With less than a week to go, the strikingly sunny and arid October of 2024 may end up as the second-driest month ever recorded in the contiguous United States, based on data going back to 1895 – and a few locations may see their first completely dry month ever observed. Yet the same October that’s been heavenly for leaf-peepers, comet-hunters, crop-harvesters, and football-game-watchers may also be a hint of potential hydrologic trouble ahead.
The weekly U.S. Drought Monitor issued on Thursday, October 24, showed 79.33% of the contiguous U.S. (the “lower 48” states) is experiencing either abnormal dryness (D0, shown as yellow on Fig. 1) or some degree of drought (D1-D4, shown as tans and reds on Fig. 1). This is the highest D0-D4 percentage for any week since November 29, 2022, and it’s not too far behind the record-highest week of 85.28% in Drought Monitor data going back to the product’s creation in 2000.
All 48 of the contiguous states have at least some abnormally dry or drought-sticken areas. The main exceptions are across areas of the Southeast hit by the massive rains from Hurricanes Helene and Milton.
Shown below are several U.S. cities with roughly 150 years of weather data where October is likely to be the first month on record without any precipitation at all – not even a trace, meaning not a single raindrop or snowflake observed. Also shown are the current record-low months and the periods of record, or PORs, for each city.
- Philadelphia, Pennsylvania: 0.09 inch, October 1924 and October 1963 (POR 1871-)
- Atlanta, Georgia: trace, October 1963 (POR 1878-)
- Nashville, Tennessee: trace, October 1963 (POR 1871-)
Several other long-record cities are on track to end October having measured a trace of precipitation but less than 0.01 inches of rain or melted snow in total, which would make it their driest month ever recorded or would tie the previous driest month, including:
- New York/Central Park, New York: 0.02 inch, June 1949 (POR 1869-)
- Trenton, New Jersey: 0.05 inch, October 1963 (POR 1865-)
- Sioux City, Iowa: trace, October 1952 and October 1958 (POR 1889-)
If the rest of the month matches forecasts, some locations are set for the driest two-month beginning of autumn (September plus October) ever observed, including:
- Wilmington, Delaware: 0.33 inch (current record 2.64 inches, 1922) (POR 1894-)
- Philadelphia, Pennsylvania: 0.77 inch (current record 1.53 inches, 1879) (POR 1872-)
- New York/Central Park, NY: 1.59 inches (current record 1.65 inches, 1892) (POR 1869-)
- Tulsa, Oklahoma: 0.33 inch (current record 0.36 inch, 1952) (POR 1893-)
- Sioux City, Iowa: 0.22 inch (current record 0.54 inch, 2011) (POR 1889-)
- Omaha, Nebraska: 0.25 inch (current record 0.97 inch, 1895) (POR 1871-)
It’s likely that this month will be the warmest October on record for many U.S. cities, and it might approach 1963 as the warmest October for the contiguous U.S. as a whole, depending on how a couple of Northeast and Northwest cold fronts play out before Halloween.
Is this becoming a flash drought?
Meteorological drought is simply a lack of normal precipitation, whereas a flash drought is marked by an especially rapid onset or strengthening of drought conditions (e.g., agricultural or hydrological drought, related to deficits in soil moisture or water storage). Meteorological drought can occur without unusually warm temperatures, but drought impacts are intensifying as a result of human-produced warming that’s increased the prevalence of “hot droughts.”
Read: Climate change and droughts: What’s the connection?
Flash droughts are typically caused by extreme spikes of dryness during the warm, high-sun months of spring or early summer, thus leading to high rates of evapotranspiration (moisture release from plants and soils). Flash droughts at that time of year can be especially damaging to warm-season crops, as they rob them of moisture at a critical point.
The unusual blend of this month’s dryness, warmth, and cloudlessness could have easily triggered a widespread flash drought had it occurred in May or June, but the less intense sun of October has tempered the impact of the dryness on the landscape. Still, by at least one definition, many areas scattered across the U.S. from Wyoming to New Jersey are now in flash-drought territory (see Fig. 3).
A 2019 paper in the journal Atmosphere, “Flash Drought Characteristics Based on U.S. Drought Monitor,” defines flash drought as a degradation of at least two categories in a U.S. Drought Monitor rating over a four-week period. As of the October 24 release of the Drought Monitor, many patches of the central U.S. now qualify as being in flash drought, as shown in Fig. 3 above. Overall, dryness or drought has intensified across most of the central third of the nation.
Most U.S. summer crops were at or near harvest stage as the fall dryness set in, so the rain-free weather has actually served as a boon for getting crops out of the fields.
If you happen to find a cloud within 300 miles of us, please let us know. pic.twitter.com/Z8xnmn1hCK
— NWS Louisville (@NWSLouisville) October 20, 2024
An unsettling precedent: October 1952
Across more than 1,500 months that populate the NOAA database going back to 1895, there’s only one that has a clear edge on October 2024 for national-scale dryness: October 1952.
As of October 21, this month has notched about 0.57 inches of precipitation when summed across the contiguous United States, according to climatologist Brian Brettscheider (see embedded post below). Typically, each calendar month produces between two and three inches. A handful of uncommonly dry months have yielded on the order of an inch, including 0.95 inch in October 1965 and November 1917. But the extreme outlier was October 1952, which saw only about half of that amount – a mere 0.54 inch, according to NOAA (0.52 inch in the ERA5 reanalysis data used by Brettschneider).
Given the large-scale forecast through October 31, this month is quite likely to end up at second place behind October 1952 as the driest month in U.S. history.
As it turns out, October 1952 landed during the early stages of the great U.S. drought of the 1950s. Across some parts of the Southern Plains, this event actually outdid the 1930s Dust Bowl in terms of both precipitation deficits and intense heat, forcing more than 100,000 farms and ranches to close in Texas alone and pushing many thousands of people off the land.
“The 1950s drought was no secret, but it did not have a large media presence such as later droughts of lower severity and shorter duration,” noted John Wiener and co-authors in a 2016 paper, “Bite without bark: How the socioeconomic context of the 1950s U.S. drought minimized responses to a multiyear extreme climate event.” At least in part because of innovations introduced in the wake of the catastrophic Dust Bowl, the 1950s drought had much less impact than the 1930s drought on farm output and national food supply. According to Wiener and co-authors, “the basic repertoire worked: urban reservoirs, highly engineered public water supplies, protective farm policy, including aid, insurance and price supports, and efforts to take the most fragile lands out of cultivation.”
Long-range models are pointing toward a major pattern change in the first week of November that could bring substantial precipitation to the Pacific Northwest and across the Mississippi Valley. There are also recurrent hints in long-range ensemble output that a tropical cyclone may form in the western Caribbean during the first week of November. Typically, such systems would stay south of the United States so late in the season, but in this case a northward movement toward the U.S. isn’t out of the question, so the situation will certainly bear watching. It remains to be seen whether any of these one-off events might change this autumn’s mostly dry U.S. trajectory (even with the enormous rains recorded in parts of the Southeast slammed by hurricanes).
La Niña is closely linked to U.S. drought, and a strong two-year La Niña played out at the heart of the 1950s drought from mid-1954 to mid-1956. The strong La Niña of 2020-2022 didn’t produce a similarly intense U.S. drought, and experts at NOAA and the International Research Institute for Climate and Society now expect only a weak La Niña event during 2024-25. But with the preconditioning for widespread drought impacts having fallen into place, it’s time to start keeping a close watch.
1 year ago tonight: Otis -> Cat. 5
Today: #Kristy -> Cat. 5
If only Otis could have been a 🐠, too. pic.twitter.com/7Kjm2YNBG1
— Jonathan Erdman (@wxjerdman) October 24, 2024
Kristy hits Category 5 in the Northeast Pacific
In the remote Northeast Pacific, Hurricane Kristy went from the bottom of the Category 1 range on Tuesday to the top of the Category 4 range just 24 hours later, then went on to become Earth’s fourth Cat 5 storm of 2024 at 5 p.m. EDT Thursday, using ratings from the Joint Typhoon Warning Center and National Hurricane Center. The other Category 5 storms on the planet this year so far were two Atlantic hurricanes, Beryl and Milton, and one Western Pacific typhoon, Yagi.
The 1990-2023 average globally for an entire calendar year is 5.3 Cat 5s, so we are not quite up to average so far this year. The record is 12 Cat 5s in a year, set in 1997. Last year had 10.
Jeff Masters contributed to this post. Special thanks to Christopher Burt and Jasper Deng for assistance with this post.
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