Preview of Denver's May Weather - The One Constant - Change!

Colorado natives and those that have lived here long enough know that Denver and Colorado weather changes considerably throughout the year. The month of May almost seems to pack four seasons of weather conditions into 31 days. You name it, it can happen.

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, the past 19 Mays have seen very little snow. Ten saw no snow whatsoever (including 2009), 0.1 inch in two years and a trace in two other years.

The one notable year out of the last 12 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. Remember that it was on May 22nd of 2009 that the Windsor Tornado struck so the danger is very real.

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 2010

As mentioned above, May's weather can bring just about every condition and this held true in May 2010. It is perhaps most notable however for the unusually cool temperatures during the first part of the month.

The month seemed to be on track to finish in the top 10 coldest Mays on record but it finally warmed up in the last third and pulled us out of the ranking. Denver saw an average temperature of 54.0 degrees which was still 3.2 degrees below normal. Thornton was just a touch warmer with a monthly average temperature of 54.2 degrees.

Temperatures ranged from a high of 90 degrees on the 28th down to a low of 28 degrees on the 1st and the 8th. The 90 degree day on the 28th was the first one of the year. There were seven days with temperatures below freezing which is five more than normal. Thornton's temperatures were not far off of the marks recorded at DIA. Our warmest day saw us hit 91.8 degrees and the coldest was 27.9 degrees.

In terms of precipitation the month started out wet but finished below normal. In all 1.52 inches of precipitation was recorded, 0.8 inch below the normal of 2.32 inches. Eight days saw measurable precipitation, 2 of those with more than 0.1 inch. One day, the 11th, accounted for more than half of the monthly total as 0.98 inch was recorded in the rain bucket. Thornton fared much better in the precipitation department than DIA as we saw 2.58 inch of precipitation.

Snowfall was exactly equal to average as 1.3 inches was recorded on the 12th. Like with precipitation, Thornton recorded more snow than the official measurement at DIA as we saw 2.4 inches of the white stuff fall.

Thunderstorms made an appearance during the month on five days. A storm on the 18th brought small hail and a tornado was observed west of Denver International Airport on the 26th. No damage was recorded from the twister.

• Thornton's May 2010 climate report
  

May 2011 Outlook

The Climate Prediction Center's 30-day outlook model indicates that Denver will have temperatures in May slightly above normal with slightly below normal precipitation expected. See the normals listed below for guidance.

For More Information

Temperature Normals and Extremes for May

Monthly Temperature, Rainfall and Snowfall Extremes for May

MAY AVERAGE STATISTICS * Normals & Means, 1971 - 2000
TEMPERATURE
AVERAGE HIGH	70.5
AVERAGE LOW	43.8
MONTHLY MEAN	57.2
DAYS WITH HIGH 90 OR ABOVE	0 (* Less than one)
DAYS WITH HIGH 32 OR BELOW	0
DAYS WITH LOW 32 OR BELOW	2
DAYS WITH LOWS ZERO OR BELOW	0
PRECIPITATION
MONTHLY MEAN	2.32 INCHES (Denver's wettest month)
DAYS WITH MEASURABLE PRECIPITATION	11
AVERAGE SNOWFALL	1.3 INCHES
DAYS WITH 1.0 INCH OR MORE SNOWFALL	0 (* Less than one)
MISCELLANEOUS MAY AVERAGES
HEATING DEGREE DAYS	267
COOLING DEGREES DAYS	23
WIND SPEED (MPH)	9.3 MPH
WIND DIRECTION	SOUTH
DAYS WITH THUNDERSTORMS	6 (4th most)
DAYS WITH DENSE FOG	1
PERCENT OF SUNSHINE POSSIBLE	64
MAY EXTREMES
RECORD HIGH	95 ON 5/26/1942
RECORD LOW	19 ON 5/3/1907
WARMEST	64.6 IN 1934
COLDEST	48.7 IN 1917
WETTEST	8.57 INCHES IN 1876 (Wettest month in Denver history)
MAXIMUM 24 HOUR MOISTURE	6.53 INCHES IN 1876 (Most in Denver history)
DRIEST	0.06 INCH IN 1974
SNOWIEST	15.5 INCHES IN 1898
MAXIMUM 24 HOUR SNOWFALL	10.7 INCHES IN 1950
LEAST SNOWIEST	0.0 INCH (40 YEARS WITH ZERO SNOWFALL)

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