Seminar

Abstract

During the second week of September 2013 a seasonally-uncharacteristic weather pattern stalled over the Rocky Mountain Front Range region of northern Colorado bringing with it copious amounts of moisture from the Gulf of Mexico, Caribbean Sea, and the tropical Eastern Pacific Ocean. This feed of moisture was funneled towards the east facing mountain slopes by a series of mesoscale circulation features resulting in several days of unusually widespread heavy rainfall over steep mountainous terrain.

Radar and disdrometer observations collected during the event are used to diagnose the spatial and vertical structure of clouds and precipitation during episodes of intense rainfall. The analysis focuses on 30 hours of intense rainfall in the vicinity of Boulder, CO during 2200-0400 UTC on 11-13 September. The strongest rainfall occurred along lower parts of the Colorado Front Range at >1.6 km MSL and on the northern side of the Palmer Divide. Vertical structure of clouds and horizontal distribution of rainfall are strongly linked to upslope flow and low-level forcing, which resulted in surface convergence. Particular focus is placed on documenting how circulation features, embedded within the larger synoptic flow, served to funnel moist inflow into the mountain front driving several days of sustained orographic precipitation. The performance of several quantitative precipitation estimates, quantitative precipitation forecasts, and hydrological forecast products are also analyzed with the intention of identifying what monitoring and prediction tools worked and where further improvements are needed.