Can you believe it is already May? Weather records show it is one of the peak months for severe weather locally. As we have reviewed severe weather climatology for both March and April, how does May compare?
That’s one busy map! It is obvious that May is a very active severe weather month for Washington, D.C. and the surrounding areas. Within the map extent there are approximately 100 tornado, 700 severe hail, and over 1,100 damaging wind reports since 1950. (Basically add March and April together and you get May.)
With over a thousand severe wind reports across our region in May from 1950 to 2011, damaging wind is the most dominant severe weather type for the D.C. area. (Remember: the National Weather Service severe wind criterion is 50kts/58mph and higher.) In other words, a severe thunderstorm during the month of May is more likely to cause damaging winds gusts than hail or tornadoes.
By raw report count, we are 10 times more likely to experience damaging winds from a thunderstorm than a tornado in the month of May. In reality, wind damage is under-reported significantly, so the odds are much higher for violent straight-line winds than a tornado in any one spot.
That’s a lot of hail! The amount of hail that falls in May puts April hail events to shame. Within the map extent there are roughly 700 hail events. (Severe hail criterion is having a diameter of 1” or larger.)
Now, this is not big-hail country so if you want to experience the big stuff (golfball, softball, grapefruit-sized) travel out to juicy Texas or the western High Plains (but you might want to bring a helmet). Most of the severe hail that falls during the month of May is between one and three inches according to the map, but delving deeper into the reports most of the hail that falls is really in the 1 to 2 inch -diameter range.
Percentage breakdown of May hail events by size (disclaimer: percentages were rounded to the nearest whole number):
Some of the more recent major hail events for our area during the month of May include:
May 26, 2011
May 14, 2010
May 10, 2000
These three events featured 50 or more hail reports in the mapped region on each day.
In the past 60 years the area depicted on the map has experienced roughly 100 tornadoes. While this is not an impressive number for states across tornado alley, this number makes May one of our more active tornado months in the D.C. area.
Even though May is an impressive month for tornado events, no recorded tornadoes have been stronger than F/EF3 magnitude during the month. This is in contrast to April, which has featured two F4 tornadoes locally, including the La Plata, MD tornado.
Here is the breakdown of the tornadoes visible on the map by F/EF category:
F/EF 0: 36
F/EF 1: 44
F/EF 2: 11
F/EF 3: 3
Some days during the month of May that featured at least five tornadoes or more include:
May 10, 1990 – 6 tornadoes across the Delmarva Peninsula
May 22, 2001 – 5 tornadoes in Southern Maryland, south of the District
May 13, 2002 – 5 tornadoes across the Delmarva Peninsula
Here you see another contrast to April. April may have seen less tornadoes overall (67) than May but April not only contains the region’s strongest tornadoes, but also more outbreak days of five tornadoes or more in a single day.
Also, it appears the Delmarva Peninsula is the hotspot for serial tornado days during the month of May.
May is an active severe weather month, but I know what you’re thinking, “We need storms for there to even be severe weather!” Unfortunately for thunderstorm fans, our chance for thunderstorms does not look promising for the first one to two weeks of the month.
For all the fellow thunderstorm lovers out there, we may have to be patient and wait to see if the pattern for the second half of the month is more promising for thunderstorm days.