787
FXUS63 KLOT 160534
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1234 AM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Multiple rounds of thunderstorms may occur in the general
  region Tuesday through Wednesday evening. Some storms may be
  severe and have torrential rainfall, particularly on
  Wednesday. Many (most) hours will be dry.

- Hot and humid conditions are on track to arrive next weekend.

&&

.DISCUSSION...
Issued at 225 PM CDT Sun Jun 15 2025

Through Monday night:

A primarily quiet short-term period still appears probable for
most of the area, with a possible exception late Monday night in
parts of far northern Illinois.

It`s a weak MCV "fest" mainly west of the MS River this afternoon,
with the nearest of these from eastern Iowa to southwest
Wisconsin. Exceptionally weak flow of 5-10 kt at 500 mb and only
up to 20 kt at upper jet level will result in this feature only
slowly drifting east-southeast from its current position through
Monday morning. Partly to mostly cloudy skies through the night
due to the upstream MCVs will result in lows for most locations
in the lower to mid 60s, just a bit above normal for the date.

A modest flare up in showers may occur later overnight to the
northwest of the CWA from the closest MCV, and some of these may
sneak into areas west of I-39 in northwest Illinois Monday
morning. Not currently expecting lightning to accompany any
morning showers in the far northwest CWA with little/no MUCAPE
progged. Monday afternoon, another weak impulse should cross the
MS River, with the initial remnant MCV over central Illinois.
Really the only modest destabilization progged for the local area
Monday afternoon is west of I-39 in northwest IL and south of US
Highway 24. An isolated shower or thunderstorm or two can`t be
ruled out in these areas.

Otherwise, expect a partly cloudy, very warm (highs in the mid-
upper 80s), and moderately humid (dew points in the 60s) start to
the workweek inland of Lake Michigan. Light southeasterly
synoptic winds will turn onshore near the lake as a lake breeze
takes shape by midday. This will keep highs near 70F along the
immediate shore and in the 70s a few to several miles inland.

A MCS should develop over the upper MS River Valley Monday evening
and then push southeast. Decreasing MUCAPE with southeastward
extent, marginal deep layer effective shear, and poor diurnal
timing point towards this possible MCS steadily weakening before
it can reach portions of far northern Illinois. However, there`s a
small chance, if the MCS becomes forward propagating that it could
push into the far northern CWA on a still weakening trend, but
enough of a punch to be accompanied by some lightning, localized
downpours, and gusty outflow. Introduced slight/~20% chance PoPs
for areas near/north of a Harmon (southwest Lee County) to Lake
Bluff IL line to account for this currently unlikely (but worth
some mentioning) scenario. It will be a warm and muggy night
Monday night with lows in the mid to upper 60s.

Castro


Tuesday through Sunday:

The upper-level pattern across the Central United States
Tuesday through Wednesday will be characterized by broad zonal
(west to east) flow with embedded shortwave-length
troughs/vorticity maxima. Meanwhile, the surface pressure
pattern will be dominated by a broad Bermuda high over the
middle Atlantic and troughing across the southern Plains. Such a
pattern will be favorable for warming temperatures and humidity
levels, altogether supporting episodic thunderstorm events
(including severe weather) from the Plains to Midwest.

Owing to cascading influences of successive convective events
on the evolution of each subsequent shortwave and the
integrity/position of the instability reservoir, forecasting
when and where thunderstorms will occur as well as consequences
on temperatures and cloud cover in this type of pattern can be
an unforgiving endeavor more than 48 hours ahead of time. With
that said, do still see a signal for a convective event locally
in the Tuesday afternoon/Tuesday night timeframe, followed by
another in the general region in the Wednesday afternoon
timeframe. In addition, there remains a signal that convection
Tuesday/Tuesday night may act to offset part of area from the
peak in coverage of thunderstorms on Wednesday, though this is
obviously an item of (very) low confidence. In all, the message
is that the Tuesday through Wednesday timeframe will feature
warming temperatures and humidity levels, as well as periods of
thunderstorms in the broad Midwest region.

Toward the end of the week and into the weekend, ensemble model
guidance exhibits an unusually strong signal for deep troughing
to develop across the western United States and pronounced
ridging to the east. As this occurs, a plume of very warm and
humid air originating over the Plains will shift eastward and
encompass the Lower Great Lakes. Ensemble mean high temperatures
nose into the low to even mid 90s by this weekend, which with
dew points climbing above 70F will result in afternoon heat
indices exceeding 100 degrees. Of course, such a pattern may
attracts additional clusters of showers and thunderstorms, which
may delay the onset of heat. At any rate, the message for the
end of the week and beyond is that the first instance of summer
heat and humidity is on the horizon.

Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1234 AM CDT Mon Jun 16 2025

Key Aviation Messages for the current TAF period:

- Less than 30 percent chance for a shower/storm at KRFD

VFR conditions are expected through the TAF period. Winds are
expected to be light and northeasterly, with the potential for
even variable directions during the pre-dawn hours. After
sunrise, winds are expected to shift to the southeast and
eventually south-southwest after 00Z. However, wind speeds
should be around 10 knots in the afternoon, and therefore no
impacts expected to terminals.

There are two opportunities for shower chances near KRFD
today. First, there is a weak disturbance over SW Wisconsin.
Perhaps a brief shower develops near/at the KRFD terminal this
morning, but confidence is low. Additionally, instability and
moisture will increase through the afternoon away from the
Chicago Metro area. This could allow for isolated showers and
storms late afternoon/early evening. However, with both the
morning and evening scenarios, the chance for precip is less
than 30 percent and thus was kept out of the TAF presently.
There is no precip expected at Chicago terminals.

DK

&&

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

&&

$$

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