Nationwide
The mid-level height anomaly pattern during the week exhibited an omega-block type pattern, with mean troughing over Alaska and both the West and East, with the western trough cutting off over California, and strong ridging between the troughs across the central contiguous US. This pattern promoted below-normal temperatures across the Southwest for much of the period, with colder air pushing eastward towards the end of the week followed by warming temperatures.
Across the East, cooler air overspread New England and the mid-Atlantic, keeping evapotranspiration rates slightly below normal. In contrast, much above-normal temperatures were observed throughout the week across the northern Plains and upper-Midwest, though colder weather and storminess overspread the northern Rockies and adjacent High Plains at the end of the week.
An active pattern was noted across the Plains, South, and Southeast as a mean frontal boundary provided a focus for stormy weather. These rains, in conjunction with a wetter pattern overall during May, prompted widespread additional drought relief across the South and Southeast, as well as portions of the High Plains. In contrast, hot, dry weather across the northern Plains and upper Midwest caused the expansion of drought and abnormal dryness, with widespread degradation occurring in the western portions of the Midwest.
Towards the end of the week, a storm system brought heavy precipitation to western and central Montana, bringing some drought relief following a period of hot, windy weather. Across the Northeast, additional rainfall benefited portions of New England, while drier weather overspread the mid-Atlantic and southern New England following a wet week previously.
The West
A late-season storm system brought heavy rainfall to southern Oregon and northern California, sparking a few modest improvements but overall doing little to change the current drought depiction.
Some degradations were noted across portions of California, Oregon, and the Great Basin, where impacts from a lack of snowmelt recharge, especially low streamflows, are beginning to be felt. Temperatures during the week were near to above average across the Northwest, but below average across California, helping keep evapotranspiration demands below average.
The High Plains
Stormy weather brought soaking rains across much of the High Plains, with the highest coverage and accumulations over Kansas and Nebraska.
While beneficial, this precipitation competed with much above-normal temperatures during the week, which maintained high evapotranspiration demands. Accordingly, areas that missed out on significant rainfall, including portions of the Dakotas and far northern Nebraska, experienced some degradation, while reductions were noted across much of Kansas and eastern Nebraska. Further west, beneficial precipitation brought some relief to portions of the Colorado Plains and a few spots in Wyoming, while drier conditions resulted in deterioration in southwestern Colorado.
The South
Soaking rains overspread most of Texas during the week, further reducing drought, primarily across southern Texas and the Big Bend country. Rainfall also spread over eastern Oklahoma, but conditions worsened across the western half of the state, which had been drier during the week.
Along the lower Mississippi Valley, heavy rains, exceeding 6 inches in some locations, fell across northern Arkansas, promoting drought reduction. Soaking rains were less intense across Louisiana and Mississippi but still sufficient to reduce drought substantially at the tail end of a wet May. Although conditions have improved overall across the Southern Region, widespread D3 to D4 continues across northern Texas and western Oklahoma, and long-term drought impacts to groundwater remain a concern heading into the summer months across the whole region. — UNL Drought Monitor
