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 eventually 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 (below).
This GOES 1 km visible image was valid at 331 pm CDT 18 October 2012. The plume of dust is indicated by the light gray colors stretching from SW Nebraska across Kansas into northern Olkahoma. An area of low clouds (bright white colors) can be seen to the northeast across the Midwest. Notice winds gusting around 40-50 knots in this region.
However, the dust showed up very well in MODIS Dust RGB imagery (Figures 3-6) produced by NASA's Short-term Research and Prediction Center. 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 in the series of images below.
The dust can easily be seen in this MODIS 1 km resolution Dust RGB product valid 131 pm CDT 18 October 2012 provided by NASA/SPoRT (viewed in Google Earth via KML file). The yellow circle indicates the dust plume that originated in SW Nebraska. The dust shows up as the bright pink/red colors in the dust RGB imagery. Unfortunately, the data availability was along the edge of the swath from the Terra satellite.
In this MODIS 1 km resolution Dust RGB product valid 2013Z 18 October 2012 (below). The yellow circle indicates the dust plume that originated in SW Nebraska. The dust plume is captured completely in this better pass of the Aqua satellite a little later.
In this SPoRT 1 km resolution Dust RGB product valid 1058 pm CDT 18 October 2012, the yellow circle indicates the dust plume that originated in SW Nebraska. In this nighttime image, the dust shows up as a brighter pink/purple color when compared to the softer pinks and light purples of the cooling surface. Notice the highest concentration of dust was across central portions of Oklarhoma into western Arkansas.
Although much more diffuse and less discernible by early in the morning, the yellow circle shows the likely location of the best concentration of dust (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 in the RGB satellite "recipe" 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 below, the ceilometer began to detect dust aloft at about 0700Z. The dust becomes thicker aloft and appearently reaches the surface shortly after 0800Z at the MIPS site just off Sparkman Drive at the NSSTC building.
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. This picture was taken at about 730 am CDT.