Weather Wednesday — April 9, 2015 Illinois Tornado Outbreak

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.

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AP

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.

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PBrooks Photography

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.

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Wedge tornado and wall cloud near Hillcrest, Illinois. Larissa Sebree via NOAA.

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.

Weather Wednesday –New Definitions from the Storm Prediction Center

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.

Understanding Categories
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.

 

Weather Wednesday – Hail

On this April Fools Day, we’ll be discussing hail. Hail is widespread throughout the world, but doesn’t often have the top of mind awareness of other storm-related topics…unless, that is, you’re growing crops or insuring buildings or vehicles. According to the National Weather Service’s hail page, the average loss from hail each year is about a billion dollars. However, in 2001 there was one storm event that eventually stretched from Kansas City to Illinois that caused $2-billion damage on a single day.

Hail is not normally considered a major threat to human life. The last reported fatality in the United States was in 2000 when a Texas man died after being struck by a softball sized hail stone. Two children reportedly perished in Russia in 2014. Livestock losses are reported from time to time.

The National Weather Service rates hail from less than a quarter inch or pea sized to over 4 inches or softball sized. The preferred references are actual measurements or approximations based on fixed sizes such as a quarter or a regulation sized softball. “Grapefruit sized” is a far less precise term. One of the reasons for using common objects as references is it allows storm spotters and others to report the size without venturing out into a storm with its associated risks to take actual measurements.

vivian_hailThe largest hail stone reported in the U.S was over 8 inches in diameter with a circumference of over 18 inches.

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Phil Katz-MSU Extension

Crop loss from hail is a significant risk to producers. Depending on where crops are in the growth cycle and the extent of the damage, growers are often cautioned to have a little patience to determine if the crops can bounce back. Many state extension services can provide more information.

 

hail carDamage to vehicles is usually pretty obvious in terms of dents and broken glass. There are some DIY fixes for smaller dents including letting the vehicle sit in the hot sun so the metal expands a bit. The best advice though is to contact your insurance carrier and/or a competent body shop. A worst case scenario is when a new car dealer’s lot or other parking lot is hit. Damage can easily escalate into six figures or more. Several years ago here in the Champaign-Urbana area, dozens and dozens of cars parked at the local airport were badly damaged.

thHail can also damage roofs constructed of various materials. Again, working with your insurance carrier to arrange for an inspection by a qualified roofer is always a good idea. Some damage may be hard for the untrained eye to see and ladder work is often best left to professionals anyway.

Siding on homes also can be easily damaged. Steel or aluminum siding can be dented and still maintain its structural and weatherproof integrity.Bad_Siding_Hail_Damage Hail can absolutely shred vinyl siding and immediate action to cover exposed underlayment or insulation is necessary to avoid more widespread water damage.

 

 

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NOAA Graphic

One question that is often asked is, does the presence of hail, especially large hail, tell us anything about the structure of a thunderstorm? Since hail is formed when water droplets freeze as they are lifted above the 32-degree line by updrafts, it stands to reason that the presence of ever larger hail stones in a storm reflects the strength of that updraft so it can be an indicator of both the strength and height of a thunderstorm cell. Hail is easily seen on radar because of its dense mass. Many videos shot by storm chasers show large hail as part of some tornadic thunderstorms.