A strengthening shortwave trough ejecting into the central US plains resulted in widespread damaging winds, wildfires, and visibility-reducing blowing dust on 15 Dec 2021.
NWS forecast offices leveraged satellite imagery throughout the event. In particular, water vapor imagery was used to track the progression of the mid-upper low, including areas of most pronounced subsidence (drying), where strong synoptic winds were most likely (Figure 1). Water vapor imagery also showed abundant gravity waves emanating from the center of circulation, helping to characterize the turbulent system. During the early afternoon from NWS CYS:
“Mesmerizing GOES WV loop for Windsday as a strong, progressive low continues to deepen and move off to the northeast into central KS/NE. Back edge of this system continues to move through the CWA with drying starting to become evident along the South Laramie Range aided by downsloping winds.”
and from NWS BOU slightly later:
“Winds have clamed down in most areas. However, satellite data shows enhanced subsidence in the nrn foothills. This is allowing for wind gusts in the 50 to 60 mph range in the normal windy areas.”
NWS Pueblo forecasters mentioned they used “all 3 water vapor channel’s to get a good feel of the intensity of the system.”
The system brought widespread wind gusts over 60 mph across the plains, including several reports over 100 mph. NWS Pueblo provides a great summary of the event. Some of the strongest wind gusts for southern Colorado occurred during the morning hours as the surface low deepened and strong subsidence developed across the area. GOES-East 1-min Geocolor imagery with NWS LSRs overlayed captures this period in Figure 2, just prior to the lofting of widespread blowing dust.
Over the next couple of hours, GOES-East 1-min Geocolor imagery captured widespread lofting of dust, particularly in the Pueblo area, and over the far eastern CO plains (Fig 3). Forecasters leveraged GOES-East satellite imagery to detect and track the blowing dust: “Satellite imagery shows more widespread blowing dust over the eastern plains with some roads closed due to winds and visibility. Issued dust storm warning for the plains east of the Interstate 25 corridor. The I25 corridor remains in a blowing dust advisory with some areas reporting visibilities below 1 mile.”
A day long Geocolor animation shows continuing evacuation of dust from southeast Colorado and surrounding areas, and transportation across the central plains (Fig 4).
In the infrared, the 10.3 minus 12.3 um split window difference (SWD), discussed numerous times on this blog, depicts the dense blowing dust plume clearly as areas of relatively dark gray to black (negative values; Fig 5). The SWD is available to forecasters in AWIPS with a different default color range and table. However, a grayscale color table such as what is shown can easily be employed.
The Dust RGB, which includes the SWD and is available in AWIPS, reveals the blowing dust as pinks/reds, along with information about clouds (Fig 6).
The Dust-Fire RGB, available in AWIPS on request, similarly includes both the SWD and IRW, but also adds the 3.9 um SWIR in order to reveal wildfire hot spots as well (Fig 7). The RGB is also able to differentiate dust from clouds. Given the strong gusty winds, numerous hot spots developed and spread across the plains, appearing as red pixels amongst the blowing dust (green). Note that the infrared dust products continue to capture dust after sunset, which is not possible with the vis/nir methods, such as Geocolor.
The DEBRA-Dust product, available online and in AWIPS upon request, was leveraged by both NWS PUB and BOU for dust detection during the event (Fig 8). This product also leverages the SWD, along with more advanced techniques, to highlight blowing dust. From NWS/PUB: “the dust -DEBRA (CIRA) product on Colorada State’s RAMMB/CIRA Slider page was very helpful to monitor how bad the dust was getting across the far eastern plains.” And NWS/BOU wrote in an AFD: “The DEBRA dust satellite product shows the extent of the dust across SE CO and all of W. KS. There is a fair amount of dust across the northeast corner of Colorado, but with mid level clouds we can’t see it on satellite but ASOS and trained spotters have been all over it. Will keep dust in the forecast through this evening across mainly the northeast corner.” DEBRA-Dust also works at night.
Another useful “windy day” display that can be made in AWIPS combines the Geocolor product with below zero SWD (yellow), SWIR hot spots (red), and GLM flash points (blue), resulting in a multipurpose display that captures blowing dust, wildfires, smoke, and thunderstorm details (Fig 9).
Finally, VIIRS providing even more detailed views of the blowing dust and wildfire hot spots in the early afternoon via the Natural Fire Color RGB (Fig 10). The exact locations of dust initiation, and the thickest plumes, can be diagnosed in the imagery, along with a detail of the wildfire hot spot location and size.
Bill Line, NESDIS and CIRA
Input from NWS/PUB forecasters, and NWS text products