May is also the final month of meteorological spring (Mar.-May), and by the end of it -- when 80-degree days are the norm -- summer’s presence is usually widely known.
Keep reading for more in this secondinstallment of a year-long series of posts detailing specific statistics on climate norms, extremes, and averages for the each month in Washington, D.C…
May’s average rainfall is 3.99” (previously 3.82” from 1971-2000)*. As noted, this ranks first among the months at D.C. Whereas April jumped several spots in the new 1981-2010 averages, May retained its previous rank as number 1.
The maximum daily rainfall in May is 3.24” and it fell on the 5th in 1953. One other day, all the way back in 1900 also saw a 3”+ rainfall. In total, there have been 17 occurrences of daily totals over 2”. Compared to April, average days with at least a trace of rain are slightly higher, 15.6 vs. 15.2. Disruptive rains of .1” or more are also a bit more frequent with 7.3 compared to 6.5 in April.
Highs are typically in the 70s and 80s, 41% and 29% of the time respectively. The coldest high temperature in May was 46 on the 5th in 1917. The warmest high temperature was 99 in 1991.
Nighttime lows are on the way up too, with lows mainly in the 50s (51%) and 60s (31%). There have been no freezes at D.C. past April until the next cold season. May’s coldest temperature fell just short of freezing back on May 11, 1906 with a reading of 33. More recently, the coldest DCA has seen was 34 in 1947. The warmest low temperature in May was 78 on the 30th in 1991.
Though 90+ in April is not super uncommon, May is the typical start of the 90-degree day season at D.C., coming in at 1.6 days per year out of the broader average of 36.4. 1991 was the clear standout in this regard, with a week-long stretch of 90+ to finish the month catapulting it to the warmest May on record.
30-year (1981-2010) Averages / Overall (All history) Averages...
Highs 70 or above: 23.3 / 22.6
Highs 80 or above: 10.6 / 10.4
Highs 90 or above: 1.6 / 1.6
Highs below 70: 7.7 / 8.4
Lows below 50: 4.8 / 7.1
Lows 60 or above: 10.3 / 9.3
Days with a trace of rain: 15.6 / 15.9
Days with .1” of rain or more: 7.3 / 7.2
Days with .5” of rain or more: 2.9 / 2.6
Days with 1” of rain or more: 0.9 / 0.8
Days with thunder: 4.9 / NA
Days with hail: 0.1 / NA
-This count is done through records on Weather Underground, and does not include the entire historical period.
All-Time Records (High / Low)...
Highs 70 or above: 30 (1953, 1969) / 14 (2003)
Highs 80 or above: 21 (1911, 1944) / 2 (1924)
Highs 90 or above: 11 (1991) / 0 (54 years)
Highs below 70: 17 (2003) / 1 (1969)
Lows below 50: 19 (1967) / 0 (1887, 1953, 1991, 1998)
Lows 60 or above: 23 (1944) / 0 (1901, 1924)
Days with a trace of rain: 25 (1943) / 6 (1880)
Days with .1” of rain or more: 15 (1933, 2003) / 2 (6 years)
Days with .5” of rain or more: 8 (1889, 2009) / 0 (7 years)
Days with 1” of rain or more: 5 (2008) / 0 (71 years)
Daily climate records for National Airport (DCA), 1871-present
- See selected and additional statistics compiled for this post (Excel)
*All averages, unless otherwise noted, refer to the 30-year period of 1981-2010.
**All instances of monthly temperature average, daily temperature average or daily precipitation average refer to the 1971-2000 climate normals as presented by the National Weather Service. NWS smooths some averages without daily data in a method described here. Monthly rainfall is a simple average and new 1981-2010 data is used here. NWS data on temperature averages should update shortly and will be reflected in these posts.
While numerous local climatology statistics including daily, monthly, and seasonal normals and records are available from National Weather Service Baltimore/Washington, there are myriad other pieces of information which help frame the story. Rather than attempt to recreate what is already available, this series of posts will act as a companion to most information presented there.
This is the second installment of a series of living documents. Through early 2012, each month will be broken down in a similar or evolving way. As input is taken from the community, some items may be added to or changed in older postings. These postings will be updated as necessary to reflect changes when needed. Other articles may also become part of this series.
Learn more about each month:
-April Weather in Washington, D.C.
-May Weather in Washington, D.C. (viewing)
Article last updated: May 4, 2011.