Lombard, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

196
FXUS63 KLOT 142019
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
319 PM CDT Thu Aug 14 2025

.KEY MESSAGES...

- Uncomfortable heat and humidity returns this weekend with heat
  indices 95 to 105 degrees. Storms/outflow could disrupt heat
  for some, particularly near the lake/NE Illinois.

- Threat for strong thunderstorms increases Friday night and
  into early next week, though there will be several periods of
  dry time.

&&

.DISCUSSION...
Issued at 319 PM CDT Thu Aug 14 2025

A mid-level shortwave impulse over IA early this afternoon will
shift eastward across northern IL tonight. It appears unlikely
that this disturbance will result in any precipitation over our
area tonight, though an increase in mid and higher level cloud
cover is likely through the evening. Otherwise, expect another
seasonably cool night tonight, with lows generally in the 60s.

Heat and humidity will be returning to the area into the weekend
as upper-level ridging begins to build back over the Midwest.
Warming conditions will commence on Friday as the surface flow
turns southerly and fosters warming inland temperatures into the
low 90s Friday afternoon. The one expectation to these very warm
temperatures on Friday will be areas along the northeastern IL
lakeshore, where an onshore wind component through the day will
keep conditions several degrees cooler. Dew points are also
expected to gradually increase into the upper 60s to low 70s
through the afternoon, which will foster afternoon heat indices
topping out in the 95 to 100 range across interior sections of
northern IL.

An increasing belt of westerlies will set up across the Upper
Midwest Friday night into Saturday along the northern periphery
of the roughly 594 dam 500 mb high building over the Mid
Mississippi Valley into the weekend. Unfortunately, the evolution
of this pattern will place our region in an area favorable for
convection at times Friday night through the weekend. There is
certainly going to be a good amount of dry time this weekend, so
it will not be a "wash out" by any means. However, with some
periods of convection and the associated outflow possible in and
near our area, the temperature (and heat index) forecast has a
large bust potential this weekend, particularly on Sunday across
northern/northeastern IL.

Our first round of showers and thunderstorms could come late
Friday night into Saturday morning. Forecast guidance continues
to support a southwesterly low-level jet over the Upper Midwest
impinging upon a conditional unstable airmass across northeastern
IA, and adjacent areas of western WI and southeastern MN Friday
night. Any thunderstorms that develop in the regime will be
favored to dive east-southeasterly along the thickness gradient,
which points right into our area. With this in mind, we have opted
to add some low end 20-30% chances for storms late Friday night
into Saturday morning. Strong gusty winds may accompany these
storms into far northern IL, and this has prompted the SPC to
increase a level 1 of 5 severe weather threat into far northern IL
Friday night.

The impacts these early morning storms and outflow have on
temperatures on Saturday remains to be seen. At this time, have
opted not to change temperatures or heat indices on Saturday, with
the expectation that the airmass will recover through the
afternoon. However, if cloud debris hangs on longer then
expected, peak afternoon heat indices on Saturday may not reach
the currently advertised 100-105 degree readings.

The signal in the medium range guidance continues to support the
potential for additional rounds of showers and thunderstorms
into, or very near, northern IL Saturday night through early early
next week as our area remains along the northern periphery of the
500 mb high. Again, there will be several periods of dry weather
through this period. However, the moist and very unstable airmass
will be supportive of instances of strong showers and
thunderstorms with instances of strong wind gusts and heavy
rainfall.

Temperatures and heat index values on Sunday will be largely
dependent upon the coverage of this convection and its associated
outflow. Accordingly, confidence in the temperature and heat index
forecast for Sunday is of low confidence at this time,
particularly over northern IL. However, in areas that remain
removed from the more widespread convection, heat indices are
likely to climb in excess of 100 degrees Sunday afternoon. At the
present time, this seems to be most favored for areas south of
I-80.

A synoptic cold front will eventually push through the entire
region, but this may not take place until Tuesday night into
Wednesday which will keep off-and-on thunderstorm chances going
in the region. In the wake of this cold front, there`s a strong
signal in the guidance suite for cooler conditions in the region
during the middle and end of next week.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1218 PM CDT Thu Aug 14 2025

No major forecast concerns are expected for this TAF period as
high pressure will remain in control. Therefore, expect VFR
conditions to prevail through the period with diurnally driven
cumulus during the afternoons and some mid-level clouds
overnight. Winds will continue to become easterly this afternoon
behind a lake breeze (southeast at RFD) with speeds remaining in
the 6-8 kt range before easing to 3-5 kts overnight. Directions
will gradually turn southeasterly overnight and then settle into
a southerly (180-190) direction Friday morning with speeds
picking up into the 6-8 kt range.

Yack

&&

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

&&

$$

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