Creative Re-Construction of Historical Extreme Convective Precipitation Events using Radar, Cloud-to-Ground Lightning and Conventional Observations

Our understanding of historical extreme convective precipitation events has been limited, for the most part, to post-storm rain bucket surveys and detailed studies of the pre-storm, storm and post-storm atmospheric conditions. Detailed studies of the actual storm rainfall patterns to include the aerial and time distribution and the intensity of the rainfall patterns has been limited by the available observations from which these details could be directly inferred. The development of cloud-to-ground lightning observation networks since the early 1980s and the National Weather Services WSR-88D Doppler radar network since 1992 has created new opportunities to document extreme precipitation events.

The relationship of cloud-to-ground lightning observations and the aerial and temporal distribution of associated rainfall has used to re-construct rainfall for the Opal, Wyoming, July 1980 flash flood; the Rifle Creek, Colorado of May 1992 and the Robideau Creek, Colorado July 1993 flash floods in the Colorado mountains. Comparisons of the flash rates and flash density patterns to observed rainfall resulted in both new temporal and aerial rainfall distributions for these three storms. In the case of both the Rifle Creek and Robideau Creek events, the re-constructed rainfall patterns were used to initialize basin runoff models that verified closely with observed downstream stream gauge observations. Since radar observations of these events were not available, the cloud-to-ground lightning observations provided very useful approximations of both the time distribution and aerial coverage of the events that was not otherwise available. In the case of the Opal event comparisons with paleohydrologic post-event analyses resulted in close approximations of the storm's aerial coverage and intensity.

Radar re-constructions of the July, 1996 Buffalo Creek, Colorado, July, 1999 Saguache Creek and the July 1999 Dallas Creek rainfall patterns have provided detailed aerial, temporal and intensity descriptions of the three events. The WSR-88D radar observations provided the opportunity to describe storm rainfall at 5 to 6 minute time intervals and at aerial resolutions of about 1/2 mile. These three high elevation storms provide the first insight into extreme convective precipitation events in the Rocky Mountains of Colorado. The radar and rainfall observations were developed were then compared to the related cloud-to-ground lightning observations to refine the interpretation of the earlier storm rainfall patterns that relied only on lightning observations. Additionally, these patterns were compared to paleo-hydrologic estimates of the storm runoff and inferred precipitation patterns to assist in the refined use of paleo-hydrologic estimates of other events.

The integration of new observation technologies into the re-construction of extreme precipitation events will enhance or abilities to understand these events. The relationship of these re-construction to paleo-hydrologic reconstruction opens new doors for developing quantitative aerial and temporal storm guidelines for designers and doe risk assessment studies. The application of these new technologies to extreme precipitation events is limited only by the availability of the observations.