The calendar and Mother Nature butted heads in a serious way on Sunday.

Sure, Sunday was officially June 9, but with a high of just 63 degrees in Denver, it felt more like April or October rather than the start of the summer season. Sunday’s high made it the coldest summer high temperature since July of 2014.

Meteorologists officially measure seasons by month. So June, July and August count as summer; March, April and May count as spring.

The last time Denver had a high temperature below 63 in the months of June, July or August was on July 30, 2014, when the mercury topped out at 62.

An unusually powerful late season cold front marched through Denver on Saturday, producing large hail across parts of the metro area. By Sunday, the colder air mass behind the front settled in, dropping temperatures significantly below seasonal averages. Morning cloud cover prevented temperatures from rising; Denver’s 1 p.m. temperature was just 55 degrees. A mid-afternoon burst of sunshine allowed temperatures to finally crack into the low 60s, but still far from more typical June levels.

Denver’s average high on June 9 is 80 degrees. Sunday’s high of 63 is also the average daily high temperature for April 21. The forecast keeps temperatures on the comfortably cool side through most of the work week, with highs in the 70s through Wednesday.

Temperatures are expected to climb back into the 80s — normal levels for this time of the year — later this week and into this weekend.