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576
FXUS63 KILX 032033 CCA
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
318 PM CDT Fri May 3 2024

.KEY MESSAGE...

- Near daily chances for showers and thunderstorms over the next
  week as a series of fronts advance across the region. The
  Tuesday through Wednesday period looks particularly active, with
  medium confidence in thunderstorms capable of producing all
  severe weather hazards.

&&

.DISCUSSION...
-- Changed Discussion --
Issued at 127 PM CDT Fri May 3 2024

Current GOES WV imagery depicts a strong upper-level low
positioned over western Ontario with more subtle shortwave energy
ejecting out of the Great Basin. Model guidance remains in excellent
agreement that shortwave energy lifts into the Northern Plains and
Upper Midwest regions overnight, ultimately helping to force a
synoptic cold front into western Illinois Saturday afternoon.

A plume of low-to-mid 60s dewpoints is progged to advect northward
ahead of the cold front, and SBCAPE values should be able to achieve
1000-1500 J/kg with CINH eroding in the presence of steep 0-3 km
lapse rates (> 7.5 C/km). This all adds up to likely (> 60% chance)
thunderstorm development Saturday afternoon along and ahead of the
cold front.

Coverage of Saturday storms could be limited by somewhat
underwhelming deep-layer shear profiles, with much of the area at
or below 30 kts in the vicinity of the cold front. Updrafts may
struggle to become organized or struggle to stay organized,
especially some of the early updrafts, and recent CAMs hint at
this as well. Nevertheless, CAPE/Shear profiles are just good
enough to support the potential for an isolated severe hail and
wind threat.

As storms move toward and east of I-55 Saturday evening, the
severe potential should gradually fade. This will largely be due
to the loss of daytime heating and the lack of a LLJ to help
augment instability. This thinking lines up well with SPC`s Day 2
Marginal Risk, which ends the threat near the I-57 corridor.

Flooding should not be a concern with the Saturday storm event.
NBM Mean QPF is around 0.25", and this guidance only offers a 10%
chance that rainfall exceeds 0.75", which is well below 3-hour
flash flood guidance.

The rest of the weekend through Monday should be fairly low drama,
with the main frontal zones displaced just to our south. Attention
quickly turns to the Tuesday - Wednesday timeframe as persistent,
deep southwest flow envelops the region ahead of an elongated
upper-level low. While we`re running lean on details at this
timeframe, the synoptic pattern (kinematics/thermodynamics) being
modeled supports a multi- day severe weather threat across
portions of the Plains and Midwest. This strong signal in the
global models is also reflected in the analogs and machine
learning tools for severe weather potential.

MJA
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&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1242 PM CDT Fri May 3 2024

Areas of broken stratus will continue to be observed in the
vicinity of the surface cold front. The BMI/DEC/CMI terminals may
experience broken MVFR ceilings through 23z/6pm before the front
departs further east and skies clear out. Surface winds will
become light and variable overnight with patchy fog developing.
Coverage and confidence in fog remain too low to include mention
in this TAF cycle.

MJA

&&

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

$$