A severe thunderstorm moved across parts of northeast Illinois during the morning of September 1st.
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.
A severe thunderstorm moved across parts of northeast Illinois during the morning of September 1st.
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 Sep 1, 6:00 AM CST, 1 hour 15 minutes earlier.
Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 700 AM CDT Sat Sep 1 2018 .SHORT TERM... 337 AM CDT Through tonight... Quite a challenging forecast for today and tonight, especially as it comes to assisting those with outdoor plans or holiday weekend events. Confidence in timing and extent of convective trends is low this morning and throughout the day, though there is greater confidence in redevelopment of activity overnight into Sunday morning. The main issue is that we have a multitude of factors both supporting and inhibiting convective development. Upstream during the overnight hours a large cluster of storms has developed over Iowa with support from a low level jet feeding Gulf moisture over a warm front extending east from a low over eastern Nebraska. Pockets of shortwave energy wrapping around an eastern CONUS ridge provided additional support for this activity, just as they, along with diurnal heating, supported a smaller cluster of storms earlier last evening which developed over the local area. A similar cluster formed over Iowa on Thursday night but tracked southeast and fell apart rather than moving into the local area. The lack of convective debris Friday was yet another factor favoring the diurnal redevelopment last evening. Over the past 2-3 days the large scale flow across the CONUS has slowly been amplifying, digging a longwave trough into the Plains and building the ridge across the eastern US. The effect locally has been to bring the most favorable axis of convective activity gradually closer. For this reason, it appears more likely that the existing cluster of storms moving out of Iowa will hang on a bit longer as it moves into northern Illinois this morning. As the low level jet eventually relents, the afternoon may dry out for a while and the remnant cloudiness may hinder additional widespread development this afternoon, at least compared to what we saw on Friday. Overnight tonight, the low level jet again ramps up but is positioned more directly over the local area. This would favor the development of convection overhead rather than upstream. The longer residence time of the activity expected overnight, in addition to rainfall expected this morning, prompted discussion of flash flood headlines between the MKX, DVN, and LOT offices. The outcome is reflected in the existing watches in place from central WI across northwest IL into eastern IA. For now, given the slightly more favorable axis that has been in place to the northwest, we elected to keep southeast WI and the local CWA out of the watch. WPC continues to have much of the area in their excessive rainfall outlook, so this situation will continue to be monitored. Lenning && .LONG TERM... 320 AM CDT Sunday through Friday... Have made little change to the long term forecast as the guidance remains relatively consistent on the long-wave pattern over the CONUS. However, while there is relatively decent confidence on the general trends of the extended forecast period, the finer scale details have considerable uncertainty. In general, the Bermuda High should build west across the sern CONUS to the Lower Mississippi Valley as broad upper troughing is carved out over the wrn CONUS by a series of shortwaves dropping into the Pacific Northwest. There should be little progression to the long-wave pattern as it slowly increasing in amplitude over the next several days. This will set up an extended period of broad swly flow aloft that will persist through the middle of next week. Through this period, the center of the Bermuda High will gradually lift north to the Mid-Atlantic region bringing a trend of height rises to the Midwest as a series of shortwaves, ranging from relatively weak to relatively strong, ripple through the fast swly flow aloft. Given relatively high confidence in the long-wave pattern, confidence remains relatively high for temperature/moisture trends with warm and humid conditions expected to persist well into next week, with highs in to middle 80s to arnd 90 F and dewpoints in the 70s. Peak heat indices should reach into the upper 90s and possibly approach 100 F at times. For pcpn and convective trends, confidence is lower and will largely be influenced on finer scale details. For Sunday, guidance continues to indicate moderately strong instability through the day, surface forcing should be weak but there will be stronger flow aloft. Periods of rain and thunderstorms are likely for Sunday into Monday, but timing of the periods of rain remains somewhat uncertain. Some damaging wind threat may exist with the strongest storms, though locally heavy rainfall and flooding may end up being the bigger concern should training thunderstorms develop in line with the flow aloft as pwats reach arnd 2 inches over the area. Uncertainty in convective trends will decreases with time through the period though the longer range guidance generally indicates that the main focus should trend northward as the center of the upper ridge over the mid Atlantic coast retrogrades slightly to the Appalachians. Daily convective potential will likely focus on mesoscale features and where outflow boundaries set up each day. But in general, will continue to carry some pcpn potential through the period. && .AVIATION... For the 12Z TAFs... Convective trends so far appear to be evolving generally as anticipated. There is always the question of how effectively the existing activity across northwest IL will hold together after daybreak as it moves east toward the metro terminals. Multiple signs point to it persisting, and even if the leading edge erodes there is ongoing development occurring back near the Quad Cities area. Additionally, satellite cloud tops have been warming farther west across southern Iowa but are staying relatively cold to our immediate west, which is further indication this activity still has some life to it. A break still appears likely toward early afternoon, with additional redevelopment possible in the evening but more likely, or more widespread, overnight into Sunday morning. Lenning && .MARINE... 320 AM CDT High pressure is moving off the New England coast while another area of high pressure spreads across the Northern Plains with a weak, dissipating cold front extending from Lake Superior to the Central Plains. South to southwest winds will persist over Lake Michigan through tonight. By Sunday morning, the front will completely wash out and the highs will merge into a sprawling ridge extending from the East Coast through the Middle Mississippi Valley. A weakness in the pressure gradient will set up Sunday through early next week, with relatively light and variable winds over the lake. By midweek, an area of high pressure is expected to build out of Canada and into the Northern Plains. A cold front in advance of the high is expected to push across the lake Wednesday as the high spreads east across the Upper Great Lakes region. This should set up a period of northeast to east flow over the lake by Wednesday night and then persist for the next few days. && .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
457 AM CDT Sat Sep 1 2018
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
021000-
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-
457 AM CDT Sat Sep 1 2018 /557 AM EDT Sat Sep 1 2018/
This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.
.DAY ONE...Today and Tonight.
Weather hazards expected...
Significant Thunderstorm Risk...with an associated:
Limited hail risk...up to quarter size.
Limited damaging wind risk...up to 60 mph.
Elevated Flooding Risk.
DISCUSSION...
Thunderstorms are spreading across into northwestern Illinois this
morning and are expect to continue into the morning. Additional
periods of thunderstorms are likely today, though exact timing and
coverage is still uncertain. Some of the stronger storms will have
the potential to produce damaging winds and large hail. In addition,
heavy rainfall may occur in some of the storms and could lead to
localized flooding.
.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Sunday...
Limited Severe Thunderstorm Risk.
Limited Flooding Risk.
Limited Excessive Heat Risk.
Monday...
Elevated Flooding Risk.
Elevated Thunderstorm Risk.
Limited Excessive Heat Risk.
Tuesday and Wednesday...
Limited Thunderstorm Risk.
Limited Excessive Heat Risk.
Friday...
Limited Thunderstorm Risk.
DISCUSSION:
A period of unsettled weather is expected through at least mid-week.
Warm and humid conditions are expected with periodic chances for
thunderstorms. For Sunday, there is a chance that some of the
stronger storms may be severe, with strong winds and large hail
being the primary severe threats. In addition, heavy rainfall may
occur in some of the storms and could lead to localized flooding.
.SPOTTER INFORMATION STATEMENT...
Spotters may be needed today into this evening.
GENERAL STORM MOTION OF THE DAY:
Moving toward the east at 30 mph.
LMZ740>745-021000-
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-
457 AM CDT Sat Sep 1 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...Today and Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Limited thunderstorm wind gust risk...up to 50 knots.
.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Sunday...
Elevated Thunderstorm Risk.
Monday through Wednesday...
Limited Thunderstorm Risk.
Friday...
Limited Thunderstorm Risk.
LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-021000-
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-
457 AM CDT Sat Sep 1 2018
This Hazardous Weather Outlook is for portions of the open waters
of Lake Michigan.
.DAY ONE...Today and Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Limited thunderstorm wind gust risk...up to 50 knots.
.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Sunday...
Elevated Thunderstorm Risk.
Monday through Wednesday...
Limited Thunderstorm Risk.
Friday...
Limited Thunderstorm Risk.
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www.youtube.com/nwschicagoThe Chicago radar (KLOT), 43 km away, was scanning. The volume nearest the first event began at 13:15 UTC.
1 thunderstorm wind. Local standard time, as filed.
Several large trees and tree limbs were blown down in a localized area near the 3500 block of North Opal Avenue in the Belmont Heights neighborhood. One tree fell onto a house producing minor roof damage.
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, September 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: 781141.