Fall heat breaks records across the southern and central US

A persistent upper-level ridge of high pressure developed in late-October 2016 and brought unseasonal heat to much of the central US.[1] Daily record highs have fallen in cities across Arizona, Utah, Colorado, Kansas, Texas, Louisiana, Mississippi, Alabama, Georgia, Virginia, West Virginia, Tennessee, Kentucky, Ohio, Missouri, and Wisconsin.[2]

On November 1 and 2, numerous cities set all-time highs for any day in November, including New Orleans, LA, Austin, TX, Jackson, KY, Huntsville, AL, Chattanooga, TN, Cincinnati, OH, and Milwaukee, WI.[3][4]

Phoenix set a record for the number of days in October that saw highs of 90°F or warmer, with October 30 marking the 26th day that the mercury topped 90 that month.[1] On October 27, Phoenix broke its record for the latest day experiencing a high temperature of 100°F by four days.[5]

Dozens of cities in the southern states of Kansas, Arkansas, North Carolina, Alabama, and Florida broke daily record highs on Monday, October 31, making it the hottest Halloween on record. Atlanta set a new record high on October 31 at 86°F, the latest day on record the city has experienced such heat.[2]

Denver finished the month of October with no measurable snow for the third-consecutive October, which is the first time this happened in Denver weather history.[6]

Extreme heat events, such as this heat wave, are the kind of weather events that increase the most as the climate warms. The more extreme the heat wave, the more likely it is due to the change in the climate. And global warming has led to a dramatic surge in the frequency of the most extreme heat events.

Global warming dramatically increases frequency of the most extreme heat events

A small shift in climate leads to a dramatic increase in the frequency of temperatures at the high end. The very most extreme events are the events most affected by climate change. As the average global temperature rises and the climate shifts, hot temperatures that were extreme under the old climate are closer to the middle of the new temperature range. Under the earth's climate system events closer to the midpoint of the climate range occur much more frequently than events closer to the extremes, as shown in the graphic on the right. The shifting bell curve also leads to the occurrence of never-before-seen extremes in high temperatures.[7][8][9]

"...it is the rarest and the most extreme events - and thereby the ones with typically the highest socio-economic impacts - for which the largest fraction is due to human-induced greenhouse gas emissions." [10]

Due to global warming, the most extreme heat events now impact a global area 10 times greater than in the period 1951-1980.[7]

The impact on moderate heat waves is also dramatic, with a seventy-five percent share of moderate heat events now attributed to climate change.[10]

Many urban areas across the globe have witnessed a significant increase in the number of heat waves, with the largest number of heat waves occurring in the most recent decade studied, 2003-2012.[11]

Heat waves have generally become more frequent across the US in recent decades, with western regions setting records for numbers of these events in the 2000s. Recent multi-month extreme heat events in the US are unprecedented since the start of reliable instrumental records in 1895. There has also been a dramatic increase in nighttime temperatures in the US, reducing the number of critically important relief windows during heat waves.[12]