In many ways, May represents peak spring in the D.C. area — a month when the landscape is lush, the days are long and the weather often feels close to ideal. But the region’s climate can accelerate quickly toward summer. By late in the month, temperatures sometimes surge toward the 90s.
Normal and record daily temperatures
Temperatures climb steadily through May. Average highs rise from the low 70s at the start of the month to around 80 degrees by its end, while typical overnight lows increase from the mid-50s to the low 60s.
The hottest temperature ever recorded in May occurred on the final day of the month in 1991, when it reached 99 degrees. At the other extreme, the temperature has dropped as low as 33 degrees, recorded May 11, 1906.
Record daily precipitation
Thunderstorm season ramps up in May as humidity levels rise. The month can be surprisingly wet and has produced some memorable flooding events in D.C. and across the region.
The wettest May day on record occurred May 5, 1953, when 3.24 inches of rain fell.
Monthly temperatures by the year
May's average monthly temperature of 67.2 degrees is the fifth warmest of the year as the end of springtime weather is often imminent by month's end.
The warmest May on record occurred in 2015, when the average temperature reached 73.2 degrees. The coolest came in 1882, with an average of 59.2 degrees. Long-term temperature trends for May are upward.
Monthly precipitation by the year
May is the third wettest month of the year in D.C., trailing only June and July and just ahead of September. The month averages 3.94 inches of precipitation.
The wettest May on record occurred in both 1889 and 1953, when 10.69 inches of rain fell. Several other Mays have also approached that mark, including 2008 with 10.66 inches and 1886 with 10.60 inches. The driest May came in 1939, when only 0.41 inches of precipitation was recorded.
Days at or above 90
The D.C. area averages about two days with highs of 90 degrees or higher in May. In some years, however, heat arrives early and often. The most 90-degree days recorded in the month is 11, which occurred in 1991.
May is also when the first 90-degree day of the year typically occurs. In D.C., the average date of the first 90-degree high is May 18. Across most of the region, the first 90 tends to arrive around the same time, although it often comes later in higher elevations to the west and north, as well as in some rural areas.
May is also spring's nice day peak
Using simplified “Nice Day Stamp” criteria — highs between 65 and 85 degrees with no rain — May averages about 11 such days, the most of any spring month. That’s roughly two more than April.
The D.C. area tends to have two “nice day” seasons each year, with fall usually the most reliable. In spring, cold air damming can sometimes interfere. In this setup, cool, often ocean-influenced air becomes trapped over the region, holding temperatures down and limiting warm, pleasant days.
Events of note
May 1, 1963. The coldest first day of May on record, with a high of just 51 degrees. Snow flurries were reported in the area that morning.
May 3, 1936. Amid severe storms, lightning struck the Old Post Office tower, “causing it to burst into flames,” according to a front-page report in The Washington Post.
May 5, 1953. A daily record 3.24 inches of rain fell, causing flooding in the District and Alexandria, where water in some areas reached the top of first floors.
May 10, 1906. The latest trace of snow on record. Snow fell for about a half hour but did not accumulate.
May 15, 1834. A freezing low and a high near 50 degrees marked one of the coldest mid-May days in D.C. history.
May 26, 1771. One of the worst floods in Virginia history was nearing its peak, affecting a vast region from Florida to Massachusetts.
May 27, 2018. About 8 inches of rain fell in three hours in Ellicott City, Md., engulfing parts of the historic downtown for the second time in two years.
May 31, 1889. After several days of rain, 2.25 inches fell in Washington, contributing to one of the city’s most severe flood events on record. The same storm triggered the catastrophic Johnstown, Pa., flood.
