Did the models correctly forecast the timing of shortwaves traveling through the mean flow?
During the evaluation period, several major rainfall episodes came from dynamics associated with shortwaves rotating through synoptic-scale troughs. Eta, AVN and NOGAPS analyses were examined to determine the major shortwaves, i.e., those captured by all three models. Results • In most cases, the models forecast synoptic-scale trough positions fairly well. However, no model gave reliable guidance for 48 and 72-hour forecasts of shortwaves. Fig. 5 shows poor model forecasts of an energetic shortwave west of the California/Arizona border. Splitting systems and the unusually strong southern-branch jet stream across the Pacific Ocean probably led to the poor skill of the models (beyond 24-hr) with respect to the timing of shortwaves. • The differences between the initial analyses of vorticity were also large. This reflects, in part, the “noisy” nature of the vorticity field, but also highlights the difficulty of initializing models over the data-sparse Pacific Ocean. Extended Range 1. MRF
