On Thursday, October 18th, high winds affected drought-stricken areas of the central high plains as a tight pressure gradient developed between a broad low pressure system in the upper Midwest and a ridge of high pressure centered over the Inter-Mountain West. Surface winds gusting around 50-70 mph were common across an area from the Dakotas through western and central portions of Nebraska and Kansas. With much of this area experiencing exceptional (D4) drought conditions (Figure 1), a large plume of dust was generated mainly in western Nebraska, which then spread rapidly downstream.
West to northwest winds around the base of the broad trough sent the dust plume racing across the mid-Mississippi Valley and into the Tennessee Valley regions overnight. The dust could be seen in visible imagery yesterday afternoon (Figure 2).
However, the dust showed up very well in MODIS Dust RGB imagery (Figures 3-6). Notice the spatial evolution of the dust plume, as it developed in western Nebraska, then migrated SE into Kansas and then eastward across the afore-mentioned regions.
Although much more diffuse and less discernible, the yellow circle shows the likely location of the best concentration of dust in figure 6 below. With radiational cooling conditions overnight, the colder 10.8µm channel retrievals cause less blue color in the background surface image. The highest concentration of dust continues to block the 10.8um radiation effectively, however differencing between the 12.0µm and 10.8µm channels decreases, also causing less red contribution. The result is a more intense purplish coloration for the area of dust. Notice the dust had moved into western portions of the Tennessee Valley by the time of the image below. Observations from this time (not shown) indicated cloud celings around 3-6 kft AGL in the region of dust, where clouds clearly did not exist.
The leading edge of the apparent dust plume in the imagery above corresponds well with data from the Mobile Integrated Profiling System (MIPS) located at the University of Alabama-Huntsville. As shown in figure 7 below, the ceilometer began to detect dust aloft at about 0700Z. The dust becomes thicker aloft and appearently reaches the surface shortly after 0800Z.
A picture atop the National Space Science and Technology Center bulding (Picture 1, below), which houses the National Weather Service office in Huntsville, AL and the NASA SPoRT center shows the dust in the early morning sky.