Strong winds gusting over 45 knots and dry surface conditions led to yet another southern plains blowing dust event on 6 April 2021. This time, the main source point of blowing dust was the dry San Luis Valley (SLV) of southern Colorado, and later, the eastern Colorado plains.

Forecasters at NWS Pueblo anticipated the potential for blowing dust early in the day, and had issued a High Wind Warning for the SLV with mention of Blowing Dust reducing visibility. As such, forecasters were monitoring the “Dust RGB” imagery, in addition to webcams, throughout the day. By early afternoon, widespread and dense blowing dust had developed in the northern portion of the San Luis Valley. Per the NWS, the satellite data gave them the nudge to call ALS patrol and find out what was going on up there. Nearby webcams were also utilized to confirm reduced visibilities. Based on information from satellite, webcams, and law enforcement, a Dust Storm Warning followed by a longer duration Blowing Dust Warning, was issued for much of the northern San Luis Valley (Fig 1).

A forecaster working the event went on to mention that the satellite was most valuable for observing lofted dust near the source region, where visibility was most significantly reduced and the scene clear of cloud cover. Satellite became less useful later in the event as the dust was lofted higher and become more diffuse, and as high clouds obscured the scene.

Other imagery from GOES-East and available in AWIPS that captured the blowing dust quite well during the day include a VIS-SWD sandwich procedure (Fig 2). This procedure highlights likely blowing dust as yellow (negative values of SWD), in order to attract the users attention from the otherwise gray scene.

A GOES-West mesoscale sector was available over the region for fire weather, and provided an alternate perspective of the dust at high temporal resolution. The VIS-SWD sandwich procedure is shown for comparison to the GOES-East version.

The blowing dust continued east and into the evening. Additional blowing dust developed across the far eastern Colorado plains into the evening, prompting the issuance of additional Dust Storm Warnings and Advisories by PUB and GLD, and High Wind Warnings with mention of Blowing Dust. Dust RGB imagery captures the evolution of the Dust east into the evening, but increasing cloud cover late makes analysis of blowing dust difficult.

The Day/Night DEBRA-Dust algorithm, available on CIRA Slider or in AWIPS on request, tracks the dust into the night as cloud cover overtakes the scene.

As pointed at by NWS PUB, this event gives one a good idea of how the Great Sand Dunes became what they are, where they are!

Bill Line, NESDIS and CIRA, with input from NWS PUB