Oklahoma may have 0 Twisters until May

Discussion in 'Weather In The News' started by Randall Bragg, Apr 20, 2018.

  1. Randall Bragg

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  2. Quincy Vagell

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    All it takes is a big outbreak to skew numbers, but as far as the yearly total goes, the more we slack from this point on, the harder it is going to be to recover. The odd thing is that almost every late April tends to have at least one outbreak and if not, a relatively active period. The next 7-10 days look about a dull as one can imagine for the time of year, once we get past a couple of more MRGL risk days.

    Here's a table showing the latest dates of first tornadoes in Oklahoma. The number one spot will almost certainly move to 2018. It is interesting that a couple of years (1987-88) saw zero tornadoes in April in Oklahoma.
    noOKtor.gif
     
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  3. Randall Bragg

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    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 ?
     
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    #3 Randall Bragg, Apr 21, 2018
    Last edited: Apr 21, 2018
  4. Quincy Vagell

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    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:
    storm_track_180421.gif

    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)
     
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  5. Randall Bragg

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    Thanks QV, misread 2011 stats. Great data and percentage evaluation. Let's meet back here on June 1st and see if the Vegas odds win !
    I'll be out there on enhanced days for sure...
     
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  6. Shane Young

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    Thinking maybe don't bet on this in Vegas...
    10 out of 15 of those below average Aprils isn't going to show much statistical significance. If you flip a coin 15 times, about 30% of your samples would be either <=5 or >=10 heads. So certainly nowhere near a level you can have any confidence there's a trend, because of such a limited sample size (plus additional questions of whether the samples are independent)
    But, hey, with the way models are trending, the odds are starting to go up...
     
  7. Randall Bragg

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  8. Andy Wehrle

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    Maybe my perception is skewed in thinking of mid-late April as prime time for tornadoes in the southern Plains because I grew up and got interested in severe weather in the '90s when 4/26/91 was THE outbreak all the researchers (Grazulis, Bluestein, etc) were writing about and all the TV documentaries/Weather Channel home videos were being made about. Many of those books and documentaries also included references to/footage of the "ooooh, classic!" Pond Creek, OK tornado of 4/12 that year.

    It's probably worth noting that had the Mountainburg EF2 on 4/13 touched down 15-20 miles to the west of where it did (or had the dryline overall been slightly slower that day than it was), we'd no longer be having this conversation.
     
  9. Jeff Duda

    Jeff Duda Resident meteorological expert
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    I played around with tornado counts some years back, looking particularly at correlation between tornado counts in months with N-month lag times (so April-May, May-June, April-June, March-June etc.) and found correlations to be very low...I seem to recall values generally below 0.3, which suggests little to no relationship between tornado counts one month and tornado counts in another month. This is generally consistent with Quincy's analysis that we really can't know for sure how May will go based on April.
     
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  10. Randall Bragg

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    My thread started as an awakening to the fact that my state may not have a tornado until May 1st or later. Records are made to be broken as we say. Moore OK had 4 major tornadoes in 5 years as I stood still and witnessed 3 once in a lifetime tornadoes chase me. I feel like I'm no longer as chaser but a storm "catcher". I can load my truck and wait for local broadcasters to show me where to catch a monster.
    Times have changed. I'm saying it...hurricanes, tornadoes, hailstones, lightening strikes, biblical floods, and drought.
    You gentlemen can drop all your data and stats on me....but in my heart and soul, it's only gonna get worse.
     
  11. MikeD

    MikeD EF1

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    SPC’s outlook has a 15% chance of severe weather on May 1st. We might have the no tornadoes record broken in the last day. I think we’re looking at the first high risk of 2018.
     
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  12. Brett Nickeson

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    There is nothing about this setup that says High Risk at this point.
     
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