Although the D.C. area has avoided derechos and tornado outbreaks this year, booming thunder and downpours have come seemingly nonstop. Indeed, the data show that the number of thunderstorm days this year is higher than any in at least 4½ decades.
The District has logged 54 thunder days in 2018, which is the most on record, according to data from the Iowa Environmental Mesonet.
In August, there were 16 thunderstorm days, which is the most on record for any month since 1973, when thunderstorm data first became available in the data set.
On Saturday night, it was storming yet again. “Nothing like the sound of a long, low rumble of thunder on a rainy late summer evening,” tweeted local weather-watcher Kenny Gartner: Gartner’s tweet motivated me to dive deeper into the data.
Every month since May has seen an above-normal number of thunderstorm days at Reagan National Airport, where the District’s official weather records are kept. It’s a similar story at both Dulles and Baltimore Washington International Marshall airports (whose thunderstorm days each month this year compared with the average are also presented in the image below).
The number of thunderstorm days in May and August in the District were especially noteworthy. In May, the 12 days with thunder tied for the most on record in this database for that month. August’s 16 thunder days not only demolished the month’s previous top value of 11 but also bested any month over the past 46 years. The old leader was June 2008 with 14 thunder days, which was a super-stormy stretch.
This year’s 54 days with thunder in the District surpasses the record of 50 in 2011. Like June 2008, 2011 was memorable both locally and nationally for numerous tornado outbreaks and other severe weather events. Comparatively, this year’s 54 thunder days definitely have come in a tamer fashion.
The general weather pattern this year has supported frequent storms, but seldom have they turned severe.
“We have had a larger-than-typical number of frontal boundaries either stall out or dissipate over our region,” said Jeff Halverson, the Capital Weather Gang’s severe weather expert, in explaining the environment conducive to frequent run-of-the-mill storms.
The storms that form along these dying fronts don’t pack the same vigor as those that cut through the region like a knife. Even so, they have still unleashed frequent lightning and copious rain. A bit Florida-like.
This year’s elevated thunderstorm activity fits into a long-term trend toward more storms seen in recent decades, although there is large year-to-year variability. In 1973, we might have expected a hair under 30 thunderstorm days. Today? A little less than 40. The increase seems related to an uptick in the number of thunderstorm days in the most active years.
2018’s storminess goes hand-in-hand with the persistently steamy conditions, which have served as fuel. Washington has endured a summer that ranks among its top 10 hottest and wettest, while record-challenging humidity has covered much of the Northeast.
If you’re growing tired of these storms interrupting your late-day plans and making it hard to sleep, rest assured that thunder season is mostly over, and we should be getting pretty close to our final number of thunderstorm days in 2018.
Methodology note: In counting the number of thunderstorm days, if there was one report on a day, it counted as one day; if there were 20 reports in one day, they counted as one day. The total counts include days in which thunderstorms were reported but no rain fell. Given that summer storms do tend to be hit-or-miss, the relative nearness of thunder was considered valid for inclusion.