ESRL Global Systems Division
Improved Short-Range Weather Forecasts from RAP Model Upgrade to Ver. 2
NOAA now has improved predictions of quickly developing severe weather events, including thunderstorms and winter storms, as well as aviation hazards such as clear-air turbulence and icing. The Rapid Refresh (RAP) Version 2 (v2), the newest edition of this hourly-updated assimilation/modeling system, NOAA's most frequent rapidly updated weather forecast, was installed in an operational capacity at NOAA/National Weather Service's (NWS) National Centers for Environmental Prediction (NCEP) in Maryland at 1200 UTC February 25, 2014. It replaces the previous RAPv1 that served a similar function, and also continues to extend geographical coverage of NOAA's weather situational awareness information to all of North America.
How: The key improvements in RAPv2 are 1) better use of current observations to start the RAP forecast model with the best possible knowledge of current weather ("data assimilation"), and 2) better representation of clouds and precipitation, turbulence near the surface, and other physical processes in the RAP model.
- The data assimilation of observations from radar, surface stations, and cloud observations allows improved forecasts of storms and clouds. The assimilation of surface observations is enhanced through special analysis features that promote retention of surface observations through the model boundary layer and reduce near-surface forecast biases through adjustments to the soil temperature and moisture. RAPv2 also improves this data assimilation by introducing a hybrid-ensemble technique that allows weather-adaptive inference of overall 3-d wind/temperature/moisture fields from specific observations.
- Conditions in the atmosphere in the lowest kilometer are improved by more accurate treatment of mixing in the boundary layer, especially under stable conditions, and by a nine-level soil-vegetation-snow land surface model replacing a previous six-level version. RAPv2 also uses a new version of the Advanced Research WRF model updated by a user community led by NCAR.
Who Has Helped: Many scientists from several institutions made noteworthy contributions to the development of the upgraded RAP model. These include NOAA/ESRL, CIRES and CIRA, NCEP, and NCAR. The FAA and Department of Energy have also contributed to NOAA's effort in developing the RAP model.
The RAP, developed by NOAA's Earth System Research Laboratory (ESRL)/Global Systems Division (GSD) in Boulder, Colorado and NCEP, updates every hour with a new forecast extending out 18 hours for North America. Such forecasts are especially important in aviation, where fast-developing weather conditions can affect safety and efficiency, but they are equally important for severe weather and energy-related forecasting.
RAPv2 provides improved forecasts for aviation, severe weather, and energy; for thunderstorms, especially during summer; and for winter storms.
A technical briefing on RAPv2 improvement to National Weather Service forecasters is available for download (PDF).