Wednesday, May 01, 2024

Ohio Tornado Recap Through April 30

So far this year, the Ohio tornado count has been record setting.  Preliminary numbers put the total at 43 although official tornado track analysis puts the exact number closer to 35. Either way, we haven't had a year anywhere close to this since...well, last year. 

Ohio counties that have been under a tornado warning at some point this year: 55 of the 88 counties.

Here are the totals year by year since 1950. Red bar represents total tornadoes through April 30.  The green bar are the EF2 or greater tornadoes each year.

Here is the average number of tornadoes per state through April 30:

Here is the actual number this year through April 30:

Why so many tornadoes this year?

First, we have been transitioning out of a very strong El Nino period and rapidly heading into a La Nina. These changes in the equatorial Pacific have impacted the jet stream across the central US. Throughout the winter, the storm track was absent across the US as evident by below normal snowfall across the central US.

Notice how the jet intensity was abnormally strong in mid March and April across the mid-west. Warmer colors indicate well above normal jet intensity.

The lifted index (degree of instability) was extremely favorable for rising air and storms across the Ohio Valley in mid March. Colder colors indicate rapidly rising air.

The MJO might have been a factor. Higher amplitude phase 4-6 in mid March. Moderate amplitude phase 8-1-2 in late March. However, according to this paper, the connection in March and April might be smaller. Bold print below is important:

The physical mechanism proposed in this study cannot explain the MJO–U.S. tornadogenesis relationship in the boreal early and middle spring months (March and April). Compared to MJJ, the Pacific jet is strengthened and shifted southward in March and April, but the anomalous subsidence over the northeast Pacific is very weak in March and April. Therefore, it is more likely that the relationship between MJO and U.S. tornadic environmental parameters in March and April is largely influenced by extratropical stationary Rossby waves forced by MJO-induced diabatic heating anomalies over the Maritime Continent. Thus, it is also likely that natural atmospheric variabilities originated from high latitudes such as North Atlantic Oscillation (e.g., Lin et al. 2009) and Artic Oscillation (e.g., Zhou and Miller 2005) interfere with the MJO-induced extratropical teleconnection to the United States in March and April, and thus may weaken the relationship between MJO and U.S. tornadogenesis. Additionally, in March and April, tropical Pacific sea surface temperature anomalies associated with El NiƱo–Southern Oscillation (ENSO) are of key importance in modulating the spatiotemporal variability of U.S. tornadogenesis (e.g., Weaver et al. 2012Lee et al. 20132016Barrett and Gensini 2013Allen et al. 2015Lepore et al. 2017Molina et al. 2018Chu et al. 2019).

Speaking of high latitudes, check out the height anomalies in the higher latitudes since early 2024. Heights rise, Arctic Oscillation drops. Frequent troughs track across the mid latitudes. Notice all but one of the top 7 tornado days occurred when the northern height anomalies were high. 

Here are the mid latitude 500 mB heights vs normal on those top 7 tornado days with SPC storm reports for each period:

#1 - April 26-27 (143 tornadoes)

#2 - April 1-2 (97 tornadoes)

#3 - March 14 (36 tornadoes)

#4 - April 16 (24 tornadoes)

#5 - February 27 (24 tornadoes)

Gulf of Mexico water temperatures were well above normal in March especially. Some cooling has occurred since but overall temperatures are still above normal. 

We also transitioning out of El Nino and into La Nina territory over the last 2-3 months. Notice the warmer water eroding away along the equator. This probably played a factor in the overall jet stream direction and intensity changes across the central US.