After nearly 300 years of numerous observations and stories of whirlwinds, cyclones, and tornadoes, it was in 1882 when Sergeant John P. Finley of the U.S. Army Signal Corps was placed in charge of the collection and investigation of tornadoes and the development of methods to forecast them.
During a tornado outbreak on February, 19 1884, he was able to establish fifteen rules for early tornado forecasting. He would publish these rules in 1888 in the American Meteorological Journal:
- Presence of a well-defined low pressure area.
- Slow progression of the low increasing flow northward of heat and moisture into the southeast quadrant.
- A north-south or northeast-southwest orientation of a trough-like low.
- The descent of a well-marked anticyclone in the rear of the low.
- High temperature gradients.
- Increasing wind velocities of the southeast, southwest, and northwest quadrants of the low.
- Northward curve of the isotherms in the southeast quadrant and eastern portion of the southwest quadrant of the low.
- Southward curve of the isotherms in the northwest quadrant and the northern portion of the southwest quadrant.
- High temperature gradient between the noses of opposing curves of temperature.
- Increasing high humidity in the southeast quadrant of the low.
- Maximum areas of tornado frequency for each state.
- Occurrence of tornadoes in certain parts of the country, in certain months of the year.
- Tornadoes frequently occur in groups with parallel paths, within a few miles of each other.
- Tornadoes always occur in the southeast quadrant of a low several miles southeast of its center.
- Easterly curve in the southwest and northwest quadrants of a line separating the northerly and southerly surface winds of the low.