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The PACJET Program and End UsersK.C. Koch F.M. Ralph The Pacific Land-falling Jets Experiment (PACJET) addresses short-term winter weather prediction along the U.S. West Coast, emphasizing precipitation forecasting. It builds on the California Land-falling Jets Experiment (CALJET), performed during the strong El Niño of 1997/98, an earlier West Coast experiment designed to bring researchers and forecasters together to test how new data could help better predict flood-producing storms. PACJET's first field phase will be conducted in January-February 2001. Both CALJET and PACJET examine the difficult process of weather forecasting on the West Coast, including: a) the relationship between El Niño and coastal storms, b) the value of new observations to the forecast process, c) how weather forecasts affect key sectors of California's economy, and d) how affected groups interpret and use weather information. The CALJET experiment provided forecasters with data to increase forecast lead times during a very rainy season. For example, on February 3, 1998, meteorologists at the National Weather Service's Monterey Forecast Office issued a flash flood warning for the Pescadero Creek region on the California coast six hours in advance of the actual event. Data provided by scientists flying CALJET aircraft missions hundreds of miles off the coast made it possible to issue this forecast with much greater lead time than the National Weather Service's 2005 goal of 60 minutes. Extra time in response to a flood emergency can be significant. For example, in the case of reservoirs, decisions by managers are critically dependent on the quality and lead time of precipitation forecasts. With several hours lead-time on both the beginning and end of heavy precipitation, it is possible to make adjustments to reservoir levels that carefully avert flooding and/or dam failure. Further, these adjustments can be made without compromising previous decisions regarding water supply, a particularly scarce resource in the west. Because of the value of additional lead-time, the California Department of Water Resources, the Governor's Office of Emergency Services (OES) and the San Mateo County Sheriff's Division of Emergency Response all used information from the CALJET field experiment during 1998. The intense media response to the El Niño event, in addition to the improved forecasts, led the State of California OES to request a four-week extension of CALJET. This favorable response from the state and local emergency and water management communities was a catalyst in planning for a strong user component in PACJET. Extensive outreach and briefing activities have been conducted in response to CALJET and in planning for PACJET, with the goal of linking research to operational forecasting needs and forecast users. To prepare for PACJET, the U.S. Army Corps of Engineers, the California Governor's Office of Emergency Services Coastal Region, San Mateo County, the California Nevada River Forecast Center, the Navy, the Pacific Coast Federation of Fisherman's Associations, National Weather Service forecasters, and private meteorological services provided input on the development of potential forecast products. In addition, two workshops focusing on all aspects of the weather research-to-operations process were held. One product for end users that emerged from the September 1999 workshop is a schematic designed to give users accurate descriptions of critical characteristics of storms offshore, outside the range of coastal observing systems, and often with their full characteristics not observed by satellite. The importance of particular storm characteristics for forecasters and forecast users helped PACJET scientists select which information should be included in the schematic. Of particular significance are the characteristics of the low-level jet. From these discussions, PACJET scientists also learned of the importance of the melting level, which is the altitude above which precipitation is in the form of snow. The melting level is important because of its impact on transportation and determining what fraction of mountainous watersheds would accumulate snow rather than produce runoff. Because no normal data sources offshore can observe the melting level, it is a key variable that PACJET seeks to measure. Other storm characteristics that were incorporated as part of the schematic include the width and intensity of rainbands, the speed at which storms approach the coast, ocean wave conditions and other information. Hourly updates during aircraft missions could be posted on a website for easy access. The schematic is not meant to take the place of regular forecasts, watches, or warnings issued by the National Weather Service, but rather provides additional information about the characteristics of a particular frontal system that may impact the West Coast. In addition to the workshops, PACJET planning included a series of meetings with user groups to 1) reach more groups that would benefit from PACJET data and information, 2) tap into the needs of individual groups and encourage more dialogue on how those needs might be met through PACJET, and 3) develop better methods for transferring weather information to users. Here are examples of positive outcomes from these meetings:
Outreach efforts have been built into CALJET and PACJET from their inception. They address a key challenge in meteorological research: exploring the relevancy of promising new research to the real world that decision-makers operate within. Most important, however, is the emphasis on creating a continuous feedback loop whereby new ideas from research can be combined with the real-world needs of forecasters and forecast users to help identify new directions for both research and applications. — K.C. Koch — F.M. Ralph Comments? thunder@ucar.edu
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