The National Weather Service's (NWS) mission is to provide forecasts "for the protection of life and property and the enhancement of the national economy." Accurate, skillful precipitation forecasts are an integral part of this mission. Extreme precipitation events lead to flash flooding and river flooding, which cause both tremendous economic damage and loss of life. In support of this mission, the Meteorological Development Laboratory (MDL) currently utilizes the Model Output Statistics (MOS) technique to produce probability of precipitation (PoP) and quantitative precipitation forecast (QPF) guidance from output from the National Centers of Environmental Prediction's (NCEP) "aviation run" of the Global Spectral Model (AVN), the Medium-Range Forecast Model (MRF), and the older Nested Grid Model (NGM).

In the spring of 2002, MDL implemented a brand-new Eta-based Model Output Statistics (MOS) guidance package. This will mark the first time, aside from some internal testing a few years ago, that MDL has produced any guidance from Eta model output. The Eta MOS guidance will be run twice daily (following the 0000 UTC and 1200 UTC runs of the Eta model) for 1258 stations in the continental United States. Included in this package are 6-h, 12-h, and 24-h forecasts for PoP and QPF valid at projections out to 60 hours after initialization. This first-generation Eta MOS development utilized as predictor data a relatively coarse Eta model archive, both temporally (two cycles daily, forecasts every six hours out to 48 hours) and spatially (~90 km grid spacing).

Despite the limitations of our predictor data set, initial verification of test forecasts on an independent sample showed a significant improvement over the NGM MOS and the Eta direct model output. Eta MOS guidance also generally showed skill over the AVN MOS in the early projections (out to about 36-48 hours) but the AVN MOS proved more skillful in the later projections. As is the case with the other guidance packages, cool season Eta MOS PoP and QPF guidance is much more skillful than warm season guidance.

This paper discusses details from the recent Eta MOS equation developments, as well as additional verification scores. Sample graphics of Eta MOS PoP and QPF guidance are presented. Finally, future plans, including securing a new Eta model archive with finer spatial (~30 km) and temporal resolution (4 cycles daily, forecasts every 3 hours out to 60+ hours) as well as supplemental predictand data sets (e.g., precipitation radar data), are discussed. It is hoped that the more robust data sets, combined with new predictors and statistical techniques, will help to increase forecast skill and start to narrow the gap between the performance of the warm and cool season guidance.