Champaign, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

161
FXUS63 KILX 301050
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
550 AM CDT Mon Jun 30 2025

.KEY MESSAGES...

- Showers and storms are possible today (30-40% chance), with the
  best chance during the late afternoon into the evening. There is
  a 5% chance of severe storms, with damaging winds the main
  concern. Locally heavy rainfall is also possible.

- After a brief cooldown to seasonable temperatures for the middle
  of the week, hot and humid conditions will return late in the
  week. Afternoon heat indices of 95 to 105 degrees are expected
  each day Friday (July 4th) through Sunday.

&&

.DISCUSSION...
Issued at 236 AM CDT Mon Jun 30 2025

*** TODAY ***

A relatively diffuse sfc pattern is in place across the region,
along with a moist airmass with PWAT values of 1.5-2" (highest
across SE IL). Upstream, an upper trough axis was positioned
across the Dakotas, and this feature will swing through our area
today. In the short term (07z-12z Mon AM), scattered showers are
most likely south of I-70 where there is subtle convergence
through the low- levels. Given that rich moisture (PWATs around
2"), some locally heavy rainfall could occur. Elsewhere, mostly
dry conditions are favored through 12z. Some patchy fog could
develop (Macomb was reporting 1/4 mile as of 07z/2am), but high
clouds spreading in from convection across MO could slow
additional radiational cooling.

For today, the ambient environment remains as advertised in
previous discussions, with subpar deep layer shear (20-30 kts),
weak mid- level lapse rates, and moist profiles with well-mixed
PBLs. Collectively, this kind of environment favors similar
hazards to those seen with previous days convection: isolated
damaging winds due to precipitation loading in downdrafts, and
locally heavy rainfall. The one difference from previous days is
the approaching upper trough/cold front and marginally-improved
shear could lead to slightly greater storm coverage/organization.
Still, CAMs appear fairly sparse in terms of storm coverage across
the ILX CWA today, with most likely timeframe for precip being
22z-03z (5pm-10pm) as the front moves through. Continued the
downward trend in PoPs for today, now at 30-50% chance area-wide
as CAMs depict scattered or multi-cellular convection rather than
a coherent line. The front has trended a bit slower, so storms
could linger into late Mon eve (across E IL) before finally
departing to the SE.

*** MID-WEEK ***

There were no meaningful changes to the mid-week forecast. Weak
sfc high pressure (~1016 mb) will accompany the post-frontal
airmass into the region, resulting in ample sunshine on Tues/Wed
along with our long-advertised break from the heat/humidity. Highs
will be in the mid 80s Tues, then upper 80s on Wed, but dewpoints
in the 60s will keep heat indices below 90 degrees those days.

*** LATE WEEK INTO THE WEEKEND ***

Towards late week, guidance suggests the upper pattern will
feature an amplified ridge building over the central Plains, with
upper lows near the Hudson Bay as well as along the west coast of
Canada. Additionally, a weakening upper low over California should
eventually be swept northeast, and this shortwave could play a
role in late week precip chances for IL. As the upper ridge
approaches, it will allow the heat and humidity to build back into
the region. For Friday (the 4th) through Sunday, highs are
expected to be in the low 90s with dewpoints returning to the 70s,
which will result in several consecutive days of peak heat
indices between 95-105 degrees. Heat Risk is in the moderate
(impacts to those most susceptible to heat) to major (impacts to
anyone without adequate hydration/cooling) categories on those
days.

Guidance continues to depict the upper ridge axis shifting over
IL on the 4th of July, which should help limit precip coverage due
to large scale subsidence. Blended guidance currently has just a
15-20% chance of precip area-wide during the afternoon/evening of
the 4th, and the coarser resolution model blend has had a tendency
to overdue the PoPs during this summertime pattern, some I`m
optimistic that much of the area will stay dry. The aforementioned
shortwave is progged to be too far west to provide any meaningful
forcing for ascent across our area, and therefore any convective
development seems more likely to be driven by disorganized, pop-up
thunderstorms if we reach the convective temperature.

As the pattern evolves eastward in time, our local precip chances
increase into the weekend, with a 20-50% chance on Sat/Sun.
Despite the upper trough approaching during that time frame, 500mb
flow remains weak (less than 30 kts) and lapse rates uninspiring,
so the threat of organized severe storms from this system appears
fairly low. With another high moisture environment in place
(PWATs approaching 2"), sporadic strong wind gusts due to precip
loading will continue to be a concern with any convection.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 548 AM CDT Mon Jun 30 2025

Satellite imagery shows areas of fog most prevalent west of the IL
River currently. As this fog spreads east, it could result in
visbys down to 1 mile at KPIA. At the other terminals, visbys
reductions of 2-5 miles are possible during the first hour of the
period. Winds will maintain a westerly component for much of the
day, then a front will shift winds to northwesterly this evening.
That front will also produce scattered showers and storms, mainly
between 23-04z. Aside from the patchy fog this morning and the
potential for MVFR visbys with thunderstorms this evening, VFR
conditions should prevail.

Erwin

&&

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

$$