Plainfield, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

822
FXUS63 KLOT 250624
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
124 AM CDT Fri Jul 25 2025

.KEY MESSAGES...

- Additional rounds of showers and storms into Friday morning
  with a locally heavy rain, and isolated gusty wind threat.

- A period of slow-moving showers and thunderstorms Friday night
  through Saturday may bring another round of torrential
  rainfall and the potential for flooding across portions of the
  area.

- Dangerous heat will build back across the area on Monday
  (possibly as early as Sunday), with periods of thunderstorms
  over or just north of the area Monday through Wednesday.

&&

.DISCUSSION...
Issued at 119 AM CDT Fri Jul 25 2025

Through Saturday:

Complex warm season pattern is in place early this morning, with
continued concerns for locally heavy rainfall and gusty
thunderstorms being the main near term concerns. Challenges will
center on timing individual shortwaves/boundaries that will serve as
focus for thunderstorms.

The low level atmosphere, and really the entire atmospheric column,
has not been scoured out ahead the afternoon storms, and you can
make out an outflow boundary along a line from Peru to Gary.
Dewpoints north of the boundary are still holding in the lower 70s,
but mid to even upper 70s are in place across central Illinois. THus
from an instability perspective, the atmospheric is still fairly
primed.  Similarly, an assessment of PWATs show an enhanced area of
2"+ PWATs along the boundary.  Aloft, water vapor imagery depicts
numerous MCVs/compact vort maxes from central IL extending back to
the Texas Panhandle. 850-700 mb flow from the SW ahead of the first
wave shows some uptick as well.

It appears the focus tonight into early Friday will be locally heavy
rainfall with some embedded thunderstorms. Most guidance suggests
that the environment may be a bit more conducive along and
south/east the aforementioned boundary. Higher DCAPE values will be
in place ahead of this first wave, and with a shallow stable layer,
we do still need to monitor for gusty winds south of Chicago into NW
Indiana which should peak before early-mid morning. Outflow is
surging ahead of the storms, thus at least for the time being gusts
should hold under 40 mph.

The challenge will be that there is not that much of gap
between each upstream wave, but it looks like coverage may ease
a bit through the morning into early afternoon. The next wave(s)
will be moving into northeast IL/northwest IN during the
afternoon. With extensive cloud cover, instability will be a bit
more muted. Deep layer shear will also be lower. Therefore
coverage of showers and storms this afternoon will likely be
focused on any inland surging lake boundary, and would be
scattered in nature. Locally heavy rainfall again would be the
main hazard with tall/skinny CAPE profiles and very little wind
in the steering layer.

Another nocturnal uptick in low level southwest winds will shift the
moist axis back toward more of the area overnight Friday night into
early Saturday. The shower and storm chances never really end Friday
evening, however better chances will come in this latter time frame
as a more organized trough axis aloft will come overhead in the
conjunction with the low level jet response and commensurate uptick
in 2" + PWATs areawide (versus further south on Friday). This will
be another period to watch for heavy rainfall. And with the approach
of the trough/some enhanced shear will again bring some concern for
damaging winds. Much depends on the arrival time of the wave.

KMD

Saturday Night through Thursday:

Saturday night the low level flow turns more westerly and it looks
like the more organized shortwaves will pass east of the area. There
will still be subtle waves in westerly flow moving in, but rising
heights aloft should limit storm coverage on Sunday.

Concern will then shift to a return to heat and humidity. Dewpoints
will again be on the rise on Sunday and a portion of the thermal
ridge across the plains will look to shift back overhead early next
week, especially into Monday as an expansive high will setup smack
dab in the middle of the country right in the heart of the
climatologically favored time of year.  Dewpoints also look to be
oppressively high, upper 70s to near 80, which would place heat
indices close to 110. Beyond that, we will see if the ridge holds
into Tuesday, it certainly may, which would continue the heat and
humidity at least for some areas, and away from the lakeshore.

It appears that a longwave trough across Canada will look to squash
the ridge axis south, opening the door first to heavy rainfall
producing storms. Severe weather would also be on the table with an
upper jet nearby, southward surging cold front, and west-northwest
flow in place. A much cooler and drier airmass toward the latter half
of the week.

KMD

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 106 AM CDT Fri Jul 25 2025

Forecast concerns for the terminals...

- Period of showers and thunderstorms late tonight into Friday
  morning, mainly along and south of a VYS to VPZ line.

- Scattered showers and isolated storms possible (20-30% chance)
  Friday afternoon and evening mainly at the Chicago area
  terminals.

- Period of MVFR ceilings late tonight through Friday morning
  with another period of MVFR and possibly IFR conditions Friday
  night into Saturday.

A series of shortwave disturbances are generating an area of
showers and thunderstorms from north-central IL to eastern KS at
this hour with the leading wave expected to bring some showers
and storms to portions of northeast IL and northwest IN late
tonight into Friday morning. While moisture is more than
sufficient for storms, there is a subtle convergence zone noted
from VYS to VPZ which should serve as the focus for these
showers and storms to traverse along tonight. Therefore, suspect
that the greatest coverage of showers/storms will remain south
of a VYS to VPZ line, but the northern fringes of the axis will
likely brush GYY and possibly MDW between 09z and 12z where
TEMPO groups have been maintained. A stray shower still cannot
be ruled out at ORD or DPA during this period as well, but
confidence remains too low for a formal mention at this time.

The first disturbance is expected to exit the area towards mid-
morning which will yield a period of dry weather until the
second disturbance (currently in eastern KS) arrives late Friday
afternoon. Given that the wave should be weakening as it moves
across north-central IL, shower and storm coverage looks to be
much more hit and miss. However, a lake breeze is expected to
move inland during the afternoon hours which may provide just
enough support to kick off some scattered showers and isolated
thunderstorms mainly over the Chicago terminals. With this being
more lower-confidence (20-30% chance of showers/storms at the
Chicago sites) have opted to maintain the PROB30s for now.

Regardless of what happens Friday afternoon, the third and more
formidable disturbance is forecast to move into northern IL and
northwest IN late Friday night. While it does appear that a much
better coverage of showers and storms would be associated with
this wave, current guidance trends show this round arriving
near the very tail end of the 30-hour TAF period (after 10z).
Thus, have opted to forego a formal mention for this round in
the current TAFs, but will likely need to add something with the
12z set.

Outside of the shower and storm chances, MVFR ceilings are
expected to develop towards daybreak Friday morning and persist
through midday before lifting back to VFR. Additionally, there
remains a chance for some patchy fog to develop across
northwest IL tonight where lesser mixing is occurring. Given
that temperature-dewpoint spreads remain in the 4-6 degree
range, fog coverage remains a bit uncertain especially with
eastward extent. Therefore, only have a BR mention at RFD but
will continue to watch trends and adjust as needed. A second
period of MVFR ceilings is expected to develop late Friday night
ahead of the aforementioned showers/storms with some IFR
ceilings possible where moisture pools. How long these lower
ceilings last Friday night will be dependent on the coverage of
showers and storms so will have to refine this part of the
forecast as we get closer.

Finally, winds tonight will be light and generally out of the
west-northwest but will become more northerly towards daybreak.
Winds will then become more easterly behind the lake breeze with
speeds around 8-10 kts before directions turn more southeasterly
Friday evening and overnight.

Yack

&&

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

&&

$$

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