Rosemont, Illinois Weather Forecast Discussion

781
FXUS63 KLOT 041951
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
251 PM CDT Sat Oct 4 2025
.KEY MESSAGES...
- July-like warmth will continue through Monday.
- Stronger winds and continued dry conditions will result in
  heightened fire danger and areas of blowing dust Sunday
  afternoon.
- Cold front will bring rain chance Monday and especially Monday
  night, followed by more seasonable temperature for the rest of
  the upcoming work week.
&&
.DISCUSSION...
Issued at 251 PM CDT Sat Oct 4 2025
Our stretch of unseasonably warm and dry conditions will continue
through Monday before cooler weather arrives following a cold
frontal passage Monday night. A period of showers and some
thunderstorms will also accompany this frontal zone Monday night.
Fire weather concerns increase in our area on Sunday as the
unseasonably warm weather combines with increasingly breezy and
very dry afternoon conditions (reference the fire weather section
below for more on this). A tightening pressure gradient and deep
and efficient boundary layer mixing during the day will foster
stronger gusty southwest winds from late Sunday morning through
late afternoon, particularly over western portions of the CWA.
Conditions continue to support the idea for at least a couple hour
period in the afternoon with peak gusts to around 30 mph. With
the very dry conditions and increased farming activity, the gusty
winds could also result in some areas of blowing dust in open
areas, but not currently expecting this to cause big enough
problems to require a blowing dust advisory. Nevertheless, we will
maintain the going mention of blowing dust in the forecast.
The weather pattern will begin to transition on Monday as an upper
trough slides eastward into the upper Mississippi Valley and
western Great Lakes late Monday and Monday night. As it does, an
associated surface cold front will shift southward into far
northern IL by late Monday afternoon. Unseasonably warm weather
will persist in advance of the front, so expect high temperatures
for Monday to once again climb into the 80s.
A period of showers (and even a few storms) are expected Monday
night into early Tuesday as we make this transition to a cooler
airmass. The anafrontal nature of the cold front should result in
most of the precipitation occurring behind the front, thus making
the Monday night through early Tuesday morning period the most
favored for rain. WHile this pattern does not look to support
overly high rainfall amounts, the combination of mesoscale forced
ascent along the baroclinic zone with the larger scale forcing
within the entrance region of the upper jet may support some
narrower corridors of higher rainfall amounts into Tuesday
morning. Nevertheless, it appears unlikely that this period of
rain will significantly cut into our large precipitation
deficits over the past couple months. Accordingly, large scale
major drought improvement appears unlikely at this time.
Cooler, more seasonable temperatures are expected Tuesday thought
much of the upcoming work week. After rain ends Tuesday, dry
weather should resume for much of the remainder of the week. The
only exception being a small (20%) chance for a few showers with
another weak impulse on Friday. Otherwise, the general idea of a
trough-ridge-trough upper-level longwave pattern across the North
American continent late next week into next weekend continues to
be supported amongst the various medium range ensemble suites.
While there does continue to be differences in the longitude of
where these long waves will set up, there is a general consciences
that conditions will be turning warmer again (above average highs
in the 70s) into next weekend.
KJB
&&
.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1226 PM CDT Sat Oct 4 2025
Key Messages:
- Gusty south-southwesterly winds expected tomorrow.
While a stray shower couldn`t completely be ruled out this
afternoon at the Chicago metro terminals (~10% chance), expect
dry and VFR conditions to prevail through the TAF period.
South-southwesterly gusts up to around 20 kts should be
observed this afternoon, though stronger gusts -- possibly into
the 25-30 kt range at times -- are expected from a similar
direction during the late morning and afternoon tomorrow. The
highest sustained wind/gust magnitudes both today and tomorrow
are forecasted at RFD, while the lowest magnitudes are expected
at GYY.
Ogorek
&&
.FIRE WEATHER...
Issued at 251 PM CDT Sat Oct 4 2025
No change in thinking regarding potential fire weather concerns
on Sunday as stronger winds combine with the very warm and dry
conditions. In addition to the stronger winds, it continues to
look favorable for dewpoints to mix out Sunday afternoon,
resulting in min afternoon RH values between 20 and 30 percent.
There remains notable spread in model guidance with regards to
min RH values Sunday, with some guidance substantially higher
than our forecast, and a couple of models a bit lower. Have
continued to lean toward the lower end of the guidance spectrum
given the worsening short term drought and expectation for deep
mixing.
The forecast still largely keeps conditions just below Red Flag
Warning criteria. However, with conditions likely to be near Red
Flag criteria for a short period Sunday afternoon, we have
opted to heighten awareness with a SPS.
- Izzi/KJB
&&
.CLIMATE...
Issued at 821 PM CDT Fri Oct 3 2025
High temperatures may approach record highs this weekend. Here are
the current records for October 4th and 5th:
Saturday       Sunday
Chicago    90 (1951)     88 (1997)
Rockford   90 (1922)     90 (1922)
- Izzi/Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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