According to the October 10, 2017, U.S. Drought Monitor, moderate to exceptional drought covers 14.1% of the contiguous United States, a decrease from last week’s 14.4%. The worst drought categories (extreme to exceptional drought) also decreased from 1.4% last week to 1.1%.
This U.S. Drought Monitor week, the main atmospheric circulation pattern continued to be an upper-level trough over the western contiguous United States and an upper-level ridge over the East. Temperatures were below normal in the West beneath the trough and above-normal in the East beneath the ridge.
Weather systems migrated through this pattern, dragging Pacific and Canadian cold fronts along with them. The fronts tapped Gulf of Mexico moisture when they crossed the Rockies, bringing above-normal precipitation to the central Plains to Midwest.
Late in the week, Hurricane Nate and its remnants were caught up in a cold front and dropped above-normal precipitation across parts of the South to Northeast. A northerly flow, associated with the western trough, kept much of the West drier than normal, while the frontal rains mostly missed the extreme portions of the Northern and Southern Plains, lower Mississippi valley, and Mid-Atlantic Coast.