89th American Meteorological Society Annual Meeting

Tuesday, 13 January 2009: 2:15 PM
Convective weather forecasting to support better NAS network flow decision making in severe weather
Room 132A (Phoenix Convention Center)
James E. Evans, MIT Lincoln Laboratory, Lexington, MA
Thunderstorm-related delays dominate the overall U.S. airspace delay statistics and have continued to

increase since 2000, even though a number of new weather information systems and air traffic management

(ATM) decision support tools have been deployed since 1999. Operational decision makers must mitigate

the network congestion that arises from rapidly varying capacity loss in both en route and terminal airspace.

Improving decision making in such an environment is generally agreed (FAA REDAC, 2007) to require:

1. Forecasts that can be “translated” into forecasts of ATC impacts (including handling of

uncertainty in the convective weather forecasts),

2. Developing integrated weather-ATM decision support tools (DST) to enable decision makers to

more fully utilize available capacity, and

3. Improving the overall process for filing routes and making adjustments to routes for flights in the

air so as to achieve a higher degree of adaptive, incremental decision making

Since a key element of the problem is the network congestion that arises when rerouting planes away from a

region of severe weather causes operationally significant congestion problems in fair weather regions,

determining appropriate ATM strategies can be very challenging.

The question of the relative importance of investments in short term forecasts/ATM DST versus improving

longer lead hour forecasts/DSTs is a key question in the overall investment strategy. The REDAC WAIWG

noted that although current convective weather forecasts have much more accuracy in 0-2 hour “tactical”

time frame, than the 2-10 hour lead time “strategic time frame the size and shape of the 0-2 hour solution

space is much smaller and with increasing congestion, more decisions will have to be made in the latter.

Conversely the more the tactical solution space can be expanded, the more decisions can be delayed

adaptively and traffic optimized to meet business objectives.

The degree to which convective weather delays can be reduced through contemporary improved forecasts,

integrated weather-ATM DSTs and improved processes for adjusting flight routing has been investigated by

two different methods:

1. assessment of the extent to which severe weather delays are “avoidable” by translating “translating”

three-dimensional weather radar data and other germane capacity impact weather data (e.g., terminal

ceiling and visibility, terminal surface winds) into time-varying estimates of the capacity reductions

in affected airspace regions, together with an objective, automatically-generated, broad-area airspace

usage algorithm (Bertsimas and Stock-Patterson, 1998) that considers the time-varying estimates of

airspace capacity and the demand in determining optimal reroute strategies (and, when necessary,

minimally disruptive ground or airborne delay initiatives ), and

2. observations and analysis of decision making in the use of both tactical [the Route Availability

Planning Tool (RAPT) ] and strategic [e.g., Airspace Flow Program (AFP) and Ground Delay

Program (GDP)] tools over the past two years

These results suggest that a balance of investments between “tactical” and “strategic” weather-ATM

development will be required. The current longer lead time strategic forecasts (e.g., the CCFP) cannot be

easily translated into forecasts of capacity impacts. As a consequence, both over supply and under supply of

aircraft into weather impacted airspace is frequently observed. Due to the lack of tactical decision support

tools and operational doctrines for making shorter lead time adjustments to flows, the effectiveness of

tactical DSTs such as RAPT is often diminished by other tactical adjustments (e.g., use of departure airspace

for arrivals due to inability to anticipate arrival route blockages).

Recommendations are made for a balanced program of forecast and ATM development to better address the

challenging problem of convective weather for the NAS.

∗This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-05-C-0002.

Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed

by the United States Government.


FAA REDAC, 2007, “Weather-Air Traffic Management Integration Final Report,” Weather – ATM

Integration Working Group (WAIWG) of the National Airspace System Operations Subcommittee, Federal

Aviation Administration (FAA) Research, Engineering and Development Advisory Committee (REDAC)., 3

October 2007

Bertsimas, D. and S. Stock-Patterson, 1998: The Air Traffic Flow Management Problem with En Route

Capacities, Operations Research, 46, 406-422.

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