4.2 Further analysis of SFO Stratus Decision Support System and its impact on ground delay programs and NAS efficiency

Tuesday, 25 January 2011: 3:45 PM
310 (Washington State Convention Center)
David W. Reynolds, CIRES/Univ. of Colorado, Boulder, CO; and J. A. Thomas

During summer, marine stratus encroaches upon interior regions of the San Francisco Bay Area.  These low ceilings impede landings at San Francisco International Airport (SFO) where parallel runways require that aircraft maintain visuals on approach.  Marine stratus results in a high number of arrival delays, which in turn cause major impacts on the National Air Space system.  In fact, SFO can be the only airport reporting ground delays on a given summer day.  The Marine Stratus Initiative, a 7 year research effort funded by the FAA, developed a decision support system to aid in the prediction of stratus clearing times.  This system issues its forecast both deterministically (specific breakout time) and probabilistically, probability of clearing by a given time.   In 2002 the National Weather Service took over operation of the system.   It has been operational through the summer of 2010.  

The decision to issue a ground delay program (GDP) for SFO is made by a consensus of human inputs including the FAA Command Center, the Traffic Management Unit at the FAA Oakland ARTCC , the Center Weather Service Unit (CWSU), the  NWS Terminal Aerodrome Forecast (TAF), and United Airlines.  The final decision on the GDP is with the FAA Command Center.  The final consensus forecasts may not agree with the deterministic and/or probabilistic forecasts issued by the decision support tool.  Previous analysis, (Delman et al, 2008), showed little correlation between forecast uncertainty and either the spatial extent, planned arrival rates, or temporal length of the GDP issued.  An analysis of the summer of 2009 and preliminary results of 2010 indicate that forecasts are now influencing GDP issuance either through not issuing a GDP on days where forecast clearing times precede expected arrival rates of  greater than 30, or by modifying the planned arrival rates to between 30 and 45, the rate when clearing has occurred.  Results will be shown substantiating these conclusions as well as showing the economic impact of these forecasts.     

In addition, a new study funded by NASA Ames, based on the error characteristics of the decision support system described above, provides guidance to Command Center decision makers on a “best GDP” to issue to reduce arrival delays (Clark, 2009, and Cook and Wood, 2009).   This system is to be implemented during the summer of 2010 and will be described briefly.  Figure 1 summarizes the project and highlights forecast impacts on GDP issuance and current cost savings.


Clark, D., 2009: Investigating a new ground delay program strategy for coping with SFO stratus.  Aviation, Range, and Aerospace Meteorology, Long Beach, CA, January 2009.

Cook, L. and B. Wood, 2009: A model for determining ground delay program parameters using a probabilistic forecast of stratus.  8th USA/Europe Air Traffic Management Research and Development Seminar.

Delman, M.J., N.M. Ray, and D. W. Reynolds, 2008: The marine stratus initiative and effect of stratus on arrival rates at SFO.  13th Conference on Aviation, Range, and Aerospace Meteorology, New Orleans, LA.   



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