The active wildfire season over the western US this summer has resulted in periodic days of smokey skies downstream. Forecasters are concerned with the detection of smoke since it has impacts on local air quality and visibility, and is the source of public inquiries. During the daytime, smoke is easily diagnosed by forecasters using GOES and VIIRS visible, near-IR and multispectral products, such as Geocolor. At night and in the absence of these channels/products, smoke is much more difficult to discern using IR-only-based products save for the most dense of smoke plumes. For example, ABI IRW imagery from the evening of 19 Sep 2021 is shown in Fig 1. Signs of smoke are not readily apparent.
A nighttime smoke detection option available to forecasters in AWIPS is the VIIRS Day Night Band (DNB) Near Constant Contrast (NCC) product. Available from both SNPP and NOAA-20, this product is available 2-4 times per night over a given location across the CONUS due to overlapping swaths. During the early morning, pre-dawn hours of 19 Sep 2021, forecasters at NWS Bismark, ND were analyzing the NCC imagery. They noted in surface obs slightly reduced visibility at locations within the CWA (8 SM in southwest ND), and highlighted in an AFD update: “VIIRS Near Constant Contrast satellite product at 08Z shows areas of smoke across eastern Wyoming and Montana, pushing into western North Dakota.” Figure 2 captures the 08Z NCC product at hand.
An animation of the three overnight VIIRS passes captures the evolution of smoke across the region (Fig 3). The smoke becomes less apparent later in the evening with shifting viewing angle, but can still be tracked with careful analysis. During the 1.5 hour period, the smoke is observed shifting north and east across the BIS CWA.
BIS went on to mention: “HRRR Smoke guidance indicates smoke moving eastward alongside the thermal ridge.” The VIIRS NCC provides a check on HRRR smoke model analyses and forecasts overnight (Fig 4). Combined, the forecaster could make a assessment on where smoke was at present, and where its influence would be during the day.
This case provides a great example of a forecaster leveraging the VIIRS NCC product to diagnose smoke coverage across the region overnight, confirm the likely source of reduced visibility, and provide a check on model smoke output.
Bill Line, NESDIS and CIRA