According to the December 10, 2024 U.S. Drought Monitor (USDM), moderate to exceptional drought covers 36.8% of the United States including Puerto Rico, an increase from last week’s 36.5%. The worst drought categories (extreme to exceptional drought) increased from 3.9% last week to 4.1%.

The upper-level circulation pattern over the contiguous U.S. (CONUS) during most of this U.S. Drought Monitor (USDM) week (December 4-10) was a continuation of a broad ridge of high pressure over the West with a trough of low pressure over the East. The ridge inhibited precipitation over the West, while a northwesterly flow between the ridge and trough inhibited precipitation over the central and eastern parts of the CONUS. Pacific weather systems migrated through this ridge/trough pattern, but they were generally moisture-starved and produced precipitation only over northern tier states. Cold Canadian air was directed southward across the eastern CONUS by the trough. These cold fronts encountered moist air from the Gulf of Mexico and generated limited areas of precipitation in the Gulf states. A more potent weather system late in the week penetrated the western ridge. Its surface lows and cold fronts spread precipitation from Texas to the eastern Great Lakes as the week ended. Total precipitation for the 7-day period was above normal for only parts of Texas to the Tennessee Valley, from northern Minnesota to parts of New England, and over parts of Colorado. 

The rest of the CONUS had a drier-than-normal week, with much of the West and Great Plains to Midwest receiving little to no precipitation. Temperatures averaged colder than normal beneath the upper-level trough, from the Lower Mississippi Valley to the East Coast, with much of the West, Great Plains, and Upper Midwest warmer than normal due to the upper-level ridge.

The western ridge extended across western North America, bringing a warmer-than-normal week to Alaska with a mixed precipitation anomaly pattern. Hawaii was mostly drier than normal with a mixed temperature anomaly pattern. Puerto Rico and the U.S. Virgin Islands were mostly warmer and drier than normal.

Drought and abnormal dryness contracted or reduced in intensity in parts of the Northwest and Deep South, and a few parts of the Great Lakes. But drought or abnormal dryness expanded or increased in intensity in parts of the Desert Southwest, Texas, Mid-Mississippi Valley, Florida, and Hawaii.

Nationally, expansion was more than contraction, so the nationwide moderate to exceptional drought area percentage increased this week. Abnormal dryness and drought are currently affecting over 244 million people across the United States including Puerto Rico—about 78.5% of the population.