Evaluating Modeled Variables Included in the NOAA Water Vapor Flux Tool

Abstract:

The NOAA/ESRL/Physical Sciences Division has a Water Vapor Flux Tool showing observed and forecast meteorological variables related to heavy precipitation. Details about this tool will be presented in a companion paper by White et al. (2015, this conference).

We evaluate 3-hr precipitation forecasts from four models (the HRRR, HRRRexp, RAP, and RAPexp) that were added to the tool in Dec. 2014. The Rapid Refresh (RAP) and the High-Resolution Rapid Refresh (HRRR) models are run operationally by NOAA, are initialized hourly, and produce forecasts out to 15 hours. The RAP and HRRR have experimental versions (RAPexp and HRRRexp, respectively) that are run near-real time at the NOAA/ESRL/Global Systems Division.

Our analysis of eight rain days includes atmospheric river events in Dec. 2014 and Feb. 2015. We evaluate the forecasts using observations at two sites near the California coast - Bodega Bay (BBY, 15 m ASL) and Cazadero (CZC, 478 m ASL), and an inland site near Colfax, CA (CFC, 643 m ASL).

Various criteria were used to evaluate the forecasts. (1) The Pielke criteria: we compare the RMSE and unbiased RMSE of the model output to the standard deviation of the observations, and we compare the standard deviation of the model output to the standard deviation of the observations; (2) we compare the modeled 24-hr precipitation to the observed 24-hr precipitation; and (3) we assess the correlation coefficient between the modeled and observed precipitation.

Based on these criteria, the RAP slightly outperformed the other models. Only the RAP and the HRRRexp had forecasts that met the Pielke criteria. All of the models were able to predict the observed 24-hour precipitation, within 10%, in only 8-16% of their forecasts. All models achieved a correlation coefficient value above the 90^th percentile in 12.5% of their forecasts. The station most likely to have a forecast that met any of the criteria was the inland mountain station CFC; the least likely was the coastal mountain station CZC, most likely due to model terrain issues.

The results will be presented in the context of the presence or absence of an atmospheric river approaching the California coast. The presentation will also include the analysis of modeled and observed integrated water vapor. Comparisons of model output to observations from more stations may also be included.