933
FXUS63 KLOT 100532
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1232 AM CDT Tue Mar 10 2026

.KEY MESSAGES...

- Severe thunderstorms Tuesday afternoon and evening, with the
  potential for very large hail, damaging winds and tornadoes.

- Potential for heavy rain and localized flash flooding Tuesday
  afternoon into Wednesday morning.

- Possible very strong winds (40+ mph) Thursday night/Friday.

&&

.DISCUSSION...
Issued at 250 PM CDT Mon Mar 9 2026

Through Tuesday Morning...

It`s a mild early spring day out there today with temperatures
in the mid 60s to around 70 early this afternoon. These mild
temperatures were made possible by breezy SW winds which have
been regularly gusting to between 20 and 30 mph. A reservoir of
higher theta- e air and marginal elevated instability is
advancing northward into central IL on the nose of a building
LLJ and will extend into southern and southeastern portions of
our CWA this evening. Guidance advects over 1,000 Joules of
MUCAPE over our south and southeast. However, with the low
levels being so warm, there will be appreciable capping to mixed
layer parcels with little forcing around to break it. If
parcels do poke through or precip initiates above the cap, very
dry air aloft should help choke out updrafts. Putting this
altogether, the forecast calls for a low chance for isolated
showers primarily into parts of northwest Indiana this evening
with a pulsey storm or two not out of the question.

Meanwhile, a cold front is dropping southeast across western WI
and northeastern IA this afternoon. The front will advance into
our north early this evening before stalling in the area and
becoming a quasi-stationary front. Guidance favors areas of
largely sub-dense fog this evening and overnight around the CWA.
But a handful of high res camps track some dense fog
immediately along and south of the front. Some fog may linger
into the morning tomorrow before the inversion lifts mid-late
morning. Fog is also favored over southern Lake Michigan this
evening into tomorrow.

The front will drop south of I-80 during the morning before
stalling again into the afternoon. Areas of drizzle may develop
early afternoon where a saturated boundary layer will interact
with some low level lift north of the front. Quite a spread in
high temperatures is anticipated tomorrow on either side of the
front. Middle to upper 70s are forecast in our far south while
temperatures may be stuck in the 40s in our far north and
especially closer to the lake in our north. The rain and
thunderstorm potential, including expectations for severe
weather, can be found in the focused discussion below.

Doom


The Rest of Tuesday into Early Wednesday...

Overview:

Weak surface low pressure of between 1000-1005 mb will be located
near Kansas City, MO at midday on Tuesday. The surface low will
then reach southeast Iowa in the early evening and only slowly
track east-northeast through Wednesday morning, to southern lower
Michigan by midday Wednesday. A backdoor cold front sagging
southward tonight into Tuesday morning will be making inland
progress through Tuesday afternoon before slowing/stalling
somewhere south of I-80. This boundary will mark a very sharp
divide between a much cooler and moist marine influenced air mass
(temps in 40s and 50s and dew points in upper 30s to around 50F)
and with a stable boundary layer to the north and an unseasonably
warm and humid air mass (temps in 70s and dew points in 60s) to
the south. Fog and drizzle may very well develop north of the
slowly sagging boundary, particularly near Lake Michigan. We`ll
have to monitor for at least locally dense fog, similar to what
happened last week.

Where the boundary stalls will ultimately dictate exactly where
an appreciable `all-hazards` surface-based severe threat
(including strong tornadoes) will likely unfold along and to its
south late Tuesday through early Wednesday. To the north of the
boundary, the tornado threat will likely be essentially nil,
though there will still be a threat for large, damaging hail, and
isolated damaging wind gusts punching through the low level
stability. With Lake Michigan water temperatures in the upper 30s,
early spring climatology of the all important surface boundary
position suggests a southward lean from the global ensemble
depiction. This is where the high resolution guidance can often
better resolve the farther inland propagation of the shallow but
dense cool marine layer. And indeed, the 12z CAM guidance (to
varying extents on the specifics), trended farther south with the
surface front late Tuesday, which is the direction we nudged our
temperature and dew point forecast.

Big Picture Convective Trends:

An impressive EML (elevated mixed layer) plume with very steep
mid-level lapse rates will be advected east-northeastward tonight
into Tuesday morning. The presence of an EML is typically quite
important in terms of higher end severe potential (more on that
later), but it also results in formidable capping needing to be
eroded (whether it be MLCIN near/south of boundary or MUCIN
near/north of boundary). There`s meaningful spread in the capping
magnitude across guidance solutions into Tuesday afternoon, owing
to modest at best large scale forcing, with neutral mid-level
height tendencies. It may come down to a subtle 700 mb impulse
being able to cool and moisten the column sufficiently to erode
CIN as early as 2-3PM or so.

Otherwise, the more expansive convective footprint should
correspond with the arrival of stronger forcing by Tuesday evening
and especially overnight. We kept our PoPs in the chance (30-50%)
range by 5-7 PM and then dramatically ramp up Tuesday night. As a
possible caveat here, the subtle nature of the forcing could keep
open warm sector convection into Tuesday evening scattered or
even widely scattered before higher coverage arrives overnight.
Rain and embedded thunderstorms will persist near the surface low
path through early Wednesday, with precip then ending northwest to
southeast Wednesday PM behind the robust system cold front
(details in the Wednesday onward discussion section below).

Severe Threat:

Seasonably strong wind fields will result in supportive effective
bulk shear profiles for severe storms upon convective initiation
(whenever that occurs Tuesday PM). Along and south of the surface
front, the highly favorable deep layer shear profile will be
enhanced by strong low-level destabilization (0-3km MLCAPE of 100+
J/kg) and a looped/curved low to mid level hodograph. Right moving
supercells that remain south of the front will have the potential
for tornadoes, some strong, and large, destructive hail
continuing fairly deep into the night.

Pertinent to the boundary location discussion in the overview,
there appears to be a realistic play for the surface-based severe
threat to focus primarily near and south of US-24. However, with
the inherent wiggle room and uncertainty in this element, plus the
global ensemble guidance still holding farther north in its
frontal position, SPC`s updated day 2 outlook kept the 10% tornado
probabilities just south of I-80. We`ll have a much better idea on
the higher end threat zone informed by observational trends on
Tuesday.

To the north of the boundary, large MUCAPE due to the 7.5-8C/km or
greater mid-level lapse rates and highly favorable effective bulk
shear will present a threat for elevated supercells capable of
large, damaging hail. In addition, isolated severe downburst winds
will be possible even in the presence of a stable boundary layer,
often aided by gravity wave propagation that is not predictable in
advance. The surface low track Tuesday night will probably
temporarily drag the surface front farther north and its
associated surface-based hazards later Tuesday night, though by
then storm mode should be quite a bit messier than just after CI.

Flooding Threat:

Corridors of heavy rainfall and associated flooding are a distinct
possibility, if not probability. Deep, moist convection with 300%
of normal PWATs and the slow system movement through Tuesday night
will introduce the potential for swaths of the area that receive
successive rounds of heavy rainfall (amounts of 2-3" or more
possible in 6 hours). Where these corridors of training convection
evolve will likely also be tied to the exact position of the
surface boundary. If the boundary gets more quickly reinforced
south by initial elevated convection late Tuesday- Tuesday
evening, the training convection may tend to focus primarily south
of I-80. While parts of central Illinois and Indiana are in a D3
drought, this is not typically a significant mitigating factor
when it comes to areal flash flooding.

On the other hand, if the footprint of heavy rain is farther
north and includes more of the Chicago metro, especially the city
and flashy small stream basins in the south suburbs and northwest
Indiana, urban flash flooding potential will commensurately
increase. With the range of plausible outcomes generally
suggesting locations near and south of I-88 having a higher threat
for corridors of flooding rainfall, an ESF (Hydrologic Outlook)
was issued this afternoon.

Castro


Wednesday through Monday...

The back edge of the double-barrelled surface low will work
across the CWA Wednesday morning and drag the front along with
it, moving off to our east by the end of the morning. The
thunder threat should wrap up in our south early-mid morning
with some post frontal showers possible into the afternoon.
Profiles cool enough in the cold advection that some wintry mix
or non-accumulating snow showers may scoot across northern
portions of the area.

Another strong storm system is expected to move across the
northern Plains and upper Midwest Thursday night and across the
northern Great Lakes region Friday. Strong southerly winds will
develop across the area Thursday evening ahead of a trailing
cold front from this storm system which will move across the
area Friday morning. Winds will shift west/northwest behind the
front and continue to be strong on Friday. Still several days
away but given the track and strength of this system, wind gusts
40+ mph are possible. The local area appears to be on the south
edge of the precipitation, which could end as a rain/snow mix
Friday morning.

No significant changes to the model trends for this weekend
into early next week. It still appears active with a system
moving across the area this weekend with the potential for a
rain/snow mix then a pattern shift to colder early next week
with perhaps additional snow chances.

Doom/cms

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1232 AM CDT Tue Mar 10 2026

Primary forecast concerns include...

Wind shift to northeast after daybreak this morning.
Low mvfr/ifr cigs through the period.
Chance of thunderstorms this afternoon/evening.
Potential for fog and ifr/lifr vis at times.

Southerly winds will turn more southwesterly overnight and then
shift north/northeast with a cold front after daybreak. Winds
will turn more northeasterly then easterly later today with
speeds in the 10-12kt range and some higher gusts at times.

A low mvfr cig continues to develop and expand across northeast
IL early this morning as low level moisture continues to
increase from the south. While confidence is low, what guidance
does show this, shows it continuing through daybreak though
there will likely be breaks and perhaps a southern edge that may
work its way north through the terminals. For now, opted to
carry a 1kft cig through daybreak. Cigs are likely to lower into
ifr and possibly lifr later this morning behind a cold front
with only medium confidence for this time period. Low confidence
for cigs lifting back to low mvfr this afternoon.

There is also patchy fog developing across parts of north
central IL, as well as over Lake Michigan. Fog is likely to
expand in coverage early this morning and then when winds turn
northeast off the lake, additional fog may move inland. For now
have held with mvfr vis but this may end up too high and lower
visibilities may be needed with later updates.

Scattered thunderstorms are expected to develop by late this
afternoon. While there is reasonable consensus these first
storms will be just south of the terminals, they will be close
enough to warrant prob thunder mention for ORD/MDW/DPA, tempo at
GYY. Additional thunderstorms are expected this evening and
current tempo mention seems reasonable during this time period.
Any thunderstorms that form may become severe with large hail
the main threat for thunderstorms at the terminals, except at
GYY where all severe threats will be possible. Heavy rain will
also be possible with these thunderstorms.

Outside of the thunderstorms this evening, there may be lifr and
even vlifr cigs along with fog. Confidence is low for how low
visibilities may drop with fog and changes can be expected with
later forecasts.

Most of the thunderstorm activity is expected to be moving east
and southeast of the terminals after 06z with lingering showers
or drizzle and winds turning northerly then north/northwest. cms

&&

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

&&

$$

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