A broad upper-level ridge dominated the central U.S., bringing very hot temperatures (90+ to 100+ readings) to much of the West and Southeast and up and down the Great Plains. All-time record hot temperatures were reported at 15 stations in South Dakota, Wyoming, and Nebraska July 15-18, with many in South Dakota reaching as high as 111 to 117°. Many other daily records were set from the Great Plains to the Southeast. In the Red River Valley of the northern Plains, this was the strongest heat wave in over 11 years. Only a few parts of the drought area received significant precipitation. The blisteringly hot temperatures magnified evapotranspiration, erased any benefits from recent rains, and further desiccated suffering crops. Water restrictions were in place in many communities across the drought area. Nearly two dozen large wildfires erupted across eastern Montana, northeastern Wyoming, and South Dakota.
The Plains and Midwest: Scattered thunderstorms brought locally an inch or two of rain to parts of north central North Dakota and a few areas in Minnesota. More widespread rain fell over eastern Kansas, northeast Oklahoma, southeast Missouri, northwest Indiana, and parts of Illinois. D1 was pulled back where up to 5 inches of rain fell west and southwest of Kansas City, D0 was eliminated in northwest Indiana, and D0 was pulled back in extreme northeast Arkansas and parts of Illinois.
Otherwise, a dry pattern was the rule across the Plains where the lack of rain and oppressive heat ravaged farm and ranch land. The heat wave and dry weather came at a critical time for Midwest crops. Corn is in the midst of its critical reproductive stages. Heat and moisture stress during this period leads to significant yield loss. With the exception of Kansas, the USDA rated 80% or more of the topsoil as short or very short (dry or very dry) across the Great Plains States, which amounted to increases of 10 to 20% compared to last week. Fifty percent or more of the pasture and range land was in poor to very poor condition across the Plains States (except for Kansas). In Michigan, Minnesota, and North Dakota, these numbers were 10 to 20% worse than last week. Fish kills were occurring in the Red River near Grand Forks, North Dakota, due to decreased oxygen levels in the water associated with the low flow rates. In central Texas, inflows into the Colorado River since the first of the year have been tracking below those of the 1950s drought of record, with many tributaries reporting zero flow. Area reservoirs were at 6-year lows and aquifers were very low, with some wells running dry. In parts of northwest Oklahoma, wells were running dry and most farm ponds and many streams were dry. The USDA designated 49 Nebraska counties as drought disaster areas, and the governor of South Dakota has requested a federal drought disaster designation for 23 counties. D0 expanded in east central Wisconsin. D1 and D2 expanded from Minnesota and Wisconsin to Montana, from North Dakota to Nebraska, and across parts of Oklahoma and Texas. Spots of D2 were added to Iowa. D3 expanded in the Dakotas, Nebraska, and central Texas. D4 expanded in South Dakota and southern Texas.
The Southeast: A weak frontal boundary sagged across the South, triggering scattered showers and thunderstorms. But the rainfall did little to compensate for significant deficits accumulated over several months and was quickly negated by temperatures surpassing the 90s across much of the region. Sixty percent or more of the pasture and range land was in poor or very poor condition from Mississippi to Georgia, and reaching 83% in Alabama. These are increases of up to 20% compared to last week. More than 90% of the topsoil was rated short or very short in Alabama and Mississippi. Hay yields in South Carolina were less than half of normal.
D0 expanded from northern Florida to North Carolina, and into southwestern Tennessee. D1 expanded into the Piedmont of the Carolinas, into south central Georgia and northern Florida, northern Alabama and Mississippi, northwest Louisiana, and western Arkansas. D2 and D3 expanded northward in Alabama and Mississippi and further into the Florida panhandle, where rainfall deficits over the last 6 months were 10 to 20 inches. D2 expanded into southeastern and southwestern Arkansas and northwestern Louisiana.
West: Stifling heat and general lack of precipitation this week erased benefits from rain that fell last week. Soils continued to dry and agriculture continued to suffer. Sixty percent or more of the pasture and range land was in poor or very poor condition in Wyoming and Colorado, with 70% in New Mexico and 81% in Arizona, which were increases (except for New Mexico) from last week. July 1 statewide reservoir levels were below to significantly below normal in Colorado, Montana, New Mexico, and Wyoming. Local observations between Chama and Tres Piedras, in northeastern New Mexico, revealed about 20% of the aspen dead or dying, while the grass underfoot was green, indicating short-term wetness on top of severe long-term dryness.
D1 expanded across eastern and central Montana and northwestern Wyoming. D2 expanded into southeastern Colorado and bridged northeastern New Mexico across an area of significant 8-60 month deficits to join the D2/D3 region near Las Vegas. The reservoirs this New Mexico city depends on continued to fall and Las Vegas continued water restrictions. The D3 in northeastern Colorado expanded into southwestern Nebraska, and D3 was added to southwestern Wyoming. Streams in southern Montana were extremely low, with the Tongue and Powder rivers at new record lows. D3 was added to south central Montana and north central Wyoming at the headwaters of these rivers. D0 was expanded into the western valleys of Montana where streamflows were dropping and wildfires were igniting.
Outlying Areas: Continued dry weather affected the Hawaiian Islands as the trade wind layer has been unusually stable during the last few weeks. D0 expanded to cover most of the islands to reflect dry conditions which began in April at many stations. No change was made to the depiction in Alaska, where month-to-date temperatures have been cooler than normal and a mixed precipitation pattern has occurred.
Looking Ahead: Over the next 5 days (July 19 - 23), an upper-level pattern consisting of a ridge in the west and trough in the east will dominate the Lower 48 States. Hot and dry conditions are expected to prevail in the western third of the country and the southern half of Florida. Normal to below normal temperatures are forecast for the rest of the country. Dry conditions are likely to continue throughout the Plains. Increased possibilities of precipitation are forecast for Colorado and New Mexico eastward through Texas, as well as much of the Southeast and East Coast.
For July 25 - 29, conditions are favorable for warmer than normal temperatures for the western and eastern thirds of the Lower 48. Normal to below normal temperatures are expected for the rest of the Lower 48. Precipitation opportunities are expected to increase for the East Coast to Gulf Coast States and for parts of the Desert Southwest. The outlook for Hawaii is for isolated precipitation opportunities. Alaska is forecast to have below normal temperatures for the southern coastal areas and near to above normal temperatures for the rest of the state, and above normal precipitation in the south with drier than normal conditions in the north.
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http://www.drought.unl.edu/dm/monitor.html
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