2010 has been off to a slow start to the tornado season nationwide, despite recent outbreaks in the Deep South. Oklahoma is in the same situation, as we saw just our 3rd tornado of the year on April 22nd in Beaver County in the Oklahoma Panhandle. How does this compare historically? It is the 5th latest date that we've seen our 3rd tornado of the year in Oklahoma (records dating to 1950). From January 1st through April 22nd, Oklahoma averages 12.2 tornadoes.

Latest Dates That Oklahoma Recorded 3 Tornadoes (since 1950)
Date May 6 April 27 April 26 April 25 April 22
Year 1998 1962 1970 1989 2010
May/June Tors 44 54 21 13 ???
Annual Tors 83 67 50 20 ???

You can see from the table above that despite extremely slow starts to the tornado season in 1998 and 1962, both years had very active May and June months, and their final yearly tornado count was well above the long-term average of 53 tornadoes. Even 1970, third on the list above, had approximately an average year in terms of tornadoes.  The one exception was 1989, which was close to a record low year for tornadoes in Oklahoma.

The fact that a slow start to the tornado season in Oklahoma doesn't necessarily forecast how May and June will turn out corresponds nicely with a recent post on the Norman Weather Partners website. These are important findings, because it means that just because we haven't had too many tornadoes so far doesn't mean you should let your guard down. We are headed into the most active part of the tornado season climatologically for Oklahoma.

Refresh yourself on tornado safety procedures by clicking this link.

Of course, it is important to involve some more statistics to gain a true historical perspective on the start to the 2010 Oklahoma tornado season. By taking a look at the number of tornadoes in Oklahoma through April 22nd in all years back to 1950, we can calculate the return interval for similarly quiet tornado seasons.

Since 10% of the tornado seasons in the record had 3 or less tornadoes on April 22nd, the return period for a January 1 - April 22 with only 3 tornadoes in Oklahoma is 10 years. This doesn't mean that every ten years we will have this slow of a start to the tornado season, nor does it mean that once every ten years it will happen. It simply means that, over time, you would expect this sort of thing to happen approximately every decade. While that does indicate an unusually slow start to the tornado season, it is not all that uncommon.

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