Hail and Damaging Winds in Illinois, May 15, 2025

Area Forecast Discussion
National Weather Service Lincoln IL
209 PM CDT Thu May 15 2025

.KEY MESSAGES...

- Near-record warmth and humidity through this evening will
  increase the risk for heat-related illness, especially in
  vulnerable populations.

- There is a level 2 of 5 (slight) risk for severe weather this
  evening, mainly near and east of roughly I-55. Large (possibly
  significant) hail and damaging straight line winds are the main
  risks, but there is a low (5%) chance for tornadoes as well.

- There is a level 4 of 5 (moderate) risk for severe weather
  Friday afternoon and evening south of I-70, and a level 3
  (enhanced) risk further northwest. All severe hazards are in
  play.

- Tomorrow, southwest winds gusting 35-45 mph will combine with
  relative humidity values below 30% to result in increased fire
  danger, mainly north of I-72. These winds will also result in a
  risk for localized blowing dust, which could briefly diminish
  visibility for motorists.

&&

.DISCUSSION...
Issued at 134 PM CDT Thu May 15 2025

An upper level trough evident in water vapor satellite imagery
across the Northern Plains/Upper Midwest early this afternoon is
slated to drift east-southeast into our area by tomorrow night.
Ahead of that feature, several disturbances will offer central and
southeast IL active weather, while behind it the pattern turns
benign for the upcoming weekend. At some point early next work week,
thunderstorm chances will return with the approach of another
trough lifting out of the Great Plains.

***** SEVERE WEATHER RISK THIS EVENING *****

The most imminent forecast concern is the prospect of severe
weather this evening. Unfortunately, this remains a conditional
risk as a capping inversion continues to prevent the realization
of abundant mid level instability. If and when that cap breaks,
the hellacious severe weather parameter space characterized by
3000-4000 J/kg MLCAPE and 40-50 kt EBWD will prove ample for
explosive convective development, as well as the longevity of
storms that do fire. Given relatively weak forcing along the dry
line (vs the stronger forcing we would expect along a true cold
front) and a large component of the shear oriented normal to that
boundary, we'd expect a discrete storm mode with large to
significant hail being the primary risk; entrainment CAPE, or
ECAPE (a parameter closely tied to potential hail size), values
from RAP/HRRR forecast soundings are in excess of 3000 J/kg across
our eastern counties this evening. Prolific mid level dry air and
PWATs nearing record values will favor efficient evaporational
cooling and hence strong downward momentum in thunderstorm
downdrafts for severe winds as well, with DCAPE values on the
RAP's most recent mesoanalysis between 1300-1500 J/kg. While LCLs
are higher than ideal for tornadogenesis, increasing the
difficulty for surface convergence to connect to thunderstorm
mesocyclones, we certainly don't want to downplay that threat
because of the anticipated strength and longevity of those
mesocyclones. Thankfully, the relatively fast storm motion will
confine the risk to just a few hours this evening, with storms
quickly sailing into the Hoosier State; at this time, we're most
concerned about the 6-10pm timeframe, though again it's not
entirely plain when the cap will vanish.

***** SEVERE WEATHER RISK FRIDAY AFTERNOON-EVENING *****

After our glancing blow with severe storms this evening, all
attention turns to the set up for tomorrow. Deterministic guidance
is in agreement another shortwave will soar into the Prairie
State during the afternoon, but precisely how far northwest
moisture returns ahead of the attendant incoming dry
line/prefrontal trough will dictate destabilization and hence
storm intensity along that boundary during the afternoon and
evening. The magnitude and northward extent of that moisture
return itself will also be conditional on if/where storms form
this evening, how far south they push the effective boundary, and
whether convection initiates further south during the early
afternoon as a few of the CAMs are indicating. In any case, even
the more bullish guidance suggests instability will be at least
marginally lower tomorrow compared to today, but that comes at the
expense of a weaker cap and slightly stronger forcing for ascent.
Once again, all severe hazards will be in play tomorrow, with
perhaps a higher risk for tornadoes and damaging straight-line
winds given (1) slightly lower LCLs and (2) more mid level dry air
with the encroaching upper trough. The CAMs comprising the 15.12z
HREF seem to be converging on roughly the I-55 corridor for
convective initiation, though there are some discrepancies with
the NAMNest firing storms west of the IL River and the ARW
igniting those updrafts nearer I-57. Storm motion will once again
be quickly towards the northeast, with the convective threat
shifting out of the area after around 8-9pm.

***** GUSTY WINDS TODAY AND ESPECIALLY TOMORROW ****

Outside of thunderstorms, it'll be seasonably breezy this afternoon
as south winds gust 20-30 mph, sporadically higher especially near/west
of I-55 where deeper mixing and steeper low level lapse rates
will materialize behind a dry line into the early evening.
Tomorrow will be even windier with some potential for gusts to
kiss Wind Advisory criteria (45 mph). Confidence in that is too
low at this point, with Bufkit soundings mixing technique
suggesting a high degree of uncertainty in the depth of mixing,
and also variability between models. In general, top of channel
winds are running around 30-35 kt, though there could be a brief
period where deeper mixing allows us to tap into the 40-45+ kt
winds around 850-900mb during the afternoon-evening. Winds ahead
of the frontal boundary crossing the region will be from the
south-southwest, while behind it they'll blow from the west. Just
noticing the 10-40% deficit in soil moisture north of roughly I-72
and observed 0.25 2-inch soil moisture (wfv) at SPI, one wonders
whether these winds will result in a risk for blowing dust,
especially (1) if the stronger winds come to fruition and (2) in
the vicinity of any ongoing agricultural activities.

***** DRY AND COOLER OVER THE WEEKEND *****

The upper trough will shift east and surface high pressure build
into the region in its wake Friday night into Saturday, giving us a
dry and seasonably cool weekend with daily highs in the low to mid
70s. The next opportunity for precipitation will arrive Monday into
Tuesday of next week as another system lifts out of the Central
Plains. A lot remains unclear about that system, including its
arrival time and warmth/moisture return ahead of it, which suggests
vast uncertainty surrounding both precipitation amounts and any
severe weather potential.

Bumgardner

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1225 PM CDT Thu May 15 2025

VFR conditions are expected to be predominant throughout the
forecast period, though some stratocumulus around FL035 to FL040
is percolating across the Prairie State early this afternoon.
South winds, veering to southwest behind a dryline later this
afternoon, will gust to around 25 kt through the evening, ease
overnight, and then pick back up from the south mid to late Friday
morning.

The biggest wild card and greatest forecast concern remains the
20-30% chance for a thunderstorm going over one/more of the
terminals. For this, prob30 groups are in the TAFs at all
airfields accept PIA for the 2-3 hour time period of highest
thunderstorm probabilities. Any of these storms could be severe,
with the risk highest at BMI, DEC, and CMI where GR and strong
wind gusts were added to the prob30 group.

Bumgardner

&&

.FIRE WEATHER...
Issued at 134 PM CDT Thu May 15 2025

Behind the dry line this afternoon, various high res guidance, most
notably the RAP/HRRR, advertise dewpoints dropping sufficiently to
bring RH values into the 20s mainly west of I-55. Combining this
with southwesterly winds gusting 25-30 mph will increase the risk
for erratic fire behavior, so we'd recommend limiting (or at least
using extra precautions with) any burning activities during the
latter portion of this afternoon into the evening. Tomorrow, the
risk appears to be even higher as the residual dry airmass across
our northwest counties combines with even stronger southerly wind
gusts (35-45 mph) from the late morning into the afternoon. While
confidence was too low to issue on this shift due to model
variability, a Red Flag Watch/Warning may become necessary.

Bumgardner

&&

.CLIMATE...
Issued at 727 PM CDT Wed May 14 2025

Record temperatures for Thursday and Friday:

Location       Thu Record    Thu Record     Fri Record
.                 High        Warm Low         High
=============  ==========    ==========     ==========
Bloomington      94/1894       70/1962        92/1900
Champaign        90/2001       66/1962        92/2001
Charleston       92/2001       69/2013        94/2001
Decatur          94/1894       68/1968        92/2001
Jacksonville     91/2013       68/1962        90/2001
Lincoln          90/1987       65/2013        92/2001
Olney            91/2018       69/1962        91/2001
Peoria           93/1894       68/1894        93/1894
Springfield      91/1962       69/1962        93/2001

Geelhart

&&

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

Hazardous Weather Outlook
National Weather Service Lincoln IL
330 PM CDT Thu May 15 2025

ILZ027>031-036>038-040>053-162030-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-Logan-De Witt-Piatt-Champaign-Vermilion-Cass-Menard-Scott-
Morgan-Sangamon-Christian-Macon-
330 PM CDT Thu May 15 2025

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

.DAY ONE...Tonight.

A conditional risk for significant severe storms exists this
evening. All severe weather hazards including large hail exceeding 2
inches in diameter, thunderstorm wind gusts exceeding 60 mph, and a
tornado will be possible. The chance of severe storms is greatest to
the east of I-55. The risk of severe storms should come to an end
area- wide by 10 PM.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

An additional risk for significant severe weather exists Friday
afternoon across portions of central and southeast Illinois. All
severe weather hazards including large hail exceeding 2 inches in
diameter, thunderstorm wind gusts exceeding 70 mph, and a strong
tornado are possible. The severe storm potential is highest to the
south of I-72.

Dry and gusty conditions could support rapid fire spread and blowing
dust on Friday in areas where rainfall does not occur.

The risk for severe weather then returns on Tuesday as a frontal
system lifts across the region.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 5 PM and 10 PM this evening.
Additional spotter activation may be needed Friday afternoon.

Expected storm motion is toward the northeast around 50 mph.

ILZ054>057-061>063-066>068-071>073-162030-
Moultrie-Douglas-Coles-Edgar-Shelby-Cumberland-Clark-Effingham-
Jasper-Crawford-Clay-Richland-Lawrence-
330 PM CDT Thu May 15 2025

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

.DAY ONE...Tonight.

A conditional risk for significant severe storms exists this
evening. All severe weather hazards including large hail exceeding 2
inches in diameter, thunderstorm wind gusts exceeding 60 mph, and a
tornado will be possible. The risk of severe storms should come to an
end by 10 PM.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

An additional risk for significant severe storms exists Friday
afternoon across central and southeast Illinois. All severe weather
hazards including large hail exceeding 2 inches in diameter,
thunderstorm wind gusts exceeding 75 mph, strong tornadoes, and
isolated flash flooding are all possible.

The risk for severe weather then returns on Tuesday as a frontal
system lifts across the region.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 5 PM and 10 PM this evening.
Spotter activation will also likely be needed Friday afternoon.

Expected storm motion this evening is toward the northeast around 50 mph.

Erwin