An upper-level ridge of high pressure dominated the western contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week. The ridge inhibited precipitation and kept temperatures warmer than normal across much of the West. Weekly mean temperatures were as much as 8 degrees above the long-term average from the Southwest to northern High Plains. Pacific fronts and weather systems rode over the top of the ridge, taking a northerly track which brought them across the drought-plagued northern Plains then into a trough over the eastern CONUS 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. But only a few of these storms brought above-normal precipitation to the Plains. Summertime convection and frontal lifting brought rain to parts of the southern Plains and areas east of the Mississippi River. The prolonged and intensifying drought ravaged crops and rangeland in the northern Plains, while soils continued to dry out across the West, Plains, and into the Mid-Atlantic region. Exceptional Drought (D4) returned to the USDM map this week as spots of D4 developed in the northern Plains where below-normal rain fell, and D0 expanded in parts of the Southwest where the monsoon precipitation was below normal. Persistent below-normal precipitation and enhanced evapotranspiration due to excessive heat expanded areas of drought and abnormal dryness in the central Plains to Midwest…
Locally heavy rains fell in southern parts of the High Plains, with over 3 inches reported at several stations in southeast Colorado and southern Nebraska. A few stations in the Dakotas and Kansas received an inch or more of rain this week, but the showers and thunderstorms were spotty and amounts varied significantly. Most stations in the region were drier than normal this week with many receiving a tenth of an inch of rain, if any. With daily temperatures exceeding 90 degrees F, the 7-day average maximum temperature was above 90 in a band from Montana to Kansas. The excessive heat increased evapotranspiration, as reflected in the extreme ESI and EDDI values, and further dried soils which were already parched. According to July 17 USDA reports, topsoil and subsoil moisture was short to very short across 88%/80% (topsoil/subsoil) of Montana, 85%/79% of South Dakota, 65%/58% of North Dakota, 65%/57% of Nebraska, and 62%/58% of Wyoming. The heat and dryness have ravaged crops, with 61% of the spring wheat crop in poor to very poor condition in Montana and 40% in North Dakota. In South Dakota, 74% of the spring wheat was in poor to very poor condition, 38% of the corn crop, 33% of soybeans, and 45% of sorghum. The pasture and rangeland statistics (in poor to very poor condition) were 74% for North Dakota, 68% for South Dakota, 58% for Montana, and 26% for Nebraska. As noted by the North Dakota State Climatologist, the spotty rains might have been enough to green-up the vegetation, but not enough to increase the vegetative volume. Reports from the field include many reports of extensive drop damage, livestock water holes drying up, and cattle losing weight due to poor or nonexistent grazing land. The South Dakota State Climatologist reported that corn is in tasseling stage now; under drought stress, this can lead to an 8% yield loss per day, which is the highest rate of yield loss of any crop stage. The agricultural impacts were compounded by low streamflows. According to the Bureau of Indian Affairs, the Ft. Peck and Ft. Belknap Tribes in Montana declared disaster emergencies in June that remain in effect; the Rocky Boy’s reservation, south of Havre, is experiencing drastic water shortages; and several Tribes in the eastern part of Montana have enacted burn bans.
With many indicators, such as SPI, EDDI, ESI, and soil moisture, converging to exceptionally dry conditions, spots of D4 were added to the USDM depiction in Montana and North Dakota. D0-D3 were expanded in the Dakotas with collateral expansion in adjacent states (Nebraska, Iowa, and Minnesota). D0-D1 were expanded in Nebraska and Kansas, but D0-D1 were trimmed in other parts of Nebraska and Kansas where an inch to several inches of rain fell…
In the Southwest, several inches of rain fell with monsoon showers and thunderstorms in central to southern Arizona, with 1-2 inches in parts of northwest Arizona and parts of New Mexico. But other parts of these states had less rain, and amounts tapered off to zero farther north into the Great Basin. Pasture and rangeland conditions continued to deteriorate in spite of the rain, with poor to very poor classifications increasing from 43% last week to 53% this week in Arizona, and from 36% to 45% in New Mexico. In California, 35% of the pasture and rangeland was rated in poor to very poor condition. D0 expanded in Arizona, Utah, southern Nevada, northwest New Mexico, and southwest Colorado where precipitation was generally below normal for the week. But D0 was pulled back along the east slopes of the Rockies in central Colorado where 2-4 inches of rain was reported.
In the Northwest and northern Rockies, a few tenths of an inch of rain was recorded at coastal stations in Oregon and Washington, and at a few stations in the Rockies, but the week was essentially dry across much of the Pacific Northwest. Even though this is the dry season for much of this region, the rain that did fall was almost universally below normal. D0 was added to parts of Washington, Oregon, and Idaho, based on 90-day indicators and drying soils, and expanded in western Montana. July 17 USDA reports indicated that topsoil/subsoil moisture was short or very short across 54%/42% of Oregon, 57%/33% of Washington, and 47%/44% of Idaho…
In the 2 days since the Tuesday morning cutoff time of this week’s USDM, additional frontal storms have moved across the northern and central Plains, and monsoon showers and thunderstorms have brought additional rain to parts of the Southwest. For July 20-24, 1 to locally 4 inches of rain is forecast for the Four Corners States and from the eastern Dakotas to Northeast, and half an inch to an inch is predicted for the central to northern Plains and most of the country along and east of the Mississippi River. Areas expecting little to no rain include much of the West from California to central Montana, most of Texas, and parts of the western Carolinas. Temperatures are forecast to be above normal for most of the CONUS. Little relief from the heat can be expected as above-normal temperatures are in the outlook for most of the CONUS and Alaska for July 25-August 2, with only the Northeast and parts of the coastal Northwest maybe having cooler-than-normal temperatures. Odds favor below-normal precipitation for coastal southern Alaska, the Pacific Northwest to northern Rockies, and most of the Plains into the Midwest. Above-normal monsoon precipitation is likely to continue for the Southwest, and Alaska is expected to be wetter than normal. The Northeast may start out drier than normal, then turn wetter than normal.