Mild temperatures across vast swaths of the country suggest that spring is in full swing across much of the US. One other tell-tale sign of spring across the Midwest tomorrow: Severe Weather. A significant severe weather outbreak is expected across much of the region, especially over the mid-Mississippi Valley which is likely to be the focal point of numerous violent tornadoes. Severe thunderstorms are also possible over the Ohio Valley through the lower Mississippi Valley but these storms are less likely to produce tornadoes.
Morning thunderstorms from eastern Iowa to Ohio will dissipate by early afternoon as a powerful low pressure system over the Plains pushes a warm front northward into the Great Lakes. The morning storms will leave the surface moist, helping to reinforce the moisture being pumped into the Midwest from the Gulf of Mexico. Temperatures in this highly unstable air mass will rise into the mid-60s and mid-70s across the Mid-Mississippi and Ohio Valleys before thunderstorms redevelop by mid-afternoon.
New thunderstorms will first begin to pop up across northeastern Missouri, eastern Iowa, and northwestern Illinois as distinct storms in the middle of the afternoon. Storms here will intensify throughout early evening as weaker storms spread northward into southern Wisconsin and eastward into northwest Indiana and southwest Michigan before sunset.
Pronounced flow from the Gulf of Mexico will favor enhanced instability over the Mid-Mississippi Valley late Saturday afternoon. The passage of the mature low pressure system over the Plains toward the Upper Midwest will force ascent over this region ahead of its attendant cold front. The strong wind shear produced by this system will help many storms here rapidly develop rotation and become super-cellular through early evening.
The thunderstorms over far northeastern Missouri, eastern Iowa, west-central and north-central Illinois will be particularly violent. Many storms here could produce strong tornadoes, tennis-ball sized hail, and downbursts of wind locally capable of damaging roofs and knocking down trees and power lines. Downbursts are areas of powerful downward-moving winds produced by thunderstorm downdrafts that spread outward upon reaching the ground. They can spread destructive winds sometimes faster than 100 mph over large areas that are typically up to 2.5 mi in diameter.
Communities across this portion of the Mississippi Valley including Davenport, Peoria, and Bloomington ought to be sure to have emergency supply kits prepared in advance of these storms. Supplies should include three days’s worth of non-perishable food items, one gallon of water per person per day, first-aid supplies (bandages, ointment, disinfectant wipes, etc.), a can opener, a wrench/pliers to turn off utilities, a flash light with extra batteries, and a charged power bank for cell phones, among other items recommended by FEMA and the National Weather Service.
The extent of modest instability will spread northward into Wisconsin and southern Michigan during the evening as the low pressure system driving Saturday’s severe weather propagates toward Lake Superior. The warm front will arrive too late here to warm temperatures into the 70s, but instability aloft could be sufficient to produce isolated damaging wind gusts and large hail (though notably smaller than tennis-balls).
Further south and east, the low’s cold front will help spark several squall lines of thunderstorms. The squall lines will span southwest to northeast from northeast Texas and Arkansas during the afternoon to Kentucky, middle Tennessee, and western Ohio late in the evening. The storms will fire too early in the day for much of a severe threat in the Arklatex. However, the storms could be capable of producing damaging wind gusts and isolated large hail by the time they reach the lower Mississippi Valley late in the afternoon. The line will evolve throughout the evening as it spreads across the Tennessee and Ohio Valleys, where a few weak tornadoes could develop due to enhanced lift and shear. Nashville, Frankfort, Chicago, Louisville, Indianapolis, and Columbus are some of the cities that could be impacted by these strong lines of thunderstorms.
Residents across all threat areas should be on the alert for warnings from the National Weather Service and local emergency management. For those without access to a tornado shelter, take shelter in a small interior ground-floor room away from windows should a tornado warning be issued.
The storms will spread into the Northeast Sunday but wind from the Atlantic will hinder severe weather from manifesting. Instead, showers and possibly a thunderstorm for inland locations can be expected.