972
FXUS63 KLOT 031155
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
555 AM CST Tue Mar 3 2026

.KEY MESSAGES...

- Warmer and occasionally wet weather is in store from the mid
  to late week period onward. Confidence is higher in more
  widespread rain late Wednesday night into Thursday and again
  late Friday into early Saturday.

&&

.DISCUSSION...
Issued at 320 AM CST Tue Mar 3 2026

Through Wednesday:

We continue to monitor a weak mid-level impulse drifting east
across Iowa and northwest Illinois early this morning which
could bring spotty showers to the area early this morning. A
stout 800-600 mb dry layer has kept this mainly as virga, aside
from an area of deeper saturation in northeast Iowa. This part
of the band of precipitation is expected to track east across
southern Wisconsin and remain north of the area. As low-level
stratus increases in coverage here locally, steepening steep
lapse rates within a saturated DGZ layer may be sufficient for
seeder-feeder processes to support rain punching through the dry
layer on an isolated basis. Accordingly, have maintained the
potential for isolated showers in the forecast early this
morning.

Temperatures have been very gradually moderating over the past
few hours with the majority of the area above freezing, however,
portions of interior northern Illinois, roughly between I-39
and the Fox Valley and north of I-88, is still hovering around
freezing in low-lying areas. Given the expected limited shower
coverage, suspect that the window for patchy slick spots is
closing quickly, but still can`t be fully ruled out on untreated
colder surfaces prior to daybreak. Any sprinkles/spotty showers
will shift east of the area shortly after sunrise with any
additional shower potential expected to remain well south of
I-80 for the remainder of the day.

Farther to the south an axis of warm advective showers and
embedded thunderstorms have developed over parts of Missouri
early this morning. Hi-res guidance lifts the northern periphery
of this activity toward the region through the morning.
Confidence in how far north this activity reaches is on the
lower side, but it felt prudent to maintain rain chances for
areas south of a Pontiac to Rensselaer line mid to late morning.
Additional waves of showers and possible embedded storms are
expected to continue through the afternoon and evening within
the vicinity of an elongated east to west oriented baroclinic
zone and associated convergence axis that sets up across central
Illinois and Indiana. This activity could continue to graze far
southern portions of the forecast area (particularly near and
south of US 24) this afternoon and evening, but could also
remain just south of the area.

As for temperatures today, onshore flow will likely hold highs
in the upper 30s near the lakeshore with lower 40s extending
will inland. Western and southern fringes of the forecast area
could still manage upper 40s to near 50 west of I-39 and south
of US 24.

Looking ahead to tonight into Wednesday morning, hi-res
guidance also favors showers remaining well south of I-80, which
the ECMWF has remained consistent in depicting the past few
days. Have accordingly continued the trend toward lowering
precip chances across much of the area, keeping areas north of
the Illinois/Kankakee Rivers dry through the morning on
Wednesday. Visibility trends will have to also be monitored
during this timeframe, first across central Illinois and Indiana
where low- level moisture pooling could support fog
development. Farther north, if skies manage to clear out there
may be sufficient radiational cooling for shallow fog
development, particularly north of I-88 into Wisconsin. Still
not enough confidence for a formal addition to the forecast yet.

A weak MUCAPE axis may lift north across parts of the area
Wednesday afternoon (mainly south of I-88), which could support
increasing shower coverage and possible embedded storms.
Confidence in the northern extent of showers remains low, with
some model camps remaining south of the area through the entire
day on Wednesday. Temperatures on Wednesday could end up fairly
similar to today, with upper 30s along the Illinois shore, lower
to mid 40s across northeast Illinois. and upper 40s to lower
50s south of I-80.

Petr


Wednesday Night through Monday:

There`s still some uncertainty regarding rain trends Wednesday
night, though highest shower coverage will likely be after
midnight. Despite lingering ensemble spread, suspect that the
still consistent ECMWF/EPS suite (which seemingly will have led
the way prior to Wednesday evening) is on the right track here.
This suggests that surface high pressure over the Great Lakes
will likely continue to exhibit a drying influence through
Wednesday evening and possibly a chunk of the overnight as well,
especially with northward extent (ie. north of I-80).

A neutrally tilted mid-level short-wave tracking toward the mid MS
Valley by early Thursday should finally help shower coverage
expand farther north of weak surface low pressure reflection over
central Illinois. Shower activity will continue into Thursday
morning and then shift east during the afternoon. Mid-level lapse
rates are forecast to be rather steep as the aforementioned
short-wave tracks overhead into Thursday morning, so sufficient
MUCAPE is plausible for embedded thunderstorms and localized
downpours. The modest magnitude of large scale forcing is such
that the setup doesn`t currently appear favorable for widespread
heavy/beneficial rainfall totals, and some locations may end up
missing out relatively speaking. The favored track of the weak
surface low pressure on Thursday will keep cool onshore flow going
into northeast Illinois and far northwest Indiana. We`ll also have
to keep an eye on the potential for fog oozing inland from the
lake as dew points well above current lake surface temps press
northward.

Thursday night into the pre-dawn hours of Friday continues to
appear primarily dry, with lingering ~20% PoPs probably tied to
time-lagged ensemble members. With weak surface high pressure
over the Great Lakes Thursday night, this may end up being a
favorable setup for fog development for inland areas as well
(vs. primarily near the lake during the day). Can envision fog
from a build-down of existing stratus, radiational fog if cloud
cover is less extensive than forecast, or of course both if
there`s only pockets of clearing. The fog potential will be
assessed for formal inclusion in the official forecast with
subsequent updates.

On Friday, mid-level southwesterly flow will strengthen as a mid-
level jet ejects northeast across the Plains into the Upper
Midwest. This will send a low amplitude mid-level shortwave racing
northeastward into the Upper Midwest sometime late Friday morning
or early Friday afternoon, though there is variance in the
guidance regarding the track and strength of this feature.
Scattered showers and isolated elevated thunderstorms (if
sufficient MUCAPE is realized) accompanying this feature may
impact parts of the region into early Friday afternoon. Outside
of the late morning and early afternoon potential though, it
appears there will be a good amount of dry time during the day
(more than implied by the currently high gridded PoPs).

Temperatures on Friday are expected to soar well into the 60s to
around 70F for most through the afternoon as a surface warm front
surges northward across Illinois and Indiana. However, as is
typical this time of year, onshore flow ahead of this front across
far northeastern IL (including parts of Chicago) may keep
conditions much cooler through much of the day until the warm
front clears this area. The combination of these very warm
temperatures and unseasonably high dew points, into the upper 50s
to near 60, will support an unstable and strongly sheared warm
sector in the wake of the earlier day convection. However, it
appears there will not be much of a focus for additional
convection in our area following the earlier day impulse.
Instead, shower and thunderstorm chances and coverage look to be
the greatest late Friday night into Saturday morning in
association with a cold frontal passage. The currently
unfavorable diurnal timing of the cold front passage may also
limit the threat for well organized convection locally.

Rain chances will come to an end following the cold frontal
passage on Saturday, at least for a few days. Temperatures will
cool down a bit immediately behind the front Saturday PM, but
generally remain well above average through early next workweek.
For areas that don`t receive much rain in the upcoming stretch,
we`ll need to monitor for elevated fire danger on Sunday due to
mild temps paired with fairly low dew points and gusty southwest
winds. Current medium to long-range ensembles point towards a
stronger cold front passage in the wake of a possible formidable
mid-latitude cyclone with potentially widespread precipitation mid
next week, bringing a return to colder conditions by later in the
week/mid-March.

Castro/KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 555 AM CST Tue Mar 3 2026

Main Items of Note:

- Lower CIG trends

- Some potential for BR/fog tonight into early Wednesday

Any additional showers will likely remain well south of the
terminals the rest of this TAF period. Predominantly MVFR CIGs
are expected until scattering early this evening. Light winds
and mostly clear skies tonight may be conducive for light fog/BR
development, especially away from Chicago. Our current thinking
is that any guidance depicting higher coverage of dense fog
late tonight is likely unrealistic. MVFR CIGs may then return
sometime Wednesday morning.

East to east-southeast winds this morning will become
northeasterly this afternoon due to lake influence. Easterly
winds around 10 kt are expected after sunrise on Wednesday.

Castro

&&

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

&&

$$

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