WSDDM is a real-time weather system designed to improve decision making at airports during winter storms. Graphical user displays are located at airline station and operational control facilities, ground control towers, airlines and city snow desks, and air traffic control facilities. The snowfall and weather information are used by ground personnel conducting aircraft deicing operations, airline station control managers and dispatchers coordinating flights, airport managers coordinating runway plowing activities, and air traffic managers involved with gate hold programs. The information allows decision makers to anticipate both the onset and termination of snow at the airport and surrounding regions, its intensity, and water content.
The principal sources of data for the system are shown in Figure 1, and include Regional area Doppler radars (currently WSR-88D), surface weather stations, and snow gauges situated within the terminal area which measure the liquid equivalent snowfall rate. Research conducted by R. Rasmussen, J. Vivekanandan and J. Cole indicates that the icing hazard for aircraft on the ground corresponds to the amount of water in the snow, rather than the visibility. Results from field and laboratory tests of deicing fluids have shown that the liquid-equivalent snowfall rate is the most important factor determining holdover time (time until a deicing fluid fails to protect against further ice buildup). Thus, an important capability of the system is the ability to measure liquid equivalent snowfall rates using snowgauges. The gauges chosen to measure the snowfall rate were evaluated against manual snow measurements during the previous two winters at the NCAR Marshall test site.
The radar data are processed by a radar echo tracking system called TREC developed by J. Tuttle to produce 30 min nowcasts of estimated storm motion. These storm motion vectors are also used to produce a 30-minute predicted snowfall accumulation. The user has the option to animate the past radar data, and also to zoom and pan to different locations, with the option of choosing from 3 to 5 WSR-88D radars surrounding either Chicago O'Hare or New York LaGuardia airports. Current National Weather Service surface weather observations are also available in a decoded form, as well as time series from WSDDM weather stations deployed at various locations around the terminal area.
WSDDM was demonstrated to a variety of users at LaGuardia Airport in New York and O'Hare Airport in Chicago. The New York users included Delta Airlines, USAIR airlines, and New York TRACON. Delta had WSDDM displays at their dispatch office in Atlanta, their Tower in LaGuardia, and their Shuttle operations office in LaGuardia. USAIR had a display at their dispatch office in Pittsburgh, and the FAA had a display at the New York TRACON in Westbury Long Island. In Chicago, United and American Airlines had displays. United had a display at their station control office and in their Tower, and American had a display at their Tower. The system required the use of 25 workstations, and displays at the 8 user sites mentioned above. Communications were designed and implemented by T. Hofmeister, F. Hage, and R. Tescher, and required the use of 56 kB dedicated phone lines and local networks all linked and working together. This communications system enabled all the users to access the workstation as an independent user, with no degradation of performance during high weather demand periods. This network is one of the most complicated networks ever set up at RAP.
An important aspect of the system was the ability to rapidly loop the radar data in order to examine snowband motions and growth or decay trends visually. The response of the system to user commands was excellent, with new movie loops or reflectivity images appearing typically within a second or two of selection. This is a tribute to the excellent system designed by Hage and Hofmeister. The system also included a real-time depiction of surface weather information decoded from METAR code into a simple column format from the surrounding states (Figure 2, Top panel on the right side of the display). This information was used by the users to determine the type of precipitation approaching the airport, as well as the expected temperature and winds. In addition, Cole deployed weather stations and snowgauges at three sites in New York and three sites in Chicago. Information from these sites was provided to the users in the form of a simple, easy to read table indicating temperature, dewpoint, wind speed and direction, snowfall rate, and time ( Figure 2, second panel from the top on the right hand side of the display). The data were typically updated every 1 minute to 5 minutes depending on the site. This information provided the users with a means of determining the nearby weather conditions, including the snowfall intensity. These data were also displayed graphically in time series form using a strip chart for the last two hours (Figure 2, third panel from the top of the display on the right hand side). Using this chart, the users could easily tell the trend in temperature, wind speed, direction, snowfall rate, and snow accumulation during the last two hours at the three snowgauge sites. A significant achievement this year was the incorporation of three of the New York snowgauge stations into Surface Systems Incorporated (SSI) units on the field at LaGuardia and John F. Kennedy airports. This required significant interaction with SSI, and a significant amount of software engineering by Hage and N. Rehak.
Of particular benefit was the 30-min nowcast of the radar reflectivity using TREC data, as well as their expected position 30 min into the future as indicated by TREC storm motion vectors. The implementation of the TREC software into the system by R. Ames was a significant achievement this year, with TREC providing very reliable motion vectors and performance throughout the evaluation period.
The FAA Technical Center performed a User Evaluation of the system, and the Volpe Transportation Center performed a User Benefits study. Both studies showed that the system enabled users to operate more efficiently by being better able to anticipate storm start and termination, and also enabled them to take advantage of gaps in the storm and to operate more safely during deicing operations. Volpe estimated that annual savings for one airport using the system would exceed $1 million.
The above significant accomplishments were achieved under a very short deadline due to the final approval to start the project occurring in late September. The system was deployed in New York by the first week of January, and in Chicago the third week of January. The system in New York was deployed before the first snowfall of the year, and was used effectively during that first snowfall and during subsequent snowfalls. Despite having low snowfall in New York this year, the users found the system to be very useful to better plan and perform their winter operations. The Chicago system was found to be quite useful by United, to the point that they are seriously exploring the possibility of buying a system commercially.
