Active weather prevailed over much of the south, east and midwest, as well as parts of the plains, through mid-July, followed by widespread showers moving south. Meanwhile, a robust monsoon circulation provided limited drought relief in the southwest, particularly parts of Arizona, New Mexico, and southwestern Colorado.
In the drier parts of the northern and western United States, the impact of drought on water supplies, as well as rangelands, pastures and various crops, has been magnified by the heat. keep on going. Weekly temperatures averaged up to 10 ° F above normal in the northwest interior north of the High Plains. On July 19, temperatures as high as 110 ° F were reported in eastern Montana. Another pocket of warm weather centered on the mid-Atlantic states. In contrast, near or slightly below normal temperatures dominated the plains, the Midwest, and the south.
Areas of drought (D0) and moderate drought (D1) were relegated to a few areas of Oklahoma, Tennessee and Texas. Overall, there are few drought-related impacts in the South. Frequent summer rains maintained adequate to abundant soil moisture. On July 18, Mississippi led the region with topsoil moisture rated at 33% excess, according to the US Department of Agriculture.
An axis of heavy rain extended from southern Missouri to northern Ohio. Secondary areas of locally heavy showers extended from Iowa and southeastern Minnesota to Michigan. The Midwestern rains intersected some existing areas of drought (D0) and moderate to extreme drought (D1 to D3), resulting in some reductions in coverage. Some of the most dramatic improvements have occurred in central Wisconsin and northern Lower Michigan. From July 13 to 15, more than 2 inches of rain soaked in La Crosse, Wisconsin and Traverse City, Michigan. Oshkosh, Wisconsin, received 3.34 inches.
In contrast, little or no rain fell during the drought watch period around Lake Superior and in central and northern Minnesota, where coverage of severe to extreme droughts (D2 to D3) was significantly expanded. A wide range of indicators and indices, including stream flow, soil moisture, vegetation health index, evaporative demand drought index and index precipitation standard, showed that very severe drought conditions exist at various time scales over much of northern and central Minnesota. On July 18, Minnesota led the Midwest with 63% of its pastures rated very poor to poor, along with 42% of its spring wheat, 34% of its oats, 33% of its barley, 18% of its corn and 17% of its soybeans. Minnesota also led the Midwest on that date, according to the US Department of Agriculture, with topsoil moisture rated at 78% from very short to short.
Scattered showers largely ceased at the start of the drought watch period. During this time, extreme heat returned to the northern parts of the region. The effects of agricultural drought in the northern high plains remained widespread and severe, despite patchy downpours. According to the U.S. Department of Agriculture, topsoil moisture as of July 18 was rated 86% very short to short in North Dakota, with 84% in South Dakota and 74% in Wyoming. Rangelands and pastures were rated at least half of very poor to poor in Wyoming and the Dakotas, with South Dakota leading at 78%.
On July 18, North Dakota was the national leader for oats ranked very poor to poor (50%; tied with South Dakota), along with soybeans (41%) and corn (32%). South Dakota led the country, among the major producing states, for sorghum rated from very bad to bad (29%). Nationally, the U.S. spring wheat crop was rated just 11% good to excellent and 63% very poor to poor on July 18, the lowest overall condition at this time. of the year since July 18, 1988, when the crop was graded 7% good. to excellent and 73% from very poor to poor. Early estimates released by the USDA on July 12 indicated that US spring wheat production in 2021 would be down 41% from last year, while the yield would be down 37%. If achieved, the 2021 U.S. spring wheat yield of 30.7 bushels per acre would be the lowest since 2002.
Showers associated with the circulation of the southwest monsoon brought limited drought relief in Arizona, New Mexico and southwest Colorado, while drought generally worsened in the northern Rockies and the interior of the northwest. The western drought continued to act on several time scales, ranging from a few weeks (mainly agricultural impacts) to two decades (ecological and hydrological effects).
Dozens of wildfires, mostly in northern California and the northwest, continued to burn hundreds of thousands of acres of wood, brush and grass, aided by hot, dry conditions, dry soils and many fuels. Smoke from wildfires has continued to degrade air quality in many parts of the country, well outside the West. In southern Oregon, the nation’s largest active wildfire, the lightning-triggered Bootleg Fire, destroyed more than 394,000 acres of vegetation and destroyed at least 184 structures. Meanwhile, Washington has dominated the country in several drought-related agricultural categories, according to the US Department of Agriculture.
In terms of longer-term impacts, some of the largest reservoirs and lakes in the West continued to show surprising declines. The surface elevation of Lake Mead, on the Colorado River behind the Hoover Dam, dropped 135 feet over the 21-year period from July 1, 2000 to July 1, 2021, from 1,204 to 1,069 feet above sea level. On July 20, the elevation of Lake Mead was 1067.79 feet. Prior to the 21st century, the surface elevation of Lake Mead briefly fell below just 1,100 feet during two periods of drought: 1955-57 and 1964-65. Since March 2014, the lake’s surface elevation at the end of the month has been continuously below 1,100 feet and is currently at an all-time high since impoundment over 80 years ago. Further upstream, water is released from the Flaming Gorge Reservoir in Wyoming and Utah to raise the level of Lake Powell in an effort to protect hydropower generation capacity. Elsewhere in Utah, the surface elevation of Great Salt Lake fell to 4,191.4 feet on July 20, tying the previous record set in 1963. In California, 154 intra-state primary reservoirs gained only 1.7 million acre-feet of water in the 2021 melt season, just 20% of the historical recharge average of 7.9 million acre-feet. By the end of June, the 154 reservoirs contained only 62% of their typical volume for this time of year and had lost 16.6 million acre-feet of water (49% of original volume) over the 2 last years. Current storage in California (17.5 million acre-feet) is less than 5.8 million acre-feet above what these reservoirs held on June 30, 1977, when storage at scale The state eventually fell to a record month-end volume of 7.5 million acre-feet by the end of October. Finally, the terrible western drought was accompanied by record temperatures. The most recent northward heat change occurred when monsoon-related showers intensified in the southwest. On July 19, Glasgow, Montana, reported a maximum temperature of 110 ° F — the highest reading there since July 18, 1936. It was also Glasgow’s third highest temperature (tied with 17 June 1933) never recorded, behind only 113 ° F on July 31, 1900 and 112 ° F on July 18, 1936.