New NGM-Based MOS Guidance for Maximum/Minimum Temperature, Probability of Precipitation, Cloud Amount, and Surface Wind

In this paper, we describe the development and use of new nested grid model (NGM)-based model output statistics (MOS) guidance that has been available since 26 July 1989 for 204 stations in the contiguous United States. The new guidance, which replaced the NGM-based perfect prog package that had been operational since May 1987, consists of forecasts of max/min temperature, probability of precipitation, cloud amount, and surface wind. Guidance for all four elements is available for projections of 1 and 2 days from 0000 and 1200 UTC. The limited-area fine-mesh model (LFM)-based MOS guidance package is still available and was not affected by this change. Verification on independent data shows that NGM-based MOS and LFM-based MOS temperature forecasts are about equally accurate and that both sets of MOS guidance are clearly superior to the NGM-based perfect prog guidance. For the probability of precipitation, the NGM-based MOS guidance is consistently more skillful than the perfect prog guidance, and usually more skillful than the LFM-based MOS guidance. For cloud amount, the NGM-based MOS forecasts are more skillful than either the LFM-based MOS or the NGM-based perfect prog. Finally, the NGM-based MOS and perfect prog wind forecasts are about equally skillful, and both sets are superior to the LFM-based MOS guidance.