Let us spin the clock back a century… On March 28th, 1920, one of the largest tornado outbreaks in the modern era affected a large swath of states in the Deep South and Midwest in what became known as the Palm Sunday tornado outbreak of 1920. This outbreak saw the spawn of 37 confirmed total tornadoes of which 16 of them were rated F3 or higher (based on the traditional Fujita scale for tornado strength). All in all, 380 lives were lost during the event. Of course, this was long before any weather forecasting technology or public awareness for severe weather came about as the current-day National Weather Service (then known as the U.S. Weather Bureau) didn’t implement the watch/warning system until 1953. 1920s forecasting guidelines and techniques were still being crafted and given the accepted regulations at the time, were rather crude and vague which did not convey as much information as the public.
The surface analysis shared above depicts an environment conducive for such intense convective activity to occur. A mature lee cyclone developed east of the Rockies and traversed over the central Plains. A trailing cold front sagged southward over the southern Plains while a warm front moved poleward across the mid-south and well into the Midwest states. The result is a setup which provided ample moisture fetch across many of the southern and Midwestern states and, coupled with decently warm temperatures and favorable winds, set the stage for a potentially dangerous outbreak. Also, let’s recall that during the 1920s, the science of meteorology was nowhere near the levels of today so parameters such as storm helicity, jet stream dynamics, and instability were not known. Forecasters could not convey such information so they relied on basic weather observations. Severe thunderstorms were numerous across many states including Michigan, Indiana, and Illinois were multiple tornadoes touched down and caused considerable damage to farms and houses in rural areas to buildings and established business in the more concentrated suburbs and cities. Storm motion was rapid; most storms had forward motion exceeding 50 mph which is presumed to be due to strong steering flows aloft.
Since writing this piece, this event has risen to relevance in recent times as the latest severe weather outbreak that affected states such as Missouri, Iowa, and Illinois. March 28th, 2020 had similar features observed on the surface analyses and upper-air charts such that the environmental setup favored organized development of surface-based supercells. The Storm Prediction Center issued a 15% risk of significant tornadoes across portions of central Illinois even…
Since the devastating outbreak in 1920, weather forecasting, modeling, and verification has gone to great lengths to provide the useful information needed by the general public to prepare and be weather-aware for significant severe weather events. But whether it is 1920 or 2020, the mission of forecasters remains the same: Protecting life and property.
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© 2020 Meteorologist Brian Matilla