211
FXUS63 KLOT 141135
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
635 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 /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 635 AM CDT Tue Oct 14 2025

Forecast concerns include...

Mvfr cigs through early afternoon.
Chance of showers Wednesday morning.

Low mvfr cigs have spread across parts of the Chicago area and
additional low mvfr cigs and some patchy ifr cigs have developed
across southeast WI. Low mvfr cigs are expected to fill in
across much of the area over the next few hours and continue
through late morning/early afternoon. At that time, the models
are in good agreement for this cloud cover to lift and scatter
out. Any ifr cigs this morning will likely be across far
northwest IL and possibly at RFD, but should also be brief.

There remains some light/patchy fog this morning, which is
slowly improving from north to south. Low level winds are strong
enough that current mainly mvfr vis with fog should not lower
any further.

There will be a chance for showers overnight into Wednesday
morning with the best timing still looking around daybreak for
the Chicago area terminals. Have maintained prob mention and
extended it to 14z for ORD/MDW. Overall duration of showers is
expected to be less than this time period and later forecasts
can refine timing with tempo mention possible. Once these
showers end Wednesday morning, there may be a period of mvfr
cigs. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM this morning to 1 PM CDT
     Wednesday for Winthrop Harbor to Wilmette Harbor IL.

     Small Craft Advisory from 1 PM this afternoon to 1 PM CDT
     Wednesday for Wilmette Harbor to Calumet Harbor IL.

     Small Craft Advisory from 7 PM this evening to 7 AM CDT
     Wednesday for the IN nearshore waters.

&&

$$

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