Most often, weather-related flight delays are due to the interaction of two factors. One, how many planes can an airport accept during a given time period based on the weather (airport capacity). Two, how many planes are scheduled to arrive (airport demand) during the same given time period.

No two airports are created alike; airport capacity is unique to each airport, given the same weather conditions. Runway layout and configuration, local terrain, local flight paths, the number of runways, and several other factors determine how much traffic an airport can handle during any given weather event.

By using our NAMS forecast model output, which forecasts weather for each airport on an hourly basis, our TripCast flight delay prediction model predicts airport capacity for every airport on an hourly basis. Then, by comparing the airport capacity with the airport demand, TripCast forecasts the airport delay potential for all airports for every hour of our forecast period.

Why is TripCast better?
Because TripCast focuses in on the precise cause of airport delays. No other commercial source of similar information can claim that today. This precision is crucial: due to the differences in capacity and demand at each airport, one major airport may have frequent and lengthy delays, while another of the same size may only have delays on rare occasions. For example, low clouds in Denver would rarely cause flight delays, while low clouds at New York LaGuardia often causes extensive delays.

No other airport delay prediction information source available to the public accounts for the real causes (capacity vs. demand) of flight delays. Additionally, most of these other sources do not predict flight delays on an airport by airport basis. None forecast airport delay forecasts on an hourly basis.*

*Hourly airport delay forecasts will soon be available to Weather Depot Premium users.

Who issues airport delays?
The FAA Air Traffic Control System Command Center is the agency responsible for issuing 'airport delays'. These delays take one of three forms, ground delay programs, ground stops, and general airport delays. 

Generally, 'flight delays' are the responsibility of the airline. Each airline has a certain number of hourly arrivals and departures allotted per each airport. If the airline is not able to get all of its scheduled flights in or out each hour, then representatives of the airline will determine which flights to delay and which flights to cancel.

When airport demand is greater than the determined airport capacity, then a ground delay program may be instituted. Generally, ground delay programs are issued when inclement weather is expected to last for a significant period of time. These programs limit the number of aircraft that can land at an affected airport. Because demand is greater than the aircraft arrival capacity, flight delays will result.

Second, ground stops are issued when inclement weather is expected for a short period of time or the weather at the airport is unacceptable for landing. Ground stops mean that traffic destined to the affected airport is not allowed to leave for a certain period of time.

Lastly, there are general arrival and departure delays. This usually indicates that arrival traffic is doing airborne holding or departing traffic is experiencing longer than normal taxi times or holding at the gate. These could be due to a number of reasons, including thunderstorms in the area, a high departure demand, or a runway change.

Causes of Weather-Related Delays
There are a whole slew of weather parameters than cause flight delays. The most significant and common weather variables that cause delays are low clouds and low visibility. Low visibility may be due to fog, haze, smoke, and falling precipitation. When these conditions occur, planes may be spaced farther apart, thus resulting in fewer planes landing in any given hour.

Other typical factors can also have a significant impact on flights. Strong low-level winds or wind shear may require that planes are spaced farther apart. Strong crosswinds may make some runways unusable. Thunderstorms near the airport may limit the flight paths available into and out of the airport. Thunderstorms en route may cause a reduction in the number of flight paths, causing delays. Heavy snow requires frequent plowing, possibly making some runways unavailable. Freezing rain and snow usually necessitates the use of anti-icing and de-icing procedures.

The Future of Weather-Related Delays
Air traffic is expected to continue to increase in the coming years. All other things constant, this would mean longer and longer delays at some airports already experiencing frequent delays. At other airports that do not currently experience frequent delays, the increase in traffic could change this also.

Advances in air traffic control equipment may help alleviate the situation in the coming years. This new equipment would allow for flexible flight paths across the nation's airways and in and out of some airports.