A Preview of Thornton's July Weather - A Hot and Stormy Month

Change is of course the one constant in Denver's weather but come July, things actually get pretty consistent. The standard formula for a day in July is a sunning morning, clouds developing in the late morning and early afternoon. Come mid-afternoon, thunderstorms are rolling off of the foothills and into the metro area and the eastern plains. These storms do occasionally reach severe status containing hail, gusty winds and heavy downpours of rain.

In fact, the worst hail storm on record in Denver history hit western sections of the city on July 11th, 1990. Baseball and softball sized hail from this ferocious storm caused millions of dollars worth of property damage.

July is the most stormy month of the year in fact with thunderstorms occurring on average 11 days per month - or once every three days. These slow moving storms are one of the reasons July is Denver's second rainiest month with an average of 2.16 inches of rain (second only to May). However, these storms are also often very localized and cause widely varying precipitation amounts across the metro area. It is not unusual for one area of down to be deluged while others remain entirely dry. With these severe storms, flash flooding remains a possibility.

Being our hottest month, July daytime temps average 88 degrees and is when we typically see the most consecutive days above 90 degrees. 15 times streaks of 10 or more consecutive days above 90 degrees have been recorded entirely in July or at least partially starting in June or ending in August.

The longest 90 degree streak on record occurred just three years ago in 2008. 24 days straight from July 13th to August 5th saw the 90 degree mark hit or broken. Despite that, the month ended as only the 3rd warmest July on record. It was also the 3rd driest.

The second longest 90 degree streak was 18 days long and actually occurred twice - once in 1901 from July 6th through July 23rd and again in 1874 from July 1st to July 18th. In 2000, 17 consecutive 90 degree days occurred from June 29th through July 15th.

Many of us will hearken back to July 2005 which was a record heat setting month. Six record high temperatures were set, all in the 100's. In fact on July 20th the mercury soared to 105 degrees tying the all time Denver high temperature set on August 8th 1878 and breaking the 102 record for July 20th. Other records were 102 degrees on the 16th, 101 on the 19th, 105 on the 20th, 104 on the 21st, 102 on the 22nd, 102 on the 23rd, and 101 degrees on the 30th. July 2005 became the 2nd hottest July on record and also the 2nd hottest Denver month ever. In all there were 25 days registering 90 degrees or higher which ties for the 3rd most ever with 1963.

Looking back at July 2010 – Warmer and wetter than normal

Denver and Thornton saw a bit of an unusual July last year. Temperatures were only slightly above normal but the real story was the copious amounts of precipitation we received.

By the time the month ended Denver had recorded 3.70 inches of precipitation, far above the normal of 2.16 inches. This fell just 0.01 inch short of making the 'top 10' wettest list for Julys. During the month 13 days saw measureable precipitation of at least 0.01 inch. Five days had a tenth of an inch or more, two days had a half inch or more and two more days registered more than one inch of precipitation.

Unfortunately for holiday revelers, the 4th of July brought 1.84 inches of rainfall as measured at DIA. This set a new record for the date besting the previous mark of 1.44 inches recorded in 1909.

While Denver's official rain bucket at DIA recorded these heavy rains, Thornton was nowhere near as wet. In all we recorded 1.35 inches of precipitation with the single greatest amount falling on July 4th when 0.80 inch was recorded.

In terms of temperatures Denver's average was 73.4 degrees for July. This was 1.0 degree above the normal but nowhere near warm enough to make the 'top 10' warmest list. Temperatures ranged from a high of 102 degrees on the 17th down to a low of 53 degrees which was registered on three days.

In all, 18 days registered high temperatures of 90 degrees or higher with the longest streak of 90 degree days lasting eight days. One day set a new record as the mercury reached 102 degrees on July 17th.

Thornton's temperatures were slightly cooler than the measurements at DIA and closer to normal. Our average temperature was 72.7 degrees. The highest mark of 101.6 degrees was recorded on the 17th and the coolest, 50.3 degrees, was occurred on the 9th.

Click here to view Thornton's climate record for July 2010

Outlook for July 2011

The 30-day outlook from the National Weather Service indicates that both temperatures will be at or slightly above normal while precipitation is expected to be at or slightly below normal. Please use the normals below for guidelines.

For More Information

Temperature Normals and Extremes for July

Monthly Temperature, Rainfall and Snowfall Extremes for July

JULY AVERAGE STATISTICS * Normals & Means, 1971 - 2000
TEMPERATURE
AVERAGE HIGH	88.0
AVERAGE LOW	58.7
MONTHLY MEAN	73.4
DAYS WITH HIGH 90 OR ABOVE	15
DAYS WITH HIGH 32 OR BELOW	0
DAYS WITH LOW 32 OR BELOW	0
DAYS WITH LOWS ZERO OR BELOW	0
PRECIPITATION
MONTHLY MEAN	2.16 INCHES
DAYS WITH MEASURABLE PRECIPITATION	9
AVERAGE SNOWFALL	0
DAYS WITH 1.0 INCH OR MORE SNOWFALL	0
MISCELLANEOUS JULY AVERAGES
HEATING DEGREE DAYS	1
COOLING DEGREES DAYS	261
WIND SPEED (MPH)	8.3 MPH
WIND DIRECTION	SOUTH
DAYS WITH THUNDERSTORMS	11
DAYS WITH DENSE FOG	0* (Less than 1)
PERCENT OF SUNSHINE POSSIBLE	71
JULY EXTREMES
RECORD HIGH	105 ON 7/20/2005 (TIES AS HOTTEST DENVER TEMPERATURE)
RECORD LOW	42 ON 7/4/1903 AND 7/31/1873
WARMEST	77.8 IN 1934
COLDEST	67.4 IN 1895
WETTEST	6.41 INCHES IN 1965
MAXIMUM 24 HOUR MOISTURE	3.43 INCHES IN 1951
DRIEST	0.01 IN 1901
SNOWIEST (Could include hail)	NO SNOWFALL EVER RECORDED IN JULY
LEAST SNOWIEST	NO SNOWFALL EVER RECORDED IN JULY

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