Midewin National Tallgrass Prairie Illinois Weather Forecast Discussion

847
FXUS63 KLOT 140814
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
314 AM CDT Tue Oct 14 2025
.KEY MESSAGES...
- A chance (40-60%) for showers late tonight into Wednesday
  morning. Highest chances along and north of I-80.
- A more active weather pattern looks will bring increasing rain
  chances (40-60%) Friday night into at least early Saturday.
&&
.DISCUSSION...
Issued at 314 AM CDT Tue Oct 14 2025
The only forecast concern in the near term is the threat for
any substantial fog development across far northern IL during
the predawn hours this morning. A deck of stratus continues to
hang on early this morning for main areas along and south of
I-88, with the exception of my southeastern counties.
Temperatures under this more persistent cloud cover have
remained in the upper 50s to the low 60s. Conversely, areas
across far northern IL that have seen a scattering of this cloud
deck have resulted in temperatures dropping several degrees
cooler (upper 40s to the lower 50s near the WI state line).
Consequently, this has fostered some areas of fog development
overnight. Fortunately, to this point, the most substantial fog
has been just north of the area across parts of southern WI.
Given the current tendency for the status deck to redevelop
across parts of northern IL, we suspect that any reduced
visibilities in fog across northern IL will be confined to areas
north of I-88 and likely not require the issuance of a dense
fog advisory. Nevertheless, we will continue to monitor current
observations and webcams across northern IL.
Outside of the early morning fog in the north early this
morning, the weather is looking to be fairly quiet through the
daytime hours today. Cloud cover will likely linger through the
morning, before we see some breaks this afternoon. Expect inland
temperatures to top out in the low 70s north, and the mid to
upper 70s south of I-80. Closer to the lake, onshore
northeasterly flow will hold highs in the mid to upper 60s.
Tonight, several mid-level impulses emanating from the
southwest flow ahead of the deep trough in the west today will
track east- northeastward through the Upper Midwest into the
western Great Lakes. An associated modest west-southwesterly
lower-level mass response is expected to foster a region of
isentropic upglide (warm air advection) and the likely (60%+
chance) development of showers late tonight into Wednesday
morning. This should be most notable from northeastern IA and
southern WI, southward into northern IL and perhaps parts of far
northwestern IN. In this region, I have bumped POPs up into the
40-60% range after 1 am tonight through mid morning on
Wednesday. Rain chances look to diminish Wednesday afternoon,
but lingering cloud cover and a cooler airmass advecting in from
the north-northeast will keep conditions cooler (highs low to
mid 60s) than the past couple of days.
Temperatures will be back on a warming trend again Thursday,
and especially on Friday, as the lower-level flow turns back out
of the south in advance of an area of notable area low pressure
tracking northward through the Dakotas into Manitoba.
Accordingly, temperatures are expected to warm back into the
upper 60s to low to mid 70s (warmest across interior sections of
IL) Thursday afternoon. Even warmer conditions (mid 70s to near
80) are slatted for Friday, albeit with breezy south winds.
Beyond Friday, a period of showers and thunderstorms is looking
to be in the cards for our area sometime Friday night into at
least early parts of Saturday. This as the strong area of low
pressure tracking into southern Canada late Friday drives a cold
front into the region. While this is still several days away,
and uncertainty continues with the timing of the front, there
continues to be a strong signal in the ensemble guidance for
this period of rain with the cold front. The other aspect of
this system that is of low confidence at this time is the
potential for a new area of low pressure to develop into the
lower Great Lakes along the cold front on Saturday. If this were
to occur as the ECMWF suggest, our chances of rain could
persist longer, likely into early Sunday. Otherwise, expect a
period of cooler weather in the wake of this front.
KJB
&&
.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1231 AM CDT Tue Oct 14 2025
Forecast concerns include...
Possible fog early this morning.
Mvfr cigs, possible ifr cigs this morning.
Chance of showers Wednesday morning.
A weak cold front is moving south across the area currently with
fog across southeast WI. Some of this fog will likely spread
into far northern IL early this morning though there remains
uncertainty for how widespread it will become. Current guidance
suggests the best chance for fog will remain northwest of the
Chicago terminals and for now, have only included mention at
RFD/DPA.
Guidance also suggests that mvfr cigs will develop over the next
several hours and persist through late morning/early afternoon
before lifting and possibly scattering out. There is some
potential for brief or pockets of ifr cigs. Confidence is low
for specific cig heights and opted to maintain mvfr cigs for all
locations, though did include a tempo ifr cig at RFD with the
potential for fog there.
Light northerly winds will turn to the north/northeast overnight
with speeds increasing to 10kt by daybreak which will continue
today, perhaps in the 10-12kt range. Winds look to increase some
early Wednesday morning, when gusts into the 15-20kt range are
possible, especially for the Chicago terminals.
There will be a chance of showers Wednesday morning with the
best chances for the Chicago area likely centered around
daybreak Wednesday morning with the overall duration possibly
just a few hours at any one location. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM this morning to 7 AM CDT
     Wednesday for Winthrop Harbor to Wilmette Harbor IL.
Small Craft Advisory from 1 PM this afternoon to 7 AM CDT
     Wednesday for Wilmette Harbor to Calumet Harbor IL.
&&
$$
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NWS LOT Office Area Forecast Discussion