May offered a wide range of temperatures in Washington, which made setting our thermostats a day-to-day challenge. The month’s lowest high temperature of 58 degrees on Sunday came only one week after it was 94 degrees on May 23.

Taking the warm and cool extremes together, May turned out to be a pretty average month. The month’s average temperature of 66.1 was 0.1 degrees above the 1981 to 2010 normal, but 1.1 degrees cooler than the new and warmer 1991 to 2020 normal. Dating to 1871, it ranked as the 53rd-warmest May on record.

May’s extraordinarily cool Memorial Day weekend arguably marked the month’s most memorable weather event. The high temperatures of 59 and 58 degrees on May 30 and 31 were the second-lowest on record both days in the District (trailing only dates in 1893 and 1915). It was the coolest weather so late in the season since 1997, when the high was 58 on June 3, according to the Capital Weather Gang’s Ian Livingston.

Despite a dry spell in the middle of the month, rainfall was close to average overall. The month’s precipitation of 3.77 inches was 0.22 inches drier than the 1981 to 2010 normal and 0.17 inches drier than the 1991 to 2020 normal. It ranked as the 87th-driest on record.

The month featured cool moments, more in keeping with March and April, but also some hot periods that offered a summer appetizer.

You can see the month’s warm (orange) and cool (blue) periods colored by calendar date below. We experienced a notable dry spell from May 9 to May 23, culminating in the month’s hottest day.

Extremes

From the lowest low temperature on May 8 to the highest high on May 23, temperatures spanned 50 degrees during the month:

Several records, for both warm and cold extremes, were set during the month.

On May 23:

  • Dulles Airport tied 1962′s record high of 92 degrees.
  • The District tied 2004′s record warm low of 74 degrees.
  • Baltimore set a record warm low of 70 degrees, topping 69 from 2004.

On May 26:

  • Dulles tied 2007′s record high of 92 degrees.
  • Baltimore tied 1914′s record high of 94 degrees.

On May 29:

  • Baltimore’s high of 56 degrees was the lowest on record for the date, below the previous mark of 57 in 2014.

On May 30:

  • Baltimore’s high of 57 degrees was the lowest on record for the date, below the previous mark of 58 in 1915.
  • Dulles’s high of 57 degrees was the lowest on record for the date, below the previous mark of 62 in 1971.

Pattern

The overall national pattern was quite variable through the month, with both hotter and cooler periods, but the final result was a cool month overall for the United States. Faster-than-normal wind speed around the Northern Hemisphere kept the nation’s weather very active and varied overall.

Year-to-date

The near-average temperatures and precipitation in May kept 2021 in the middle of the pack in the context of the past decade of weather:

How’d we do?

On May 2, we predicted a lot of variability in the temperatures in the month ahead, which worked out well. We predicted an average temperature of 65 to 68 degrees and it was 66.1. We called for rainfall in the range of 3.5 to 4.5 inches and 3.77 inches fell. As both predictions fell within the predicted range, we give ourselves an A grade.

Jason Samenow contributed to this report.