The day before the earliest vernal equinox (0349 UTC on 20 March) in more than 100 years (explanation) is depicted above in an image (courtesy Rick Kohrs, SSEC)  that includes vertical slices of local noon imagery on 19 March.  The sun was directly overhead, passing from the southern hemisphere to the northern hemisphere, at noon 20 March at 121.7 degrees East Longitude, close to Bukaan on the island of Sulawesi in Indonesia.

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As a winter storm began to organize over Colorado on 19 March 2020, GOES-16 (GOES-East) Mid-level Water Vapor (6.9 um) images (above) showed the developing  middle tropospheric cyclonic circulation across the Colorado/Kansas/Nebraska border area. Peak wind gusts included 60 mph in Colorado and Nebraska, and 62 mph in Kansas (WPC Storm Summary).

As a result of the strong winds, several areas of blowing dust were seen in GOES-16 “Red” Visible (0.64 um), Split Window Difference (10.3-12.3 um) and Dust Red-Green-Blue (RGB) images (below): (1) a well-defined plume that originated in southeastern Colorado and moved northeastward across western Kansas, (2) a smaller plume originating north/northwest of Lamar, Colorado which moved eastward toward the Colorado/Kansas border, (3) a small plume that originated over the burn scar from the 07 March “Beaver Fire” in the Oklahoma Panhandle, and (4) multiple narrow plumes of dust in the wake of a cold front that moved southeastward across the region late in the day (which reduced the surface visiblity to 2 miles in southwestern Kansas).

A NOAA-20 True Color RGB image as viewed using RealEarth (below) provided a more detailed view of the dust plume north of Lamar, Colorado as well as the longer plume which stretched from southeastern Colorado into western Kansas.

GOES-16 Visible images with plots of GLM Groups (below) revealed a few clusters of lightning associated with convective elements that were likely producing thundersnow across northeastern Colorado and near the Colorado/Nebraska border. Where warmer air was still present near the Colorado/Kansas border, a more longer-lived thunderstorm was producing rainfall at the surface.

This poor TV tower was blasted with #lightning about 60 times yesterday during the winter storm. @JimCantore we had a huge #thundersnow event in #COwx yesterday triggered by TV towers and wind turbines. Check out the blog I wrote here: https://t.co/9lqqL1cK78 pic.twitter.com/F7rkDOhCVM

— Ch?is Vagas|?y (@COweatherman) March 20, 2020

===== 20 March Update =====

On the following day, GOES-16 Day Cloud Phase Distinction RGB images (above) showed the large swath of fresh snow cover (shades of green) produced by this storm as it moved northeastward across the Upper Midwest. Clouds persisted over much of eastern Colorado, masking the extent of the snow cover there.

===== 21 March Update =====

On 21 March, a decrease in cloudiness over eastern Colorado allowed much of the snow cover (shades of cyan) to be seen in a swath of 30-meter resolution Landsat-8 False Color imagery as viewed using RealEarth (above). The effects of terrain were evident, with a lack of snow cover seen in areas where downslope flow was prevalent during the winter storm.

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GOES-16 (GOES-East) “Snow/Cloud Discrimination” Red-Green-Blue (RGB) images (above) revealed a west-to-east oriented band of fresh snow cover (1-4 inches, shades of red) across central Illinois on 15 March 2020. With a low-level northeasterly flow of cold air across the region, boundary layer cumulus clouds began to develop as solar heating warmed the surface — but this cloud development was suppressed over deeper portions of the snow cover. These RGB images use “Red” Visible (0.64 µm) data as the Red component, and Near-Infrared “Snow/Ice” (1.61 µm) data as the Green and Blue components; bare ground appears as shades of cyan, with supercooled water droplet clouds appearing as brighter shades of white.

A sequence of VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP (below) showed a closer look at the band of snow cover and its effect on modulating the afternoon development of cumulus clouds.

A 30-meter resolution Landsat-8 False Color RGB image viewed using RealEarth (below) provided a detailed view of the band of snow cover (shades of cyan) at 1622 UTC.

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A sequence of GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed a subtle wave propagating westward — against the ambient flow within the mid/upper-tropospherc (500 hPa | 300 hPa) — across far eastern Georgia during the afternoon and evening hours on 14 March 2020. There was a “back door cold front” (surface analysis) moving inland from the coast — so this was likely a vertically-propagating frontal gravity wave, similar to those occasionally seen lee of the Rocky Mountains. Although they are less common in this region, another cold frontal gravity wave was observed along the East Coast in April 2008.

Plots of GOES-16 Water Vapor weighting functions calculated using rawinsonde data from Charleston, South Carolina, Jacksonvlle, Florida and Peachtree City, Georgia are shown below. With abundant moisture aloft, much of the sensed radiation was from middle to upper troposphere — giving an indication of the depth of these vertically-propagating frontal gravity waves..

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