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This loop of GOES-8 3.9 micron shortwave IR imagery shows convective snow squalls that developed over parts of Iowa, Illinois, and Wisconsin on 12 February 1999. Cloud tops over the region were a mixture of supercooled water droplets (dark gray enhancement, due to solar reflection) and ice crystals (warmer than -10 C, light gray enhancement; -10 C and colder, blue enhancement). Surface reports of weather are also plotted on the imagery.
(a similar loop with full hourly surface reports is available here)