Monday, December 23, 2024

Autumn 2024 was the warmest in U.S. history, NOAA says » Yale Climate Connections

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Even as an incredibly dry, hot autumn relaxed slightly in November, the contiguous United States still recorded its warmest fall in 130 years of record-keeping, NOAA reported on Monday.

The nation also completed its warmest January-to-November period on record, which sets up a sizable chance that 2024 will end up as the hottest year in U.S. history.

Last month was the sixth-warmest November in contiguous U.S. records that go back to 1895, following the second-warmest September and second-warmest October. For the three months combined (i.e., meteorological autumn), the average of 57.62 degrees Fahrenheit came in just 0.04 degrees above the previous record-holder, autumn 2016 (see Fig. 1 below). All other autumns on record were at least 0.75 degrees cooler than these two.

A chart shows the average temperature in the contiguous U.S. between September and November, showing a clear warming trend between 1895 and 2024
Figure 1. Temperatures averaged across the three months of meteorological autumn (September through November), 1895-2024. (Image credit: NOAA/NCEI)

The contiguous-U.S. warmth of autumn 2024 was extraordinarily widespread. Every one of the lower 48 states but Oregon had a top-10-warmest autumn, and most were in the top three. Six states – Maine, Minnesota, Nebraska, Texas, and Wisconsin – had their warmest autumn on record (see Fig. 2 below).

A map of the contiguous U.S. shows statewide average temperature ranks, September-November, between 1895 and 2024. Every state had an above-average autumn, with most states much above average. A map of the contiguous U.S. shows statewide average temperature ranks, September-November, between 1895 and 2024. Every state had an above-average autumn, with most states much above average.
Figure 2. Rankings of average September-to-November temperature in each contiguous U.S. state for 130 years of records going back to 1895. Darker red colors indicate hotter conditions. (Image credit: NOAA/NCEI)

The relentless warmth extended well into November in many areas before more seasonable cool fronts started to bring temperatures closer to average by late in the month. Even so, Alabama, Maine, Mississippi, and Louisiana had their warmest Novembers on record, and every state east of the Mississippi had its top-10-warmest November.

The tale of autumn 2024’s U.S. heat can also be vividly told by looking at record highs versus record lows. For the three autumn months, the contiguous U.S. saw 9,228 daily record highs broken (not just tied), as opposed to 1,081 daily record lows broken – a ratio of more than eight to one across autumn as a whole. The ratio is ever more wildly skewed for all-time monthly records: 364 monthly highs versus eight monthly lows. That’s 45.5 monthly record highs for every monthly record low!

Fast-worsening U.S. dryness abates slightly in November

As we noted in last month’s roundup, the uncannily sunny, mild start to autumn was paired with stark dryness almost everywhere outside those parts of the Southeast ravaged by Hurricane Milton and especially Helene. Based on data through November 5, the weekly U.S. Drought Monitor showed that 87.78% of the contiguous U.S. was experiencing drought or at least abnormal dryness. That’s the highest weekly percentage in the 25-year history of the Drought Monitor (previous record: 85.28% on November 1, 2022) and a stark increase from the 70.65% dryness/drought coverage reported on October 1.

That week marked the peak of this autumn’s drought, as beneficial rains and mountain snows have reached many parts of the contiguous U.S. since then, especially over the nation’s midsection. In fact, last month was the 17th-wettest November for the 130-year period of record. Oklahoma got its wettest November on record, and Colorado, Kansas, and Nebraska each saw a top-10-wettest November (see Fig. 3).

A map of the contiguous U.S. shows statewide precipitation ranks for November 2024, with the Plains states getting above-average precipitation and many East Coast and New England states remaining below average A map of the contiguous U.S. shows statewide precipitation ranks for November 2024, with the Plains states getting above-average precipitation and many East Coast and New England states remaining below average
Figure 3. Rankings of average November precipitation in each contiguous U.S. state for 130 years of records going back to 1895. Darker green colors indicate wetter conditions; darker brown denotes drier conditions. (Image credit: NOAA/NCEI)

Based on data through December 3 (see Fig. 4 below), the Drought Monitor showed the coverage of drought and abnormal dryness had dropped to 71.48% over the contiguous United States. Even so, 43.64% of the Lower 48 was covered by drought (levels D1 to D4), which is down from a peak of 54.08% in late October but still a disconcerting expanse. As noted by the Washington Post, areas of at least moderate drought can be found in 49 U.S. states (every state except Alaska). And severe to extreme drought still covers much of the northern High Plains and parts of the Southwest, as well as most of the Interstate 95 corridor from Washington, D.C., to Boston.

A map of the contiguous U.S. released December 5, 2024 (data valid: December 3, 2024), showing the intensity and impacts of drought across the U.S.A map of the contiguous U.S. released December 5, 2024 (data valid: December 3, 2024), showing the intensity and impacts of drought across the U.S.
Figure 4. Drought and dryness across the contiguous U.S. as of the December 5 installment of the weekly U.S. Drought Monitor. (Image credit: National Drought Mitigation Center)

A two-acre brush fire broke out in Brooklyn’s Prospect Park in November, leaving up to $275,000 in damage and serving as a freakish instance of what protracted dryness can do to a typically lush landscape. New York’s Central Park has received only a trace of moisture in December, just weeks after one of the city’s longest-ever streaks without any measurable rain or snow: from September 30 through October 28. The city’s total precipitation from September 1 through December 7 was 5.04 inches – the lowest for that period in 155 years of Central Park record-keeping, below the previous record of 5.22 inches in 1909.

Will this be the hottest year in U.S. history?

Although the first 11 months of 2024 were the warmest on record for the contiguous United States, it’s still possible this year will be far short of the current full-year record-holder, 2012. That year had the 20th-warmest December in U.S. history, whereas this month to date has seen cold temperatures in the East roughly balancing warmth in the West. Another sharp cold intrusion will sweep across the eastern U.S. later this week, but widespread warmer-than-average air is projected to take hold yet again next week.

Jeff Masters contributed to this post.

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