Preview of Thornton's August Weather - The Winding Down of Summer

As summer vacations wind down and families prepare to send their kids back to school in August, Colorado weather also starts to settle down. The chances for severe weather decrease markedly during August and by the end of the month daytime temperatures are dropping quite a bit as well.

At the start of the month Denver usually averages around 88 degrees for a high temperature. By the end of August that drops to 82 degrees. Similarly, nighttime lows drop from 60 to 53 from the start to the end of the month. Generally clear skies can be expected between midnight and noon but the afternoon often brings showers and thunderstorms. These storms typically develop over the foothills then bring precipitation to the Denver metro area.

Despite that moisture, the chance for severe weather decreases considerably compared to the first two months of summer. Cooler air near the surface helps to create a stable atmosphere thus keeping thunderstorms from usually becoming too intense. After the middle of August, tornadoes and damaging hail are pretty rare. The slow movement of storms this time of year are more likely to produce potentially heavy rain.

As the end of the month comes, we start to notice our daylight hours getting fewer and even a bit of a nip in the early morning air. Historical temperature extremes for August are somewhat interesting. First, the highest temperature ever reached in Denver was actually recorded in August - 105 degrees on August 8, 1878 (also tied on July 20, 2005). Second, while there has never been snow in Denver in August, twice the mercury has dropped to 40 degrees to serve as a reminder the white stuff isn't too far off - those occurrences were on August 22, 1904 and August 24, 1910.

Looking back at August 2010 - Cooler but drier than average

Last year the month of August was notable primarily for its unseasonably warm temperatures. Accompanying the warm weather was a lack of precipitation. While both were notable, neither were record-setting marks.

In terms of temperatures, the month flirted entering the record books as one of the top 10 warmest. A fast cool down at the end of the month however prevented that from happening.

Overall the month saw an average temperature of 73.8 degrees. Despite the last minute cooling, this was still 2.1 degrees above normal but 0.3 degrees short of the top 10 list. In all, 12 days saw high temperatures of 90 degrees or higher which is three more than normal.

Temperatures ranged from a high of 97 degrees on the 22nd down to a low of 47 degrees on the 17th. Neither of these were records.

As is often the case, Thornton’s measurements were a bit cooler than those taken way out at DIA. We recorded an average temperature of 72.3 degrees. We ranged from a high of 93.9 degrees set on the 22nd down to a low of 51.1 degrees on the 17th.

Two temperature records were tied during the month, both record high minimums. The low on the 18th only dropped to 67 degrees tying the mark last set in 1986. Similarly, the 28th was 66 degrees which tied the same mark set on the date in 1898.

The month started strong with 1.03 inches of precipitation being recorded within the first seven days. The picture quickly changed however as a mere 0.02 inch fell in the rain bucket over the balance of the month. In the end August finished with 1.05 inches of precipitation, more than three quarters of an inch below the normal of 1.82 inches.

Thornton fared better than Denver in terms of precipitation as we recorded 1.41 inches in our rain bucket. Our rainiest day was the 16th of the month when we saw 0.54 inch fall.

• Click here to view the August 2010 climate report for Thornton.

Outlook for August 2011

The latest long-term outlook from the National Weather Service does not favor any notable temperature or precipitation trends. However monsoonal moisture may linger into the first part of the month which could lead to better chances for precipitation.

For More Information

Temperature Normals and Extremes for August

Monthly Temperature, Rainfall and Snowfall Extremes for August

AUGUST AVERAGE STATISTICS * Normals & Means, 1981 - 2010
TEMPERATURE
AVERAGE HIGH	87.2 (86.0)
AVERAGE LOW	57.9 (57.4)
MONTHLY MEAN	72.5 (71.7)
DAYS WITH HIGH 90 OR ABOVE	9
DAYS WITH HIGH 32 OR BELOW	0
DAYS WITH LOW 32 OR BELOW	0
DAYS WITH LOWS ZERO OR BELOW	0
PRECIPITATION
MONTHLY MEAN	1.57 INCHES (1.82 INCHES)
DAYS WITH MEASURABLE PRECIPITATION	9
AVERAGE SNOWFALL	0
DAYS WITH 1.0 INCH OR MORE SNOWFALL	0
MISCELLANEOUS AUGUST AVERAGES
HEATING DEGREE DAYS	10 (9)
COOLING DEGREES DAYS	244 (217)
WIND SPEED (MPH)	8.0 MPH
WIND DIRECTION	SOUTH
DAYS WITH THUNDERSTORMS	8
DAYS WITH DENSE FOG	1
PERCENT OF SUNSHINE POSSIBLE	71
AUGUST EXTREMES
RECORD HIGH	105 ON 8/8/1878 (TIED AS HOTTEST DAY IN DENVER HISTORY)
RECORD LOW	40 ON 8/26/1910, 8/25/1910, 8/24/1910, 8/22/1910
WARMEST	76.8 IN 1937
COLDEST	66.5 IN 1915
WETTEST	5.85 INCHES IN 1979
MAXIMUM 24 HOUR MOISTURE	3.43 INCHES IN 1951
DRIEST	0.02 INCH IN 1924
SNOWIEST (Could include hail)	NONE EVER RECORDED IN AUGUST
LEAST SNOWIEST	NONE EVER RECORDED IN AUGUST

* Historical weather statistics gathered from the National Weather Service's Denver / Boulder forecast office data archives. Numbers in parentheses reflect "old" normals from 1971 to 2000 before recent updating by the NCDC.