Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

992
FXUS63 KLOT 231148
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
648 AM CDT Mon Jun 23 2025

.KEY MESSAGES...

- Dangerously hot and humid conditions will continue through
  this evening with heat headlines expiring at midnight tonight.

- The magnitude of heat should lessen by Tuesday, though heat
  indices will still be in the upper 90s to near 100 through
  much of the week.

- Periodic shower and storm chances exist through this week.
  Some may be severe with damaging winds and flash flooding.

&&

.DISCUSSION...
Issued at 339 AM CDT Mon Jun 23 2025

Through Tuesday:

It`s another warm night out there with most sites reporting
middle 70s to lower 80s at 3 AM setting the stage for day 3 of
the heatwave. Today should feel very similar to yesterday;
temperatures are forecast to again reach the middle 90s area-
wide, maybe a degree or two warmer in general than yesterday.
Dewpoints expected in the upper 60s and lower 70s should again
put afternoon heat indices in the range of 100 to locally 105.

A sharp cold front will approach the CWA from the northwest
later today getting into northeast IA by late afternoon. A
linear cluster of showers and thunderstorms is expected to
develop along this front early in the afternoon. The precip will
march eastward with the front through the afternoon until it
gets hung up just to our northwest this evening and tonight
likely leaving a majority, if not nearly all, of the activity
just outside of the CWA possibly until Tuesday. Models agree
that the bulk of the precip later today will focus over
northwest IL and south-central WI, although there`s certainly a
chance that some showers and storms make it into our northwest
CWA. Layer moisture will cling onto the front with profiles
looking much drier to the south and east around our area.
Accordingly, we should find a rather sharp cutoff in instability
along the boundary, so the thunder environment will quickly
become more hostile away from the front itself, but it`s unclear
just how far east the thunder coverage will make it. The line
is expected to fizzle into scattered showers overnight into
early Tuesday as the front continues to meander to our
northwest.

One feature we`ll have to look out for this evening is a
potential outflow boundary moving across our area from this line
of storms. A number of higher-resolution models have been
picking up this outflow recently, and a few of them even trigger
some localized convection along it this evening and take it
into the Chicago metro. Looking at forecast soundings around the
metro, this seems very plausible as low level stability is
rather weak and I`d imagine could be easily overcome by such a
feature. If so, parcels will be granted access to as much as
several hundred Joules of CAPE aloft which could result in a few
elevated thunderstorms. Being a newer signal with not a ton of
support, extended only some slight chance PoPs into the metro
this evening for this potential.

The surface front will move into our CWA Tuesday morning, but
the stronger baroclinicity aloft will remain displaced to the
northwest through the morning. Early in the afternoon, the
better forcing and moisture aloft is expected to pivot south
over our area which will increase scattered shower and storm
chances for Tuesday afternoon and evening. Deep shear will be
very meager, so nothing too organized is anticipated. But, a
unidirectional shear profile oriented roughly parallel to front
with lots of mid-upper moisture does provide a threat for
localized instances of training convection which could lead to
flooding. Most of our convective-allowing models paint small
splotches of 1-2" of QPF around the area through the end of
Tuesday. Some small hail and locally strong wind gusts may also
be possible in the strongest storms given the instability.

There is some uncertainty in what temperatures will look like
on Tuesday, but guidance is generally trending a bit cooler.
It`ll remain hot, but not quite as oppressive as what we`ve been
seeing. A number of model camps, including nearly the entire
HREF suite, suggest a large portion of our northern CWA, if not
more, will not make it into the 90s. Around the area, Tuesday
afternoon is looking like upper 80s to lower 90s with heat
indices in the 90s to around or just over 100, especially south
of I-80. Therefore, no changes were made to the going heat
headlines with today expected to be last day under the Heat
Advisory, or Extreme Heat Warning in the case of Cook County.

Doom


Tuesday Night through Sunday:

The upper level ridge responsible for the oppressive heat from
earlier in the week will continue to flatten out midweek with a
surface boundary draped near and over the area. A series of low-
amplitude waves are expected to move along the quasi-zonal
northern periphery of the ridge. These features paired with
diurnal heating will lead to periodic showers and storms across
the area through the end of the week and into early next week.

While the jet stream will remain solidly north of the area
(along with the better deep layer shear), a reservoir of moist
and unstable air will still reside along and south of the
aforementioned surface boundary. This combined with high PWATs
and relatively weak lapse rates will be supportive of
precipitation loaded downburst leading to localized damaging
winds. This matches up well with SPC`s Level 1 of 5 Threat for
Severe Winds both Tuesday and Wednesday (which may continue
later into the week with later updates). Given PWATs potentially
in excess of 2", a localized flooding threat exists as well.
There will be plenty of dry hours during the next several days
but pinpointing when those dry windows occur remains lower
confidence at this range.

While summer-like conditions continue through the end of the
week, it won`t be nearly as oppressive as experienced earlier in
the week thanks to greater cloud coverage from periodic
showers/storms and times with onshore flow/lake breezes off Lake
Michigan. Expect highs generally in the upper 80s to lower 90s
and heat indices in the 90s to locally near 100, warmest toward
central Illinois and cooler along the lakeshore on days with a
lake breeze.

Petr

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 645 AM CDT Mon Jun 23 2025

- Gusty SW winds develop again today with peak gusts in the
  25-30kt range in the afternoon.

- Outflow from thunderstorms in Wisconsin late afternoon could
  result in a gusty north wind shift this evening.

Winds gradually increase through the morning with gusts over
20kt by mid morning. Peak gusts in the 25-30kt range are
expected during the mid to late afternoon.

Showers and thunderstorms are expected to erupt along a cold
front across Iowa, far northwest Illinois, and southern
Wisconsin this afternoon into early evening. Some of this
activity may attempt to drift in and near RFD in the evening
where a PROB30 for -TSRA has been introduced. Closer to the
Chicago metro terminals, hi-res model guidance remains
consistent in these storms pushing out an associated outflow
boundary that propagates across the area (focused near/north of
I-80) which would turn winds NNW to possibly NNE nearest the
lake. Spotty showers/storms initiating along this boundary also
can`t be fully ruled out (20% chance), though confidence remains
too low to include in the TAFs with this update. Thus, opted to
maintain TEMPO groups ~4-7Z for a gusty north wind shift. Winds
then turn somewhat variable under 10kt in the wake of the
outflow boundary overnight into early Tuesday morning.

Petr

&&

.CLIMATE...
Issued at 339 PM CDT Mon Jun 23 2025

Temperatures will continue to threaten record highs and record warm
lows for Chicago and Rockford. Here are the current records for today:

Chicago              High       Warm Low
Monday 6/23        97 (1930)    79 (1923)

Rockford             High       Warm Low
Monday 6/23        97 (1923)    74 (1908)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until midnight CDT tonight for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ106-ILZ107-
     ILZ108.

     Extreme Heat Warning until midnight CDT tonight for ILZ103-
     ILZ104-ILZ105.

IN...Heat Advisory until midnight CDT /1 AM EDT/ tonight for INZ001-
     INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 10 PM CDT this evening for the IL
     nearshore waters.

     Small Craft Advisory from 1 PM this afternoon to 10 PM CDT
     this evening for the IN nearshore waters.

&&

$$

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