U.S. Drought Monitor Update for January 12, 2021

According to the January 12, 2020, U.S. Drought Monitor, moderate to exceptional drought covers 37.5% of the United States including Puerto Rico, a decrease from last week’s 38.3%. The worst drought categories (extreme to exceptional drought) increased slightly from 17.6% last week to 17.7%.

So far this winter, the upper-level circulation seems to be stuck in a pattern consisting of a long-wave ridge over the western contiguous U.S. with numerous Pacific weather systems moving through the pattern in the jet stream flow. These weather systems, or upper-level short-wave troughs and closed lows, weaken as they cross the western ridge and are rejuvenated once they reach the Plains and move eastward. They tend to track along a southern trajectory, tapping Gulf of Mexico moisture as they move across the southern Plains and Southeast.

These systems bring above-normal precipitation to the Pacific Northwest when they hit the coast, then spread above-normal precipitation across the Plains (mostly the southern Plains) and parts of the Southeast. The upper-level long-wave ridge keeps the rest of the contiguous U.S. dry.

Clouds, precipitation, and cold fronts far to the south brought below-normal temperatures to the Southwest, southern Plains, and Southeast this week, while the ridge kept temperatures warmer than normal across the northern tier states. With wet weather in the South, drought and abnormal dryness contracted in the southern Plains and along the Oregon coast, but expansion occurred in parts of California, the northern High Plains, and Upper Midwest.

Drought contraction exceeded expansion, so the overall U.S. drought footprint decreased this week. Abnormal dryness and drought are currently affecting over 114 million people across the United States including Puerto Rico—about 36.7% of the population.