Nationwide
Above-normal precipitation and below-average temperatures resulted in another week of targeted improvements across portions of the Intermountain West, adding to recent precipitation totals that have continued to improve long-term drought conditions.
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The exception is the Pacific Northwest, where below-average precipitation and above-normal temperatures resulted in worsening drought conditions along the northern Cascades. There is a mix of improving and worsening drought conditions across the Great Plains. Improvements are mainly confined to the western Great Plains, where widespread 7-day rainfall totals exceeded 200% of the average for the week, further adding to short-term precipitation surpluses.
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From the eastern Great Plains to the Eastern Seaboard, 7-day rainfall surpluses are more scattered, leading to only modest improvements in areas with the heaviest amounts. In areas that received below-normal rainfall this week, drought worsened as rainfall deficits continued to increase.
The West
The Intermountain West is the beneficiary of another week of widespread above-normal precipitation for many locations, with large portions of the Four Corners region, the Great Basin, and the southern and central Rockies also experiencing below-normal temperatures.
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Improvements are warranted in locations where long-term drought indicators, such as groundwater, continue to improve. In addition, the above-normal snowpack from the active winter rainy season across much of the West continues to keep stream flows near and above average.
Unfortunately, degradations are warranted across parts of the Cascades in the Pacific Northwest, which experienced a near- to below-average winter rainy season, which has been exacerbated by below-average precipitation since that time. Soil moisture and groundwater continue to decline and 7 to 14-day average stream flows have fallen into the bottom 30% (and, in many cases, the bottom 10%) of their historical distributions. In addition, above-average temperatures this week (4-10 F above average) have accelerated this deterioration.
The High Plains
Although much of the High Plains region received above-normal precipitation this week, the region as a whole is a tale of two halves.
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Improvement to the drought depiction is warranted across western portions of the Central and Northern Plains, where 7-day precipitation totals exceeded 200% of average across most areas, adding to precipitation surpluses in recent weeks and improving long-term drought indicators.
Conversely, deteriorating conditions are warranted across eastern parts of the High Plains region where heavy, convective rainfall was not enough to overcome predominantly near and above-normal temperatures and high rates of evaporation from the soils and vegetation (known as evapotranspiration). For example, parts of South Dakota reported evapotranspiration rates from crops averaging around 0.25 inches per day, which varied slightly depending on the type of crop, essentially eliminating the effects of beneficial rainfall for several locations.
The South
Several locations across Louisiana, Mississippi, and Tennessee experienced degradation this week, as the frontal boundary draped across the southern tier states did not result in enough precipitation to stave off degradation for those experiencing antecedent dryness. This is also the case in portions of central Texas and parts of the middle Red River basin, where targeted degradations are also warranted.
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However, farther westward across western portions of the Southern Plains, pockets of heavy rainfall continued to add to 60-day precipitation surpluses, particularly for parts of the Texas and Oklahoma Panhandles. Rainfall has been plentiful in these areas in recent weeks and months. For example, Amarillo, Texas, recently set a new record of 20 days with measurable precipitation during May; the previous record was 15 days. In addition, Lake Meredith, located north of Amarillo, has reached 45.8% of its capacity, its highest since 2001, according to Texas Water Development Board data. — UNL Drought Monitor
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