Severe Threat Shifts South And East Monday

Sign up for the Morning Brief email newsletter to get weekday updates from The Weather Channel and our meteorologists.

A​ line of thunderstorms moved through the southeastern U.S. this weekend with heavy rain and life-threatening flash flooding across the Ohio Valley and Appalachians and severe weather across the Southeast.

T​ornado and severe thunderstorm warnings were issued in the Southeast Saturday through Sunday morning as a powerful squall line toppled trees and caused widespread power outages.

(​LIVE BLOG: Latest News and Updates)

F​lash Flood Emergencies were issued for Tazewell County in western Virginia and for Mercer and Summers counties in West Virginia.

(EXPLAINED: What Is A Flash Flood Emergency And What Should You Do About It?)

Grundy, Virginia, saw rushing water sweeping through town Saturday afternoon. Multiple swift water rescues have occurred near Princeton, West Virginia. Numerous roads are impassable in southern West Virginia and western Virginia due to flooding. More than five inches of rain has led to flash flooding and the increased likelihood of land- and rockslides.

Flooding was reported in parts of Clarksville, Tennessee, about 40 miles northwest of Nashville near the Kentucky border, early Saturday. Water rising up to property has recently been reported in northeastern Tennessee.

S​ome roads in Kentucky have been washed out. At least one vehicle has been pushed off the road in Corbin, Kentucky, and a swift water rescue was performed Saturday morning west of Bowling Green.

Rare 'High Risk' Flood Outlook

H​eavy rainfall spread across the South and central Appalachians through Sunday morning.

Heavy rain across the South and central Appalachians fell on ground saturated from multiple rounds of rain over the past several days. Melted snowpack from Winter Storm Harlow earlier is also contributing to streams, creeks and rivers running high right now.

Given all this, NOAA's Weather Prediction Center issued its highest level of excessive rainfall threat from western Tennessee into Kentucky.

T​his rarely-issued high risk highlights what could be a "very impactful, life-threatening and significant heavy rainfall and flash flood event", NOAA-WPC wrote in their Friday afternoon forecast. WPC also noted this moist, unstable setup is "anomalous for mid-February".

(​PERSPECTIVE: Why 'High Risk' Flood Outlooks Are Important)

D​ozens of river gauges reached moderate flooding levels across the Deep South and Ohio Valley, according to the National Water Prediction Service. More gauges are likely to reach moderate and major flood stage as water continues to run downhill.

A​s of Sunday morning, some stations are already reporting 36 hour rainfall totals over half a foot. Union City, Tennessee, reported 6.75 inches of rain from Friday evening to Sunday morning.

J​ennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.