997
FXUS63 KILX 201931
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
131 PM CST Thu Nov 20 2025

.KEY MESSAGES...

- Low clouds and patchy drizzle will once again be a concern this
  evening ahead of the rain.

- Rain will lift into the region Friday morning, with the highest
  rainfall totals expected to be south of a Quincy to Terre Haute
  line where there is currently a high (60-90%) chance of
  exceeding 0.50"; source 06z REFS.

- A sharp cold front will push through by the middle of next week,
  sending overnight temperatures into the 20s by Thursday morning;
  source 13z NBM.

&&

.DISCUSSION...(through next Thursday)
Issued at 121 PM CST Thu Nov 20 2025

Low clouds and patchy drizzle will persist through this evening
across central and southeast Illinois as we get spurious periods
of sufficient upward omega through an otherwise non-uniformly
saturated near-sfc layer (0-1.5 km). The primary impact will be to
general aviation, though motorists may experience damp pavements
and occasional reductions in visibility.

Our main weather story comes tonight into Friday.

New guidance trends indicate a tighter gradient in Quantitative
Precipitation Forecast (QPF) along the northern edge of our
approaching frontal system, alongside a slightly delayed onset of
precipitation. The reasons for this shift are evident in this
afternoon`s mid-level Water Vapor (WV) imagery, which highlights
the impending clash of two notable features over the Midwest late
tonight.

The first feature is a negatively-tilted trough pivoting across
the Big Bend region of Texas. This trough is drawing both Pacific
and Gulf moisture northward into the Southern Plains and will be
the primary driver of rain chances into Friday as it lifts toward
our area. The second is a dry, subsident air mass pushing
southeastward into the Great Lakes region.

As these two air masses phase together late tonight, a sharp
north-south rainfall gradient is expected to develop, roughly near
or just south of a Quincy-to-Terre Haute line. Recent LPMM QPF
output from both the REFS and HREF ensembles strongly supports
rainfall totals between 0.25"-1.25" south of this line, with
amounts quickly diminishing to 0.10" or less with northward
extent.

The upcoming weekend will see a return to dry and mild weather as
the departing frontal system gives way to high pressure building
across the central US. Expect afternoon temperatures to warm into
the mid-to-upper 50s on both Saturday and Sunday, driven by low-
level warm advection beneath an amplifying ridge axis.

Our attention then shifts to the Monday night-Wednesday timeframe
with the arrival of another frontal system ejecting out of the
Southern Plains and lifting across the area. Convective chances
and moisture return ahead of this system appear limited, which may
keep Quantitative Precipitation Forecast (QPF) totals in the
0.1"-0.5" range. The more significant aspect of this system will
be the dramatic temperature shift. A sharp cold front is expected
to move through on Wednesday, ushering in blustery northwest winds
and causing overnight lows to bottom out in the 20s, just in time
for Thanksgiving Day.

MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1110 AM CST Thu Nov 20 2025

Visibility is gradually improving, with some 1 to 2SM lingering
from KSPI-KCMI for another hour or two. Ceilings remain very low
and do not substantially improve through the period, though some
low MVFR conditions are possible near KPIA late afternoon into
early evening. Morning model guidance points to another period of
lower visibility developing late evening and continuing into
Friday morning, mainly east of a KBMI-KSPI line. These should lift
later in the morning as rain becomes more widespread.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$