Mid-October heat breaks records across the eastern US

Much of the Central and Eastern United States experienced record warmth for mid-October due to heat and humidity associated with an expansive high pressure weather system that stretched from Bermuda over the eastern US as well as from winds in the upper atmosphere that drew heat up from the South.[1] More than 330 record high and record warm low temperatures were tied or broken between October 15 and 19.[3]

On October 19, temperatures in the DC region hit levels typical of the height of summer—surging to 86 or 87 degrees.[2] For two days in a row, the temperature at both Dulles International and Baltimore-Washington International Marshall airports set record highs, recording temperatures of 86°F and 87°F, respectively.[2] Further north, Bridgeport, Connecticut recorded a high temperature of 86°F on October 19, breaking the record for the date as well as for the hottest temperature so late in the season.[3] John F. Kennedy International Airport in New York also hit 86°F, beating the 51-year-old record for the date by 11°F.[3]

On October 18, over two dozen record highs were tied or broken across the Eastern US.[4] Jackson, Kentucky reached 87°F, breaking the previous record of 81°F by 6 degrees.[4]

On October 17, the unseasonably warm weather shattered temperature records in 44 cities.[5] McAllen, Texas recorded its latest 100-degree day on record, and Dodge City Kansas recorded the first ever 100°F October day on record, topping out at 101°F.[6][7]

Record warm low temperatures were also set in ten states on October 17.[6]

On October 16, Oklahoma set a new record temperature on October 16 of 102°F — the hottest temperature ever recorded this late in the calendar year for the entire state.[8]

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.[9][10][11]

...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.[12]

Due to global warming, the most extreme heat events now impact a global area 10 times greater than in the period 1951-1980.[9]

The impact on moderate heat waves is also dramatic, with a seventy-five percent share of moderate heat events now attributed to climate change.[12]

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.[13]

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.[14]