One of the side effects of drought is that usually reduces the amount of severe weather we experience in Illinois. This year was a good example of this. After the deadly Harrisburg tornado on February 29, things have been relatively quiet. Here is the monthly breakdown of tornado reports in Illinois, as reported by the NOAA Storm Prediction Center:
2 in January
4 in February
8 in March
0 in April
8 in May
0 in June
1 in July
23 total by the end of July
Severe weather reports in Illinois for 2012 through the end of July. Figure courtesy of NOAA’s Storm Prediction Center.
Tornado Drought in the US
Harold Brooks of NOAA wrote about the US tornado drought on his blog. Here is the figure he used in his post for the US. The number of tornadoes reported across the US from April 15 to July 31, for 2012 (red line at the bottom) as well for the most active year (2003) and the last widespread tornado-land drought (1988). Figure courtesy of NOAA.
It was somewhat strange seeing lightning and hearing thunder yesterday evening, considering that it was January. The NOAA Storm Prediction Center listed two reports of 1 to 1.5 inch hail around Mt. Vernon. There were other reports of high winds and wind damage such as trees down. Meanwhile, tornadoes were reported in Arkansas, Tennessee, Mississippi, and Alabama. You can see the preliminary report at http://www.spc.noaa.gov/climo/reports/120122_rpts.html
While tornadoes are rare in Illinois in January and the other winter months, they do occur. Here are the number of tornadoes by month for Illinois (first figure) and their distribution around the state (second figure). You can see more figures like these here and here. Click to enlarge.
And here is their distribution across the state for January: Click to enlarge.
According to statistics compiled by NOAA’s Storm Prediction Center, so far in 2011 Illinois has had 58 reports of tornadoes, 298 reports of significant hail (1 inch or more), and 674 reports of wind damage. That’s about average for us. Fortunately, we escaped the worst of the 2011 season that centered on the southeastern U.S. and Joplin, MO.
See the first figure below for the distribution of events. In some cases, we may have multiple tornado reports from the same tornado as it travels along.
The second figure shows the distribution of severe weather reports by month for Illinois. After a quiet start to 2011, severe weather activity picked up in April and continued through July before tapering off in August and September. You can see the monthly raw data and chart in Google Docs. Severe weather reports for 2011. Red dots are tornadoes, green dots are hail, and blue dots are wind damage. Click to enlarge.
At the national level, 2011 has become a very active tornado season. While the reports are preliminary, the number of tornadoes this year stands at 1189. And we are only five months into the year. At least 483 people have died this year, compared to 45 in 2010 and 21 in 2009.
I’ve been asked by several people if there are any trends in the tornado records for Illinois. If we look at the number of stronger tornadoes since 1950 in Illinois, we see a lot of year to year variability. However there is no significant trend over time – either up or down (Figure 1). Stronger tornadoes are identified here as F-1 to F-5 events from 1950 to 2006 (using the Fujita Scale), and EF-1 to EF-5 events from 2007 to 2010 (using the Enhanced Fujita Scale). By definition, these stronger tornadoes cause at least a moderate amount of damage. See the Storm Prediction Center for a discussion on the original Fujita and Enhanced Fujita (EF) scales. Figure 1. Strong tornadoes in Illinois, 1950-2010. The red line represents the linear trend. Click to enlarge.
What we have seen is a dramatic increase in the number of F-0 (EF-0) tornadoes from 1950 to 2010 (Figure 2). These are the weakest of all tornado events and typically cause little if any damage. These events were overlooked in the early tornado records. The upward trend is the result of better radar systems, better spotter networks, and increased awareness and interest by the public. These factors combined have allowed for a better documentation of the weaker events over time. Figure 2. Weak tornadoes in Illinois, 1950-2010. The red line is a 3rd order polynomial, representing a smoothed trend line. Click to enlarge.
If we combine both data sets together, we see the apparent upward trend caused by the increasingly accurate accounting of F-0 (EF-0) tornadoes (Figure 3). As a result, the number of observed tornadoes in Illinois has increased over time, but without an indication of any underlying climate change.In my opinion, the tornado record since 1995 (shaded in yellow) provides the most accurate picture of tornado activity in Illinois. From that part of the record we see that the average number of tornadoes per year in Illinois is now 63. All tornadoes in Illinois, 1950-2010. Shaded area represent the most accurate era of tornado records. Click to enlarge.
