The Pacific Landfalling Jets Experiment (PACJET): Building Bridges Between Research and Operations

NOAA will be conducting a major field experiment this coming winter along the West Coast of the U.S. The goal of this experiment is to improve the 0-24 forecasts of damaging weather caused by land-falling winter storms moving in from the data sparse Pacific Ocean. A major goal of the experiment is to have researchers and forecasters work together to test new ways to improve forecasts which focus on mesoscale QPF and issuance of flood and flash flood warnings.

Key to assessing the impact of new ideas and data, is an awareness of how QPF guidance is issued in the NWS. The NWS recently made a decision to focus all quantitative precipitation forecasting (QPF) necessary to support hydrologic flood forecasting of main stem rivers in the western U.S. within the Hydrometeorological Prediction Center (HPC), part of the National Weather Service's National Centers for Environmental Prediction (NCEP). In order to assure the most efficient and rapid transfer of results from PACJET to operations there is an obvious need to coordinate the research objectives and field observations to the requirements of the operational HPC QPF forecaster, as well as to the forecasters issuing warnings from the Weather Forecast Offices along the west coast.

The HPC QPF forecaster is required to make 6-h estimates of rainfall over the complex terrain of the west out through 72-h. The first 24-h of this forecast is the most critical to the proper forecast of river stage height as the skill levels beyond the first 24-h are such as to be useful for guidance purposes only. These results indicate that one of the major forecast problems is the timing of the rainfall amounts within these narrow 6-h windows, especially beyond 12-h..

PACJET plans to focus on several key issues that have potential to improve the 6-h QPF forecast. The observations planned for testing in PACJET include reconnaissance/research flights by the NOAA P-3 aircraft into approaching storms 0-24 h before their land-fall, coastal wind profilers, a buoy-mounted wind profiler, and new satellite products such as specialized GOES rapid scan winds for the PACJET domain. The data gathered will explore several approaches to improving mesoscale precipitation forecasts in the 0-24 h period: 1) developing improved conceptual models of key physical processes (e.g., orographic forcing, air-sea interaction), 2) improved numerical model forecasts through better model parameterizations of air-sea fluxes and microphysics, 3) assimilation of experimental data into numerical models and use of parallel real-time runs, 4) development of an ensemble of mesoscale models, and 5) exploration of how to better use existing data and experimental measurements through direct forecaster use.

Of particular potential for immediate impact are the development of reconnaissance messages created out of the P-3's extensive array of radars and other sensors during flights that will provide 6-12 h lead time before the heaviest part of the storm reaches the coast.. These messages will be transmitted in real time via satellite, and will include quantitative information on the position, motion, and intensity of rain bands, the strength, direction, and moisture content of the low-level jet, and sea state characteristics. The use of these and other relatively new data from coastal wind profilers and satellites will be tracked during the experiment, both in terms of NWP and direct use by forecasters.