Joliet, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

718
FXUS63 KLOT 301738
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1238 PM CDT Sun Mar 30 2025

.KEY MESSAGES...

- There is a threat for severe weather areawide on Sunday
  especially between 11 AM and 5 PM CDT that includes all
  hazards (damaging winds, damaging hail, tornadoes).

- A period of below average temperatures is expected Monday and
  Tuesday before another storm system (with a threat for severe
  weather) arrives on Wednesday.

&&

.MESOSCALE...
Issued at 1048 AM CDT Sun Mar 30 2025

We continue to closely monitor and analyze the mesoscale
environment across our area and to the southwest for the
development of severe convection over the next several hours. A
MCV tied into the broader mid-level trough is well-defined and
centered roughly 100 miles west of St. Louis as of 10am. While
the MCV has been mostly benign through the morning, it will
begin to interact with a plume of mid 60s dew points and notable
ongoing clearing just east of the Mississippi River and into
central Illinois.

Expectations are that convection should erupt within the next
hour or so over or just east of the MS River. An incoming 60
knot mid-level jet, 0-1km shear surpassing 25 knots with more
than 60 degrees off the orientation of the convection, and
impressive 0-3km CAPE values over 150 j/kg should yield rapid
upscale growth of a line of severe convection east of I-55
through mid-afternoon. Damaging wind can be expected, with large
hail also possible with any embedded supercell structures. Also,
significant wind (>75 mph) would be favored with any localized
bowing segments of the convection.

With the MCV/wave expected to track within a county or so of
I-55, severe convection could extend well into the Chicago
metro. A localized tornado threat will also exist over the
Chicago metro (and with any kinks in the main line) where the
trajectory of convection arcing into the MCV would maximize
effective low-level shear.

Kluber

&&

.DISCUSSION...
Issued at 313 AM CDT Sun Mar 30 2025

Through Monday:

Primary forecast concern remains severe potential today.

In the short term, widespread light rain and drizzle developed
late Saturday evening and is slowly lifting northeast across
northeast IL. This is expected to end by daybreak. The frontal
boundary will slowly lift back north, though only medium
confidence on how fast this occurs. While areas of fog will
remain possible, especially along the Lake Michigan shore, low
level winds are already in the 20-30kt range and this is likely
keeping the low levels mixed just enough to prevent dense fog,
but will continue to monitor trends early this morning.

An area of thunderstorms across northeast IA will continue
lifting northeast through daybreak and may move across the far
northwest cwa and possibly the Rockford area. These storms are
not expected to be severe but gusty winds and small hail would
be possible.

Attention then turns to ongoing convection moving northeast into
western MO and how this activity will influence the convective
evolution for the local area later today. It appears there are
three possible scenarios. The first, the current convection
continues moving northeast and into the western half of the cwa,
perhaps west of I-57. While this activity would likely have
gusty winds and small hail and perhaps even an isolated severe
storm, this would help stabilize the northern cwa with later/new
convection likely ending up across the southeast half or third
of the cwa. Current timing would suggest an arrival into the
southwest cwa in the 14z hour and then spreading across the cwa
through late morning. The HRRR has been consistently showing
this possibility for many runs.

The second scenario is the activity entering MO slows and
weakens and then reignites midday over the cwa, which will would
then allow for a severe threat further north, including much of
the Chicago metro. The RAP and to some extent the NAMnest
suggest this possibility.

The third possibility, the activity moving in MO weakens/
dissipates and this morning is somewhat quiet, until new storms
develop. This too would bring the severe threat further north
and into the Chicago metro area. The ECMWF had been showing this
possibility for several runs but with the 00z run, now has at
least isolated activity this morning, making this probably the
least likely of the three possibilities.

Despite the uncertainty, the overall message remains the same.
Low pressure will pass across the northern cwa this afternoon,
with thunderstorms expected, some severe, with the highest
coverage and best severe potential, likely south of I-80. The
new SPC Day1 outlook is very similar to the previous Day2
outlook. Higher confidence will materialize as trends emerge
with the convection moving through MO this morning.

Any storms that develop today will be racing to the northeast
at 50-60 mph and it appears the activity will be east of the cwa
by 22z-23z. Have adjusted pops accordingly, going dry in the
west by late afternoon as a cold front moves across the area.
After highs in the mid/upper 60s northwest, lower 70s rest of
the area today, temps will steadily drop tonight with lows
Monday morning in the lower/mid 30s. Southwest winds may gust as
high as 35 mph today, then turn west/northwest behind the front
and while speeds/gusts will diminish some by Monday morning,
wind chills may be in the 20s for much of the area.

Precip trends for tonight have steadily lowered with most of the
models suggesting only a few rain/snow showers across the
northeast cwa and have lowered pops to low chance. Much of the
southwest/southern cwa may end up dry. Highs only reach the mid
40s Monday with winds turning off Lake Michigan Monday
afternoon. cms


Monday Night through Saturday:

After a chilly start to the work week temperatures will
gradually moderate toward midweek when multiple rounds of
thunderstorms are possible late Tuesday night through Wednesday,
some of which could be severe.

Another low pressure system is forecast to lift across the
Upper Midwest toward midweek which will bring yet another period
of inclement weather to the local area. Guidance has trended
more consistently earlier with the onset of showers and
thunderstorms, with strong to possibly severe thunderstorms
moving into the area as early as the pre-dawn hours early
Wednesday morning (potentially in a weakening phase) near and
west of I-39. This coincides with where the Storm Prediction
Center introduced a Level 2 of 5 severe weather threat on Day
3. Additional waves of showers and storms are possible through
the day on Wednesday. Depending on the timing of storms exiting
in the morning there is a window for another round of strong to
severe storms in the afternoon and early evening. Similar to
today`s (Sunday) setup, given the conditional nature of the
severe threat, expect updates over the coming days to the
forecast.

Uncertainty increases late week into the weekend when another
system is forecast to move across the broader region, though
differences in its placement remain. For now NBM rain chances
seem appropriate (highest south of I-80) with temperatures
generally in the 50s to lower 60s.

Petr

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1238 PM CDT Sun Mar 30 2025

Key Aviation Messages for the current TAF period:

- Scattered storms are expected through 21Z, some of which may
  become severe

- Gusty southwest winds through the TAF period, before a lake
  breeze arrives Monday afternoon for northeast winds

- MVFR cigs through Monday morning

- Brief showers that may have some snow mixed in around 06Z
  close to the Wisconsin/Illinois stateline

Cloud cover has broken up for a brief VFR window through
18-1830Z. However, the clearer skies to the south which has
allowed for destabilization in southern Illinois with storms
starting to develop. TAFs were issued with prevailing -SHRA at
the start, but there may be a delay for when showers are
specifically at terminals. No changes were made to the TEMPO for
Chicago terminals with 19Z to 21Z being the main window for
stronger scattered storms to pass over terminals, some of which
may be severe. For RFD, however, is expected to have lower
instability dropping the probability for thunder below 30
percent. Therefore, with decreased confidence in having thunder,
it was kept out of the TAFs and will be handled tactically if it
does materialize. As storms pass over terminals, expected lower
cigs near IFR levels, lower vis from heavier rainfall, and
strong wind gusts.

As the front moves through, other than some lingering showers
trailing behind, drier conditions are expected after 21Z, but
the MVFR cigs are expected to remain through the evening. There
is a slim chance for some lowering to IFR overnight, but not
generally expected.

The surface low driving today`s storms will continue to move
east-northeast through the night. Moisture will wrap around the
low and temperatures will drop. There is a brief window for
showers, but confidence was for terminals closer to the
Wisconsin stateline. As temperatures drop, there is a chance for
some snow to mix in for a brief window of -RASN.

Lastly, winds are expected to be out of the southwest through
most TAF periods. Gusts will slowly diminish through this
evening, but gusts around 20 knots are certainly possible
through Monday early afternoon. However, a lake breeze is
expected to develop in the mid afternoon. Later TAF packages
will likely fine tuned the timing for clearing to VFR as well as
the flip to northeast winds for Chicago terminals.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CDT Tuesday for the IL and IN
     nearshore waters.

&&

$$

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