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908
FXUS63 KILX 212023
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
323 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

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- 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.
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&&

.SHORT TERM...
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(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
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&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1237 PM CDT Sat Sep 21 2024

1730z/1230pm radar imagery shows a broken line of convection
extending from KGBG to just west of KIJX. This activity has been
steadily pushing eastward, but is encountering a drier/more stable
environment as it does so. Based on latest radar trends, have
opted to add thunder mention at both KPIA and KSPI between 18z and
20z...but have left the remaining sites dry as the line will
eventually dissipate as it crosses I-55. Winds are initially
southeasterly, but will veer to the south late this afternoon and
evening, then to the southwest overnight. The next wave of
precipitation is still on target for late tonight, with HRRR/RAP
timing similar to the previous TAF forecast. Have only made a few
minor adjustments, bringing predominant light rain into KPIA by
09z then further east to KCMI by 12z. Ceilings will initially be
VFR, but will lower to MVFR an hour or two after the rain begins.
MVFR ceilings will then persist through the remainder of the 18z
TAF period.

Barnes

&&

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

$$