293
FXUS63 KLOT 092344
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
644 PM CDT Thu Jul 9 2026

.KEY MESSAGES...

- A threat for isolated to widely scattered thunderstorms
  through this evening.

- Mainly dry and increasingly warm weather this weekend onward,
  though it will be cooler lakeside until later next week.

&&

.DISCUSSION...
Issued at 237 PM CDT Thu Jul 9 2026

This Afternoon:

A weak remnant MCV (mesoscale convective vortex) has slowly
pushed across the area through early this afternoon. It appears
that the timing of the disturbance was early enough to curtail
stronger destabilization from a combination of thicker cloud
cover and already marginal mid-level lapse rates of <6C/km.
Forcing on the backside of the MCV, subtle confluence, and a bit
better destabilization south of I-80 recently enabled an uptick
in coverage of smaller footprint pulse type convection. As the
forcing from the MCV pushes farther east, a somewhat subsident
regime may result in the current activity struggling for a bit.
Farther north, the aforementioned more subsident regime as well
as meager low-level convergence from close to due westerly
boundary winds will probably keep convective coverage at a
minimum for a few hours.

Late Today through Tonight:

Based on upstream radar presentation as of this writing, a weak
approaching cold front should provide enough lift for a modest
uptick in showers and isolated to widely scattered thunderstorms.
Winds shifting onshore near the lake from an early evening lake
breeze could plausibly provide modestly a modestly enhanced
focus. However, the weakly forced, weak deep layer shear, and
modest mid-level lapse rate environment does not appear that it
will be conducive to much in the way of storm organization.
Earlier concerns of localized flash flooding appear to be
trending downward even if a few storms materialize into this
evening, as they will likely continue to be smaller footprint
and pulse-type (shorter-lived). Favorable moisture parameters
and high freezing levels would thus be offset by limited areal
coverage and duration of any heavy rainfall. If a more focused
corridor of showers and embedded storms does not materialize by
this evening, with a likely diurnal component to the activity,
the flood threat for the rest of the night should be limited.

Overnight into early Friday as the cold front sags south, light
winds and low dew point spreads may support fog development and
localized visibility below 1 mile. Maintained areas of fog
mention closer to the lake in northeast Illinois and far
northwest Indiana, though confidence isn`t all that high.

Friday Onward:

The sagging front will force the instability axis southward
Friday and Saturday, and with it the threat for any showers and
storms. Have confined chance PoPs to near and south of the
Kankakee River Friday afternoon and evening and then primarily
south of US-24 on Saturday afternoon (which may be too generous).
For the rest of the area, a couple pleasant days with more
comfortable humidity levels, and seasonably warm temperatures
in the lower to mid 80s are in store. Synoptic onshore flow from
surface high pressure settling over the Great Lakes will keep
highs near the lake in the mid 70s to around 80F.

For Sunday into early to mid next workweek, an expansive and
anomalously strong/warm mid-level ridge will establish itself
from the central and northern Plains to the Midwest.
Increasingly warm 850 to 925 mb temps underneath the influence
of the ridge will result in a warming trend away from the lake.
Meanwhile, the surface high pressure will remain in place until
midweek or thereabouts, resulting in daily lake breezes and
associated lake cooling. In addition, dew points and thus
humidity levels will be held in check vs. our previous very warm
to hot stretch. The ridge may become sufficiently flattened
sometime later next week for a return of convective chances.
Until then, a several day stretch of continued drying will help
river and streams to return back to more typical flows.

Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 644 PM CDT Thu Jul 9 2026

Forecast concerns include...

Chance of thunderstorms through late this evening.
Wind shift to northeast this evening.
Low mvfr, possible ifr, cigs/vis overnight/early Friday morning.

A cold front will move across northern IL this evening, shifting
winds to the northeast, with west/southwest winds ahead of the
front. Once winds shift to the northeast, they are expected to
remain northeast for the rest of the period, possibly increasing
into the 10-15kt range Friday afternoon.

Showers and scattered thunderstorms have developed along this
front and are expected to slowly increase in coverage as they
move southeast across the terminals this evening, though overall
coverage remains uncertain. Have maintained prob thunder mention
and adjusted timing later based on current guidance trends but
additional refinement may be needed this evening. Showers may
lingering into the early overnight hours. Scattered showers and
a few thunderstorms will be possible Friday afternoon, but
should remain south of the terminals.

With the frontal boundary nearby and moist low levels, fog will
be possible overnight into early Friday morning, especially west
of the Chicago terminals across northwest IL. Low mvfr cigs and
possibly ifr cigs will also be possible. Overall confidence is
only medium for fog/low cloud trends and only tweaked timing,
though added ifr cigs for RFD. Trends will need to be monitored
overnight. Whatever fog does form should dissipate quickly after
sunrise and cigs will slowly lift through mvfr and into low vfr
by early Friday afternoon. cms

&&

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

&&

$$

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