Linda Lam
The triple-digit club is elusive for many cities, but in others, being a member is an annual occurrence.
High temperatures can soar past the century mark each summer in some areas and blistering heat becomes the norm. For some locations, 100-degree heat can last for months, but for others, it has never happened since records began.
(MORE: Hottest Temperatures Ever Recorded in All 50 States)
Climate and geography can have major impacts on how often cities experience temperatures climbing to 100 degrees.
Below we take a look at some interesting statistics for selected cities across the Lower 48.
Where 100-Degree Heat Is Most Common
Many cities in the West typically experience temperatures above the century mark every year, but that's particularly the case in the Desert Southwest.
Las Vegas, Phoenix and Tucson are all premium members of the triple-digit club, as the average number of 100-degree days for all three cities is well above 50 per year.
Death Valley comes to the minds of many when thinking of very hot conditions because it holds the world record for the hottest temperature at 134 degrees, set on July 10, 1913. (The validity of this record is often debated.)
(MORE: Death Valley Heat Records)
The average number of 100-degree-or-hotter days per year in Death Valley is an astonishing 147 – just 2 days more than the current record for most 100-degree days in Phoenix, which was set in 2020.
Unsurprisingly, Seattle and Portland, Oregon, often do not have 100-degree days. Seattle has only recorded a 100-degree reading three times, most recently on July 29, 2009, when the high reached 103 degrees.
One-hundred degree temperatures are more common east of the Cascades; even locations in Montana experience temperatures that soar to 100 degrees from time to time. The most 100-degree days in Missoula, Montana, were 11 in 2007, and the highest temperature on record there is 107 degrees.
These very hot conditions are due to a combination of factors, including elevation, humidity and location.
Locations farther south in the U.S. benefit from a higher sun angle, which results in an increase in solar radiation. Lower elevations also tend to experience higher temperatures, as temperatures decrease when moving higher into the atmosphere. Air tends to be drier in much of the West in the summer, and dry air is able to heat more readily than moist air.
Temperatures in areas closer to the West Coast are influenced by the cool Pacific Ocean, reducing the 100-degree heat there.
Triple-Digit Heat Common In Parts Of The Plains
The Plains is also an area of the country that typically experiences 100-degree heat each summer. The Rocky Mountains, to the west of the Plains, are a major influence on these high temperatures. Downsloping winds can aid in higher temperatures, and the region's location between the Rockies, but also far enough away from the Gulf of Mexico, can lead to drier air.
Unsurprisingly, the Southern Plains – which has several cities in the triple-digit club – experiences more frequent extreme heat compared to the Northern Plains due to the difference in latitude.
Dallas is one of those cities. The average date for the first of many 100-degree days is July 3. The year with the most 100-degree temperatures in Dallas was 2011 when highs topped the century mark 71 times. That year exceptional drought was widespread across the region.
To the southwest in El Paso, Texas, 27 days per year typically have triple-digit temperatures. Farther north in Oklahoma City, there are about 13 days per year when the mercury reaches 100 degrees or higher.
The 100-degree mark becomes a little more elusive closer to the Gulf of Mexico due to the increase in moisture. Houston only usually sees seven days each year with a high of at least 100 degrees. Brownsville, Texas, sees even fewer 100-degree days. The most recorded in a year was 12 in 2019.
The Northern Plains experiences its share of triple-digit heat, usually when a strong upper-level ridge of high pressure builds across the region.
The highest temperature on record for the North Dakota towns of Bismarck and Fargo is 114 degrees and was set in July 1936. In fact, many cities in the Central and Northern Plains set temperature records and saw the greatest number of 100-degree days during the Dust Bowl in 1936. North Dakota even once reached 121 degrees near Steele on July 6, 1936.
100-Degree Days Possible In The Midwest
Temperatures can occasionally soar to 100 degrees or higher during the summer in the Midwest. This is more likely to occur when high pressure dominates the Midwest in the summer with a southerly flow.
(MAPS: Average Temperatures By Month)
St. Louis and Kansas City both usually see about three days of 100-degree temperatures each year. Much of the region experiences triple-digit heat every few years.
The highest temperature on record in both Chicago and Milwaukee is 105 degrees, set July 24, 1934. Both cities also saw the most 100-degree days in 1988 – seven in Chicago and six in Milwaukee. A widespread drought took hold in portions of the U.S. in 1988, contributing to the extensive and unusual heat.
Many other cities in the Midwest set temperature records in 1936 and were influenced by the Dust Bowl just like in the Plains.
Minneapolis saw the most 100-degree days on record in 1936, with nine. Detroit and Indianapolis also set records for the most 100-degree temperatures in 1936, with eight and 12, respectively.
Sizzling In The South
The South certainly experiences hot conditions each summer, but 100-degree temperatures are not as common as one may think.
Although the region is at a latitude conducive for triple-digit heat, higher dew points and humidity levels, as well as proximity to the Gulf of Mexico and the Atlantic Ocean, inhibit higher temperature readings.
Occasionally, a hot and dry air mass develops across the region and allows the mercury to soar across the South. Areas farther from the water typically have a better chance of seeing triple-digit heat.
Nashville had 20 days of 100-degree highs in 1954. The highest temperature on record there is 109 degrees, set June 29, 2012. The next day, Atlanta set its highest temperature – 106 degrees.
Closer to the Gulf of Mexico, New Orleans and Mobile have seen far fewer 100-degree days. The most recorded in a year for New Orleans is five in 1980 and eight in 2000 for Mobile.
Florida is usually thought of as hot and humid, but the persistent humidity plays a large role in limiting how high the thermometer goes.
Tampa has never recorded a high of 100 degrees in records dating to 1890. The mercury only reached 100 degrees once in Miami – July 21, 1942. Away from both coasts, Orlando has seen 100-degree highs several times, most recently on June 19, 2015.
Even though the thermometer may not read 100 degrees often, the combination of heat and humidity – a measure of temperature and dew point – can make it feel like it is 100 degrees based on the heat index.
Northeast Typically Escapes Triple-Digit Heat
As expected, 100-degree temperatures are not a regular occurrence in the Northeast.
The lack of triple-digit temperatures is due to the region's higher latitude and general lack of dry air. However, sometimes the right setup takes shape with a strong area of high pressure that allows temperatures to rise above the 100-degree mark.
Triple-digit heat is more common closer to the mid-Atlantic. In the last 10 years, Washington D.C. and Baltimore have seen 100-degree temperatures in about half of the years.
Meanwhile, New York City has seen only three years with 100-degree heat during the same time period. Boston has seen even fewer 100-degree temperatures and last reached 100 degrees on July 22, 2011.
Portland, Maine, and Burlington, Vermont, have also cracked the triple-digit mark; the highest temperature on record is 103 degrees in Portland and 101 in Burlington.
Some cities in the region have never recorded a 100-degree high, including Buffalo, New York, and Caribou, Maine.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.
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