100
FXUS63 KLOT 180005
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
705 PM CDT Sun May 17 2026

.KEY MESSAGES...

- Additional rounds of showers and thunderstorms Monday through
  Tuesday, some of which could be severe at times.

- Summer-like warmth and breezy winds at times will prevail
  through Tuesday before cooler temperatures return for the
  middle of the week.

&&

.DISCUSSION...
Issued at 130 PM CDT Sun May 17 2026

A robust convectively-augmented MCV continues to pivot north out
of southern Wisconsin and away from our region early this
afternoon. Modest large scale height rises will develop over the
local region which will promote precip-free conditions across
the area the rest of the afternoon. The one exception might be
across our far northwest where some lingering glancing ascent
co-located with cooler mid-level temperatures may support some
lingering spotty sprinkles.

In advance of our next weather-maker, tonight will feature warm
and somewhat humid conditions. With a tightening surface
pressure gradient and only modest decoupling, should see at
least intermittent gusty southerly breezes through the night.

Expansive strong to severe convection is expected to develop
later this afternoon and evening across the central and
northern Great Plains along an eastward-advancing cold front.
Given the strong nature of low-level forcing with the front,
it`s not surprising that there`s good model agreement suggesting
upscale growth into one or two expansive MCSs through the
evening hours. While some timing discrepancies remain, there`s a
general consensus for this activity to approach our forecast
area just prior to daybreak Monday morning. Deep layer shear
over the local area is not forecast to be particularly robust,
and generally oriented from southwest to northeast, roughly
parallel to the progged MCS(s). This overall is not favorable--
combined with the time of day and nocturnally-stabilized
boundary layer--for robust convective sustenance.

At this time, it appears the most probable scenario is for a
decaying thunderstorm complex, potentially with lingering strong
gusty outflow and maybe some cores with a small hail potential,
to push into the region through Monday morning. In this
scenario, expansive cloud cover, trailing stratiform rain, and
some embedded thunderstorms may linger well into Monday
afternoon across the northwest half of the CWA (roughly NW of
I-55). This would obviously significantly reduce the subsequent
afternoon severe weather threat across this area.

If this morning complex doesn`t just surge through the entire
forecast region (which remains a potential), muted insolation,
with the bulk of the anvil blow off likely streaming northeast
as opposed to easterly, may facilitate destabilization through
midday and into the afternoon south and east of I-55. This could
support gradually-increasing storm organization and
intensification. That said, progged shear profiles still aren`t
anything spectacular with the main mid/upper jet cores still
relegated well to the west. Given this, it seems like the
locally greatest threat for strong-severe storms exists across
the eastern half of the CWA from about midday through the
afternoon. In this scenario, deeper boundary layer mixing would
also promote increasing southwesterly wind gusts, possibly
pushing 40 mph. If the overnight complex fizzles prior to
reaching our area, the severe threat would likely increase
across more of the region, although this currently looks like a
lower potential at this time based on the latest multi-model
consensus.

Today`s guidance paints a similar picture/evolution to things
for Monday night into Tuesday as the main cold front will sweep
west to east through the region Tuesday afternoon. Once again,
a potential for mainly sub-severe morning convection exists,
followed by a threat for more robust storm development on the
advancing cold front midday into the afternoon. While deep layer
shear is forecast to be a bit more significant than Monday,
instability could once again be muted significantly by morning
convection.

In the wake of the cold front, breezy northwesterly winds will
develop Tuesday/Tuesday night before turning north/northeasterly
on Wednesday as high pressure builds into the region. A period
of tranquil weather is in store until the end of the week and
next weekend when the next series of disturbances will bring
additional chances of showers and perhaps some thunderstorms to
the area.

Carlaw

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 705 PM CDT Sun May 17 2026

Main Concerns:

- Potential for TSRA at times Monday from pre-dawn through
  midday in the wake of a weakening area of showers and storms

- Notable wind variability and occasional gustiness is probable,
  assuming the weakening showers and storms do move across the
  terminals

Widespread thunderstorm development from the central Plains to
southwest Minnesota is expected to evolve into a linear complex
tonight as it approaches the region. As long as the anticipated
line of SHRA/TSRA doesn`t fall apart before reaching the
terminals early Monday, it will likely have brief period of
gusty northwest winds (possibly up to ~40 kt in spots) on its
leading edge outflow boundary. Behind the outflow boundary,
forecast soundings suggest enough lingering instability for
embedded TS potential, warranting continued PROB30 mention.

In addition to the potential for on station TS impacts, the
wind field will likely become quite erratic, spending at least
some time at east to south-southeast, with occasional gusts to
25 kt still possible. Breezy southwest winds will likely
redevelop in the afternoon and continue Monday evening. While
renewed TS development over the region is possible Monday
afternoon, favored area may end up safely southeast of the TAF
sites. Therefore, confidence was too low for any additional
SHRA/TS mention.

Prior to the possible TS and variable/gusty winds Monday
morning, south-southwest winds will continue to gust up to 20-30
kt, strongest prior to sunset this evening.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT this evening for Wilmette
     Harbor IL to Michigan City IN.

&&

$$

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