Electrified anvil clouds extend the threats of natural and triggered lightning to space launch and landing operations at KSC and Cape Canaveral Air Force Station (CCAFS) well beyond the immediate vicinity of thunderstorms. Generated by deep convective updrafts and transported by upper-level winds, anvil clouds emanating from thunderstorms over the Gulf of Mexico can reach the KSC/CCAFS space launch/landing complexes in 2 hours or less. Launch Weather Officers of the 45th Weather Squadron (45 WS) and forecasters at the Spaceflight Meteorology Group (SMG) have identified anvil forecasting as one of the most challenging tasks when predicting the probability of Launch Commit Criteria (LCC) and Space Shuttle Flight Rule (FR) violations. An objective technique for forecasting the potential horizontal extent of anvil clouds is needed to assist forecasters in predicting the probability of a triggered lightning LCC violation.

During 2000, the Applied Meteorology Unit (AMU) established the technical feasibility of developing an anvil forecast tool on the basis of a 45 WS pilot study and a review of the most recent theoretical and applied research on the topic. The pilot study indicated a significant statistical relationship between upper-level wind speed and the length of mature thunderstorm anvil clouds. The anvil cloud layer was found to exist between the 300- and 150-millibar pressure levels, about 31,000 to 46,000 feet. An effective transport lifetime of 2 hours was estimated from a limited sample of anvil clouds on 17 days.

During 2001, the AMU expanded the pilot study by observing the life cycle of 167 anvil clouds on 50 days during the months of May, June, and July. A statistical analysis of the database confirmed the basic results of the pilot study. Further information on the variability of the transport lifetime and the correspondence between upper-level wind direction and the propagation of anvil clouds was added. The statistical parameters were needed for the formulation of an objective, observations-based forecast tool.

The AMU developed a prototype anvil forecasting tool for use on the Meteorological Information and Data Display System (MIDDS) and successfully tested it on the AMU MIDDS. The forecaster invokes the tool with a one-line command on MIDDS, which includes a user-selected location, such as the Shuttle Landing Facility, Launch Complex 39A, or a transoceanic abort landing site. Routine, global upper-air observations are automatically queried and the average wind speed and direction in the anvil layer are computed. The tool then automatically plots an anvil threat corridor on a satellite or radar image, providing the forecaster with a quick visual interpretation of regions from which anvil clouds could threaten the space launch and landing facilities on KSC, CCAFS, or the user-selected site. Several command options and an on-line help function are available.

Figure 1 shows a satellite image on the morning of May 13, 2001, prior to the onset of thunderstorm activity. An anvil threat corridor is plotted for Launch Complex 39A using upper-wind data from the CCAFS weather station. The threat corridor originates from a 20-nautical-mile stand-off circle and includes 3 upstream arcs that would be traversed by anvil clouds within 1, 2, and 3 hours (outer arc). Figure 2 shows a satellite image for the afternoon of May 13, 2001. Thunderstorm activity over Central Florida generated several long, narrow anvil clouds that were transported east-northeastward over the KSC/CCAFS area, consistent with the guidance provided earlier in the day by the anvil forecast tool.

Key accomplishments:

• 2000: Established technical feasibility of developing an observations-based forecast tool from analysis of pilot study and literature search.
• 2001: Derived statistical parameters of forecast tool from anvil data archive and developed prototype forecast tool. Tested forecast tool on MIDDS in the AMU. The tool is designed for operational use and is invoked by a single command line.

Key milestone:

• 2002: Implementation of the anvil forecast tool on the operational MIDDS in the Range Weather Operations facility.

Contact: Dr. F.J. Merceret (Francis.Merceret-1@ksc.nasa.gov), YA-D, (321) 867-0818
Participating Organizations: ENSCO, Inc. (W.C. Lambert, D.A. Short, and M.M. Wheeler) and 45th Weather Squadron (J.E. Sardonia)

Figure 1. A Visible Satellite Image of the Florida Peninsula at 1515 Local Time on the Morning of May 13, 2001 (The threat corridors indicated that anvil clouds generated by thunderstorm activity in Central Florida would be transported over the Cape within less than 2 hours after formation.)

Figure 2. A Visible Satellite Image of the Florida Peninsula at 1632 Local Time on the Afternoon of May 13, 2001 (The anvil clouds were generated around 1430 local time by thunderstorm activity in Central Florida and transported 90 nautical miles east-northeast within 2 hours, as predicted by the anvil forecast tool.)