Updates will appear above the orange squiggle. Further information about today's severe weather event can be found below the orange squiggle.
UPDATE 11 1046PM CT: Doppler radar measures a 96 MPH wind 5,000 feet off the ground in the middle of the bow echo in Indiana. NWS is warning for 80 MPH winds. This is it. It's happening.
UPDATE 10 1008PM CT: As promised, here your mesoscale convective system, or the line of storms that could become a derecho as the night progresses. It's starting to take on a southeasterly component to its motion. Eastern Indiana and western Ohio need to be on alert through the evening hours as this system continues to organize and strengthen. 70+ MPH winds are possible.
UPDATE 9 755PM CT: Current models show that these storms will be the ones that form into a dangerous bow echo (potentially a derecho) and race across Indiana and Ohio later tonight.
UPDATE 8 655PM CT: Heads up Milwaukee and Kenosha.
UPDATE 7 615PM CT: Gigantic mess of storms over Wisconsin and Illinois right now, producing very strong damaging winds and large hail. Waiting to see if any will coalesce into a strong bow echo.
Also, there are more watches in effect. Purple is a PDS Tornado Watch (900PM CT). Orange is a PDS Severe Thunderstorm Watch (100AM CT). Red is a regular tornado watch (12AM ET).
UPDATE 6 538PM CT: Golf ball sized hail and 80 MPH winds are moving into the southwestern suburbs of Chicago, including Joliet.
UPDATE 5 515PM CT: Very dangerous tornado-warned storm moving into Yorkville IL, southwest of Chicago, with a possible tornado, 70+ MPH winds, and tennis ball sized hail.
UPDATE 4 427PM CT: Two distinct lines of storms are beginning to develop. The one near Chicago should be the troublemaker. We need to keep an eye on the one up in Iowa and Wisconsin, though.
UPDATE 3 417PM CT: Never seen this before, a PARTICULARLY DANGEROUS SITUATION SEVERE THUNDERSTORM WATCH for the counties shaded in blue.
* EFFECTIVE THIS WEDNESDAY AFTERNOON AND THURSDAY MORNING FROM
400 PM UNTIL 100 AM CDT.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
* PRIMARY THREATS INCLUDE...
NUMEROUS SIGNIFICANT DAMAGING WIND GUSTS TO 80 MPH LIKELY
SEVERAL VERY LARGE HAIL EVENTS TO 2 INCHES IN DIAMETER POSSIBLE
A FEW TORNADOES POSSIBLE
UPDATE 2 400PM CT: Tornado warning for Lee and Ogle Counties in Illinois, west of Chicago, and for Winnebago County, including the western half of Rockford.
INITIAL UPDATE 340PM CT: First severe thunderstorm warning issued for a supercell west of Chicago producing half-dollar sized hail and 60 MPH winds. It looks like it's going to start wrapping up pretty quickly. Be on alert, western Chicago suburbs.
Also, note the line of storms developing in northeastern Iowa/extreme southwestern Wisconsin.
Here is the particularly dangerous situation tornado watch in effect until 9PM.
* EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 150 PM
UNTIL 900 PM CDT.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
* PRIMARY THREATS INCLUDE...
SEVERAL INTENSE TORNADOES LIKELY
SEVERAL SIGNIFICANT DAMAGING WIND GUSTS TO 80 MPH POSSIBLE
SEVERAL VERY LARGE HAIL EVENTS TO 3 INCHES IN DIAMETER POSSIBLE
See my earlier diary for more information about today's outbreak, including more charts and graphs I didn't post below for those with slower connections.
See my diary from yesterday for a comprehensive overview of derechos.
Here's the main risk today:
The two-part severe weather outbreak predicted over parts of the Midwest and Great Lakes region is beginning to play out this afternoon, with the explosive development of intense thunderstorms across Iowa, Wisconsin, and Illinois around 330PM Central Time.
The first part of the outbreak will be from individual supercell thunderstorms that have to potential to produce significant, long-live tornadoes, large hail (over baseball size at times), and extremely strong winds in excess of 80 MPH.
The second part of the outbreak is the most dangerous threat, and that will come in the form of something called a mesoscale convective system (MCS), or a powerful line of thunderstorms that could turn into a derecho -- a long-lived powerful line of thunderstorms that produces significant wind damage along a 240+ mile path.
In anticipation of this one-two severe weather punch, the Storm Prediction Center has issued a rare high risk for severe weather across northern Illinois and Indiana, with a larger moderate risk area surrounding the bullseye.
We face three big questions right now:
- The environment is hyper-conducive for a derecho-like system to form. Will these storms form into a line, and when?
- How strong will the potential derecho get once it forms?
- Where will the potential derecho move once it forms?
Forecasters have a reasonable idea as to what the three answers are, but storms have minds of their own. It'll come down to watching what happens once they form, and warning accordingly.
Prepare, but don't panic. Secure all loose items outside, as they will easily blow around in winds. Grills, patio furniture, garden gnomes, and whatever else you've got should go inside a shed, come inside, or get tied up against a sturdy object.
Make sure your cell phones are charged and you've got gas in your car.
Wear sneakers/tennis shoes/whatever you call them tomorrow in case you have to walk through broken glass or debris outside.
Make plans in case you lose power for an extended period of time.
Keep a very close eye on the Storm Prediction Center and your local National Weather Service office. Like I said, it'll happen very quickly once the storms form and the line(s) develop. People closer to the Appalachians will have more time to react than people in Illinois or Indiana.
Hopefully a derecho will not happen, but the risk exists, and it's better to be informed than scared by the news stations that can't be bothered to do in-depth reporting.
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