142
FXUS63 KLOT 012337
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
537 PM CST Sun Nov 1 2026

.KEY MESSAGES...

- Periods of showers or sprinkles continue this afternoon.
  Additional showers and drizzle possible this evening and
  through the day on Monday.

- Greatest chances for more widespread showers and perhaps a few
  thunderstorms late Tuesday afternoon and evening/early
  overnight.

- Warmer conditions on Tuesday expected to eventually trend
  slightly below average by next weekend.

&&

.DISCUSSION...
Issued at 153 PM CST Sun Nov 1 2026

Broad mid-level troughing across the region, combined with
numerous embedded perturbations and an expansive mid and upper-
level cloud deck will continue to yield intermittent sprinkles
or light showers across the area today. Guidance suggests there
may be an additional flare up of light showers this evening
associated with a modest increase in 295-300 K isentropic
upglide. Later this evening and overnight, deep-layer moisture
will shift east of the area as lower-level moisture surges out
of central Illinois. As low stratus arrives, drizzle may
develop and could persist through Monday morning. While an
additional plume of moisture above 600 mb will arrive Monday
afternoon, model soundings show a persistent dry wedge in place,
and this may end up resulting in periods of drizzle just
continuing intermittently through the rest of the day. Have cut
high temperatures several degrees under NBM-delivered values
(generally in the low 60s), and it`s possible these may still be
a few degrees too warm if cloud cover and drizzle remains
persistent and widespread through the day. A tightening pressure
gradient will result in a gradual increase in southeasterly
breezes through the day.

On Monday evening and overnight, a robust shortwave will round
the base of a long-wave upper trough and will eject out across
the Texas/Oklahoma Panhandles. Strengthening southwesterly flow
off the deck will lead to increasing warm advection which will
maintain steady south to southeasterly breezes across the region
through the night. Temperatures will likely hold steady or even
slowly rise through the night. Most of the large scale forcing
for ascent and attendant instability is forecast to remain west
of the Mississippi River during this time. That said, a few
waves of showers may develop and push across the region within
the burgeoning warm advective regime.

The primary surface low is forecast to slowly progress across
the Upper Mississippi Valley on Tuesday. As this takes place,
initial sprockets of mid-level vorticity and associated height
falls suggest large scale forcing will gradually increase across
the area through the afternoon hours. This will likely result in
an increase in shower and possibly some thunderstorm coverage,
particularly west of the Fox Valley. The temperature forecast
is a bit tricky as cloud cover looks to be expansive, but this
will probably be offset to some degree by strengthening
southerly winds, possibly gusting near 35 mph at times. Have
trimmed highs a few degrees near and west of I-39, but felt NBM-
delivered temperatures in the low to mid 70s farther east look
appropriate at this point.

The most robust upper-level dynamics are forecast to arrive in
our area Tuesday evening, during which time a notable uptick in
NE/SW oriented 850-600 mb frontogenesis is progged to develop in
the vicinity of the I-55/57 corridors. A period of steadier
showers and a few embedded thunderstorms may develop in this
corridor. The overlap of stronger jet forcing looks maybe just a
bit too brief to raise a widespread heavy rainfall concern,
although some localized corridors of enhanced precip amounts
will certainly be possible wherever the main frontogenetic
forcing develops, particularly if this ends up stalling and
pivoting a bit more.

Showers may linger into Wednesday morning but coverage should
tend to diminish with time. Low-level lapse rates will increase
during the afternoon, and given the presence of the main upper-
low still hanging around overhead, some renewed scattered shower
development can`t be ruled out. Gusty southwesterly winds
(perhaps near 30-35 mph) will be possible on Wednesday.

Confidence in forecast details then decreases mid to late week,
due to model differences in the further evolution of the slow-
moving upper low across the region - complicated somewhat by the
degree of phasing with a northern stream short wave across the
upper Midwest/northern Lakes. Overall, the Wednesday night-Friday
period continues to look at least intermittently unsettled as
the closed upper low and occluded surface system track slowly
east across the region, though some timing differences linger in
the guidance at this distance. While no strong intrusion of
colder air is evident at this time, temperatures do look to
eventually cool to/slightly below average on the back side of
this departing system.

Carlaw/Ratzer

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 537 PM CST Sun Nov 1 2026

Forecast concerns include...

Low mvfr cigs, possible ifr cigs, Monday/Monday night.
Chance of showers/drizzle Monday.
Gusty south/southeast winds Monday/Monday night.

Vfr cigs are expected through the early overnight hours and then
low mvfr cigs are expected to develop and spread north across
the terminals around/after daybreak Monday morning. Low mvfr
cigs are then expected to continue through Monday night. There
may be ifr cigs mid/late Monday morning when isolated showers
and patchy drizzle will be possible. Ifr cigs will then be
possible again Monday night into Tuesday morning. Low confidence
for ifr cigs and current prob mention for both drizzle and ifr
cigs seems reasonable for now. There may also be isolated
showers at any time through Monday night.

East/southeast winds under 10kt this evening will turn more to
the southeast this evening and to the south/southeast by
daybreak. Wind directions are expected to remain south/southeast
into Monday evening as speeds increase into the 12-15kt range
and gusts into the 20kt range develop by late Monday morning or
early Monday afternoon. Wind gusts into the lower 20kt range
will likely continue Monday night as directions turn more
southerly. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 6 PM Monday to 6 AM CST Wednesday
     for the IL nearshore waters.

&&

$$

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