Waukegan, Illinois Weather Forecast Discussion

524
FXUS63 KLOT 191942
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
242 PM CDT Fri Sep 19 2025
.KEY MESSAGES...
- Clusters of scattered showers and some thunderstorms are
  expected through Saturday morning, initially around and west
  of the Fox River Valley late this afternoon and evening, and
  generally east of I-55 overnight into Saturday morning. Any
  shower or storm through this evening will be capable of
  producing gusty winds.
- Periodic chances for showers and some thunderstorms through
  early next week, though there will continue to be plenty of
  dry hours too.
- Afternoon temperatures will remain above normal through the
  Autumn Equinox (Monday at 1:19 PM CDT), though not quite as
  warm as they`ve been the past few to several days.
&&
.DISCUSSION...
Issued at 241 PM CDT Fri Sep 19 2025
Through Saturday Night:
A messy forecast is in store through Saturday as a series of
weak perturbations rotating around an upper-level low to the
west interact with ribbons of mid-level moisture marginally
favorable for precipitation. Mid-afternoon regional analysis and
radar/satellite data indicate a trough axis arcing from far
eastern Missouri north and westward to the parent low over
eastern Nebraska. Plenty of mid and upper-level cloud cover has
steadily expanded eastward across Illinois through early
afternoon, but not before abundant morning sunshine and modest
low-level mixing allowed temps to rise into the mid to upper 80s
(locally 90) for much of the area.
Have seen several attempts and stronger showers and some
thunderstorms across central Illinois early this afternoon, but
a rather dry airmass on either side of a narrow corridor of mid-
level moisture has limited coverage and growth so far this
afternoon. This axis is east of the main trough and well east of
higher low-level moisture west of the Mississippi River.
However, veering low-level winds have become more favorable for
gradual moisture advection toward western portions of the CWA
this afternoon.
Broader expectations are for the current axis of struggling
showers over central Illinois (as far north as Bloomington as of
2pm) to continue to drift northward ahead of the main trough
over the next couple hours before increasing in coverage and
intensity as they interact with the trough and increasing low-
level moisture. This should result in an area of scattered
showers and some embedded thunderstorms to affect areas around
and west of the Fox River Valley through mid-evening. A decent
DCAPE reservoir and high cloud bases mean any shower or storm
will be capable of producing gusty winds, with outflow
boundaries possibly extending well away from mature or decaying
cells.
A trailing wave over Missouri will then shift northeastward
toward the area while overtaking the then highly-sheared and
stalled remnant trough over the southeast half of the CWA
overnight through mid-morning Saturday. Another area of
scattered showers and some storms is expected during this
period, with overall coverage less clear given marginal forcing
and the continued limited spatial extent of favorable moisture
profiles. However, mostly unidirectional and seasonably weak
deep-layer flow nearly parallel to the slowing trough will
support slower/training showers and storms in narrow SSW to NNE
corridors.
After a lull in overall activity late morning through mid-
afternoon, the combination of another wave clipping the
northwest CWA and higher low-level moisture over the area will
support an increase in potential for surface-based convection
across northern Illinois mid afternoon into the evening.
Kluber
Sunday through Friday:
Any scattered showers leftover from late Saturday night may
linger past sunrise on Sunday. There could also be an isolated
storm until mid morning mainly near/east of I-65 in Indiana.
During Sunday afternoon, forcing mechanisms continue to look
nebulous, with the main large scale height falls and DCVA
(differential cyclonic vorticity advection) focusing north of
the Wisconsin state line. The potential remains for
convectively augmented MCV(s)/flow-enhancement to serve as a
trigger for additional showers and isolated thunderstorms, as
shown on some of the recent cycles of the NAM. However, this
element has little/no predictability at this range.
The deepest boundary layer moisture may tend to be shunted off
to the east a bit as well, and as such the highest blended PoPs
(~50%) are focused into portions of northwest Indiana, with
generally 20-40% chances elsewhere. Given the modest forcing,
marginal lapse rates, and potential for extensive cloud cover,
there is a realistic scenario for little/no convective re-
development in the afternoon. Finally, if any thunderstorms are
able to develop there`s a low chance threat, albeit one worth
monitoring, for a few stronger storms, mainly into parts of
northwest Indiana. This would also be conditional upon
sufficient destabilization paired with sufficiently strong
shear.
Intermittent shower and thunderstorm chances will persist Sunday
night through Tuesday as additional disturbances ripple through
the west to northwesterly flow aloft. A chaotic upper pattern
into the middle and end of next week will likely continue to
result in lower-than-typical forecast confidence. There`s some
modest signal in the extended guidance for at least a brief
return to drier conditions (especially near/north of I-80) in
the wake of a cold front towards midweek, but depending on the
influence of another upper low towards the end of the week, this
could end up being short-lived.
Temperatures this upcoming week will start out solidly above
normal (along with fairly humid conditions as well), with highs
well into the 70s to near 80F through Tuesday, then trending
closer to normal and a bit less humid in the mid to late week.
Castro/Carlaw
&&
.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1254 PM CDT Fri Sep 19 2025
- SCTD -SHRA and ISOLD TSRA expected in and around the terminals
  from late this afternoon/early this evening at times through
  Saturday.
Scattered showers and isolated thunderstorms are expected to
develop this afternoon across western and central Illinois.
While this activity is will be moving mostly northerly, it is
expected to slowly spread east this evening into the immediate
Chicago area. While there will likely be some ISOLD TSRA around,
confidence in a TSRA directly impacting one of the Chicago area
terminals is a bit too low to justify going with a TEMPO. The
PROB30 nicely covers the time period with the highest
probability for a thunderstorm at the terminals. There will
likely be a break in the rain developing Saturday morning into
the early afternoon, but additional SCTD SHRA/TSRA could develop
later Saturday afternoon.
Cloud bases should remain fairly high, so largely VFR conditions
are expected this TAF cycle. Any heavier shower or storm could
briefly reduce VSBY to MVFR and possibly even IFR.
- Izzi
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Air Quality Alert until midnight CDT tonight for INZ001-INZ002-
     INZ010-INZ011.
LM...None.
&&
$$
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NWS LOT Office Area Forecast Discussion