Publications

This report describes a formal Assessment of the Terminal Convective Weather Forecast (TCWF) algorithm, developed under the FAA Aviation Weather Research Program by MIT Lincoln Laboratory as part of the Convective Weather Product Development Team (PDT). TCWF is proposed as a Pre-Planned Product Improvement (P3I) enhancement to the operational ITWS currently scheduled for deployment at major airports in 2002. The TCWF Assessment in Memphis, TN ran from 24 March to 30 September 2000. The performance of TCWF was excellent on the large scale, organized storm systems it was designed to predict, and the software was extremely stable during the Assessment. Small changes to the algorithm parameters were made as a result of the 2000 testing. The TCWF performance can be improved on airmass storms and on forecasting new growth and subsequent decay of large-scale storms. These are active areas of research for future ITWS P3I builds.

Air traffic delay due to convective weather reached historically high levels in 1999, as passengers blamed airlines and airlines blamed the FAA for the massive inconveniences. While coordination between the FAA's System Command Center and the regional centers and terminals can be expected to improve with the FAA's new initiatives, it is clear that air traffic management and planning during convective weather will ultimately require accurate convective weather forecasts. In addition to improving system capacity and reducing delay, convective forecasts can help provide safer flight routes as well. The crash of a commercial airliner at Little Rock, AR in June 1999 after a one-hour flight from Dallas/Ft. Worth illustrates the dangers and potential tactical advantage that could be gained with frequently updated one-hour forecasts of convective storms. The Terminal Convective Weather Forecast (TCWF) product has been developed by MIT Lincoln Laboratory as part of the FAA Aviation Weather' Research Convective Weather Product Development Team (PDT). Lincoln began by consulting with air traffic personnel and commercial airline dispatchers to determine the needs of aviation users (Forman, et. al., 1999). Users indicated that convective weather, particularly line storms, caused the most consistent problems for managing air traffic. The "Growth and Decay Storm Tracker" developed by Wolfson et al. (1999) allows the generation of up to 1-hour forecasts of large scale, organized precipitation features with operationally useful accuracy. This patented technology. represents a breakthrough in short-term forecasting capability, providing quantitative envelope tracking as opposed to the usual cell tracking. This tracking technology is now being utilized in NCAR's AutoNowcaster (Mueller, et al., 2000), the National Convective Weather Forecast running at the Aviation Weather Center (Megenhardt, et al., 2000) and by private sector meteorological data vendors. The TCWF has been tested in Dallas/Ft. Worth (DFW) since 1998, in Orlando (MCO) since 1999, and in New York (NYC) since fiscal year 2000 began. These have been informal demonstrations, with the FAA William J. Hughes Technical Center (WJHTC) assessing utility to the users, and with MIT LL modifying the system based on user feedback and performance analyses. TCWF has undergone major revisions, and the latest build has now been deployed at all sites. The TCWF is now in a formal assessment phase at the Memphis international Airport as a prerequisite to an FAA operational requirement. The FAA Technical Center will make a recommendation on whether TCWF is suitable for inclusion in the FAA's operational integrated Terminal Weather System (ITWS), which has an unmet requirement for 30+ minute forecasts of convective weather. Memphis was selected for the TCWF Assessment since it has not been exposed to the forecast product during prior demonstrations. Operations began on March 24, 2000 and operational feedback is being assessed by the FAA Technical Center (McGettigan, et al., 2000) and MCR Corporation is performing a quantitative benefits assessment (Sunderlin and Paull, 2000). This paper details the refined TCWF algorithm and display concept, gives examples of the operational impact of terminal forecasts, and analyzes the technical performance of the TCWF during the early stages of the Memphis Assessment.

A large percentage of serious air traffic delay at major airports in the warm season is caused by convective weather. The FAA Convective Weather Product Development team (PDT) has developed a Terminal Convective Weather Forecast product (TCWF) that can account for short-term (out to 60 min) systematic growth and decay of thunderstorms. The team began work three years ago by evaluating air traffic user needs and requirements. We found that users were willing to trade off forecast accuracy for longer lead times, especially for air traffic management plans that were easy to implement or that incurred low risk (Forman, et al., 1999). The PDT was able to develop an operationally useful forecast product that has been demonstrated in Dallas, TX since March, 1998 (Hallowell, et al., 1999). Further improvements have been made, and testing is now taking place at both Dallas and Orlando, FL. This paper summarizes the basic algorithm methodology and presents quantitative results on optimization of the scale separation filter, which is an integral aspect of the forecast algorithm.

The prediction of convective weather is very important to aviation, since almost half of the serious delay at major airports in the warm season is caused by thunderstorms. The need for accurate 0-6 hr forecasts for NAS users has been the subject of extensive publications, forums, and advisory committees in the aviation weather community over the last several years (Wolfson, et al; 1997). The Convective Weather Product Development Team (PDT), a core team of scientists and engineers from NCAR, NSSL, and MIT LL, was formed in 1996 as part of the reorganization of the FAA Aviation Weather Research Program. The team is developing convective weather forecast algorithms that produce operationally useful products for both the terminal area and enroute airspace. The products are designed to meet specific users' air traffic planning and safety needs. Before major algorithm development began, PDT members visited terminal and enroute Air Traffic (AT) personnel and airline dispatchers to understand the forecast products that were currently available to them and their needs for a near future product. Also, in order to reach the pilot community, a pilot survey about existing convective weather information and how to improve it, was created and distributed at the OshKosh Fly-In in August of 1997. This needs assessment took advantage of interviewees that had extensively used state-of-the-art weather information products (ITWS) in an operational setting for years. Their requirements, based on personal experiences with operational products during convective weather events, were less stringent than those reported in the recent requirements document pertaining to ARTCC TMUs (Browne, et al; 1999). The results of these investigations were used in the creation of the DFW Terminal Convective Weather Forecast (TCWF) product and the National Convective Weather Forecast (NCWF) products that were demonstrated throughout the summer of 1998 (Hallowell, et al; 1999; Mueller, et al; 1999). These demonstrations also provided additional insight into user needs. In this paper we describe Air Traffic users and their specific responsibilities. We then summarize AT and airline needs based on interviews conducted in 1997 and 1998. Information on pilots' needs for convective weather information is presented at the end.

An elliptical filter/tracker capable of accounting for systematic growth and delay, designated the Growth and Decay Storm Tracker, has been developed and tested. Its performance depends on the size and shape of the filter, the performance of the cross-correlation tracker, the time interval between successive scans, the forecast lead time, and the type of storm being tracked.

The FAA Convective Weather Product Development Team (PDT) is tasked with developing products for convective weather forecasts for aviation users. The overall product development is a collaborative effort between scientists from MIT Lincoln Laboratory (MIT/LL), the National Center for Atmospheric Research (NCAR), and the National Severe Storms Laboratory (NSSL). As part of the PDT, MIT/LL is being funded to develop algorithms for accurately forecasting the location of strong precipitation in and around airport terminal areas. We began by consulting with air traffic personnel and commercial airline dispatchers to determine the needs of aviation users. Users indicated that convective weather, particularly line storms, caused the most consistent problems for managing air traffic. These storms are by far the major cause of aircraft delays and diversions. MIT/LL has already developed the Integrated Terminal Weather System (ITWS) which combines a variety of near-airport sensors to provide a wide range of current weather information to aviation users. Raytheon is currently building the production ITWS system which will be deployed at 45 major airports by 2003. The initial capability ITWS already provides some convective weather predictive capabilities in the form of storm motion vectors and "Storm Extrapolated Positions" (SEP; leading edge of storm at 10 and 20 minutes). But ITWS users indicated a desire for enhanced forecasts which showed the full spatial extent of the weather, how the weather would change (grow or decay) and extended forecast time periods to at least out one hour. Our approach is to develop an algorithm which may be added as a future product improvement to the ITWS system. Previous attempts at producing forecasts have focused on convective initiation and building from short-term (20-30 min) cell forecasts. Our "reverse time" approach of attacking longer time scale (60 min) features first is an outgrowth of addressing user needs and the discovery of improved tracking techniques for large scale precipitation features. The "Growth and Decay Tracker" developed by MIT/LL (Wolfson et.al., 1999) allows us to generate accurate short and long term forecasts of large scale precipitation features. This paper details the Terminal Convective Weather Forecast (TCWF) demonstration ongoing at Dallas/Ft. Worth International Airport (DFW) and discusses the underlying algorithm being developed.

Accurate, short-term forecasts of where thunderstorms will develop, move and decay allow for strategic traffic management in and around the aviation terminal and enroute airspace. Pre-planning to avoid adverse weather conditions provides safe, smooth and continuous air traffic flow and savings in both fuel cost and time. Wolfson, et. al ( 1997) describe the problem of convective weather forecasting for FAA applications. In 1995, National Center for Atmospheric Research (NCAR), MIT Lincoln Laboratory (MIT-LL) and National Severe Storms Laboratory (NSSL) scientists and engineers agreed to collaborate on the development of a convective weather forecasting algorithm for use in airport terminal areas. Each laboratory brings special strengths to the project. NCAR has been developing techniques for precise, short-term (0-60 minutes) forecasts of thunderstorm initiation, movement and dissipation for the FAA over the past ten years and has developed the Auto-Nowcaster software. MIT-LL has been developing real-time algorithms for the Integrated Terminal Weather System (ITWS), including techniques for storm tracking, gust front detection, and calculating storm growth and decay (as part of predicting microbursts) . NSSL has been working on the NEXRAD Storm Cell Identification and Tracking (SCIT) algorithm, and on understanding the predictive value of the storm cell information. Thus by using the latest research results and best techniques available at each laboratory, the collaborative effort will hopefully result in a superior convective weather forecasting algorithm. Our goal in the immediate future is to develop a joint algorithm that can be demonstrated to users of terminal weather information, so that the benefits of convective weather forecast information can be realized, and the remaining needs can be assessed. As a first effort in the collaboration, the laboratories fielded their individual algorithms at the Memphis ITWS site. This paper gives an overview of our collaborative experiment in Memphis, the system each laboratory operated, some preliminary analysis of our performance on one case, and our plans for the near future.

Lincoln Laboratory, under funding from the Federal Aviation Administration (FAA) Terminal Doppler Weather Radar program, has developed algorithms for automatically detecting microbursts. While microburst detection algorithms provide highly reliable warnings of microbursts. there still remains a period of time between microburst onset and pilot reaction during which aircraft are at risk. This latency is due to the time needed for the automated algorithms to operate on the radar data, for air traffic controllers to relay any warnings and for pilots to react to the warnings. Lincoln Laboratory research and development has yielded an algorithm for accurately predicting when microburst outflows will occur. The Microburst Prediction Algorithm is part of a suite of weather detection algorithms within the Integrated Terminal Weather System. This paper details the performance of the Microburst Prediction Algorithm over a wide range of geographical and climatological environments. The paper also discusses the full range of the Microburst Prediction Algorithm's capabilities and limitations in varied weather environments. This paper does not discuss the overall rationale for a prediction algorithm or the detailed methodology used to generate predictions.

Wind shear detection algorithms that operate on Doppler radar data are tuned to primarily recognize the velocity and reflectivity signatures associated with microbursts and gust fronts. Microbursts produce a divergent pattern in the velocity field that is associated with a descending column of precipitation. Gust fronts produce a convergent pattern that is often associated with a thin-line reflectivity feature. On April 12, 1996 at Dallas-Fort Worth International Airport (DFW) three pilots reported encounters with wind shear in a five minute period (2329-33 GMT). The third pilot (AA 1352) reported an encounter with "severe wind shear", which we refer to as "the incident" throughout the paper. He used maximum throttle to keep the MD-80 in the air and reported that it was only "by the grace of God" that the aircraft did not crash (Dallas Morning News, 4/19/96). The plane, originally bound for Pittsburgh, was diverted to Tulsa where the passengers were offloaded to another aircraft, the black box was removed, and the engines were checked according to procedures required whenever maximum throttle is utilized.