Normal, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

249
FXUS63 KILX 141037
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
537 AM CDT Wed May 14 2025

.KEY MESSAGES...

- Near-record warmth is forecast for Thursday.

- A conditional risk for severe weather exists both Thursday and
  Friday.

- After a brief reprieve this weekend, the severe weather
  potential returns next week.

&&

.DISCUSSION...
Issued at 1241 AM CDT Wed May 14 2025

Early morning GOES WV imagery depicts an upper trough carving across
the Intermountain West. Model guidance is in excellent agreement
that this trough will help kick our pesky upper low eastward into
the Mid-Atlantic region this afternoon, with subsidence working
in across Illinois behind the departing wave. The net effect will
be a drier day across the region, and warmer too, as a hot
continental airmass begins to advect across the Plains ahead of
the upper trough. Temperatures will surge into the mid 80s today,
ratcheting up near 90 by Thursday as the upper trough lifts/pivots
toward the Upper-Mississippi Valley and drags a warm front
northward across our area. Scattered showers and an isolated
thunderstorm may accompany the warm front this evening, but a
strong capping inversion should limit most lifted parcels from
tapping into the elevated instability.

Attention then turns toward the Thursday afternoon/evening period
as a bulging dryline pushes across central IL. Explosive
instability (MLCAPE > 3500 J/kg) across the warm sector will be
buoyed by low 70s sfc Tds, a stout EML and steepening mid- level
lapse rates (> 8 C/km). Deep-layer shear will also be on the
increase (> 50 kts) as a mid- level jet core noses across the
Mid- Mississippi Valley atop the dryline. A quick glance at the
shear vector orientation with respect to the dryline suggests a
favored storm mode of isolated supercells, while the elongated
hockey stick hodograph supports an attendant giant hail and/or
significant tornado risk. Despite the absurd parameter space,
there remains a few mitigating factors that continue to apply a
downward pressure on predictability. These factors include
residual capping, dry air entrainment, and displacement from the
more favorable upper- level forcing; all of which could prevent
updrafts from reaching the LFC. Unfortunately, the 00z suite of
CAMs did not flash a consistent signal for deep convection to
initiate over central IL Thursday afternoon/evening. Given the
continued high degree of forecast uncertainty, we think SPC`s
decision to keep our area under a MRGL/SLGT risk is reasonable.

As an aside, there could be a brief fire weather and blowing dust
risk that develops late Thursday afternoon across west central IL
behind the dryline. The latest HRRR/RAP are on the drier end of
guidance, but each support RH values tanking below 25% with wind
gusts exceeding 30 mph.

A similar parameter space will redevelop for Friday, though it`s
not clear yet where the sfc boundary will become focused. In other
words, the evolution of the pacific-front/dryline may become
altered by any convective outflows that develop Thursday night
across central or southeast IL. Nevertheless, there has been an
increasing signal in convective QPF noted among the global models
for Friday afternoon, and NCAR`s experimental MPAS output
suggests violence will erupt somewhere in between I-72 and I-64.

Saturday looks convincingly dry as a high-pressure ridge builds
across the Plains behind the departing upper-level wave.
Temperatures will come down a bit but remain elevated for the
season (near 80 degF). Rain chances may then creep into portions
of western/southern IL as early as Sunday morning as shortwave
energy crests the upstream ridge axis and spawns nocturnal precip
somewhere across the Mid- to Lower-Mississippi Valley. A similar
deal could unfold Monday morning. The better precip signal arrives
Tuesday as yet another upper trough lifts across the central US
and pushes a cold front across the area. The analogs (CIPS) and
various ML tools are already highlighting Tuesday for additional
severe weather potential.

MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 529 AM CDT Wed May 14 2025

A weak surface ridge over central Illinois this morning has
resulted in light and variable winds and shallow fog to develop.
This fog will dissipate by around mid morning as a modest
south/southeast breeze around 10 kts sets up through the
remainder of the day. Once the fog mixes away, VFR conditions will
persist through the remainder of the TAF period, though clouds
will increase and lower this evening ahead of a warm front. There
remains a consistent signal for scattered showers to accompany the
front, and have therefore maintained the PROB30 group this
evening.

MJA

&&

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

$$