Heat remains fixture in Plains

The upper-level circulation over the contiguous United States, known as CONUS, during this U.S. Drought Monitor week of Sept. 20 to 26 consisted of an upper-level ridge of high pressure. It extended from the southern Plains to Hudson Bay, and a low-pressure trough over the eastern Pacific.

The trough sent weather systems spinning across the CONUS, with their fronts and surface low pressure systems generating areas of rain across the Pacific Northwest, northern Rockies, and Great Plains to the Mississippi Valley.

It was drier than normal across the rest of the West, large parts of the central to southern Plains, and most of the country between the Mississippi Valley and Appalachians. The continued dry conditions from the Ohio Valley to central Gulf of Mexico Coast resulted in expansion or intensification of drought and abnormal dryness in these areas.

Temperatures averaged warmer than normal beneath the ridge across the Plains, Mississippi Valley, and Great Lakes. The week was cooler than normal in the West and across the East Coast states.

South

Bands of heavy rain fell across eastern Oklahoma, western Arkansas, and the ArkLaTex, with amounts over 5 inches recorded. Amounts of half an inch to 2 inches extended outward from this central band.

But the western half of Texas and Oklahoma, and much of Mississippi and Tennessee received little to no rain. Hydrological impacts were severe in parts of the South region, with Falcon International Reservoir in south Texas near record-low levels, comparable to the levels reached during the droughts of 2002 and 1956 (during the Great Plains 1950s Drought).

Temperatures were warmer than normal across most of the region, with anomalies reaching 8 to 12 degrees above normal over Texas. Moderate to exceptional drought expanded in Mississippi, extreme drought expanded in southwest Oklahoma and southern Texas, and abnormal dryness and some moderate drought spread across parts of Tennessee.

Abnormal dryness and moderate to exceptional drought were trimmed in parts of Oklahoma, Texas, and Louisiana, with 2-category changes occurring in places. Arkansas had contraction of drought in the west and expansion or intensification in the central to eastern parts.

The lack of precipitation and persistently hot temperatures during the last several months in the South have severely dried out soils.

According to September 24 U.S. Department of Agriculture statistics, 80% of the topsoil moisture in Louisiana was short or very short (dry or very dry). The statistics were 75% for Mississippi, 66% for Texas, 63% for Oklahoma, 62% for Arkansas, and 38% for Tennessee.

Midwest

Western parts of the Midwest region were inundated with heavy rain while eastern parts received little to no rain this week. Large areas in Minnesota and Wisconsin, and parts of Iowa, Illinois, and Missouri, received 2 inches or more, with locally 5+ inches of rain observed.

Abnormal dryness and moderate to exceptional drought were reduced in these states, with some 2-category changes occurring. Meanwhile, abnormal dryness and moderate drought expanded across much of Indiana, Ohio, and Kentucky/ Doils were drying, streams were low, and the last one to two months were extremely dry, and in parts of Michigan, Missouri, and Illinois.

Reports received by the Indiana Extension Office included rapid maturation of crops, trees losing leaves, plants dying, large cracks in soils, stunted lawns, and dropping pond levels across the state, with burn bans in place. In Missouri, there were reports of dry ponds in the Bootheel.

Temperatures were warmer than normal across most of the region, with anomalies reaching 8 to 12 degrees above normal over parts of Minnesota and Wisconsin. Soils continued to dry in the Ohio Valley. According to USDA statistics, 68% of the topsoil in Indiana was short or very short of moisture. This was an increase of 12% compared to last week.

The statistics were 55% in Ohio (an increase of 12% compared to last week), 52% in Kentucky (up 9%), and 30% in Michigan (up 16%). The rain in the Upper Mississippi Valley improved soil moisture, but not by much. In Iowa, 73% of the topsoil moisture was still short to very short, 70% in Minnesota, 60% in Wisconsin, and 58% in Missouri.

High Plains

Northern and eastern parts of the High Plains region received half an inch to over 2 inches of rain this week, while Colorado and parts of Wyoming and Kansas received little to no rain.

D0-D4 contracted in Nebraska, D0-D3 were reduced in Kansas and North Dakota, and D0-D2 shrank in South Dakota. On the other hand, abnormal dryness returned to Wyoming and abnormal dryness and moderate drought expanded in Colorado. Two-thirds of the topsoil in Kansas was still short or very short of moisture, according to USDA statistics.

West

Much of Montana and parts of the northern Rockies received widespread 1 to 3 inches of precipitation; this resulted in contraction of D0-D2 in Montana. The rest of the West region received little to no precipitation.

Abnormal dryness and severe drought expanded in Arizona, and extreme to exceptional drought expanded in southern New Mexico. USDA statistics indicated that three-fourths or more of the topsoil moisture was short or very short in Washington (82%), New Mexico (78%), Montana (77%), and Oregon (74%).

Looking ahead

In the two days since the Tuesday valid time of this USDM, the atmospheric river continued in the Pacific Northwest and rain has fallen across parts of the Midwest, Texas, and Florida.

For Sept. 28 to Oct. 3, a slow-moving weather system will drop 1 to locally 2 inches of rain across the Ohio Valley and parts of the Upper Mississippi Valley. A Pacific weather system will move across the northwestern CONUS, spreading 1 to 2 inches of precipitation across the Pacific Northwest and Montana. Heavier amounts (up to 4 inches or more expected) could fall in coastal areas of Washington and Oregon. The Florida peninsula is forecast to get 2 to 4 inches of rain, while the Gulf Coast, Rio Grande Valley, and Mid-Atlantic states can expect an inch or less.

The Southwest, New England, Carolina Piedmont, and most of New York and the southern Plains to Iowa are predicted to receive little to no precipitation. Temperatures are progged to be above normal from the Plains to Northeast and near to below normal across the Southeast and West.

For much of the next 2 weeks, the atmospheric circulation will consist of an upper-level trough over the western CONUS and a ridge over the Mississippi Valley. The trough/ridge system will slowly shift east during the period.

The Climate Prediction Center’s six- to 10-day outlook for Oct. 3 to 7 and eight- to 14-day outlook for Oct. 5 to 11 favor a fairly stable pattern of warmer-than-normal temperatures from the Plains to East Coast. Also it indicates a cooler-than-normal temperatures over the West and over the southeastern half of Alaska.

The outlook is for above-normal precipitation over the Plains, Upper Mississippi Valley, northern half of the West, and most of Alaska. Odds favor below-normal precipitation over the Northeast and Appalachian Mountain chain, extending into the Ohio Valley and to the central Gulf Coast, as well as in the Alaska panhandle.

Richard Heim, NOAA, is with the National Centers for Environmental Information.