781
FXUS63 KLOT 180500
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1100 PM CST Mon Nov 17 2025

.KEY MESSAGES...

- Rain and drizzle expected tonight through Tuesday.

- Another period of rain possible towards late week.

&&

.DISCUSSION...
Issued at 254 PM CST Mon Nov 17 2025

Through Tuesday:

A surface high continues to slowly move east across the area
this afternoon as a shortwave trough ejects into the central
Plains. This shortwave will pivot into the Mississippi Valley
late tonight into Tuesday morning and then across northern IL
and northwest IN Tuesday afternoon. As a result, the developing
rain showers in IA and MO will lift into our area around
midnight and persist through Tuesday morning as the system moves
through. Given that forecast soundings show the environment to
be largely above freezing, expect precipitation to remain as
rain through its duration but there will be some modest
instability aloft which may support some instances of graupel as
rain begins. Additionally, a stray lightning strike cannot be
ruled out either though the best chance for such will likely
stay in central IL closer to the surface low.

While the broader rain will gradually taper through Tuesday
morning as the mid-level dry slot moves overhead, some lingering
low-level moisture in the presence of some modest ascent should
allow some occasional light showers and drizzle to persist
through Tuesday afternoon. Otherwise, expect cloud skies and
easterly winds around 10-15 mph. Temperatures on Tuesday will be
a bit cooler than today with highs in the low to mid-40s
areawide.

Tuesday night through Monday:

The aforementioned shortwave trough will eject to the east
Tuesday evening as mid-level height rises move into the Great
Lakes. The height rises should cut off the ascent and allow the
light showers/drizzle to taper by mid-evening. While dry
conditions are then expected to prevail through the middle of
the week, a plume of low-level moisture is forecast to get
trapped beneath the subsidence inversion. As a result a
prevailing stratus deck is expected to remain in place through
Wednesday night and possibly through the day on Thursday. With
the lower sun angle and cloud cover, temperatures between
Tuesday night and Wednesday likely won`t vary much (maybe 5- 8
degrees or so) with highs currently forecast to be in the
mid-40s at best. Depending on how quickly the low-level moisture
erodes on Thursday will determine whether Thursday is another
cool and gloomy day or if temperatures are able to rebound into
the 50s. For now the official forecast has leaned towards the
clouds scattering and a warmer solution, but this could change
as we get closer so don`t be surprised if temperatures verify
several degrees cooler for Thursday.

Heading into the later half of the week, our attention turns
towards the evolution of the upper low and associated broad
trough that is just offshore of southern California as of this
writing. This trough/low is forecast to slowly meander into the
southwest CONUS through Wednesday and possibly attempt to phase
with another trough that will be diving out of the Pacific
Northwest on Thursday. As this feature begins to eject into the
southern Plains on Thursday, another shortwave trough is progged
to pivot across the northern Great Lakes. It is during this
Thursday through Friday timeframe that the forecast becomes very
uncertain. The reason is because if the southern trough moves
quick enough it may limit the overall moisture return into
northern IL and northwest IN and thus keep the bulk of any
associated precipitation to the south of our area in the Ohio
and Tennessee River Valleys. However, if the trough is slower
then sufficient moisture may be able to return ahead of this
system and the northern stream trough and allow precipitation to
return to the area as early as Thursday. Though, any
precipitation at this point looks to fall mainly as rain due to
temperatures generally above freezing.

At this point ensemble guidance is split on which of these
aforementioned scenarios will come to fruition and thus whether
or not we see any rain Thursday and/or Friday is very uncertain.
That said, it seems the general trend is for rain to stay more
to our south which is why the NBM POPs have once again trended
downward. For now have opted to maintain the 20-50% POPs offered
by the NBM for late Thursday into Friday in case the wetter
solution pans out but suspect if the drier trend continues we
may be able to cut POPs all together in the next couple days.
Regardless of how this period pans out, temperatures look to
remain seasonable through the weekend with highs in the 40s to
lower 50s with overnight lows in the 30s. On that note the
weekend does look dry with high pressure forecast to move back
into the area.

Yack

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1100 PM CST Mon Nov 17 2025

Main Concerns:

- Periods of rain tonight/early Tuesday and periodic showers
  with occasional drizzle until early Tuesday evening may knock
  visibility down at times.

- IFR to MVFR CIGs likely late tonight through Tuesday evening.

- A non-zero chance for an isolated thunderstorm on Tuesday.

A weather system will impact the area overnight through Tuesday
and bring an end to the quiet/VFR flying conditions. Widespread
light to occasionally moderate rain/showers will develop
overnight, with MVFR VSBY possible at times into the morning.
The steady rain should then give way to a showery and drizzly
regime sometime after daybreak Tuesday morning, and there`s a
chance for the drizzle to linger into the early evening (later
than in current TAF). Potential is there for VSBY temporarily as
low as IFR in persistent drizzle during the late morning, for
which PROB30 mention may need to be considered in the TAFs with
the next amendment. In addition, forecast soundings suggest
enough instability aloft to possibly generate a couple TS in the
area, which will need to be assessed for later updates.

Regarding CIGs on Tuesday-Tuesday evening, the pattern and time
of year favor them deteriorating to IFR, supported by NAM and
RAP/HRRR forecast soundings. Some guidance, particularly the
MAV/LAMP MOS and probabilistic LAMP, still aren`t excited about
prevailing IFR, which continues to lower confidence a bit.
Assuming our thinking is on the right track with prevailing IFR
developing, convective activity (SHRA and any isolated TS) may
occasionally scatter the IFR CIGs. CIGs may then improve some
later Tuesday night. Winds will be easterly (5-15 kt range)
through late in the day Tuesday, shifting northeast Tuesday
evening. Sporadic gusts in the 15-20 kt range are probable.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 6 AM Tuesday to 3 AM CST Wednesday
     for the IL nearshore waters.

&&

$$

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