Dry weather, warm temps continue on the Plains

Several weather systems moved across the contiguous United States during the U.S. Drought Monitor week of Feb. 21 to 27.

Their fronts and surface lows spread rain and snow across parts of the West at the beginning and end of the week, and over the Tennessee to Ohio Valleys and Appalachians at mid-week. These systems were associated with an upper-level circulation pattern that consisted of low-pressure troughs just off the west coast and east coast. A high-pressure ridge was found over the central part of the country.

Ridge impact

The ridge brought above-normal temperatures to much of the CONUS, from the Rocky Mountains to Appalachian Mountains, with weekly temperatures averaging 15 to 20 degrees Fahrenheit above normal from Texas to the northern Plains and Upper Mississippi Valley.

The ridge also inhibited precipitation from the Rockies to Mississippi Valley. The precipitation in the West was mainly over mountain ranges but was not enough to improve drought conditions.

The precipitation in the Midwest was enough to prevent further drought expansion or intensification where it was wetter than normal for the week. In other areas, drought or abnormal dryness expanded or intensified in parts of the Plains and Midwest.

The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the U.S. Department of Agriculture and the National Oceanic Atmospheric Administration. (Map courtesy of NDMC.)

South

Much warmer-than-normal temperatures accompanied the dryness, with daytime maximum temperatures in excess of 90 degrees were recorded in Texas. Dallas and Fort Worth reached 94 on Feb. 26, which was a daily record and 31 degrees above normal. The hot temperatures increased evapotranspiration which drew moisture out of the soils.

The recent dry weather, accompanied by low relative humidity and windy conditions, contributed to an outbreak of wildfires across parts of the region. D0 expanded in southwest Texas where air temperatures were hot, soils were hot and dry, and the last three months were drier than normal.

Dry 1- to 3-month SPI values prompted expansion of D0 in eastern Oklahoma and adjacent parts of northeast Texas and western Arkansas. Dead fields in Sebastian County, Arkansas, were reported via the Condition Monitoring Observer Reports reporting system. D0 expanded in southern Mississippi, adjacent parts of Louisiana, and southeast Texas where SPI was dry, streamflow was low, and some soil moisture indicators showed dryness.

Midwest

The past 30 days have been very dry and much warmer than normal across western and northern parts of the region, with the above-normal temperatures increasing evapotranspiration and helping to dry soils.

These short-term drought conditions resulted in expansion of D0-D1 in parts of Missouri, Illinois, Wisconsin, Michigan, Minnesota, and Iowa. In eastern and southern parts of the region, precipitation last month has kept topsoil conditions near normal but deep-layer soils are dry and streamflow is low.

High Plains

There were a few areas of half an inch to locally 2 inches of precipitation in the High Plains region this week—in North Dakota and parts of Colorado and Wyoming. But the rest of the region had little to no precipitation.

Daily high temperatures reached into the 80s some days in Kansas and up to the 50s and 60s in the Dakotas. Weekly temperatures averaged 10 to 20 degrees above normal across most of the region, increasing evapotranspiration. Since this is February and vegetation is still dormant, the above-normal ET had little effect on vegetation. Soil temperatures were well above freezing in southern parts of the region and the high ET helped to dry soils.

D0 expanded in the Dakotas, and D1 crept into northwest North Dakota, to reflect the one- to two-month dryness and unusually warm temperatures. D0 expanded in eastern Kansas where recent precipitation has been low and soils were drying.

In Wyoming, very low mountain SWE (snow water content) and dry 1- to 4-month SPI values prompted the expansion of D0-D2.

West

Half an inch to locally 2 inches were reported in the northern and central.

Outside of these areas, precipitation was generally less than a fourth of an inch, with rain shadow areas and the Southwest (Four Corners States) mostly dry. The precipitation was above normal for the week in some areas, particularly parts of the Cascades, Rockies, and southern California.

But amounts were not enough to bring month-to-date totals to near normal values, with these areas still well below normal for the month. Mountain snowpack and SWE values were still well below normal to near-record low in Montana.

Low SWE and 1- to 4-month SPEI values resulted in expansion of D0-D3 in parts of Montana.

Looking ahead

In the two days since the Tuesday valid time of this USDM, Pacific moisture continued to move across the Coastal and Cascade ranges in the Pacific Northwest, with precipitation falling in areas east of the Mississippi River and in parts of the southern Plains.

For Feb. 29 to March 5, a ridge over the eastern CONUS will bring warmer-than-normal temperatures to much of the country east of the Rockies. A trough may contribute to cooler-than-normal temperatures in the West. Forecast models predict a wet period for much of the West, in the Upper Rio Grande Valley, and from the Lower Mississippi Valley to the East Coast, as low-pressure systems and fronts bring locally heavy precipitation.

The central to northern Rockies could receive 2 to 4 inches of precipitation. Parts of southern New Mexico and western Texas could receive up to an inch of rain. Outside of these wet areas, up to half an inch of moisture could fall in the lower elevations of the West, across the northern and southern Plains, and Midwest to Northeast

 Areas that could miss out on the precipitation stretch from southern California to the central Plains, where little to no precipitation is expected, and the southern Plains and Mid-Mississippi Valley to eastern Great Lakes, where less than a fourth of an inch may fall.

Next two weeks

For much of the next two weeks, the atmospheric circulation is expected to continue an upper-level trough over the western CONUS and a ridge over the eastern two-thirds of the country.

The Climate Prediction Center’s 6- to10-day outlook and eight- to 14-day outlook from March 6 to 12 favor a fairly stable pattern of warmer-than-normal temperatures from the Plains to East Coast. Cooler-than-normal temperatures over the West and Alaska.

The outlook is for above-normal precipitation over eastern and southern Alaska and much of the CONUS, especially east of the Mississippi River, with odds favoring near to below-normal precipitation over the northern Rockies to northern Plains.

Richard Heim is with the National Oceanic and Atmospheric Administration and National Centers for Environmental Information.