Amf Ohare, Illinois Weather Forecast Discussion

711
FXUS63 KLOT 262331
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
631 PM CDT Fri Sep 26 2025
.KEY MESSAGES...
-  Dry and unseasonably warm daytime conditions through next
   week will lead to worsening drought.
&&
.DISCUSSION...
Issued at 1259 PM CDT Fri Sep 26 2025
Through Next Friday:
There`s virtually no impactful weather in store for the next week
plus, along with unseasonable/summer-like daytime warmth (80s
inland of lake cooling). An omega block will set up between
troughing over the Pacific NW and likely tropical cyclone Imelda
stalling near or over the southeast US and Humberto stalling a bit
farther offshore. At the surface, primarily west-southwest flow
inland of the lake through Saturday will transition to east-
northeast flow Sunday onward as expansive high pressure
establishes over northeastern North America. A weak cold front
Saturday night will take on back door characteristics into Sunday
and then largely wash out. Lake breeze enhancement to synoptic
onshore flow will enable the lake cooling footprint to spread
relatively far inland each day. Anticipate fairly large diurnal
temperature ranges, especially outside of Chicago, as dew points
mix out and support efficient nighttime radiational cooling.
An additional minor item of note overnight tonight into early
Saturday is the potential for patchy shallow ground fog (amidst
any otherwise modest visibility reductions) away from Chicago.
Went closer to MOS guidance for forecast lows (low-mid 50s outside
of the city), which will probably be near to a bit below this
afternoon`s crossover temps, supporting patchy fog development.
However, the very dry profile aloft will likely preclude anything
than more than highly localized dense fog near/over fields and
inland water bodies. Therefore, we`re not planning to message a
limited risk for impactful dense fog in the afternoon HWO.
Castro
&&
.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 631 PM CDT Fri Sep 26 2025
There are no significant forecast concerns this period. A lake
enhanced boundary is slowly moving across far northeast IL early
this evening and is expected to dissipate with sunset, likely
just north of ORD/DPA and near RFD. As a result, expect winds to
become light and variable though there is a small chance for a
brief light northeasterly wind direction at all three locations.
Light winds overnight will become more westerly Saturday with
speeds increasing to 10-15kt. These winds will diminish with
sunset Saturday evening. A cold front is then expected to move
across the area late Saturday evening into early Sunday morning,
shifting winds north/northeast. Timing could be near the end of
the 30 hour ORD/MDW tafs and will refine timing for this wind
shift with the 06z tafs.
Patchy/shallow ground fog will be possible overnight into early
Saturday morning, with the best chance across far northern IL in
the vicinity of where the current boundary dissipates.
Confidence for fog at any of the terminals, including RFD, is
too low for mention at this time. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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NWS LOT Office Area Forecast Discussion