National Weather Service United States Department of Commerce

Powerful Pacific Storm to Continue Impacting Northern California; Heavy Snow in the Appalachians and Portions of the Northeast

A strong atmospheric river will continue to impact northern California with heavy rain and life-threatening flooding through Friday. Unsettled weather is expected across much of the Northeast and Great Lakes over the next few days, including the likelihood of heavy snow in the central Appalachians and higher elevations of northeastern Pennsylvania and southern New York. Read More >

Overview

A major severe weather and flooding event occurred on June 23, 2023 over parts of northeastern Wyoming and western South Dakota. A long-track tornado moved across southern Campbell and Weston Counties, striking the North Antelope Rochelle Coal Mine. Elsewhere, significant flash flooding occurred from Spearfish to Saint Onge, and more widespread flooding occurred across parts of the western South Dakota plains. A few discrete storms produced hail up to 2" in diameter across western South Dakota and northeastern Wyoming. Several strong/damaging wind reports occurred later as the severe thunderstorms moved from western into central South Dakota.

As can be seen in the lightning map to the right (click to enlarge), thunderstorms occurred across essentially all of our forecast area from northeastern Wyoming into south-central South Dakota. Positive cloud-to-ground flashes were especially notable with the tornadic storm that affected the North Antelope Rochelle Coal Mine as well as the Spearfish supercell that produced flash flooding and large hail.

Image
Here is the 24-hour cloud-to-ground lightning map from 6 am MDT Friday (6/23) to 6 am MDT Saturday (6/24). Red plus signs indicate positive polarity flashes and green dashes indicate negative polarity flashes. Total flash counts in upper right.