Good afternoon! We continue to work through hundreds of damage points from last week's severe weather. This thread will cover the latest information specific to the 7/15 (Monday) derecho. A summary map of all confirmed tornadoes from 7/15 is below. (1/10) We have confirmed an additional 3 tornadoes, bringing the event total to 27. The new tornado
confirmations are: 1. Maple Park (EF-Unknown*), 2. O'Hare Airport (EF-0), and 3. Country Club Hills
(EF-0). The track maps for these 3 tornadoes are below. (2/10)

Check out this thread 🧵for our morning forecast graphics. Be sure to check these out this morning, we are in for an absolutely wild meteorological ride🎢with summer (record warmth), spring (severe storms?), and winter (snow/cold) weather all crammed into the next 24 hours! Scattered t-storms are expected this evening (6PM til Midnight) with some of the storms potentially becoming severe. The primary threat is large hail, possibly up to 2” inches diameter. There is also a threat of locally damaging winds and a tornado or two. #ilwx #INwx

[3:20 PM CST 12/22] Here are key messages for the continued winter weather through tomorrow. Gusty winds and dangerously cold temperatures will become the norm tonight and especially Friday. Stay indoors, if you can! #ILwx #INwx Although snow will taper from west to east overnight, increasingly gusty winds will lead to areas of blowing snow reducing visibility especially in open and rural areas. North to south-oriented roadways will be most susceptible to blowing snow. #ILwx #INwx

.Thu 12/22 AM Update! 1) Key Messages for the Dangerous Winter Weather Today-Early Saturday:
Conditions will deteriorate quickly late AM-aftn hours with snow, gusty winds & plummeting temperatures. The snow will taper on Friday though dangerous cold will remain. #ILwx #INwx (1/6) .Arrival time of hazardous travel conditions today: Arctic front will sweep across the area from late AM thru early aftn from west to east, with accumulating snow, plummeting temps & gusty winds. A flash freeze may cause ice covered roads, topped by the snow. #ILwx #INwx (2/6)

.Wed AM update! 1) Key messages on the dangerous winter weather Thursday into the holiday wknd. A powerful storm system will bring strong winds, falling and blowing & drifting snow, & extreme cold. Worst conditions: Thu-Fri. Threat for flash freeze on Thursday! #ILwx #INwx (1/5) .2) Timeline graphic showing our latest thoughts on the upcoming dangerous winter weather. Travel conditions will likely rapidly deteriorate on Thursday AM through the afternoon from west to east. A flash freeze may cause icy roads during the accumulating snow! #ILwx #INwx (2/5)

[4:00 AM 12/20] Confidence in a major winter storm continues to increase for the Thursday to Saturday time frame. Blizzard conditions are possible, and travel looks to become severely impacted, particularly Thursday night through Friday afternoon. #ILwx #INwx This is an updated timeline graphic showing our latest thoughts on the upcoming major winter storm. Travel conditions will likely rapidly deteriorate Thursday afternoon and evening. #ILwx #INwx.

Major winter storm Thu thru Sat with heavy snow, strong winds, severe blowing/drifting snow & bitter cold. The worst conditions will develop Thu evening & continue into Fri evening when a full fledged blizzard is possible along with dangerously cold temp. #ilwx #inwx This is a look at impacts over space and time for the expected winter storm. Note the large footprint of this system, so travel will be impacted over much of the Upper Midwest and Great Lakes.

One of the very important jobs we have here at @NWSChicago is aviation forecasting, including for Chicago O'Hare and Midway airports. We work closely with the FAA providing forecasts that they utilize to make decisions, including which runways to use for landing and taking off. Wind forecasts play a significant role in determining the runways to be used. During the spring & summer, lake breezes frequently result in wind shifts that cause the FAA to change runways being used, which during busy times involves moving around many planes on their way here.

(1/5) This hour of tornado safety for Illinois #SeverePrep Week: Know the difference between a watch and a warning and what to do during a watch #ilwx (2/5) Do you know the difference between severe weather WATCHES and WARNINGS? A WATCH means severe storms or tornadoes might form and affect your area. A WARNING means it’s time to take action! A severe storm or tornado is expected in your area. #SeverePrep #ILwx

(1/4) Continuing the theme of this morning's Twitter tornado drill, we'll continue with tornado safety on day 2 of Illinois #SeverePrep Week. This hour, what to do BEFORE a tornado. #ilwx (2/4) Some people are especially vulnerable to the dangers of tornadoes.
Those with a lower level of mobility, such as the elderly or disabled, or those who live in mobile homes, may need your help to prepare & stay safe & #WeatherReady. #SeverePrep #ilwx weather.gov/safety/tornado

Good morning!☀️ Let's talk Monday's storms.

A long-lived, large storm complex tracked from the NE/IA border, across IA, northern IL, & northern IN. This produced widespread damage to trees, toppled several semis, & caused some structure damage.

Recap: weather.gov/lot/2020aug10 The peak gusts (measured & estimated) were frequently 70-90 mph & persisted for 15+ minutes with some locations experiencing even higher. These wind speeds are equivalent to EF-0 to EF-1 tornadoes but over a vastly larger area than a tornado would impact. #ILwx