Radar loop, National Weather Service Forecast Office, Duluth, MN
Ending 12:33 AM CDT March 29, 2020 (05:33 UTC)
Heavy snow, accompanied by vivid lightning and thunder, dumped nearly 2 inches of slush from 11:30 PM Saturday, March 28 to 12:30 AM Sunday, March 29. The burst of heavy snow continued to about 1 AM. The thundersnow was the highlight of a wet, melting as it fell type snow event that began as a mixture of rain and snow earlier Saturday evening and continued through the daylight hours of Sunday morning. After the thundersnow, generally light snow fell for the rest of the event. Most of the snow accumulation for the storm occurred before 5:30 AM. After 5:30 AM, less than an inch accumulated at this author's location near the ridge crest of Central Duluth. Temperatures during the storm ranged from 33 to 36 degrees. On top of the hill, snow totals were 6.2 inches at the National Weather Service Forecast Office and 5.2 inches at this author's location. Much less snow accumulated at the bottom of the hill where temperatures were a little warmer and more precipitation fell as rain.
This author documented instances of thunder at 11:50 PM, 12:14 AM, 12:17 AM, 12:21 AM, and 12:53 AM. An updated Area Forecast Discussion issued by the National Weather Service in Duluth at 12:47 AM also noted the occurrence of thunder.
The radar animation matches the period of time that the thunder occurred. Note the very bright colors indicating strong reflectivity. The strong reflectivity is due to the large water coated snowflakes that were falling at the time. Some of the flakes had diameters around 1 1/2 inches.