MEMPHIS, Tenn. – A tornado outbreak is unfolding Wednesday for parts of the lower Mississippi Valley into the mid-South and lower Ohio Valley, including the threat of multiple long-track EF-3 or stronger tornadoes.NOAA’s Storm Prediction Center (SPC) upgraded portions of Arkansas, Missouri, Illinois, Kentucky, Tennessee and Mississippi to a rare Level 5 out of 5 “high risk” of severe weather.A massive tornado was spotted by FOX Weather Storm Tracker Brandon Copic as it roared near Lake City, Arkansas. Authorities issued a Tornado Emergency – the most dire of tornado alerts – for towns in the path of the storm, such as Leachville and Monette. Copic urged people in the warning area to get to safety.”You need to be underground,” Copic said. “You will not survive this tornado if you are above ground.”WATCH: VIOLENT TORNADO CAUSES DAMAGE NEAR LAKE CITY, ARKANSASIn Potosi, Missouri, firefighters reported responding to at least one residence that was impacted by a tornado on Wednesday afternoon.  Local authorities were still in damage assessment mode late on Wednesday, responding to calls for assistance.CREWS SEARCH FOR STORM VICTIMS IN POTOSI, MISSOURI, AFTER TORNADO STRIKEEarlier Wednesday, the fire department in Nevada, Missouri, confirmed to FOX Weather that a suspected tornado hit the city on Wednesday morning. There were no immediate reports of injuries.Video from residents showed buildings badly damaged, with roofs ripped off and debris littering local streets.Missouri State Highway Patrol Sgt. Mike McClure told FOX Weather power lines were brought down inside the city of Nevada, and several businesses were damaged, including a hotel. Kentucky Gov. Andy Beshear declared a state of emergency on Wednesday ahead of storms arriving in the Bluegrass State, but damage was already reported west of the Mississippi River on Wednesday.The SPC has even issued a ‘Particularly Dangerous Situation’ Tornado Watch for several states that make up the Mississippi River Valley from Arkansas to southern Indiana.Additional watch boxes have been issued from outside of Chicago to East Texas, which include nearly 15 million residents.HOW ARE TORNADOES RATED? THE ENHANCED FUJITA SCALE EXPLAINEDThe high risk designation marks only the second time this year, and the first instance of two such high-risk alerts in a single year since 2021, that a Level 5 threat has been issued. The previous Level 5 alert was issued on March 15 when the National Weather Service confirmed 13 tornadoes, including six powerful EF-3s, which tragically resulted in seven deaths and 12 injuries.Even as the main storm system begins to pull away on Thursday, daytime heating on Thursday afternoon will lead to another round of severe storms.Damaging winds, large hail, and tornadoes will again be possible during the afternoon and evening hours on Thursday. A Level 3 out of 5 risk encompasses a zone from east Texas, including Texarkana, to Tennessee, including Memphis. Meanwhile, a wider area faces a Level 2 out of 5 risk from central Texas to the Northeast. More severe weather is forecast through the end of the week and into the weekend, as well. The numerous rounds of rain and storms will lead to the aforementioned potentially generational flooding in the Mississippi and Ohio valleys.