In my never-ending quest to learn everything I can about South Mississippi weather, I wanted to see if March was in fact “hail season” as I’ve dubbed it, or if it just felt like a hail season.
Because as many of you know, I’m a firm believer that one of the best parts about Science is it can help to sift through the riff-raff to show if something really is something, or if it just feels like something.
So I started digging through the records since the year 2000. And found some interesting data during the last 21 years of severe weather reports for south Mississippi…
A few takeaways before we get to the Meat & Taters:
- There has been fewer severe weather reports between 2010-2020 than there were from 2000-2009. Trending toward a calmer,less severe, March
- Looking at a running 3-day average, the percent-chance for a severe weather event was book-ended, showing the highest potential at the beginning and end of the month. The lowest percent-chance day was March 20th.
- There were six dates during that 21 year span that never produced a severe weather report: March 4th, 16th, 19th, 20th, 24th, and 27th.
- The most active severe weather dates were March 2nd, 9th, 10th, 13th, and 30th.
- The data may help explain the how the “Easter Cold Snap” works and also that the claim “in like a lion, out like a lamb” or vice-versa isn’t supported by statistically significant numbers.
Some Data!
Digging through the Storm Prediction Center archives for storm reports dating back to 2000 was time-consuming, but not terribly difficult. The meteorologists over there have done a great job at keeping the catalog of data available online. And in an easy-to-find and easy-to-read way.
Here is a look at the final tallies…
| Hail | Wind | Tornado | All three | ||
| ’00-’09 Total Event Days | 31 | 25 | 18 | 9 | 6 |
| Average # event days / March | 3.1 | ||||
| %-chance of each type / event | 81% | 58% | 29% | 19% | |
| Lion & Lamb | 6/10 | ||||
| Hail | Wind | Tornado | All Three | ||
| ’10-’20 Total Event Days | 27 | 15 | 19 | 5 | 3 |
| Average # event days / March | 2.45 | ||||
| %-chance of each type / event | 56% | 70% | 19% | 11% | |
| Lion & Lamb | 5/11 |
A quick reference guide to reading this table: The top set of data are from 2000-2009 and the bottom set are from 2010-2020. Broken down by…
— “Event Days” or days when a severe report was shown in the data
— “Average number of event days in all Marches” showing the number of “Event Days” divided by the number of Marches tallied
— “%-chance of each type / event” which is the likelihood that a given severe weather report during any severe weather event day.
— “Lion & Lamb” is tallying how many times the month started with severe weather, but ended with no severe weather. Or vice-versa.
First things first: Hail Season
It turns out that March could, in fact, be the Hail Season for South Mississippi. However, that proclamation may lose its gravity in the future.
Between 2000 and 2009, 81-percent of days where people reported severe weather, the report included hail. That is pretty incredible. A number that was even higher than I was expecting. It turns out, that there may be a good reason why that number was higher than expected.
Between 2010 and 2020, only 56-percent of days where people reported severe weather, did a report include hail.
That is a 25-percent drop in hail reports!
And there have only been seven severe weather days with hail since 2016. So, looking at the total of 14 severe weather days during that span, it means only 50-percent of those days have featured hail.
Compare that to 14 hail days of the 17 severe weather days between 2000 and 2004.
So, during the last 20 years, South Mississippi has went from seeing hail reported on 82-percent of severe weather days in March to just 50-percent. Pretty incredible.
Even more incredible… That is still higher than the rest of the year. During the rest of the year, the likelihood that a severe weather day features hail is closer to around 30- to 40-percent.
That tells me two things: First, that March REALLY used to be all about the hail. And now is just somewhat about the hail. Second, either the NWS or the public may not be reporting hail as often to the NWS during severe weather.
Not that this has to do with hail, but within the same data, I have more good news. The number of tornadoes reported has decreased, too. Going from nine tornado days between 2000-2009 ro just six days between 2010-2020.
The potential reduction in people reporting hail to the NWS may be skewing the data a bit. I would imagine that since the ability to detect tornadoes has increased, people may be more focused on taking shelter from tornadoes and wind damage, and aren’t passing along the hail reports as frequently. It is also possible that the NWS is too busy tracking tornadoes to include hail reports during events, too. Or, perhaps, it is a combination of the two. Both are possible issues. I’m sure there are other wrenches in there, too, that I haven’t considered.
Spring Wedding? Plan it for March 20th!
Moving on from hail to all types of severe weather… Statistically speaking, during the last 20 years March 20th is the day least likely to have severe weather. Not only has there not been a severe weather report on March 20th since before 2000, but it is the same with March 19th! And there hasn’t been severe weather on the 21st since 2012.
Did I just inadvertently jinx the area to definitely get severe weather on the 20th in 2021? Probably. Did I jinx anyone with a wedding planned for March 20th for the foreseeable future? Also, probably.
But it looks like after two peaks early in March. One around the 2nd. The other between the 9th and 13th. Maybe a little bump around the 17th/18th, too. And then a third peak at the end of the month on the 30th.
That isn’t to say that severe weather isn’t possible on other days. It just hasn’t happened in a long time.
You can either view that as “we’re due” or “lower threat” for severe weather on those days.
What about that Easter cold snap?
This sets up an interesting situation with that “Easter Cold Snap” people are always talking about. A March Easter generally falls on the 27th or 31st of March. In 2008 it was on the 23rd, but that only happens once every ~90 years.
Looking at the graph above, you can see that peak in severe weather at tthe end of March duringthe last 20 years coincides with the late-March Easter Sunday.
A March Easter occurred in 2002, 2005, 2008, 2013, and 2016. In three of those five years, severe weather was reported on Easter or within 24 hours of Easter Sunday. And oftentimes, in order to get severe weather in south Mississippi in March, there needs to be a cooler air mass building in to replace a warmer one.
So, for a March Easter, the Easter cold snap does carry some weight.
In April, well, not as much. That isn’t to say it never happens, it is just more difficult to get a “cold snap” as you move later in Spring. And since the date of Easter bounces around more often in April, the likelihood that it coincides with a cooldown within 24 hours isn’t as likely.
And I really want to stress something that I think I don’t communicate very well on a regular basis: Saying things are “less likely” or “unlikely” does not mean impossible. I’ve noticed recently that when I say things like, “seeing snow in March is unlikely” people say, “It snowed in 1993! Look it up!”
And I know it snowed in 1993. And on other years, too.
There is a really important distinction between less likely, unlikely and impossible.
Less likely = other outcomes are more likely
For example, it is less likely to snow in March than it is to be 80 degrees. That isn’t saying it can’t snow. Or that it won’t snow. It is just showing that the likelihood of 80 is higher than the likelihood of snowfall. If it has snowed a handful of times in March during the last 40 years, but it reaches 80 degrees in March every year…. Mathematically, snow is therefore less likely to occur.
Unlikely = an outcomes has a very low probability of occurring.
For example, When I say that it is unlikely that we see snow after Valentine’s Day every year, people have mentioned that during April in 1987 it snowed in South Mississippi. I know this. It is in the record books. However, that does not change the mathematical truth that the event is unlikely. The probability that it snows in April is extraordinarily low. It has happened once or twice during the last 40 years.
Impossible = not going to happen due to the laws of Physics
For example, someone called me up at the station one day and told me that he had seen it snow in July in South Mississippi back in the 60s or 70s. When I asked him if he meant hail, not snow, he corrected me and said, “no, it was snow. Look it up!” (being told to ‘look it up’ by people is a common theme in my professional life). But, snow in July in south Mississippi is impossible during the 1960s or 1970s. It was too warm for snow to fall. Temperatures during those decades in July were between 60F and 100F – far too warm. Perhaps during the Ice Age it snowed here, but not since the glaciers receded some 10,000 years ago.
Lions and Lambs and Weather, oh my!
This one isn’t as mathematical as the March severe weather. But, saldy, I fear it will strike a chord with some folks. And I’m not here to ruin anyone’s fun or question your belief system. You are free to believe what you want.
I’m just here to Math and Science. So…
That “in like a Lion out like a lamb,” or “in like a lamb out like a lion” saying about March hasn’t carried much weight for more than 20 years.
Looking back at the data, when South Mississippi experienced severe weather during the first week of March it never precluded the area from experiencing severe weather again at the end of March.
That’s not to say it never happened. There were times when it stormed to begin March, and then did not storm to end March. And vice-versa. This isn’t “impossible” and it isn’t even “unlikely” it is just isn’t necessarily apart of a causal relationship. A lot like the Frost/Thunder deal.
Fun Fact: 2004 was the last time South Mississippi made it through a March with zero severe weather reports!
Looking back to 2000, the phrase “in like a Lion out like a lamb,” or “in like a lamb out like a lion” ended up being true 52-percent of the time. Hardly a worthwhile prediction. Since 2015, it has held true on two of the six years. In fact, last year, the area saw severe weather on the 3rd of March and on the 30th and 31st. So it came in like a Lion and went our like a Lion, too.
Looking at El Nino / La Nina impacts
While the ENSO (El Nino Southern Oscillation) cycle between El Nino and La Nina is something meteorologists keep tabs on at all times because it can throw wrenches into things when trying to make seasonal forecasts, it is also something that can be tallied when looking at monthly data, too.
For this data, I looked at which side of the cycle was present – El Nino or La Nina – during the months leading into March (January February) and March itself.
| Year | ENSO Cycle | Severe Weather Days |
| 2000 | La Nina | 4 |
| 2001 | La Nina | 3 |
| 2002 | Neutral | 4 |
| 2003 | El Nino | 6 |
| 2004 | Neutral | 0 |
| 2005 | El Nino | 6 |
| 2006 | La Nina | 2 |
| 2007 | Neutral | 1 |
| 2008 | La Nina | 2 |
| 2009 | La Nina | 3 |
| Year | ENSO Cycle | Severe Weather Days |
| 2010 | El Nino | 2 |
| 2011 | La Nina | 3 |
| 2012 | La Nina | 2 |
| 2013 | Neutral | 3 |
| 2014 | Neutral | 1 |
| 2015 | El Nino | 2 |
| 2016 | El Nino | 4 |
| 2017 | Neutral | 3 |
| 2018 | La Nina | 2 |
| 2019 | El Nino | 2 |
| 2020 | Neutral | 3 |
That leaves us with a total tally like this
| Cycle | Total Days | AVG Days/Cycle |
| El Nino | 22 | 22/6 = 3.6 |
| La Nina | 21 | 21/8 = 2.6 |
| Neutral | 15 | 15/6 = 2.5 |
The numbers don’t really tell us much. Numbers show an El Nino March is a slightly more active month (by a single extra day) for severe weather than on La Nina or Neutral years. But just by a single day.
The Bottom Line
I know that was a lot to take in. A ton of numbers and data. Some math, too. But wasn’t it fun? For those that skipped right to the end, that’s fine, too! I know you guys have busy lives. So here is the bottom line…
March is “Hail Season” for South Mississippi. But, hail reports in March are diminishing. While I think it is partially due to fewer storms with hail, there are a few potential reasons that may not be weather-related, too. I don’t have a solid single answer to why.
On the weather-side of things, it doesn’t seem like El Nino or La Nina are involved with determining if severe weather – and thus hail – are responsible for the change. Plus there is very little change in severe weather events between an El Nino and La Nina.
Looking through the last 20 years of data, if you want a March wedding, March 20th is the day to plan it! Severe weather seems to dip into a lull between the 19th and 22nd.
The Easter cold snap in south Mississippi is something that may carry weight in for March Easter’s. In April, it isn’t as likely to work.
And the saying “in like a lion out like a lamb” and vice-versa doesn’t carry any real predictive value as it only correctly forecasts the correct outcome about 50-percent of the time.
