May is severe weather season

 

May 30, 2019 severe weather reports (Source: NOAA)

May is one of the most active severe weather months of the year in the United States. “Severe weather” is defined as a thunderstorm that produces any of the following: A) wind gusts of at least 58 mph; B) hail 1” in diameter or greater; or C) a tornado. 

The most dangerous thunderstorms (supercells) can have more than one type of severe weather as large hail often precedes tornadoes. Locally, the DMV has had a number of memorable May severe weather events.   

2019:  Three tornadoes touched down in central Maryland on May 30, producing two EF-0’s and an EF-1 in Frederick and Howard Counties. Wind damage was more widespread across the DC Area, with a wind gust as high as 71 mph in Frederick County, Maryland, and a 66 mph gust that was reported at Davison Army Airfield in Fairfax County, Virginia. 

Just a week earlier, even more severe weather impacted the DMV. An EF-1 tornado was confirmed in Columbia, Maryland that caused some structural damage. There were many severe wind gusts from the thunderstorms that developed. Wind gusted as high as 68 mph at National Airport, 63 mph at Andrews AFB in Maryland, and 67 mph in Gaithersburg, Maryland. Damage was reported that ranged from downed trees and power lines to minor structural damage of homes and businesses.

2016:  Large hail sometimes occurs in the Mid-Atlantic Region. On May 2, Rockville, Maryland, had hail 2.5” – 2.75” in diameter, ranging in size from tennis ball to baseball. Baseball-sized hail was also reported in Charles County, Maryland, while golf ball-size hail occurred in Huntingtown, MD. There were other reports of hail in the DMV that were smaller, but still met severe criteria.

2013: The last EF-5 tornado in the United States occurred on May 20 in Moore, Oklahoma. It had a long and destructive track as part of a larger, three-day severe weather outbreak. Although not as EF-5 intensity during its entire track, it reached peak intensity near the town of Moore.

According to NOAA, it caused more than two dozen fatalities and remains the third costliest tornado on record having caused $2 billion in damages (unadjusted for inflation). 

2011: The town of Joplin, Missouri experienced a devastating EF-5 tornado on May 22. According to NOAA, the Joplin EF-5 remains the costliest tornado on record having caused $2.8 billion in damages (unadjusted for inflation). 

With a total of 158 fatalities, it was also the single deadliest U.S. tornado since 1947. This was one of six EF-5 tornadoes that occurred in the United States in 2011, the highest such total since 1974 (7).

A closer look at hurricane names

 

(Source: WUSA9)

It’s hard to imagine a hurricane season without names for tropical storms and hurricanes.  They weren’t always named, though.  Check out this story I wrote for the WUSA9 website on the history of hurricane names

Predicting the next heat wave

Staying cool during DC's summer heat

Although 90° heat doesn’t become “average” in the nation’s capital until July, the first 90-degree day of the season often occurs much earlier than that. The month of May, for example, has averaged between one and two 90-degree days over the last 30 years, according to NOAA. True to form, the nation's capital had its first 90-degree day of 2024 on May 2 with a high of 91° at National Airport.

There is often a high degree of variance from one year to the next of when the first 90-degree heat of the season occurs. For the 30-year period from 1994 - 2023, DC's first 90-degree heat of the year occurred 15 times in May. That's on par with what the data shows and what longtime Washingtonians might expect. 

However, there has been 90-degree heat in April eight times over the last 30 years, most recently in 2017. DC residents even experienced three consecutive days of 90-degree heat in April 2002. On the other hand, DC's first 90-degree heat of the year occurred in June seven times over the last 30 years, most recently last year with a high of 94° on June 2. 

Not having 90-degree heat until May or June has no bearing on how hot the summer might ultimately be. A good example of this was in 2016 when DC residents didn't experience the first 90-degree temperature of the year until it was 96° on June 11. The summer of 2016 went on to become one of DC's hottest on record with a total of 58 days in the 90s or hotter. 

Having the first 90-degree heat of the season earlier also doesn't indicate an increased likelihood of a warmer than average summer. Such was the case during the summer of 2000.  DC's first 90-degree heat of 2000 occurred on May 7 (90°). The summer of 2000 went on to become one of the coolest in recent memory. The three-month period of June, July and August of 2000 featured more days with highs in the 70s (23), than with highs in the 90s (9).

Early indications from NOAA's Climate Prediction Center are for a warmer than average summer in the nation's capital. The first 90-degree heat of 2024 is already in the books. My colleagues and I on the WUSA9 Weather Team, however, don't currently expect any 90-degree heat over the next seven to 10 days.