Tornado Trends in Illinois – Updated

2014-03-21photo1The tornado trends in Illinois has been updated to include data through 2013. The plots in order are the number of tornado reports by year, deaths by year, and injuries per year. Click to enlarge each plot.

These plots are based on storm data at the National Climatic Data Center (NCDC). Tornado records are notorious for not being consistent over time. It is nobody’s fault – technology changes and reporting techniques have improved over time. The newer NWS Doppler radar systems were installed in the 1990s, the spotter networks continue to improve, and everyone has a cell phone with a camera.  As a result, the number of tornadoes has increased in recent years with the better accounting.

In addition, there is always the potential for over-counting the number of tornadoes as they travel. For example, you might have a report for a tornado spotted 2 miles west of Smithville, and then another report 10 minutes later of a tornado north of Smithville. Was this the same tornado or two separate ones? Hard to tell without supporting evidence, especially before the modern-day radars.

I think the number of deaths and injuries by year in Illinois may actually be more reliable than the tornado frequency because they were just as widely reported in the media in the 1950s and 1960s as they are today. One can clearly see the spike in 1967 due to the Oak Lawn/Belvidere tornado outbreak and the 1990 spike from the Plainfield tornado. Sadly, the last two years have been bad in terms of fatalities in Illinois – 2012 with 9 deaths (Harrisburg, IL) and 2013 with 8 deaths (November 17, 2013 outbreak) after 7 relatively quiet years.

If you want to look at US trends, check out the NCDC page on tornado trends.

tornado-year

fatal-year

injury-year

April in Illinois: Part II – Plots

Here are the temperature and precipitation departures for every month in 2013 and 2014.

In the first plot you can see the remarkable string of 6 months in a row with below-average temperatures. The statewide average temperature for November-April was 31.6 degrees, 5.6 degrees below average. It was the fourth coldest November-April and tied with November 1935-April 1936. The coldest was November 1903-April 1904, which was 30.6 degrees, a full degree colder.

What hasn’t received as much notice is that we have run on the dry side since July 2013 (second plot). This April was the first significantly wet month since June 2013. The statewide precipitation deficit since July 1, 2013 is 6.1 inches.

image004

image009

April in Illinois: Warmer and Wetter

Temperature

The statewide average temperature for April was 51.9 degrees, and only 0.7 degrees below average. While it continues the string of below-average months that stretches all the way back to November, this month had the smallest departure from average.

The year to date statewide temperature was 31.2 degrees, which is 6.6 degrees below average and the fourth coldest January-April on record.

Precipitation

The statewide average precipitation for April in Illinois was 5.11 inches, 1.33 inches above the 1971-2010 average. This is the wettest month for Illinois since June 2013. Harrisburg reported a monthly total of 12.96 inches, the highest monthly total in the state.

Snowfall was light in April and confined to the northeast quadrant of the state. Amounts of 1 to 2 inches were common in the Chicago area.

Here are the April precipitation and precipitation departure maps for Illinois. While southern Illinois received the most rain, some parts of north-central Illinois were slightly below average (area in light tan). At this time, the US Drought Monitor shows Illinois to be drought-free with only a small amount of “abnormally dry” conditions near the Quad Cities area.

april1

apr2