After 25 weeks without exceptional drought—the most severe category—the condition has developed in sections of North Dakota and Montana, according to the July 18, 2017, U.S. Drought Monitor. Moderate to exceptional drought covers 10.6% of the contiguous United States, an increase from last week’s 9.6%. Extreme to exceptional drought also expanded to cover around 2.3% of the Lower 48, up from 2.2% last week.
An upper-level ridge of high pressure dominated the western contiguous United Stated during this U.S. Drought Monitor week. The ridge inhibited precipitation and kept temperatures warmer than normal across much of the West. Pacific fronts and weather systems rode over the top of the ridge, taking a northerly track. This brought them across the drought-plagued northern Plains then into a trough over the eastern contiguous United States, where they stalled out over the Southeast.
Monsoon showers developed in the Southwest, bringing above-normal precipitation to some areas, and small but intense storms developed with the fronts as they moved across the northern and central Plains. Only a few of these storms brought above-normal precipitation to the Plains.
Rain came to parts of the southern Plains and areas east of the Mississippi River, although prolonged and intensifying drought ravaged crops and rangeland in the northern Plains. Soils continued to dry out across the West, Plains, and into the Mid-Atlantic region. Persistent below-normal precipitation and excessive heat expanded areas of drought and abnormal dryness in parts of the West, Plains, and Midwest.