Evaluation of ERA5 precipitation and 10‐m wind speed associated with extratropical cyclones using station data over North America

While the ERA5 reanalysis is commonly utilized in climate studies onextratropical cyclones (ETCs), only a few studies have quantified its ability inthe representation of ETCs over land. To address this gap, this study evaluatesERA5's skill in representing the ETC-associated 10-m wind speed and the pre-cipitation in central and eastern North America during 2005–2019. Hourlydata collected from3000 stations, amounting to around 420 million reportsstored in the Integrated Surface Database, is used as reference. For the spatial-averaged ETC properties, ERA5 shows a good skill for wind speed withnormalized mean bias (NMB) of −0.7% and normalized root-mean-squareerror (NRMSE) of 14.3%, despite a tendency to overestimate low winds andunderestimate high winds. The ERA5 skill is worse for precipitation than forwind speed with NMB of−10.4% and NRMSE of 56.5% and a strong tendencyto underestimate high values. For both variables, the best and worst performance is found in DJF and JJA, respectively. Negative biases are often identified over regions with stronger precipitation/wind speeds, and a systematicunderestimation of wind speed is found over the Rockies with complex topography. ... mehrCompared to the averaged ETCs, ERA5's performance deteriorates forthe top 5% extreme ETCs with a stronger tendency to underestimate both windspeed and precipitation (NMB of−10.2% and−22.6%, respectively). Further-more, ERA5's skill is worse for local extreme values within ETCs than for spatial averages. Our results highlight some important limitations of the ERA5 reanalysis products for studies looking at the possible impacts of ETCs.