Over the Great Plains region of the United States, summertime thunderstorms often occur after sunset. Much of this nighttime rainfall is caused by large, organized storm systems and plays a critical role in the hydrology and agriculture of the region, especially over the more arid western Great Plains. During the summer months, these nighttime storm systems provide 30-70% of the region’s precipitation and can also cause severe weather, including flash floods, intense damaging winds, and large hail. Current weather and climate models have difficulty predicting the onset, location, frequency, and intensity of these nighttime cloud systems. While understanding these systems is important for improved weather forecasts and predictability of extreme events, it is also critical for improving long-term, climate-model projections of shifts in precipitation and hydrology. The multiagency Plains Elevated Convection at Night (PECAN) field campaign was sponsored by NSF, in collaboration with NOAA, NASA, and DOE, to obtain targeted observations before and during nighttime severe storms in order to learn how they form, why some become severe, and how to better predict their characteristics in weather and climate models.

The PECAN experiment took place June-July 2015, extending over most of western and central Kansas, northern Oklahoma, and southern Nebraska. A key focus was to better sample the atmospheric layer between 500-1000 meters above the ground, where rising-air motion related to rainfall initiates. The datasets collected during PECAN will help scientists characterize the conditions that lead to individual storm formation, as well as their organization into large-scale systems that can result in significant precipitation. The results will also have relevance beyond the Great Plains, as organized nighttime thunderstorms are common in mid-latitude regions around the globe.