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July-August 2017

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Weatherscapes: Denver, Colorado — The “Mile High City”

Denver, Colorado—one of the largest and fastest growing population centers in the United States—traces its roots at the foot of the eastern slope of the Rocky Mountains to gold prospecting and transportation. Its altitude, officially 5,280 feet above sea level, combined with its location in North America and proximity to the Rockies, make Denver one of the world's most meteorologically dynamic cities on the planet. While weather events in and around the city rarely reach the level of “extreme,” they are wildly diverse and sometimes surprising.

Temperature ranks as one of the most salient attributes of Denver's varying weather. Lacking the moderating effect of a nearby large body of water, the region's dry air heats and cools quickly, with a diurnal range of 30°F common throughout the year. During the winter, Chinook winds can bring rapidly increase temperatures by up to 60 or more degrees, while thunderstorms can drop it by nearly as much during summer afternoons.

Those summer thunderstorms can bring deluges of rain to very isolated pockets of Denver: where one part of the city enjoys sunshine, another might be covered by a roving cumulonimbus. These same thunderstorms can bring a winter-like look to an area with a blanket of hail—as well as tens of millions of dollars worth of damage. Also due to its proximity to the foot of the eastern slope of the Rockies—called the “Front Range” in Colorado—heavy snow can fall from fall into late spring, with temperatures pushing into the seventies in the days prior to and following a storm.

The most dramatic of Denver's changing weather arrives during the summer months: violent thunderstorms that can unleash not only torrential deluges of rain and hail, but tornadoes as well. While not the apocalyptic F-4 and F-5 monsters that occasionally occur in states such as Oklahoma, Texas, Missouri, and others, the storms that touch down in Denver and the surrounding areas can and have caused destruction and death—but most don't, fortunately. Tornadoes have occurred with such frequency in the Denver area that meteorologists studied and identified the likely cause: the “Denver Convergence Vorticity Zone,” a meteorological effect caused by the lay of the mountains to the west of the city, where moist air is forced up and over northwesterly winds that can then result in mesocyclonic activity and tornado breakouts.

Despite the potential for volatility, the skies above the “Mile High City” typically only bring diversity of weather—and a bit of inconvenience from time to time. Nevertheless, rarely has a city emerged and grown under skies so fickle and often dramatic. That drama is due in part to the very altitude after which the city was nicknamed and the mountains that dominate its sunset vistas every evening.

LOCATION:

Denver, the capital city of the state of Colorado, lies just to the northeast of the dead center of the state, near the foot of the front range of the Rocky Mountains.

FORECAST:

Situated deep in the mid-section of North America—far from large, temperature-moderating bodies of water—and at the foot of the Rocky Mountains, at an altitude of one mile above sea level, Denver experiences a semi-arid continental climate with four distinct seasons per year. January, the coldest month in Denver experiences a nighttime low temperature of 17.1°F and a high of 44°F, based on averages compiled by the Western Regional Climate Center. The warmest month, July, sees a mean daytime high of 88.1°F and a nighttime low of 59°F. Springtime brings cold nights and cool days, with April nighttime lows averaging 34.4°F and days 61.3°F. To many, fall is the best time of year in Denver temperature-wise, with October highs averaging 66.3°F and nighttime lows 36.8°F. The record high for Denver, 105°F, has been reached in June, July, and August, and the record low, −29°F, occurred in January.

Denver sees an average of 15.48 inches of precipitation per year. May, which sees a mean 2.43 inches, brings the most, and December and January the least, with 0.53 inches and 0.51 inches respectively.

Denver receives an average of 59.6 inches of snow annually, on average—just shy of five feet. March sees the most snow, by far, with 12.6 inches falling on the city, followed by April, with 8.8 inches. The months of June through August don't see snowfall in Denver.

INSIDE KNOWLEDGE:

Denver experiences a type of warm wind sometimes called a “snow eater,” or less often, an “ice eater,” but most commonly it is called a “Chinook.” As air moves from west to east over the Rocky mountains, moisture is “wrung out” as it rises over the high peaks and cools. After cresting the Rockies, the air, now much drier, heats much faster as it descends, and often accelerates on its downward trajectory. Such dry, warm winds can swing the temperature upwards of 60°F in some instances, “eating” snow and ice in a matter of hours.

While far from “Tornado Alley,” insurance risk researchers found Aurora, a suburb of Denver, to be the most tornado prone city in the United States. Although statistically frequent, tornados in the Denver area rarely develop into the deadly, destructive storms seen farther east in Texas, Oklahoma, and other states more typically associated with tornadoes. 

©ED DARACK

©ED DARACK

 

Weatherwise contributing editor ED DARACK is  an independent author and photographer who covers a broad range of topics. His next book is The Final Mission of Extortion 17, published by Smithsonian Books. Learn more at www.darack.com.

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