MEMPHIS, Tennessee — Monday, April 27 is arriving as advertised — and the forecast has not gotten any friendlier. The greatest tornado risk of the day is centered on a corridor covering eastern Missouri, northeast Arkansas, northern Mississippi, western Tennessee, western Kentucky, and southern Illinois and Indiana, with several significant EF2 or stronger tornadoes expected alongside sporadic damaging winds and large hail.
The mechanism is straightforward and dangerous. Low pressure over the Upper Midwest is pulling a massive warm sector of Gulf air northward across an enormous area. A roaring subtropical jet stream overhead is loading the atmosphere with wind shear. Any thunderstorm that grows tall enough to reach those changing winds will spin. The question that determines how bad Monday gets is whether those spinning storms stay discrete or merge into a line.
The Warm Sector Is Enormous — That Is the Problem
The orange greatest tornado risk oval on Monday’s map sits over Kansas City, St. Louis, Springfield Missouri, Fayetteville Arkansas, Memphis, and Nashville — a corridor covering hundreds of miles simultaneously. The broader yellow warm sector extends the severe storm threat from Iowa and Illinois in the north all the way south to Shreveport, Jackson, and Houston.
That geographic scale is not an exaggeration for effect. The low pressure system pulling Gulf moisture north is doing so across an extraordinarily wide warm sector. When a warm sector this large fills with juiced-up, unstable air, severe thunderstorms can blossom nearly anywhere within it — not just along the main cold front. That is why the forecast explicitly warns that severe storms are possible anywhere in the warm sector, not just in the highlighted core zones…