791
FXUS63 KILX 120838
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
338 AM CDT Mon Aug 12 2024

.KEY MESSAGES...

- Showers will spread across parts of central Illinois today.
  Rainfall will be light...with the highest amounts of 0.25 to
  0.50 focused along/southwest of a Macomb to Springfield line.

- Showers and thunderstorms will become more prevalent Wednesday
  night through Thursday night. While the severe weather risk will
  remain low (less than 5%), there is the potential for strong
  thunderstorms late Thursday afternoon into Thursday evening.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 338 AM CDT Mon Aug 12 2024

A short-wave trough currently over South Dakota/Nebraska will
track southeastward into the region today...spreading clouds and a
few showers into central Illinois. 08z/3am radar mosaic shows
clusters of showers/storms associated with the wave across
central/western Iowa into northwestern Missouri. This activity
will track E/SE and will spill into the Illinois River Valley
after 11z/6am. With the nocturnal low-level jet weakening after
sunrise and the showers pushing further east into a dry/subsident
environment across Illinois, am expecting the precip to diminish
in both intensity and areal coverage. Based on radar trends and
latest HRRR/RAP runs, it still appears the most widespread showers
will impact locations along/southwest of a Galesburg...to
Lincoln...to Effingham line where high chance to likely PoPs are
warranted. While the precip will tend to diminish toward midday,
scattered showers will linger through the afternoon and into the
evening as the wave traverses the area. Rainfall will be
light...with the highest amounts in excess of 0.25 focused across
the W/SW KILX CWA. Meanwhile, locations north of I-74 and east of
I-57 may stay completely dry. Given extensive cloud cover and
showers, temperatures will be suppressed today. Afternoon highs
will range from the lower 70s across the W/SW where rain will be
most likely...to the upper 70s to around 80 degrees near the
Indiana border. Any lingering showers will come to an end this
evening, followed by partial clearing and dry conditions
overnight. With added boundary layer moisture in place and winds
expected to be nearly calm, think fog will develop where rain
occurs today. As a result, have added patchy fog to the forecast
late tonight south of I-74 and west of I-57. After any early
morning fog burns off, a partly sunny and dry day is anticipated
for Tuesday with afternoon highs topping out in the upper 70s and
lower 80s.

Barnes

.LONG TERM...(Wednesday through Sunday)
Issued at 338 AM CDT Mon Aug 12 2024

As a more significant short-wave trough crosses the Rockies and
pushes into the Plains, downstream upper ridging will nudge the
primary baroclinic zone northward toward central Illinois by
Wednesday. A few showers may spread into the far SW KILX CWA late
Tuesday night, with scattered showers and storms anticipated
everywhere along/west of I-55 on Wednesday.

As has been advertised for the past several days, the most
significant chance for widespread beneficial rainfall will arrive
late Wednesday night through Thursday night as the Plains wave
tracks further eastward into the region. With the warm front
lifting northward and the nocturnal low-level jet strengthening
from Oklahoma to Iowa, showers and thunderstorms will become
widespread across Iowa, northern Missouri, and western Illinois
Wednesday night. The storms will remain elevated, posing only a
minimal risk for small hail/gusty winds late Wednesday night into
early Thursday morning...primarily along/west of the I-55
corridor.

Once the early day convection diminishes, a lull in rain chances
will occur for a good portion of Thursday before an approaching
cold front activates by late afternoon and evening. With low
pressure progged to be over N/NE Iowa, central Illinois will be in
the warm/unstable sector of the system. 00z Aug 12 GEFS shows a
low probability (10-20%) of SBCAPEs exceeding 500J/kg and bulk
shear increasing above 40kt. Given somewhat more favorable
instability/shear parameters and the presence of a forcing mechanism
during peak heating, think scattered strong thunderstorms will be
a good bet late Thursday afternoon and evening...especially
along/west of I-57.

The Central Plains wave will slowly shift eastward through the
region on Friday, continuing the chance for showers/thunder.
Depending on the exact speed of the wave and its associated cold
front, there may be another chance for strong thunderstorms Friday
afternoon/evening along/east of I-57, but confidence in this
scenario remains low at this time. After that, the strongest
forcing will shift into the Ohio River Valley and drier weather
will return for next weekend.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1104 PM CDT Sun Aug 11 2024

High pressure will remain perched over the area, resulting in calm
to light/variable winds through Monday evening. Late tonight, fog
is expected to form over eastern IL, and have included a few hours
of MVFR visibility at KCMI. There is a 30% chance of IFR
visibility in a 09-12z window. An upper level disturbance will
move into central IL Monday morning, and linger into the evening.
This will bring periods of -SHRA or sprinkles. Latest guidance
shows ceilings and visibility remaining VFR across the central IL
terminals.

25

&&

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

$$