River valley fog in the Upper Midwest
5-minute CONUS Sector GOES-19 (GOES-East) Nighttime Microphysics RGB + daytime True Color RGB images from the CSPP GeoSphere site (above) showed the formation of nocturnal river valley fog over parts of the Mississippi River and a few of its tributaries in Wisconsin, Minnesota, Iowa and Illinois on 03 August 2026. The river valley fog then dissipated within a few hours after sunrise.
GOES-19 Night Fog brightness temperature difference (BTD) + daytime Visible images (below) included hourly plots of Ceiling and Visibility — at some sites in the Wisconsin River valley, the visibility dropped to 1/4 mile (or even to zero) at times.
A NOAA-21 VIIRS Day/Night Band image at 0833 UTC (3:33 AM Central Time) revealed a faint signature of the river valley fog (below), as illuminated by the Moon (which was in the Waning Gibbous phase, at 75% of Full).
