Weather forecasters and the public alike in the Chicago, Dayton, Fort Wayne, Lansing, South Bend, and Toledo areas were unaware that the stage was set that day for a significant tornado outbreak that would follow a balmy and seemingly tranquil Palm Sunday afternoon. The weather maps in use in March 1920 showed a rather large and deep cyclone over northern Iowa that was forecast to move across central Lower Michigan by nightfall with a trailing cold front. Meteorologists knew rain showers and perhaps a thundershower was a good possibility, but were unaware that the helicity, lifted index, and upper level winds were being guided by a strong jet stream with a probable negative-tilt that would create favorable conditions for the development of tornadoes.