Nationwide
Much of the eastern contiguous U.S. (CONUS), south of the Great Lakes, received little to no rainfall, and this is on top of several weeks of below-normal rainfall leading up to last week. In addition, temperatures have remained hot in many locations.
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This combination of antecedent dryness, much below normal rainfall, and hot temperatures has resulted in rapidly deteriorating conditions, particularly across the Ohio Valley, Mid-Atlantic, and Southeast, with large increases in abnormally dry (D0) and moderate drought (D1) conditions. Conversely, southern Texas, the Four Corners region, the Upper Midwest and Northern Plains experienced several rounds of heavy rainfall.
The impact of Tropical Storm Alberto was significant in some locations across southern Texas and the north-central contiguous U.S. (CONUS). These areas received well in excess of 5 inches of rainfall that led to flash and river flooding, as well as improvements to drought conditions. Some localized flooding also occurred in portions of the Four Corners region, associated with a surge of tropical moisture from the remnants of Tropical Storm Alberto that came ashore in northern Mexico late last week. Across much of the western CONUS, conditions are starting to dry out a bit, particularly in the Pacific Northwest and northern Rockies.
The West
A surge of moisture from Tropical Storm Alberto led to widespread, localized heavy rainfall across portions of the Four Corners region. This led to localized flash flooding and targeted drought improvements across Arizona, New Mexico, and southeastern Colorado.
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Conversely, targeted degradations are warranted across parts of the interior Pacific Northwest and northern Rockies, where warm and dry weather prevailed. Elsewhere in the West, conditions are largely drying out, but the influx of tropical moisture from Alberto has helped stall the dryness’s progression a bit for many locations.
The High Plains
The High Plains region experienced a mixture of both deteriorating and improving drought conditions last week, which has predominantly been the case over at least the last month.
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High pressure over the eastern U.S. and an active storm track across the northern tier of the lower 48 states have been able to funnel moisture northward over the past few weeks, but precipitation has been hit-and-miss from week to week. However, last week was a little different from prior weeks, as some of the moisture from Tropical Storm Alberto was funneled northward into the Four Corners region and then into the Central and Northern Plains.
Southeastern South Dakota received in excess of 5-inch rainfall surpluses for the week, leading to flooding along the Missouri River and some of its tributaries. Heavy rain also fell across parts of southeastern Colorado and southwestern Kansas last week, associated with the surge of moisture from Alberto, leading to some targeted improvements to the drought depiction in those areas as well. Elsewhere in the High Plains region, targeted degradations are warranted due to antecedent dryness, below-normal weekly precipitation, and predominantly above-normal temperatures (with the exception of northern Montana and the Dakotas).
The South
The passage of Tropical Storm Alberto in northern Mexico resulted in a large influx of moisture into southern Texas, with widespread 5-inch rainfall totals (locally upwards of 8 inches for some locations).
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This heavy rainfall caused localized flash flooding and resulted in large improvements to soil moisture. However, leading up to last week, southern Texas was experiencing abnormally dry and moderate drought conditions, so despite some large improvements (2-category improvements in some cases), some parts of southern Texas remain abnormally dry given the rainfall deficits leading up to Alberto’s landfall. Heavy rainfall also fell across portions of the Oklahoma Panhandle, with several locations receiving in excess of 5 inches of rain, warranting some targeted 2-category improvements to the drought depiction there as well.
Elsewhere in the Southern region, conditions are rapidly deteriorating, as rainfall has been lacking for many locations over the past few weeks. Persistent heat has exacerbated the ongoing dryness, leading to degradations across parts of the Tennessee and Lower Mississippi Valleys, western Texas, and northern Oklahoma. Following a very wet May, the last few weeks have been very dry across eastern Texas, and this area will need to be monitored in the coming weeks if warmer than normal temperatures persist. — UNL Drought Monitor
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