October turned up the U.S. burners – and turned off the tap » Yale Climate Connections

Right on the heels of catastrophic flooding from two hurricanes, the contiguous U.S. had its second-driest month in official records that go back to 1895, NOAA reported on Friday. The 48-state average precipitation for October came in at 0.95 inches, which tied with October 1963 and November 1917 as the second-driest month in 130 years of record-keeping. Far outpacing all other months was October 1952, which recorded a mere 0.54 inches. (See our post from October 25 for more on that month and the related 1950s drought.)

Dryness and drought increased markedly across the United States as October unfolded. By November 7 (based on data through November 5), the U.S. Drought Monitor showed that 87.78% of the contiguous U.S. was experiencing abnormal dryness or drought. That’s the highest weekly percentage in the 25-year history of the Drought Monitor (previous record: 85.28% on Nov. 1, 2022), and a stark increase from the 70.65% dryness/drought coverage reported on October 1. Widespread moisture in early November appears likely to bring down this percentage, at least temporarily. As of September 2024, drought in the U.S. had generated over $2 billion in damages during the year so far, according to Gallagher Re. These damage totals will undoubtedly rise.

Like most calendar months of the year, October is gradually getting wetter on average across the country, with precipitation up by about 20% since the 1890s (see Fig. 1). That doesn’t mean the moisture is well distributed, though. Human-caused climate warming is leading to a well-documented trend toward “clumped,” more-intense rainfall extremes, with hotter, higher-impact dry spells in between. More variability means a tougher time adapting to extremes in both directions.

Especially striking are some of the local records set in October. Several major East Coast cities with century-plus climate data had their driest month ever recorded. Below are some of the locations where all-time driest months occurred in October, along with the periods of record (PORs), as compiled by weather historian Christopher Burt. A value of 0.00 inch means that not even a trace of precipitation (not a single raindrop or snowflake) was measured.

• New York, New York (Central Park): .01 inch (old .02 inch in June 1949); POR 1869-
• Newark, New Jersey: Trace (old .07 inch in June 1949); POR 1931- in the NOAA NOWData online database, but actual POR is 1843-. The driest month from 1843 to 1931 was .25 inch in September 1884.
• Philadelphia, Pennsylvania: Trace (old .09 inch in October 1924 and October 1963); POR 1871-
• Allentown, Pennsylvania: .02 inch (old .09 inch in May 1964); POR 1912-
• Trenton, New Jersey: Trace (old .05 inch in October 1963); POR 1865-
• Wilmington, Delaware: Trace (old .05 inch in October 1924); POR 1894-
• Salisbury, Maryland: .01 inch (old .09 inch in November 2001); POR 1906-
• Atlanta: Trace (ties with October 1963); POR 1878-
• Macon, Georgia: 0.00 inch (ties with October 1963); POR 1892-

Of the 48 contiguous states, 21 experienced a top-10-driest October. This was the driest October on record in New Jersey and Delaware, and the second-driest in seven other states (see Fig. 2). Only Florida was wetter than average, largely due to Hurricane Milton.

Warmest autumn in U.S. history so far

The contiguous U.S. had its second warmest October in 130 years of record-keeping, according to NOAA, tying with 1947 for that mark and topped only by October 1963. Every U.S. state was well warmer than average, and four large states – Arizona, New Mexico, Texas, and Utah – had their hottest October on record, as shown in Fig. 3.

More noteworthy still, autumn 2024 to date (the period September-October) is by far the warmest in contiguous U.S. history, running almost a full degree Fahrenheit above September-October 2015 (63.79°F versus 62.87°F). That’s a far larger margin than between the second and third warmest, third and fourth warmest, or any other such adjacent pairs in the 130-year database.

As for the year to date, it ranks as the second-warmest January-to-October period on record, behind only 2012. Eleven states – mostly in the Midwest and Northeast – experienced their warmest January-October on record, and 35 more states are having a top-10 warmest year to date.

Temperatures in the first week of November were warmer than average, as very mild weather in the central and eastern U.S. has more than outweighed chilly conditions in the West. That pattern is predicted to continue for much of the next two weeks.

Jeff Masters contributed to this post.