278
FXUS63 KLOT 270550
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1250 AM CDT Thu Mar 27 2025

.KEY MESSAGES...

- Rain is possible at times late tonight through Friday morning.

- Isolated to scattered thunderstorms, some with small hail, are
  possible late Thursday night into early Friday.

- Strong winds and warm weather are expected Friday afternoon.

- Rain and/or thunderstorms possible at times over the weekend
  with a substantial temperature gradient stalled across
  northern Illinois.

&&

.DISCUSSION...
Issued at 306 PM CDT Wed Mar 26 2025

Through Thursday:

Some shallow low level instability is stirring up a healthy Cu
field over the CWA this afternoon and we`re even starting to see
a few light showers pop up on radar. There is some near-
surface dry air to fend off some precip, but isolated pockets of
sprinkles or light rain will likely continue into late
afternoon, especially east of an Aurora to Gibson City line.
Temperatures have made it into the 50s around most of the area
with several sites in our south reporting mid 50s. Areas right
along the lake are stuck in the 40s and aren`t likely to escape
this afternoon as onshore flow persist near the lakeshore. Winds
are also beginning to pick up momentum as mixing deepens.
Despite being deeply mixed, flow through the mixed channel is
relatively light and gusts through the afternoon should largely
fall in the 20 to 25 mph range, although occasional gusts to
around 30 mph will be possible before subsiding for the evening.

A few rounds of showers will push through the area between
tonight and Friday with some thunderstorms possible Thursday
night. This evening and tonight, an EML and region of efficient
low level WAA will spread into the Midwest ahead of a developing
Plains cyclone. As a baroclinic zone sets up aloft, a deep
f-gen circulation is anticipated to develop on the northern
fringe of the WAA plume. This NW-SE oriented f-gen band will
initially spin up over the eastern Dakotas late this afternoon
before extending southeastward into northern IL late tonight
into tomorrow. A narrow band of showers is expected to cut
across our area beneath the f-gen overnight through the morning
tomorrow. The ambient environment overnight will feature a
noteworthy dry wedge off the surface which will make it
difficult to produce anything outside of this narrow
frontogenetically-forced axis. There is uncertainty regarding
where exactly this swath of rain tracks. Most guidance,
including a majority of latest high-res camps, favor a corridor
roughly near or just north of a Rockford to Joliet to Rensselaer
line. Several other models, including the EC and CMC suites,
are farther south and favor areas south of I-80.

After sunrise, a warm front tied to that aforementioned Plains
low will lift into IL and low level moisture will spread up
into our CWA. As a result, a swath of densely scattered to
widespread showers will traverse central IL during the morning
and afternoon and likely fall on southern portions of our CWA.
While scattered pockets of light rain may persist, a lull in
activity is expected late afternoon through most of the evening.

That warm front will lift into central IL late tomorrow and a
line or quasi-linear cluster of showers and thunderstorms will
develop atop it. They`ll go elevated as they propagate across
our CWA from the southwest overnight into early Friday. The
reservoir of more ample instability that will build over
northern MO during the day will wane by the time it lifts up
into our CWA late in the evening. A majority of models maintain
less than 1,000 Joules of tall, skinny MUCAPE into our CWA.
The warm front won`t actually pass over until Friday morning,
so the low levels will be plenty stable. But, steep mid level
lapse rates with that EML overhead may result in some elevated
hail producers. The limited instability and effective shear
should inhibit any appreciable severe threat across our CWA,
maybe with the exception of our far south where better
instability aloft could potentially allow for some marginally
severe (1") hail. The time window for thunderstorms including
the hail threat will mainly be overnight but will likely stretch
into early Friday. More details about lingering activity into
Friday can be found in the long term discussion below.

Doom


Thursday Night through Wednesday:

A low-amplitude ridge will drift across the Ohio River Valley
and southern Great Lakes Friday into Saturday night. An EML on
the leading edge of WAA under the ridge should clear the CWA to
the northeast by mid-morning Friday. Scattered elevated storms
with perhaps some hail could therefore persist for a couple
hours after daybreak across northeast Illinois and northwest
Indiana. Otherwise, expect a warm, windy and partly cloudy day
on Friday as diurnal cumulus becomes suppressed by the inversion
under the EML. Max temps in the mid to upper 70s appear likely
while southwest winds gust 30 to possibly 40 mph (conditional on
impacts of cloud cover on mixing depths).

Broad cyclogenesis across the northern Great Plains on Friday
will separate into two distinct lows by Friday night. The first
low will cross central Wisconsin Friday night and attempt to
push a resultant cold front southward across at least northern
Illinois through the day Saturday. Meanwhile, the second low
will shift over the central Great Plains through the weekend in
a strengthening phase. The opposing flow regimes between the two
systems adds plenty of uncertainty with the southern extent of
the northern cold front before it ultimately stalls (and even
potentially retreats) Saturday night into Sunday morning. The
second low will then roughly traverse the existing front to the
northeast through Monday.

The implications of the above evolution on the forecast are
substantial through this weekend, especially on Saturday when
midday temps could range from around 40 along the Illinois shore
to the mid to upper 70s inland. With regard to precip chances
Saturday-Saturday night, anywhere north of the front could see
light rain or patches of drizzle while the warm sector sees
mostly dry conditions during the day and a pocket of showers
with a few storms during the night. By Sunday, the main trough
and surface flow will bring periods of rain areawide with
perhaps some storms. If warmer solutions this weekend verify,
storm chances will be substantially higher on Sunday with a
decent severe storm risk over at least the southeast half of the
CWA conditional on the amount of cloud cover in the warm
sector.

Drier but much colder conditions will follow on Monday and
Tuesday as highs remain mostly in the 40s.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1250 AM CDT Thu Mar 27 2025

Aviation forecast concerns for the 06Z TAFs:

- Spotty VFR sprinkles this morning.

- Showers and embedded thunderstorms develop after midnight
  tonight, with MVFR conditions likely.

- South-southwest winds today, becoming southeast by early this
  evening. A few gusts 15-20 kts possible this afternoon,
  especially farther west at KRFD.

Another in a series of weak mid-level disturbances will track
southeast across the region this morning. Scattered light
showers/sprinkles are expected, though dry sub-cloud layer is
expected limit these mainly to sprinkles with no significant
wetting of pavement. Have indicated a VCSH in TAFs based on
relatively low coverage expected. Can`t rule out a few sprinkles
again later this afternoon, though best chances appear to remain
southwest of the terminals at this time. Shower chances do look
to increase for the TAF sites more significantly after midnight
tonight, as moist ascent develops atop a northward advancing
warm frontal zone. Forecast soundings indicate instability
increase above the elevated front predawn, supportive of
scattered thunderstorms after 08-09Z. VFR conditions are
expected through this evening, with MVFR or even brief IFR
becoming more likely after midnight and especially as showers
and storms develop.

Wind wise, light south-southwest winds early this morning are
expected to become a little more southwest late this morning and
may gust above 15 kt at times this afternoon, especially farther
west at KRFD. A southeasterly lake breeze may develop, but is
expected to remain east of ORD/MDW through the afternoon. Winds
are expected to synoptically back southeast by early evening,
in response to the approaching warm front.

Ratzer

&&

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

&&

$$

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