Last May, the month's weather highlight was an Arctic outbreak in the second week of the month that produced the coldest reading in May (34°) since 1891. May 2021, meanwhile, experienced one of the chilliest ends of any May, as May 28-31 tied May 1884 for the latest four-day streak with lows in the 40s. This chilly ending was responsible for the coolest three-day Memorial Day weekend on record.
Despite the month's chilly ending, an extended period of above-average temperatures from May 15-27, that was six degrees milder than average, kept the month close to average, temperature-wise. And a very wet May 28-30, in which 2.57" was measured, balanced what, up until then, had been a dry May (these three wet days had as much rain as the previous six weeks). So, when all was said and done, the month was very close to average on both the temperature and rainfall fronts (-0.3 degrees, and +0.40").
Before May's chilly and rainy close, six days in the 10-day period between May 18-27 had highs in the 80s. This included highs of 89° and 88° during the weekend of 5/22 and 5/23; by contrast, the following weekend had highs of 51° on both days. This reading (which was eight degrees colder than the average low for these two dates) tied a record for the coolest high on 5/29, and set a new record (by four degrees) on 5/30.
Besides the last four days of the month, which were 13 degrees cooler than average, there was an eight-day period from May 5-12 that was five degrees below average. (However, the chilliest reading of the month, 42°, was on 5/1.)
Finally, the last six days of the month all had measurable precipitation, the longest rainy streak since one of eight days in May 2019 (5/10-17). However, this year's streak had a touch more rainfall (2.68" vs. 2.56").
Here are recaps of the previous six Mays: