radar
trends appear to be tracking storms right toward far northern
IL, there is support for this activity to just miss our CWA to
the north later this evening. Satellite trends also show storm-
tops steadily coming down. But that`s not to say that it can`t
happen; we`ll have to keep a close eye on how the activity
trends as it nears the river. If storms do maintain themselves
across our northern- most counties, they could feature some
small hail and strong gusts of wind, but parameters on CAM
soundings even across far southern WI do not look very
supportive of severe convection later this evening. Timing on
any activity across our north would be late this evening
stretching into the early part of the overnight. All in all, the
forecast in the short term is in solid shape with no noteworthy
changes made.

Doom

&&

.DISCUSSION...
Issued at 253 PM CDT Wed Jun 11 2025

Through Thursday:

A weak west to east oriented cold frontal boundary will gradually
sag southward from southern Wisconsin tonight, reaching down to
about the I-80 corridor by early Thursday. Meanwhile, a mid-level
impulse over southwest MN this afternoon will push east-
southeastward into central lower Michigan later tonight. The
shortwave trajectory and very dry air below 600 mb with
moisture profiles not expected to improve much if any
(prohibitive MUCIN) are expected to result in convection
remaining focused north of far northern Illinois tonight. With
that said, still can`t completely rule out a weakening
shower/thunderstorm sneaking into the IL/WI state line area
later this evening (~20% chance). Outflow from storms to the
north over Wisconsin and over the lake may result in a temporary
push of breezy northeast winds into northeast IL north of the
sagging frontal boundary. Overnight lows will be seasonably
warm, in the lower to mid 60s (locally upper 60s in/near
Chicago).

The aforementioned cold front will be enhanced some by the still
cool Lake Michigan waters on Thursday. As such, high temperatures
will be ~20F+ cooler along the lakeshore tomorrow versus
today`s highs, paired with northeast winds in the 10-20 mph
range. It will be another very warm day inland though with highs
in the mid to upper 80s, along with increased humidity levels
(dew points into the 60s).

A split mid-level flow regime, along with very weak flow aloft
locally and 700-500 mb RH remaining below 30%, will translate to
primarily dry conditions for most of the area on Thursday. The
possible minor exception to this will be near the backdoor cold
front as it pushes inland through the afternoon paired with dew
points pooled as high as the mid 60s near the boundary. Once
capping erodes from afternoon heating, can`t rule out a few
isolated t-storms (~20% chance) across interior northern/north
central IL. Aside from this small but not-zero convective
chance, temperatures will steadily cool behind the backdoor
front into Thursday evening, particularly closer to the lake.

Any isolated slow moving showers/storms out over the western 1/3
or 1/4 of the CWA Thursday evening will dissipate. Then overnight,
some isolated showers may push into the far southern CWA on the
northeastern fringes of closed mid-upper level low pressure over
Missouri. 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.

Castro

Thursday Night through Wednesday:

Upper low currently over the southern Plains is still progged to
weak to an open wave as it tracks slowly toward the northeast
toward the mid Mississippi and lower Ohio Valley later this
week. Scattered showers and perhaps a couple of isolated
thunderstorms will accompany this weakening wave as it moves
north, with the primary question being how far north this
activity will get Friday into Saturday. For now, opted to
maintain the NBM pops for Friday through Saturday, though given
latest guidance trends those may be too aggressive with much of
that time period possibly ending up rain free, particularly
northern CWA.

In the wake of that decaying southern stream upper low and a
weak northern stream shortwave trough, Canadian high pressure
looks to build into the western Great Lakes for the second half
of the weekend with dry conditions expected. Peering ahead into
next week, it looks as though a fairly zonal flow will set up
through at least the first half of the week with the potential
for subtle shortwaves to ripple through and possibly become
convectively enhanced. Unfortunately, timing any of those lower
amplitude or convectively enhanced features isn`t currently
possible at this distance, so maintaining some pops each day is
best course of action at this point.

Weak frontal boundary is expected to be in the area Thursday
night and Friday, with lake enhancement likely keeping the
effective boundary south and west of the southern tip of Lake
Michigan. Biggest temp gradient with this boundary should be
near the lake where marine layer will keep temps cooler. This
boundary should push south of the area later Friday night into
Saturday with drier and slightly cooler Canadian air mass
spreading into the area in its wake. Low confidence on which
side of the boundary our area will be on through the first half
of next week with some potential for convection to push the
boundary farther south than progged.

- Izzi

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 629 PM CDT Wed Jun 11 2025

The main avn weather concerns for the 00Z TAF period include:

* A slight chance for a shower or thunderstorm late this
  evening, primarily at RFD.

SW winds will subside to below 10 kt early this evening before
turning to a NE direction late tonight, likely going variable at
around 5 kt for a few hour period in the process. Expect ENE
winds near 10 kt gusting into the teens kt during the afternoon
on Thursday before subsiding by mid-evening.

Meanwhile, a complex of showers and thunderstorms will move
across lower WI late this evening. While a majority of this
activity is expected to pass north of the TAF sites, it`s
possible that a passing storm clips the airfields, particularly
RFD. Chances are too low to include any mention in the TAFs,
however. If this were to occur, timing looks like late this
evening near RFD and around, if not shortly prior to, 06Z should
a storm move over the Chicago sites. VFR is anticipated
throughout the period.

Doom

&&

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

&&

$$

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