Verification of 24-hour quantitative precipitation forecasts over the Pacific Northwest from a high-resolution Ensemble Kalman Filter system

Abstract

nvironment and Climate Change Canada (ECCC) has recently developed an experimental High Resolution EnKF (HREnKF) regional ensemble prediction system, which it tested over the Pacific Northwest of North America for the first half of February 2011. The HREnKF has a 2.5-km horizontal grid spacing and assimilates surface and upper air observations every hour. To determine the benefits of the HREnKF over less expensive alternatives, its 24-hr quantitative precipitation forecasts are compared to those from a lower resolution (15 km) Regional Ensemble Kalman Filter (REnKF) system and to ensembles directly downscaled from the REnKF using the same grid as the HREnKF but with no additional data assimilation (DS). The forecasts are verified against rain-gauge observations and gridded precipitation analyses, the latter of which are characterized by uncertainties of comparable magnitude to the model forecast errors. Nonetheless, both deterministic and probabilistic verification indicates robust improvements in forecast skill owing to the finer grids of the HREnKF and DS. The HREnKF exhibits a further improvement in performance over the DS in the first few forecast hours, suggesting a modest positive impact of data assimilation. However, this improvement is not statistically significant and may be attributable to other factors.