Low tornado count set to continue through the end of April, but it's too early to call the season

The frequency of tornadoes in the United States usually tends to increase dramatically through the month of April. This is thanks to a gradual lift in the jet stream, allowing warm, moist air from the Gulf of Mexico to clash with cooler, drier air surging south and east from Canada.

April can be quite volatile, supporting some of the largest tornado outbreaks on record in the country. While there was a noteworthy outbreak of tornadoes from the 13th to 15th of the month, overall, April 2018 has been uncharacteristically tame and suggestions are that it will stay that way.

(Annual and monthly tornado average for each state)

Of course, April wasn’t the start of this low in tornado activity. The same general weather pattern that supported late-season snow and chilly weather across the eastern half of the nation in March has more or less continued. With troughs of low pressure digging south from Canada, almost routinely, the humid conditions that tornadoes thrive off have largely been confined to the Gulf Coast.

Oklahoma may not be the king of April tornadoes, but it averages about 14 every year per recent averages. Not only has Oklahoma avoided any twisters so far this month, but it has astonishingly not seen a single tornado this entire year.

Still no tornadoes year-to-date in Oklahoma and most forecast guidance suggests that we easily surpass the record for the latest first tornado, which was April 26th, 1962. Might even finish April entirely with zero… #okwx @USTornadoes pic.twitter.com/FNPEwKSDhC

— Quincy Vagell (@stormchaserQ) April 21, 2018

With reliable records dating back to 1950, this is already the second longest that the state has gone in a year without a tornado and if the Sooner State can make it to April 27 without a tornado, that would be a new modern record. It is worth noting that a tornado-free April would not be a record itself, as both 1987 and 1988 finished the month with not a single tornado observed in Oklahoma.

(Monthly tornado averages by state and region)

As of the publishing of this post, tornado tallies for 2018 nationwide are below average, but they’re not at all-time lows. Even recent years, such as 2014 and 2015 were off to an even slower pace at this point.

What may set this April apart from others, however, is that the final week of the month very often ends up with a noteworthy outbreak, or at least an extended period of busy tornado activity. A major tornado outbreak erupted in the final days of April 2014, while 2015’s April saw tornadoes in seven out of the final 10 days in the month.

April 27-30 tornado outbreak sequence of 2014: Recap | Videos

Virtually all of the forecast guidance is in agreement that the next week to ten days should be relatively silent in terms of tornadoes and an overall dearth of activity could continue right through the end of the month.

The culprit? The jet stream must not have received the seasonal memo, because we continue to see a tendency for a weather pattern more typical of late winter, not mid-spring. This means another blast of unseasonably chilly air to the eastern part of the country is ahead. In fact, a chunk of the polar vortex could very well break off and sit over southeastern Canada toward the final days of April.

European model forecast 500mb heights and anomalies (Pivotal Weather)

While weather enthusiasts are often tracking tornadoes in late April, they may be, instead, watching record low temperatures and possibly even more snow in parts of the Great Lakes and Northeast.

Not all hope is lost if you’re a tornado watcher, however.

A quiet month of April does not always translate into a silent May. As the saying goes, “when it’s May, you chase.” and even the quietest tornado seasons have had at least a few notable tornado episodes in the month. Oklahomans and storm chasers alike can quickly recall 2013, a year that was even quieter than 2018 at this point, and how the tornado season woke up in dramatic fashion mid-May. That spring featured a very active second half of May when it comes to tornadoes.

We don't have to go back very far (2013) to find a year that started out very quiet and then got very busy. There are many other examples. We will have tornadoes in Oklahoma this year. Don't know how many. Just be ready for one. It only takes one.

— Rick Smith (@ounwcm) April 20, 2018

Long-range tornado prediction is tricky and there’s no telling how active May will or will not be this year, but the recent trends by no means suggest that this storm season is over. If anything, it has yet to begin if you’re in the Plains or a hungry chaser. Remember, roughly mid-May through early June is the typical peak of tornado season in the country.

A glimmer of hope for chasers is that some of the long-range computer models that show a quiet end to April show some upstream hints in the jet stream that could eventually translate to more favorable tornado setups in the United States sometime in the first half of May.