A persistently dry October is pushing nearly half of the nation into a flash drought, contributing to fires in the Midwest and complicating shipping operations along the Mississippi River.

More than 100 long-term weather monitoring stations across 26 states, including Alaska, are recording their driest October to date, according to the Southern Regional Climate Center and the Midwest Regional Climate Center. Major cities exhibiting no measurable rainfall this October include New York, Houston, Dallas, Philadelphia, San Francisco, and Sioux City, Iowa, in addition to traditionally arid locations like Los Angeles, Las Vegas, and Phoenix, as reported by the National Weather Service.

“We are seeing one of the driest Octobers on record,” noted Allison Santorelli, who serves as the acting warning coordinator for the National Oceanic and Atmospheric Administration’s Weather Prediction Center. This notably includes the Southeast, where some areas had previously dealt with severe flooding from Hurricane Helene just the month prior.

In June, drought conditions affected less than 12% of the U.S., but that figure has surged to close to 50% and continues to rise, as per the U.S. Drought Monitor.

This rapid onset aligns with the definition of “flash drought,” which contrasts with slowly forming droughts, stated Brad Rippey, a meteorologist at the U.S. Department of Agriculture and author of the drought monitor. A study released last year indicated that climate change, driven by the use of fossil fuels, leads to an uptick in both the frequency and intensity of flash droughts, recalling a devastating one that caused $30 billion in damages in 2012 in the U.S. and another worse event in China in 2022.

During the first 28 days of October, one-eighth of the continental U.S. reported no rainfall. Approximately 93% of the continental U.S. is experiencing below-average rain this October, with the majority of areas receiving less than an inch, based on data analyzed by climate centers.

Cities such as Washington, D.C., are expected to reach 80 degrees Fahrenheit on Halloween, while Chicago and Detroit are also anticipated to experience unseasonably warm temperatures. “That’s unusual for this time of year,” remarked meteorologist Ryan Maue, a former NOAA chief scientist, recalling that he used to trick-or-treat in snowy conditions in Michigan.

According to Santorelli, a high-pressure system has obstructed moisture from moving northward from the Gulf of Mexico, resulting in a dry spell across much of the U.S., from the Plains and Midwest to the Eastern seaboard.