National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLOT 151129
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
629 AM CDT Mon Apr 15 2024

.KEY MESSAGES...

- A couple waves of showers and thunderstorms expected Tuesday
  through Wednesday morning. Some may be severe and produce
  locally heavy rainfall late Tuesday afternoon through early
  Wednesday.

- Windy late Tuesday through Wednesday with peak gusts 40+ mph,
  highest on Wednesday.

&&

.DISCUSSION...
Issued at 348 AM CDT Mon Apr 15 2024

Through Sunday:

A surface ridge of high pressure shifting across the western Great
Lakes will result in another sunny and warm day. Inland
temperatures this afternoon will top out in the 70s, though
persistent onshore easterly winds through the day will foster
cooler conditions near Lake Michigan.

While quiet weather will persist locally today, our main focus
during the period continues to revolve around the potent spring
storm system expected to shift across the Midwest into the western
Great Lakes late tonight through Wednesday. This developing storm
system will strengthen today across the central High Plains as
strongly diffluent upper-level flow traverses the Rockies. This
storm system will be responsible for spawning severe thunderstorms
late this afternoon into tonight well west of our area across the
Plains. However, the severe weather threat will shift eastward
towards our area late Tuesday into Wednesday as the whole storm
system tracks eastward across the Corn Belt.

An arc or two of elevated scattered showers and thunderstorms
is likely to develop northeastward into the area Tuesday morning
as warm air advection begins to ramp-up over a surface warm
frontal boundary across central IL and IN. This initial round of
morning storms is expected to be elevated and largely non- severe.
However, Tuesday afternoon, warm sector convection is expected to
fire west of the area across parts of IA and MO in closer
proximately to the strong dynamics associated with the approaching
storm system. It will be this activity we will have to monitor as
it shifts east-northeastward into our area late Tuesday afternoon
and evening. The presence of strong low and deep layer shear will
certainly support organized severe convection, with an all
hazards severe threat (including tornadoes), most notably along
and west of the I-39 corridor late Tuesday afternoon into the
early evening. The severe threat may ultimately end up continuing
with the eastward shifting convection well into the evening, even
for areas east of I-39. However, it remains a bit unclear at this
time with the eastward extent of this severe threat, as the
storms may tend to diurnally weaken with time. Nevertheless, the
SPC has the all of the northern IL in a slight risk for severe
storms.

As the upper low merges into the upper trough it takes on more
of a negative tilt early Wednesday morning with the region still
situated under the left exit of the southern stream upper jet.
While there are some questions as to how much instability there
will be to work with into early Wednesday morning and the timing
of the various waves as showers and storms wrap around the
surface low. With the slightly slower timing, forecast soundings
would support surface based convection persisting (or redeveloping)
Wednesday morning into early afternoon, especially east into
northwest Indiana. Will hopefully get a better idea of how late
the severe threat persists as high-res guidance becomes
available. Winds turn westerly on Wednesday with the strong
winds persisting and likely peaking during the afternoon on
Wednesday with gusts up to 40+ mph possible.

Beyond Wednesday can`t rule out some rain on the north side of
a weakening surface late Thursday into Friday then before
surface high pressure builds southeast into the Upper Midwest
bringing a cooler airmass for the latter half of the week with
high temperatures in the 50s to lower 60s and lows in the 30s
and lower 40s.

KJB/Petr

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 629 AM CDT Mon Apr 15 2024

Main Concern:

- Scattered SHRA and a chance of TSRA mid-late Tuesday morning

Quiet VFR conditions will continue for the next 24 hours,
followed by a more active stretch of weather starting Tuesday
morning. Winds will be northeast to east-northeast near/around
10 kt today and tonight. Easterly winds will increase Tuesday
morning with gusts to around 20 kt by mid morning or so.

There is a good deal of uncertainty regarding the Tuesday
morning precip. forecast. The most recent model guidance is
split regarding whether SHRA and potentially embedded TS will
approach prior to or after the current ORD/MDW 30-hour TAF
period. Our current thinking is that there`s enough of a signal
for SHRA and isolated TS nearby by mid-late Tuesday morning to
warrant a VCSH mention along with a PROB30 for TSRA. The
primarily dry Tuesday morning-mid day period scenario is
certainly a plausible outcome, however. Confidence is much
higher in SHRA/TSRA late Tuesday-Tuesday evening, which will be
addressed in subsequent updates.

Castro

&&

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

&&

$$

Visit us at weather.gov/chicago