Tornado Statistics

[Fabian Guerra]

After digging my driveway out of 8 inches of snow I sat down and cleared my head by looking at some recent tornado statistics. Looking through the SPC monthy tornado average I noticed that over the last three years May has come in third place behind June and April in terms of number of tornadoes reported. I have always seen May as the golden month to chase and, based on the last 50 years of stats, I think it probably still is numbers-wise. Here are the averages from the last three years:

June: 188 tornadoes
April: 181 tornadoes
May: 171 tornadoes

If anyone has done any further research on these or any other interesting tornado statistics please post them here. It would help me to pass the time until Spring...thanks.

Fabian

 

[Andrew Pritchard]

March had to be have been pretty high up there as well. Maybe not as much as those three, but I know we had some big recent March events.

 

[Gerard Jebaily]

Not enough of a deviation between the months to make much of a conclusion. I think the number of tornado reports for a month needs to be thought of as the number of tornadoes + or - 1 for every 20 reports. I think that a cusion is needed in order to account for doubled reports, non reports, funnel clouds, "sherifnadoes", grain silos ;-) Sounds about right to have the SPC tornado reports to be 95% accurate. With that taken into account, the 8 or 10 tornado deviation between months isnt significant enough to really make any solid conclusions. Of course this is just my opinion.

 

[Andrew Pritchard]

I don't this any conclusions are really being made in the thread, but rather just pointing out that generally May is well above April, and usually a solid leader over June as well but things haven't been that decisive over the last couple years.

 

[Fabian Guerra]

Gerald, I agree with you and that's why I didn't make any conclusions based on that info. I just wanted to throw out some stats and hopefully see some others post some too. A few years back I did some personal research on when the best time to chase is during the year. I came up with the conclusion that, although its not a definite science, statistically the last 2 weeks of May have yielded the most tornadoes over the last 50 years. Like I said, its not an exact science and there is a ton of variables that need to be factored in but for my purposes of needing to figure out when to take my vacation time at work (4 months in advance) it sufficed.

 

[Derek Weston]

It'll be interesting to see what this years adds on to our data set. I've figured that if we're really seeing warmer temperatures across the US as compared to the past, we're going to start noticing more early season setups.

Of course you can't just point to one or two years for proof, but over time, you'll see a shift...

As it stands now, I'm figuring that after March 1st... the game is on. I need to be ready to go by then.

 

[Jason Foster]

And remember

Don't forget that the statistics are based on confirmed touchdowns. In the last decade or a little more, tornado numbers have tripled that of earlier days. With radar, and "us" (spotters/chasers) the accurate count for tornadoes is closer, but in statistics remember that the data set is perhaps too short to see shifts, waves, etc. Just like looking at the hurricane season cycles. There could yet be a shift (just for an example) where April is the primary tornado month for a few years, or maybe June, then return to May.

I love looking at the statistics and seeing if I can find any real patterns. Right now, the only one that may actually change my chase habits is that one week in April that has seen good storms. So I might come out to the Plains for one week in April, go home, then return during May/June for the rest of the season.

Toward the bottom of this page on my website, it has a chart that I did in 2005. I'm working on the update now, which will be added later.

I've always wondered who else has charts and graphs and statistical analysis the data.

 

[Scott Bell]

A few additional points to consider:

Can the storms be chased? (mode/speed/location all play a part in this)
Personally, I'd prefer a single, slow moving, LP in the plains to a storm that kicks out 10 tornadoes doing 50mph through the Ozark "hills". Your method of analysis would say that scenario 2 is better.

Number of days with an "event". While you might get one or two big events in March or April that could comprise 1/3 or more of those confirmations and make those months look very promising, that doesn't mean that will be the best time to be out chasing. If I'm planning a week or two of chasing, I'd like to have a decent probability for several days within that time span that have severe storm events.

 

[Alan Broerse]

May in the overall average will reign as the "Month" to chase....we need to remember that years 2005 and 2006 in the southern plains were drought (lack of mositure) ...and lack of tornadoes.This disrupted the cycle temporarily. The 10 or 20 year average will hold true...just as the older chasers remember Oklahoma being in the bullseye of tornado alley. As we cycle thru....this also will return......and to add to Scott Bells post, chasing this time of the year in the Ozarks are tough with 50-60 mph storms ripping thru. All you get is a glimpse as it roars thru.......and you are on some two lane hair-pin turn on a mountain road.....been there....

 

[Andrew Pritchard]

A few additional points to consider:

Can the storms be chased? (mode/speed/location all play a part in this)
Personally, I'd prefer a single, slow moving, LP in the plains to a storm that kicks out 10 tornadoes doing 50mph through the Ozark "hills". Your method of analysis would say that scenario 2 is better.

I'm not sure if I missed something, but I don't think we're talking about setups like tomorrow's. We're discussing April and May here, not very early season setups in the deep south.

Also, unless I missed something we're not saying we prefer those... all Fabian said was that the last few years May has not been the typical leader that it normally is.