It’s been an eventful week on the weather front, so let’s highlight a few points.
What started out as a very quiet first quarter of the year as regards the number of tornadoes has become much more active since mid-April. There have been several widespread, damaging and deadly outbreaks, especially over the last ten days or so.
In addition, the storms over the past weekend (May 9 and 10) included extremely high rainfall rates in some areas which led to flash flooding and necessitated swift water rescues. Some of the rescues were broadcast live by television stations in Dallas and retransmitted to the entire country via The Weather Channel.
And if that wasn’t enough, a late season snowstorm on the same weekend buried parts of the Rocky Mountains into the Dakotas. The heavy, wet snow damaged buildings and had to be shoveled out of Coors Field before the Colorado Rockies could host their Sunday afternoon game against the Los Angeles Dodgers.
And to top it all off, Tropical Storm Ana, brought gusty winds and copious amounts of rain to the Southeast.
On this Tax Day edition of Weather Wednesday, we’ll revisit last week’s tornado outbreak in Illinois. Statewide, 11 tornadoes have been confirmed in the April 9th event. The earliest, which caused very little damage, was reported just northwest of Peoria in the afternoon hours. By early evening, strong thunderstorms were crossing far northern Illinois and eventually spawned the first EF-4 tornadoes ever reported in DeKalb and Ogle Counties (records kept since 1950) and the strongest tornado in the National Weather Service Chicago Office County Warning Area since an EF-5 devastated Plainfield, in the southwest suburbs, in 1990.
Two people were killed in the unincorporated town of Fairdale where nearly every structure, more than 70 in all counting outbuildings, was either damaged or destroyed. 22 injuries were reported in the outbreak. The tornadoes eventually approached the far western suburbs of Chicago but missed three population centers near their path. Damage was widely scattered in a multi-county area.
This outbreak was well forecast and there is general agreement there was plenty of warning. The Storm Prediction Center (SPC), as it did with the EF-3 and 4 tornadoes in Illinois on November 17, 2013, mentioned possibly tornadic storms at least four days in advance.
The National Weather Service Chicago Office updated their summary of the tornadoes just this morning. This is one of the most complete such documents I’ve ever read and includes some of the few satellite images of a tornado’s path I’ve ever seen. Read it all the way to the bottom and you’ll see the SPC guidance in the week leading up to the storms.
A couple of these tornadoes were extremely well documented via video (note: Strong language toward end) and live streaming and some of the visuals of the rotating wall clouds were just about textbook. The low sun angle contributed how well the tornadoes were captured.
There was also a significant side issue involving a motorist by the name of Sam Smith who was shooting video. That footage was widely shown on television and the driver was taken to task for getting too close to the storm, even if accidentally. (There are now licensing issues with the video so we won’t link to it here. However, it is widely available on You Tube.)
There were a couple of takeaways from his experience which are good reminders to all of us who may encounter storms. First, if a funnel cloud or tornado does not appear to be moving, it is either headed straight for the observer or dead away from the observer. To be safe, get out of that area immediately by driving at right angles to the storm. Second, this motorist backed up to take shelter in his vehicle under a bridge. Although many people have done that and survived, experts say that is a bad idea because wind speed may actually be amplified as it is compressed into that confined space. There have been fatalities of people under overpasses.
There’s been much talk in recent weeks of a more detailed method of describing the potential for severe weather now being employed by the Storm Prediction Center in its Convective Outlooks. The SPC worked with National Weather Service offices, communications experts and consumers of its products to expand its long time use of the “Slight, Moderate and High” risk categories to “Marginal, Slight, Enhanced, Moderate and High.”
In addition, the chart below describes what the storms might look like under each newly-defined category and what the main threats would be.
The Storm Prediction Center has many products that can be used by broadcast meteorologists, emergency managers and the general public to look as far as 8 days ahead. These tools are especially valuable for planning purposes and should never supplant your detailed local forecast.
The Mesoscale Discussions are particularly helpful on days when severe weather is expected. The discussions are issued on an “as needed” basis as storm threats develop. Other tools are updated as often as four times a day. If you’ve never visited the site at spc.noaa.gov, now would be a good time to familiarize yourself with the offerings.