This being the latter half of spring, May does mean warm temperatures. Temperatures in the 80’s are common and reaching into the 90’s is not unheard of. The normal highs start out at 65 on the first but by the end of the month that climbs to 76. The record high for the month was recorded on May 26, 1942 of 95 degrees.

While that warmth may sound inviting, we usually aren’t done with the cold just yet. The average day of the last freeze is May 5th but the latest date is June 8th so it can remain cold at night. In fact, the record low for May was on the 3rd of the month in 1907 when Denver got down to 19 degrees. To further drive that point home, the record low temperature for each day of May is at or below the freezing mark except on two days (the 27th and 31st). Don’t get too discouraged though as the normal low is 39 on the 1st of the month and it climbs throughout the month to a normal low of 49 degrees on the 31st.

Snow can and does fall in May with an average of 1.3 inches of the white stuff coming down in Denver. However, the onset of warmer temperatures coupled with Denver's high elevation intensifies late season cold air masses and on the average May snow occurs in about two out of every five years. This serves to somewhat skew what the average snowfall measurement really means. In essence, we have years without snow in May and years with a good bit of it.

Notably, 13 of the last 17 Mays have seen very little snow. Nine saw no snow whatsoever (including 2007), 0.1 inch in two years and a trace in two other years. The one notable year out of the last 17 was in 2003 when snow started falling on the 9th of the month and continued overnight before stopping with 7 inches on the ground in Denver. That particular storm caused tremendous amounts of damage to area trees as it was a typical spring storm and very wet. Most trees had opened up and had all their leaves out and even thick branches snapped under the weight of the snow. The year of 1898 holds the record when 15.5 inches of snow fell during May that year.

Severe weather season normally gets started in earnest in May with violent thunderstorms and large hail and tornadoes a possibility. Moisture spinning up from the Gulf of Mexico into the state collides with cold air from Canada or the Pacific Northwest making conditions ripe for these types of events.

May is the wettest month of the year and on the average precipitation occurs once every three days. An average of 2.32 inches of precipitation falls during the month. For you sun lovers, unfortunately we have to report that May is tied with November as having the lowest percentage of possible sunshine.

Looking Back - May 2007

Stormy was the key word last year as we registered 17 thunderstorms versus the normal six. Hail was reported on two days at Denver International Airport. Of those thunderstorms, only seven produced measureable precipitation in the metro area. In fact five days in a row from the 17th to the 21st saw thunderstorms reported with no precipitation.

Denver recorded 10 days of precipitation with a total for the month of 1.79 inches, 0.52 inch below normal. In Thornton we only had six days with precipitation but we got more out of those with 1.85 inches of precipitation for May 2007.

Temperatures last year in May were very near normal with an average of 58.0 degrees, 0.8 above the normal. Thornton was a touch warmer with an average of 58.5 degrees. Temperatures highes reached 85 degrees on the 13th – 87.1 in Thornton. At the other end of the thermometer the lowest temperature of 35 degrees was registered on the 24th – 35.1 on the 6th in Thornton. Normally we would expect to see two days with temperatures below freezing but that did not happen in 2007. Similarly, normally we would see at least one occurrence of 90 degree temperatures in May but not in 2007.

May 2008 Outlook

The National Weather Service 30-day outlook model indicates that Denver will have at or slightly below normal precipitation during May 2008 and near normal temperatures.

For More Information

Temperature Normals and Extremes for May

Monthly Temperature, Rainfall and Snowfall Extremes for May

* Historical weather statistics gathered from the National Weather Service's Denver / Boulder forecast office data archives.