Hail and Damaging Winds in Illinois, July 14, 2023

Area Forecast Discussion
National Weather Service Lincoln IL
345 PM CDT Fri Jul 14 2023

.SYNOPSIS...
Issued at 245 PM CDT Fri Jul 14 2023

Showers and thunderstorms will develop late this afternoon,
becoming more numerous this evening as weak frontal boundary moves
into west central Illinois. A few storms may become supportive of
damaging wind gusts before diminishing in intensity late tonight.
Saturday will be less hot and humid in wake of frontal passage,
but smoke from Canadian wildfires will begin to filter into the
region. Additional, sporadic thunderstorm activity is anticipated
into next week, helping to further ease drought conditions.

&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 245 PM CDT Fri Jul 14 2023

Key Messages:

 * Thunderstorm activity to increase this evening, possibly severe
 * Wildfire smoke expected to make a return this weekend

Evening Thunderstorms:
A couple thunderstorms have developed this afternoon along a
diffuse surface boundary, currently positioned just north of the
I-70 corridor extending from Kansas City, Missouri to Mount
Vernon, Illinois. The boundary layer within this area is supremely
buoyant and uncapped, characterized by low 90s sfc temps and mid
70s dewpoints. MLCAPE values, courtesy of the latest RAP, depict
2000+ J/kg in an otherwise weakly sheared environment. Generally
weak mid-level flow (< 30 kts) should limit the coverage of severe
convection, with the majority of updrafts struggling to get
organized. Nevertheless, the robustly buoyant airmass should help
compensate for meager kinematics, affording a couple storms the
potential to lay down severe-level downbursts and/or quarter-size
hail. And, while the tornado threat is non-zero (there will be at
least some surface vorticity enhancement along the front), the
storm-relative hodograph does not look particularly concerning.

From a timing standpoint, we expect thunderstorm coverage to
increase after 23z/6pm as a mid-level shortwave and attendant
surface boundary move across the Mid-Mississippi Valley. While
storms will be scattered in nature, we believe coverage will
become widespread enough to make any outdoor event west of
Interstate 57 vulnerable this evening; consider reviewing
evacuation contingencies.

Thunderstorm activity should begin to wane after Midnight in the
absence of a pronounced low-level jet. Still, enough elevated
instability and broad ascent could allow light convective
activity to fester into the early morning hours before departing
eastward with the surface boundary.

Haze/Smoke:
Upstream satellite imagery from the GOES Geocolor channel depicts
smoke bleeding southward into the Midwest this afternoon. This
smoke is forecast to move into central Illinois by Saturday
afternoon, with sky conditions becoming noticeably milky. Models
even indicate that this smoke may make it down to the surface,
working to reduce both visibility and air quality. Admittedly,
this has been a bit of an afterthought given impending convection,
but it's at least worth a mention for now as it could prove
impactful to sensitive groups and general aviation alike.

MJA

.LONG TERM...  (Sunday through Next Friday)
Issued at 245 PM CDT Fri Jul 14 2023

Periodic chances for showers and thunderstorms will exist through
much of the upcoming week as multiple shortwave impulses traverse
broad meridional mid-level flow. The first of these episodes
appears to come Sunday evening as another weak frontal boundary
sags into the region. CAPE/Shear profiles support marginally
severe storms, while southward progression should preclude a
flooding concern. Perhaps more notable convection will develop
during the Tue/Wed timeframe when midlevel flow increases across
the region atop a pseudo-stationary sfc boundary. Aside from the
severe convective potential, the general synoptic pattern sort of
resembles the Maddox setup for flash flooding. Late next week
appears to be a more settled period as mid-level heights increase
across the region. Meanwhile, temperatures next week look
seasonably warm, with the NBM boasting temperatures in the mid-
to-upper 80s.

MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1233 PM CDT Fri Jul 14 2023

Afternoon cumulus will continue to increase in coverage across
the regional terminals with sky coverage becoming BKN beyond
21z/4pm. Cloud bases will evolve around 5 kft AGL.

Attention quickly turns toward this evening with shower and storm
potential increasing ahead of a weak frontal boundary.
Thunderstorm coverage will be scattered in nature, but widespread
enough to warrant a TEMPO group near or shortly after 00z/7pm
across the regional terminals.

Flight categories will largely remain VFR through late evening,
deteriorating to MVFR (occasionally IFR) prior to 12z/7am as low
stratus develops in the vicinity of the front. Only slight
improvement to cigs is anticipated through late Saturday morning.

MJA

&&

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

Hazardous Weather Outlook
National Weather Service Lincoln IL
401 PM CDT Fri Jul 14 2023

ILZ038-043>046-053>057-061>063-066>068-071>073-152115-
McLean-De Witt-Piatt-Champaign-Vermilion-Macon-Moultrie-Douglas-
Coles-Edgar-Shelby-Cumberland-Clark-Effingham-Jasper-Crawford-Clay-
Richland-Lawrence-
401 PM CDT Fri Jul 14 2023

This Hazardous Weather Outlook is for central Illinois, east
central Illinois and southeast Illinois.

.DAY ONE...Tonight.

Scattered showers and thunderstorms are expected this evening. There
is a marginal risk that some of the storms may be severe with
isolated gusts up to 60 mph and isolated large hail up to 1 inch.
Lightning and locally heavy rainfall will also be a concern.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Scattered thunderstorms will continue to be possible Sunday through
Thursday as an unsettled pattern remains over the area. Strong storms
are possible Sunday, but the primary threat each day will be
lightning and locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated tonight.

ILZ027>031-036-037-040>042-047>052-152115-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-Schuyler-Mason-
Logan-Cass-Menard-Scott-Morgan-Sangamon-Christian-
401 PM CDT Fri Jul 14 2023

This Hazardous Weather Outlook is for central Illinois and west
central Illinois.

.DAY ONE...Tonight.

A severe thunderstorm watch is now in effect until 10pm. A few storms
will pose a damaging wind and large hail risk.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Scattered thunderstorms will continue to be possible Sunday through
Thursday as an unsettled pattern remains over the area. Strong
storms are possible Sunday, but the primary threat each day will be
lightning and locally heavy rainfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed this evening between 5pm and
sunset.

Expected storm motion is toward the east around 25 mph.

MJA