Weavers Weather

988
FXUS63 KLOT 062348
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
648 PM CDT Mon Oct 6 2025

.KEY MESSAGES...

- Much cooler conditions will settle in tomorrow and remain into
  the end of the week.

- Expect a few waves of showers and some embedded thunderstorms
  this afternoon through early Tuesday morning.

&&

.DISCUSSION...
Issued at 250 PM CDT Mon Oct 6 2025

Early this afternoon, we`re seeing a handful of showers, some
heavier, and a couple of embedded thunderstorms popping up
around our CWA. These are forming just ahead of a cold front
that`s pushing across northwest IL as of 2 PM. Guidance does not
have a good handle on this activity as it develops out ahead of
the more effective boundary, but model soundings do show plenty
of support for such activity to continue through the afternoon
here ahead of the front as it makes headway into the CWA.

Thus far, storm coverage has been rather isolated amid these
showers. Expectations are that shower and storm coverage will
expand into the late afternoon and evening. Guidance is in good
agreement that moisture pooling ahead of the front will result
in a degree or two jump in dewpoints over the next couple of
hours. This should give parcels uncapped access to over 1,000
Joules of MLCAPE by late this afternoon. A couple of stronger
cells can`t even be ruled out with latest RAP mesoanalysis
resolving 35 to 40 kt of effective shear near the boundary. The
front will gradually progress southeastward into the evening,
but looks to get hung up and become qusi-stationary somewhere
across the Chicago metro overnight before pushing onward early
tomorrow. The highest thunder coverage and greatest strong storm
potential will be found near and just ahead of the front
through the evening hours. Diurnal cooling will chip away at
SBCAPE into the night, but additional storms and heavier showers
will remain possible through the night near and southeast of
the front.

Behind the front, densely scattered to widespread showers are
anticipated through the night. A few storms will be possible
here and there behind the front with some elevated instability
still in place and support from a departing upper jet max, but
forecast soundings are more reminiscent of just heavier showers
vs widespread embedded thunder. These showers are likely to
still be festering around the metro into early tomorrow, but
should push east of the metro area by mid-morning and out of our
CWA altogether by the end of the morning.

A big push of cold low level air will feed in behind the front
resulting in a much cooler day tomorrow. 925mb temps will drop
nearly 10C (18F) between this afternoon and tomorrow afternoon.
Highs are forecast to only reach the middle and upper 60s,
possibly nearing 70 in spots. While this sounds quite cool
compared to recently, these sorts of values are much closer to
climatological norms for early October. The day will begin
beneath mostly cloudy skies with those showers still working out
of the area, but cloud cover should thin out from NW to SE
through the day and should allow much of the area to see some
good sunshine during the latter part of the day.

After the upper trough axis swings across on Tuesday, we`ll
find ourselves in a quiet split flow regime through the end of
the week. High pressure will meander about the Great Lakes
keeping the cooler air pumping into the region from the north
through the middle of the week. Widespread 60s are likely
through at least Thursday. Some milder return flow should then
warm things up a bit closer to this weekend. Ensemble PoP
guidance begins to light up again this weekend after the high
ejects to the NE US and another wave looks to track across the
region, but there is even stronger support for dry conditions
beyond today to prevail into early next week.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 648 PM CDT Mon Oct 6 2025

Forecast concerns include...

Wind shift to north/northeast early this evening.
Chance of thunderstorms this evening and overnight.
Low mvfr cigs, possible ifr cigs this evening into Tues morning.

A cold front is moving across far northern IL currently and will
shift winds to the north/northeast shortly at ORD/DPA and within
the next hour or so at MDW/GYY. Some gusts into the 15-20kt
range are possible and then winds will diminish some and
directions may turn back northerly later this evening with
north/northeast winds then expected Tuesday with gusts to 20kt
possible Tuesday morning.

Confidence is decreasing for thunder coverage and timing. Some
of the latest guidance is now suggesting this evening could have
just isolated coverage for showers and thunder. While showers
and even a period of rain has looked more likely overnight,
early Tuesday morning, there is now a trend for at least
isolated thunder overnight. Opted to maintain the current prob
thunder mention for this evening and monitor trends but it is
possible updates will be needed to reduce precip this evening
and possibly add thunder for the overnight hours. The rain is
expected to end from northwest to southeast during the mid
morning hours Tuesday.

Low mvfr and ifr cigs are moving south behind the cold front,
along the Lake Michigan shore. Confidence is low for how low
these cigs will be when they reach ORD/MDW. Added mvfr cigs in
the prob with scatter ifr mention and will need to monitor
trends. Prevailing mvfr cigs are likely by late evening and will
continue through late Tuesday morning. A period of prevailing
ifr cigs is possible but only medium confidence and if showers
are more widespread overnight, as recent trends suggest, that
may prevent long duration ifr cigs. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 1 AM Tuesday to 3 PM CDT Wednesday
     for the IL nearshore waters.

     Small Craft Advisory from 4 AM Tuesday to 10 AM CDT Wednesday
     for the IN nearshore waters.

&&

$$

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