663
FXUS63 KILX 111912
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
212 PM CDT Sun Aug 11 2024

.KEY MESSAGES...

- Rain will move into the region tomorrow morning, with off-and-on
  showers lingering into early Monday evening before tapering off.
  The best chances (+ 70%) and highest rainfall amounts (+ 0.50")
  are expected to occur west of a Galesburg-to-Springfield line.

- Multiple rounds of thunderstorms will pass through the region
  between Wednesday night and Friday afternoon, perhaps affecting
  central Illinois directly. The severe weather potential remains
  low at this time, but torrential rainfall will accompany these
  storms.

&&

.DISCUSSION...(through next Saturday)
Issued at 1232 PM CDT Sun Aug 11 2024

Afternoon water vapor imagery depicts shortwave energy digging
across the Black Hills, with regional radar mosaics revealing
areas of showers and thunderstorms developing in the vicinity of
this disturbance.

Short-term, hi-resolution guidance is in excellent agreement that
this activity across the Northern Plains evolves into an organized
MCS tonight as it pushes across the Corn Belt, eventually making
it across the Mid-Mississippi valley by dawn.

While the general trend is for this MCS to decay on arrival (hostile
low- level dry air and little- to- no instability), there remains
some notable variance among hi- res guidance with respect to (a)
areal extent of precip; (b) starting/ending time; and (c) the most
reasonable range of rainfall estimates.

Regarding the areal coverage of precip, the FV3 and ARW stand
together in bleeding 0.10" rainfall north to the I-74 corridor and
east to the I-57 corridor. Meanwhile, the HRRR, NSSL WRF and
NAMNEST confine measurable rainfall west of a Galesburg-to-
Springfield line. While both trends are viable outcomes, I tend to
favor the further south/west solution. Experience and pattern
recognition would suggest that decaying MCS`s tend to dive
southward toward the instability gradient, which in this case,
will be positioned in Missouri along a loose baroclinic zone.

At this point, hi-res guidance is fairly consistent with rain
entering our far west between 5-8am, with the bulk of rainfall
occurring before Noon, but with scattered, warm-advection showers
then lingering into the early evening hours before tapering off.

Thinking most locations will receive between 0.01" - 0.25"
tomorrow. What could separate the wheat from the chaff is any
mesoscale banding that occurs. Whether this happens beneath a
speculative MCV or is the result of transient frontogenetic
enhancements from strong warm advection--I`m not sure--but there
are hints of banding in some of the hi-res guidance. In such
case, there could be a few narrow corridors of 0.75"- 1.0" --
again favoring areas west of a Galesburg-to-Springfield line.

Skipping ahead, the Wednesday to Friday timeframe has the look of
a busy pattern for central IL. From a synoptic viewpoint, there
will be a warm front lifting across the region Wednesday night
into Thursday, theoretically providing the needed buoyancy for
thunderstorm activity. This, in tandem with multiple shortwaves
traversing the area, should provide the necessary forcing and
shear for an organized storm threat. Admittedly, the GEFS is much
less bullish on the severe weather potential, but when added among
EPS and GEPS guidance, probabilities increase for the late
Wednesday night through Thursday evening period.

Additional chances for showers and storms bleed into early next
weekend, but these will be highly dependent on what evolves in the
western Atlantic with regards to a tropical disturbance. If this
disturbance drifts too far west, we could be stuck beneath low
clouds and sprinkles. If it stays far enough east, it could be a
dry and seasonably warm weekend.





MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1201 PM CDT Sun Aug 11 2024

High pressure will move across central Illinois this evening and
overnight. Light W/NW winds in place today will become light and
variable or calm overnight, then set up out of the SE Monday.
Meanwhile, showers and thunderstorms will develop to our west this
evening and approach central Illinois overnight, arriving Monday
morning in a weakening phase. Confidence in precip on station is
highest in the SW (at SPI) and lowest to the NE (CMI).

Deubelbeiss

&&

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

$$