401
FXUS63 KLOT 200157
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
757 PM CST Wed Nov 19 2025

.KEY MESSAGES...

- Plenty of cloud cover expected through Thursday and possibly
  through Friday.

- Dry and seasonably warm this weekend.

&&

.UPDATE...
Issued at 757 PM CST Wed Nov 19 2025

Some adjustments made to the going forecast this evening,
namely to expand mention of drizzle and add patchy fog areawide
overnight.

Early evening surface analysis depicts high pressure ridge
extending from southern IL northeast across northern IN/lower MI.
Winds were generally calm or light south-southeast across the
forecast area, with temps and dew points generally in the lower
40s. GOES satellite imagery and surface obs indicate widespread
stratus across the region, with regional 00Z soundings depicting
the top of the saturated layer in the 1-1.5 km range. Looking
aloft, the region is along the northern fringe of a broad upper
level ridge centered over the Gulf, beneath a ~90 kt west- east
oriented upper jet. A couple of subtle low-amplitude mid-level
short waves were likely aiding in producing subtle increases in
shear/weak ascent within the extensive area of stratus.

Bloom of low-dBZ radar returns, indicative of light drizzle,
has been noted since the approach of sunset. Successive RAP runs
seem to capture this in the low-level vertical motion field and
forecast sounding wind profiles, which may suggest a period of
more widespread drizzle this evening and again during the predawn
hours of early Thursday morning. While only manned observing
sites are reporting drizzle, suspect very light drizzle is
occurring over much of the area, and thus have added it to the
forecast areawide overnight. Gradual decrease in height of cloud
bases and visibility are also likely an indication of this to
some extent. Would expect this to continue overnight along with
areas of 1-3SM fog. Can`t rule out some denser fog and will
continue to monitor visibility trends, though increasing low-
level shear predawn with the next approaching short wave
suggests more of a low stratus issue then a widespread dense fog
scenario. Therefore have added fog mention across the area
overnight as well, and held onto it for a bit Thursday morning
as well.

Otherwise, forecast appears in good shape with stratus and
subtle warm advection expected to keep temps nearly steady in
the lower 40s through the night.

Ratzer

&&

.DISCUSSION...
Issued at 156 PM CST Wed Nov 19 2025

A deamplifying mid-level ridge centered along the entire
Mississippi River Valley will give way to a low-amplitude trough
brushing the northern Great Lakes Thursday through Friday.
Meanwhile, a trough axis crossing California will pick up an
elongated upper-level (Great Basin to Baja of California) and
bring a highly sheared resultant trough across the Ohio River
Valley late Friday into Saturday.

With a surface ridge passing just east of the area tonight and
seasonably weak surface low passing well to the south Friday
night, the area will remain in a period of generally weak flow.
This has resulted in stratus blanketing the area today. With WAA
within the low-level cloud layer and a subtle low/mid-level
wave crossing far northern IL tonight, little change in the
cloud cover is expected through at least tonight. An inversion
initially around 5kft will also support a sufficiently deep
saturated layer for patches of drizzle this evening into the
early overnight hours, particularly west of the Chicago metro.
Lowering inversion heights behind the wave will begin to
suppress cloud depths overnight and especially Thursday. While
the stratus layer will ultimately thin on Thursday, the low sun
angle and lack of any low-level drying (dew points actually
steady or rising) may limit local erosion of the stratus. Have
continued the downward trend in forecast temps, with stratus
most likely to continue over northern Illinois and possibly the
entire forecast area through much of the day.

Guidance continues to come into more agreement that much of the
precip associated with the ragged system over the Ohio River
Valley will remain focused south of the forecast area late
Thursday through Friday night. Blended guidance has started to
sharpen the PoP gradient while also shifting the gradient
southward. Modest low-level drying will further lower precip
potential into at least Friday morning, but isolated mid-level
rain showers may still expand well northward into the forecast
area Friday afternoon and evening.

High pressure will bring quiet weather conditions to the area
for the upcoming weekend. Expect mostly clear skies and
seasonably warm conditions, with highs in the 50s.

A powerful trough west of British Columbia is progged to
transition to an upper-level low over the southwest CONUS before
ejecting across the Midwest next Tuesday. Given the inherent
complexities of this evolution, confidence in the forecast this
far out remains low. However, unsettled weather with period of
showers and perhaps some storms does appear likely in the
general region on Tuesday.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 537 PM CST Wed Nov 19 2025

Forecast concerns include...

Low mvfr cigs through the period.
Areas of ifr cigs/vis and drizzle this evening.

Prevailing low mvfr cigs are expected everywhere through at
least Thursday afternoon when some breaks in the cloud cover are
possible. Some of the guidance suggests the mvfr cigs may
scatter out Thursday afternoon but confidence is low.

For this evening, ifr cigs and patches of lifr cigs along with
ifr vis have developed across parts of north central and central
IL, along with patchy drizzle. These are likely to continue
through much of this evening though ifr cigs are likely to
continue through mid morning for RFD and possibly DPA. Ifr cigs
are possible for the rest of the terminals overnight into
Thursday morning, but confidence is too low for mention with
this forecast.

Light southeast winds will become light south/southwest
overnight and then increase in speeds later Thursday morning,
possibly to 10kts at times, with speeds then diminishing some
after sunset Thursday evening. Directions will turn more to the
west/southwest Thursday evening. cms

&&

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

&&

$$

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