I remember 1999, because of the Moore F5 tornado on the 3rd. That year, April had 19 tornadoes, then May spiked to 90, for an annual total of 145 in Oklahoma.
2011 had 0 April twisters, then 50 in May and another 46 in June, totaling 119 for that year.
2015 is another example of April / May spikes, only 5 in APR then 83 in May. 111 for the year.
I'm ready for storm chasing here next month, we'll see what is in store, maybe not much ?
Or a possible spike like those years presented above ?
One minor note, 2011 had 0 tornadoes in Oklahoma in
March, then 50 in April, 46 in May and 7 in June.
The 1991-2016 average number of tornadoes in April in Oklahoma is about 15, while the 1991-2010 average is only 10, due to some inflated numbers in the 2010s. For the sake of using more recent records, let's say the average is 15, which is rounded up.
From 1991-2016, Oklahoma saw less than 15 tornadoes in April 15 times, or 58% of the time. Oklahoma saw 15 or more tornadoes 42% of the time. That's a pretty good distribution and it makes sense, since a few higher-end outbreaks will skew the average number somewhat.
Also, in 12 years, or 46% of the months of April since 1991, Oklahoma saw less than 10 tornadoes, or nearly half of the years. The general idea is that sporadic tornadoes in April in Oklahoma are common, but that outbreaks and/or multiple noteworthy events in the state in April are not
as common. April has seen 25 or more tornadoes in Oklahoma only three times since 1991, which is a mere 12% of the time.
I did an analysis of the 26 years and found that the most common occurrence was that both April and May were below average. That happened a total of 10 years, or 38% of the time.
31% of the time, or 8 years, April was above average, but May was below average.
19% of the time, or 5 years, April was below average, but May was above average.
12% of the time, or 3 years, both April and May were above average.
The sample size is a bit small, but when April was below average, May was below average 2/3 of the time, or 10 out of 15 years.
This isn't to say that May will certainly be below average. If anything, it speaks to the fact that high-end outbreaks skew the average. In most months and most years (more than half), the tornado count with respect to the average will be below average. It's just statistics given the nature of tornadoes.
Summary: We really don't know what the entirety of May will have to offer, but if you were playing Vegas odds, regardless of how April performed, you'd go with a below average May.
Below is a bit of a "heat map" that I put together to compare April and May with respect to Oklahoma tornadoes:
Years that went from >50% or more below average in April to >100% above average in May:
2010 and 2015
Years that went from >50% or more below average in April to somewhat above average in May:
1997
It does happen, but not often.
(Yes, 2008 and 2013 also moved from below average in April to above average in May, but the swings were not as impressive)
