Meteorological reconstruction of the Lewis and Clark Expedition.

Abstract

Meriwether Lewis and William Clark explored the lands from Missouri northward and westward to the Pacific Northwest during the years 1804 to 1806. They kept records of the weather they encountered along their trip. These weather records were analyzed to: 1) describe the weather they encountered, 2) determine if their data fit within the range of today's observations, and 3) suggest possible explanations to account for any differences in their data. Lewis and Clark's weather data were obtained from their journals, and the National Weather Service's weather data were obtained from the National Climatic Data Center and the Climate Prediction Center. The weather data analysis focused on Lewis and Clark's two main stops on the trip, Fort Mandan and Fort Clatsop. Through analysis of the wind direction provided by Lewis and Clark at both locations, hypothetical weather maps were constructed in order to explain the weather they encountered more thoroughly. Lewis and Clark's temperature and precipitation data were compared to the National Weather Service's temperature and precipitation data visually through the construction of box plot diagrams. It was found that Lewis and Clark's weather at Fort Mandan did not deviate greatly from modern observations. December 1804 and January 1805 were found to be a few degrees Fahrenheit on the colder end of the modern range of temperatures. The number of days with precipitation was somewhat higher in March and April 1805 than it is today, but these values were not outside the range of modern data. It was also found that Lewis and Clark's time in the Pacific Northwest could have been one of the rainiest on record. Further analysis by studying tree rings or cyclic climate episodes may further support these findings.