According to the December 17, 2024 U.S. Drought Monitor (USDM), moderate to exceptional drought covers 32.5% of the United States including Puerto Rico, a decrease from last week’s 36.8%. The worst drought categories (extreme to exceptional drought) decreased from 4.1% last week to 3.8%.

The upper-level circulation pattern over the contiguous U.S. (CONUS) during this USDM week (December 11–17) shifted from a deep eastern trough to a more zonal west-to-east pattern. Several Pacific weather systems moved through the zonal flow. Their cold fronts and surface-low-pressure systems spread Pacific moisture and above-normal precipitation across much of the West Coast from northern California into the northern Rockies. When the systems crossed the Rockies and moved eastward, they tapped Gulf of Mexico and Atlantic moisture to bring above-normal precipitation to the mid-Mississippi and Ohio Valleys as well as the southern Appalachians and Mid-Atlantic coast through the Northeast. Much of the CONUS from the Desert Southwest to the Upper Mississippi Valley, from the Gulf of Mexico Coast to South Carolina Coast, and parts of Hawaii were drier than normal.

Much of Alaska was drier than normal this week, with above-normal precipitation in the east-central region. The U.S. Virgin Islands were drier than normal, while Puerto Rico had a mixed precipitation anomaly pattern.

Temperatures moderated as the circulation pattern shifted to zonal, with the week ending up warmer than normal from the northern Rockies to western parts of the central Plains, and from the southern Plains to the Southeast. Slightly cooler-than-normal weekly temperatures were limited mostly to the northern Plains and Great Lakes. Warmer-than-normal temperatures dominated Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands.

Drought and abnormal dryness contracted in the wet areas from the Mississippi Valley eastward and in parts of Wyoming. But drought or abnormal dryness expanded or increased in intensity in parts of Hawaii and a few parts of Wyoming, Texas, and the Southeast. 

Nationally, contraction was more than expansion, so the nationwide moderate to exceptional drought area percentage decreased this week. Abnormal dryness and drought are currently affecting over 233 million people across the United States including Puerto Rico—about 74.9% of the population.