-- Discussion containing changed information from previous version are highlighted. --
350
FXUS63 KILX 220042
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
742 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Beneficial rainfall is on tap late tonight through Monday
  night.

- The axis of heaviest rainfall has shifted southward from
  previous forecasts...with 1 to 3 inches anticipated everywhere
  along and south of I-72. Points further north will pick up 0.5
  to 1 inch.

- Cooler and drier conditions will prevail for the middle and end
  of next week.

&&

.UPDATE...
-- Changed Discussion --
Issued at 742 PM CDT Sat Sep 21 2024

Earlier convection lingered through about 5 pm over south central
Illinois, tracking southeast along a CAPE gradient associated with
the stationary front. Forecast area remains dry now, with regional
radar mosaics showing some showers and a few storms moving east
across central and north central Missouri. Our current balloon
sounding is showing quite a bit of dry air below 650 mb, so
despite surface dewpoints near 70 over a good part of the
forecast area, some moistening will need to take place to get
additional showers in here.

The main cold front shows up on surface obs and radar mosaics from
the SW to NE corners of Iowa, and should be near the Illinois
border toward mid morning Sunday. Latest HRRR runs continue to
show convection filling in along the boundary, though overall
remaining fairly disorganized. Main surge of showers/storms is
expected to be moving into western Illinois toward midnight and
reaching the I-57 corridor before sunrise.

Main forecast updates were to adjust the rain trends, especially
this evening.

Geelhart
-- End Changed Discussion --

&&

.SHORT TERM...(Tonight through Sunday)
Issued at 322 PM CDT Sat Sep 21 2024

19z/2pm surface analysis shows a nearly stationary frontal boundary
extending from Keokuk, Iowa southeastward to just north of
Evansville, Indiana. To the north of the front, much lower
dewpoint air has settled into the N/NE KILX CWA where readings are
currently in the upper 40s and lower 50s. Further W/SW closer to
the boundary, moisture is considerably richer as evidenced by
dewpoints in the upper 60s and lower 70s along/southwest of a
Galesburg...to Lincoln...to Effingham line. A line of convection
that formed along the primary instability axis near the
Mississippi River around midday has largely dissipated...with
lingering light showers noted from Peoria to Taylorville. Further
south where MLCAPEs are analyzed at greater than 2000J/kg, the
line has re-intensified from Litchfield to Mount Vernon. This
activity will track eastward and spill into the SE KILX CWA south
of I-70 over the next couple of hours. Further north, only
isolated showers are anticipated in the more stable environment
for the remainder of the afternoon and through the evening.

As a cold front approaches from the west and the low-level jet
energizes from Texas into Missouri, a large area of showers and
thunderstorms will develop west of the Mississippi River...then
push eastward into central Illinois late tonight into Sunday
morning. Given copious deep-layer moisture and favorable dynamics
ahead of the cold front, have carried likely to categorical PoPs
late tonight and categorical across the board Sunday morning. The
cold front will sink south of the I-70 corridor by Sunday evening,
resulting in decreasing rain chances across the northern half of
the CWA at that time.

Barnes

.LONG TERM...(Monday through Next Saturday)
Issued at 322 PM CDT Sat Sep 21 2024

The frontal boundary is progged to become nearly stationary in the
Ohio River Valley Sunday night through early Tuesday: however, as
a closed upper low evident on the latest water vapor imagery over
the Desert Southwest shifts eastward, it will interact with the
front and bring overrunning showers/thunder to much of central
Illinois. Given the expected position of the boundary, the axis
of heaviest rainfall has shifted southward from previous
forecasts. The latest projections suggest widespread rainfall
totals of 1 to 2 inches along/south of I-72...with isolated
amounts approaching 3 inches south of I-70. Further north from
I-72 northward, amounts have been decreased into the 0.50 to 1
inch range.

Once the upper low departs, the front will get nudged further S/SE
and the rain chances will come to an end by Tuesday evening. After
that, dry and cooler weather is anticipated for the remainder of
the extended as highs drop into the lower to middle 70s and
overnight lows dip into the lower to middle 50s Tuesday through
Saturday.

Barnes

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 620 PM CDT Sat Sep 21 2024

Main TAF concerns will begin after 06Z, with the approach of a
cold front from the northwest. A large area of showers will move
from west to east, impacting all TAF sites between 07-12Z. While
isolated thunder will be possible over a large part of central
Illinois, only the area from KSPI-KCMI has a high enough
confidence of thunder to include a mention at this time, focusing
on a 3-hour window at each site. Will need to watch for some
additional thunder potential as the cold front sweeps across
central Illinois early Sunday afternoon, though confidence is low
at this point.

Ceilings should hold around 10kft through the evening, then
steadily lower as the rain approaches. Ceilings should lower to
below 3,000 feet shortly after the rain begins, and remain below
2,000 feet the remainder of the forecast period.

Geelhart

&&

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

$$