Kansas State University

A large and dry storm system stalled over the central United States early this week. As a result, very strong winds overspread much of Nebraska, Kansas, Oklahoma, and Colorado during this period. Wind speed was impressive with the strongest gusts measured on Tuesday, March 6, across western and central Kansas, and especially the northwest. The Kansas Mesonet (mesonet.ksu.edu) was able to measure these winds and the top wind speeds observed at the low (6.5 feet) and high (30 feet) sensors are listed in Tables 1 and 2:

Table 1. Maximum wind speeds (mph) measured at the low (6.5 feet) sensors. Data collected by Kansas Mesonet.

Table 2. Maximum wind speeds (mph) measured at the high (30 feet) sensors. Data collected by Kansas Mesonet.

Unfortunately, a side effect of these winds consisted of substantial fire weather and blowing dust issues across the region. Fires were reported across the entire state, some of which were several thousand acres in size including ones in Clark, Ellis, Harper, Kingman, and Greenwood counties. The dust however, was limited to just western Kansas. A corridor of dust went from northwest Kansas, south/southeastward into central Oklahoma, being wrapped around the stalled upper-level low pressure over Iowa (Figure 1).

Dust on visible satellite is fairly subtle, but it had substantial impacts on ground conditions across the region. Reduced visibility is the biggest impact, with widespread reports in northwest Kansas of impaired driving conditions. Portions of I-70 and several US/KS routes were closed because it was unsafe. Even visibility in the towns became difficult (Figure 2). Current ongoing dry conditions and recent above-normal temperatures contributed to the amount of dust able to be lifted by the winds. Also, in general, the soils in the High Plains are sandier and sometimes left exposed due to agriculture. These scenarios mean soils are much more vulnerable to easy relocation and lofting by strong winds. Dust also has a different specific heat capacity than air -- meaning it warms faster than the air and absorbs solar radiation more effectively. Therefore, it modifies the air around it once lifted and continues to warm with incoming solar radiation. This increased heat was able increase lift (this process is described in more detail below) and develop small cumulus clouds which are seen in Figure 1 overtop the blowing dust.

Meteorology behind the strongest winds

While gusty winds were observed across the entire state, the blowing dust was concentrated where winds were strongest. These winds were oriented parallel and to the west of an upper-level low pressure center stalled over Iowa - very slowly spreading to the southeast (Figure 3). Very dry conditions were present due to a dry air mass that was in place. With strong solar insolation, the sun was able to warm the surface efficiently without any cloud obstruction. Therefore, the warm air was able to rise high into the lower atmosphere. This air displaces air above it at these higher altitudes forcing vertical mixing. When displaced, this upper air is mixed downward, bringing the momentum of winds aloft down with it. Winds above the surface on these days were moving very, very fast (up to 70 mph at ~14,000 feet), the height which surface air parcels were able to reach on this day. Therefore, winds up to 60 mph were achieved at the surface via this mixing of the warm surface air.

Figure 3 shows a fairly widespread area of 60 to 70 mph winds at approximately 14,000 feet above the surface in the Central Plains. Thankfully, this large area didn’t optimize all the strong winds to the surface. From the satellite image (Figure 1), note the cloud cover across much of Nebraska and eastern half of Kansas. This cloud cover shaded the earth’s surface in eastern Kansas and prevented it from warming to the values further west, as seen on the Mesonet in Figure 4. Therefore, it prevented the strongest winds above the surface from mixing down, which is why none of the strongest wind gusts were observed in eastern Kansas.

Another factor to consider is the terrain. Western Kansas is obviously much flatter than eastern Kansas. Therefore, winds are less obstructed by topography and can reach greater speeds more easily than those over the Flint Hills, Ozarks, and Missouri River Valley.

Hopefully, future storm systems in the Great Plains aren’t quite as dry (or windy). The current outlook isn’t promising with continued warmer-than-normal temperatures for most of the state and dry conditions persisting for the next 1-2 weeks. Only isolated moisture is anticipated and will be most likely in eastern Kansas.

Chip Redmond, Kansas Mesonet
christopherredmond@ksu.edu

Mary Knapp, Weather Data Library
mknapp@ksu.edu