These images show a false-color corrected reflectance (Bands M3-I3-M11) image overlaid with snow cover (normalized difference snow index (NDSI)) of rare snowfall across the southern U.S. on January 22, 2025, from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Joint Polar Satellite System's first satellite (JPSS-1/NOAA-20). Swipe the center bar back and forth to see the false-color corrected reflectance (Bands M3-I3-M11) on the left "A" side, where snow appears in dark pink, and compare with the same corrected reflectance image overlaid with the snow cover (NDSI) layer (side "B").
The snow cover NDSI layer shows an estimate of snow cover and is derived from radiance data acquired by VIIRS. Snow-covered land typically has very high reflectance in visible bands and very low reflectance in the shortwave infrared bands. The NDSI layer reveals the magnitude of this difference, with values greater than 0 typically indicating the presence of at least some snow. The VIIRS snow cover algorithm computes NDSI using VIIRS image bands I1 (0.64 µm, visible red) and I3 (1.61 µm, shortwave near-infrared) and then applies a series of data screens designed to alleviate likely errors and flag uncertain snow detections.
Snow fell along the Gulf Coast, Deep South, and Southeast U.S., with the heaviest snow between Louisiana to North Carolina, reaching up to 12 inches in some areas.
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Datasets:
VIIRS/JPSS1 Snow Cover 6-Min L2 Swath 375m, Version 2 (VJ110) doi:10.5067/JNKFY4XFDHRN