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FXUS63 KILX 220445
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1145 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...
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

&&

.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...  
-- Changed Discussion --
(For the 06z TAFs through 06z Sunday Night)
Issued at 1145 PM CDT Sat Sep 21 2024

Large area of rain and storms west of the Mississippi River will
move east overnight, though thunder extent is expected to be more
questionable the further east it gets. Will include a thunder
mention at KPIA/KSPI for now, and monitor trends for the next few
hours for potential expansion eastward. Currently think the
thunder threat should be out by about 12Z in these areas. By 18Z,
the bulk of the steadier rain should scatter out, but additional
showers will remain a threat into the afternoon as the cold front
moves across the TAF sites. Can`t rule out some additional thunder
in the 21-24Z period, but confidence is too low to include at
this point.

Once the rain begins, ceilings are expected to quickly drop to
below 2,000 feet, where they largely will remain into the evening.
Getting to the end of the forecast period, latest HREF guidance
suggests 40-60% chances of IFR ceilings by 03Z from KBMI-KCMI,
with some lower potential at KDEC.

Geelhart
-- End Changed Discussion --

&&

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

$$