Strong to severe thunderstorms moved across portions of northwest Illinois during the evening of July 13th.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LOT wrote it up.
Strong to severe thunderstorms moved across portions of northwest Illinois during the evening of July 13th.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Chicago, IL wrote its last area forecast discussion before the first event at Jul 13, 6:34 PM CST, 11 minutes earlier.
Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 734 PM CDT Fri Jul 13 2018 .MESOSCALE DISCUSSION... 734 PM CDT A weakening bow echo is pushing into Northwest IL and Southern WI. RAP analysis shows an axis of 3500+ J/kg of sfc CAPE with the bow and 900 J/kg of downdraft CAPE. Shear is negligible; therefore, much more concerned about damaging winds and downbursts than hail. MRMS estimates are showing rainfall rates of 1+" per hour, but storms are moving at 40+ MPH so I'm not concerned about flash flooding yet. If storms start to significantly train, localized flooding could occur. Additional storms are forming around Davenport, IA, and those should reach the western forecast area in a couple of hours. Main threats will be heavy rain, frequent lightning, and strong winds through the evening. JEE && .SHORT TERM... 230 PM CDT Through tonight... Robust thunderstorm development has begun in the warm sector ahead of a more organized upper level shortwave in western Iowa. Additional forcing along the front extends northeastward into SE Minnesota and western Wisconsin, with some diurnal heating storms in SW Iowa out ahead of the main line. With a moist boundary layer and decent sunshine, the environment ahead of this upper wave and front will enable further destabilization and promote renewed/continued thunderstorm development farther east toward the Mississippi River this afternoon. Wind shear is not super strong, but a bit better speed max will spread into SW Wisconsin this evening. Meso models are in good agreement in bringing this activity into the I-39 corridor and Rockford area in the mid evening time frame. With the boundary layer not likely completely decoupled at this point and with arrival of a bit stronger speed shear, a few stronger storms with a concern for gusty winds does exist. Those with outdoor events this evening should keep an eye to the sky and radar as these storms approach this evening, as lightning itself is decent likelihood regardless of the severe concerns. Heavy rain is a concern, as these storms are not moving all that fast, although storm training chances are initially somewhat low. Questions will then center on the eastern extent of this activity as it moves into a slightly less favorable environment across northeast Illinois. The concern though is potential MCS development that may allow storms to move a bit farther eastward/southeastward, the main storm motion is more easterly/slightly northeasterly. Confidence is much lower that these storms will maintain themselves to the Chicago lakefront, but some showers will likely get out ahead of the main storm area late this evening, more so after the 10-11 pm time frame or later before weakening. Overnight redevelopment is possible as instability aloft will not decrease over the area overnight. Therefore with the upper forcing sliding through and a frontal boundary in place, additional storm development could occur, but confidence on coverage is low. KMD && .LONG TERM... 300 PM CDT Saturday through Friday... A humid weekend, much like those of June, will unfold for this second full one of July. The moist atmosphere will bring thunderstorm chances, more likely on Saturday than Sunday in terms of at least coverage at this point. Some of Saturday's thunderstorm potential, coverage, and timing will depend on how storms play out tonight. A generally moist and unstable air mass should in place, with an outflow-modulated surface trough draped across the area. This will probably be somewhat broad but still a source of general low-level confluence, along with any residual outflows. While there could certainly be some morning storms, an uptick in coverage is likely during the peak heating of the afternoon along the boundary, where mixed layer CAPEs look to peak in excess of 2000 J/kg. Convection- allowing guidance shows quite a spread in convective footprints, but generally show scattered to numerous storms developing in this broad trough corridor and evolving east-southeast around the periphery of the upper level ridge. Confidence on coverage is not the greatest, but felt that "scattered thunderstorms" was the best verbiage to use in the forecast for Saturday and for mainly I-80 south Saturday evening. Much like the storms of this summer, the risk of localized heavy rainfall with PWATs near two inches and wet downbursts with 35+ mph gusts should be the primary concerns, as deep layer shear is more marginal though not non-existent (around 30 kt). Isolated multi-cell merging could bring a locally higher wind threat. Dew points south of and up to the boundary should be into the mid 70s given current upstream conditions. Temperatures are a little more uncertain especially north with some cloud cover, but in the southern CWA, 90 should be more easily attainable Saturday afternoon. Together this brings forecast heat index readings up to 100 to 105 south of I-80. A lake breeze is anticipated, which will likely keep areas near the lake only around 80. The humid conditions continue into Sunday, though less of a focus is expected for convection. Certainly the chance for scattered storms, mainly south and west. Highs look to be in the upper 80s to lower 90s depending on cloud cover, with again some lakeside cooling. The cold front to end this air mass is expected to drop through the region on Monday, though some spread on timing. This will bring thunderstorm chances as well. Prior to the frontal passage, warm and very humid conditions are expected. Could again see highs reach into the lower 90s. Temperatures will drop back to seasonal readings for mid-July during midweek. MTF && .AVIATION... For the 00Z TAFs... A line of thunderstorms moving into northwest IL will impact RFD early this evening. Some storms have produced downbursts with strong winds, and the strongest storms may produce strong winds and hail. Heavy rain is also expected with the storms. Additional showers and storms will shift southeast across the region this evening. The storms should be weakening as they approach the eastern terminals, but since storms are stronger than expected now, I put a short tempo of -TSRA in the DPA and ORD TAFs. I think the line will dissipate to showers by the time it reaches MDW, and should dissipate before reaching GYY. Confidence is still low in how storms will develop Saturday. Due to the lack of confidence, I did not adjust TSRA timing in the TAFs. Periods of thunderstorms are expected Saturday afternoon, but exact timing and location will depend on what happens tonight and where the boundary stalls. The storms will also impact how far inland the lake breeze will get. As such, I did not adjust the lake breeze timing. JEE && .MARINE... 310 PM CDT A weak surface trough will creep its way southward down the lake tonight. Thunderstorms and some outflows will likely be shifting across northern to central parts of the lake this evening, and into the south late this evening into overnight. More scattered storms are likely across the south on Saturday, but the trough will gradually weaken, so winds should be more light and variable on Saturday apart from any storms. A cold front will shift southward across the lake on Monday, turning winds northerly with 15 to 25 kt gusts possible Monday night into early Tuesday. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
330 PM CDT Fri Jul 13 2018
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
142030-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-DeKalb-Kane-DuPage-Cook-
La Salle-Kendall-Grundy-Will-Kankakee-Livingston-Iroquois-Ford-
Lake IN-Porter-Newton-Jasper-Benton-
330 PM CDT Fri Jul 13 2018 /430 PM EDT Fri Jul 13 2018/
This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.
.DAY ONE...Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Limited damaging wind risk...up to 60 mph.
Limited Flooding Risk.
DISCUSSION...
Thunderstorms are likely to spread into portions of far northern
Illinois this evening, including the Rockford metropolitan area.
Depending on how organized the thunderstorms become and how
quickly they move into the area, isolated marginally severe wind
gusts will be possible. Outside of any severe wind risk, all
thunderstorms can be expected to produce occasional to frequent
cloud to ground lightning and very heavy downpours, with a
localized flooding risk.
In addition, heat indices will be around 100 degrees this
afternoon from the far western suburbs of Chicago south to Pontiac
and then west to the Mississippi River.
.DAYS TWO THROUGH SEVEN...Saturday through Thursday.
Saturday...
Elevated Thunderstorm Risk.
Limited Flooding Risk.
Limited Excessive Heat Risk.
Sunday...
Limited Thunderstorm Risk.
Limited Excessive Heat Risk.
Monday...
Elevated Thunderstorm Risk.
Limited Excessive Heat Risk.
Limited Coastal Flood Risk
Tuesday...
Limited Coastal Flood Risk
Wednesday and Thursday...
Limited Thunderstorm Risk.
.SPOTTER INFORMATION STATEMENT...
Spotters may be needed this evening in northwest and north central
Illinois.
GENERAL STORM MOTION OF THE DAY:
Moving toward the east at around 30 mph.
LMZ740>745-142030-
Winthrop Harbor to Wilmette Harbor-
Wilmette Harbor to Northerly Island-
Northerly Island to Calumet Harbor-Calumet Harbor to Gary-
Gary to Burns Harbor-Burns Harbor to Michigan City-
330 PM CDT Fri Jul 13 2018
This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.
.DAY ONE...Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Limited thunderstorm wind gust risk...up to 34 to 50 knots.
.DAYS TWO THROUGH SEVEN...Saturday through Thursday.
Saturday through Monday...
Limited Thunderstorm Risk.
Thursday...
Limited Thunderstorm Risk.
LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-142030-
Lake Michigan from Michigan City IN to St. Joseph MI 5 NM
offshore to Mid Lake-
Lake Michigan from Seul Choix Point to Rock Island Passage 5 NM
offshore to Mid Lake-
Lake Michigan South of a line from Seul Choix Point to the
Mackinac Bridge and north of a line from Charlevoix MI to South
Fox Island 5 NM offshore-
Lake Michigan from Charlevoix to Point Betsie MI 5 NM offshore to
Mid Lake-
Lake Michigan from Point Betsie to Manistee MI 5 NM offshore to
Mid Lake-
Lake Michigan from Rock Island Passage to Sturgeon Bay WI-
Lake Michigan from Sturgeon Bay to Two Rivers WI 5 NM offshore to
Mid Lake-
Lake Michigan from Two Rivers to Sheboygan WI 5 NM offshore to
Mid Lake-
Lake Michigan from Sheboygan to Port Washington WI 5 NM offshore
to Mid Lake-
Lake Michigan from Port Washington to North Point Light WI 5 NM
offshore to Mid Lake-
Lake Michigan from North Point Light to Wind Point WI 5 NM
offshore to Mid Lake-
Lake Michigan from Wind Point WI to Winthrop Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Winthrop Harbor to Wilmette Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Wilmette Harbor IL to Michigan City IN 5 NM
offshore to Mid Lake-
Lake Michigan Holland to Whitehall MI 5 nm off shore to mid-
line of lake-
Lake Michigan from Whitehall to Pentwater MI 5 NM offshore to Mid
Lake-
Lake Michigan from Grand Haven to Whitehall MI 5 NM offshore to
Mid Lake-
Lake Michigan from Holland to Grand Haven MI 5 NM offshore to Mid
Lake-
Lake Michigan from South Haven to Holland MI 5 NM offshore to Mid
Lake-
Lake Michigan from St. Joseph to South Haven MI 5 NM offshore to
Mid Lake-
330 PM CDT Fri Jul 13 2018
This Hazardous Weather Outlook is for portions of the open waters
of Lake Michigan.
.DAY ONE...Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Limited thunderstorm wind gust risk...up to 34 to 50 knots.
.DAYS TWO THROUGH SEVEN...Saturday through Thursday.
Saturday through Tuesday...
Limited Thunderstorm Risk.
Thursday...
Limited Thunderstorm Risk.
MTF
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www.youtube.com/nwschicagoThe Milwaukee radar (KMKX), 85 km away, was scanning. The volume nearest the first event began at 00:47 UTC.
1 thunderstorm wind. Local standard time, as filed.
A three foot diameter tree was uprooted on Route 75, one mile east of Wheeler Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2018Every state in 2018This day in weather historyWarnings in Illinois, July 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 773298.