NOAA HYSPLIT provides critical public safety information before major events

May 1, 2026

Professional soccer player in action in a stadium, kicking ball for winning goal. Credit: Master 1305, stock.adobe.com

In 2025, forecasters from NOAA’s National Weather Service’s Weather Forecast Office (WFO) in Seattle coordinated with scientists at the Air Resources Lab (ARL) for support with a request from city planners before the Club World Cup games.

WFOs routinely use a custom-designed version of ARL’s HYSPLIT model with their forecasts, particularly at the request of local officials responding to dangerous situations such as chemical leaks, fires involving hazardous materials, and even during the Grand Canyon Dragon Bravo fire last year. 

HYSPLIT is a transport and dispersion model widely used by the atmospheric community. It ingests data such as weather and atmospheric processes that drive the reaction, dispersion, and travel of a material once it is released into the atmosphere. It can track many things including chemicals, ash, radioactive material, and has even been used to forecast the path of insect swarms. If emergency responders know where a hazardous chemical is traveling through the air in their communities, and how much of that chemical is in the air over a particular area, they can make better informed decisions regarding public safety.

ARL developed a WFO-specific version of the HYSPLIT model that has more capabilities than the publicly available version of the model. When community officials are responding to an emergency event, such as those listed above, they often contact the local WFO for information about where the hazardous material is likely to travel. WFOs use HYSPLIT to provide critical information to support local decision-making, such as determining where to send first responders and identifying areas in the  community that might need to evacuate or shelter-in-place.

Google Earth image of Seattle. Shows Lumen Field and the railway that runs right next to it to the east.
HYSPLIT model forecast of a hypothetical chlorine leak from a rail tanker close to Lumen Field stadium in Seattle, WA. The plume shows the likely direction and dispersion from the site and into the surrounding area. Credit: NOAA ARL

When preparing for a large public event, such as a major sporting event, community officials may ask their corresponding WFO for hypothetical HYSPLIT dispersion forecasts from different areas. These forecasts provide critical information to planners as they make logistical decisions.

ARL frequently supports the WFO with these requests when they need a tailored product beyond the normal capabilities of their HYSPLIT model. This is why the WFO in Seattle reached out for help before the Club World Cup games at Lumen Field last summer. In the past, community officials only asked for generic atmospheric releases, but this time they requested to model specific materials. ARL’s HYSPLIT modeling team worked with the Seattle WFO to create custom, automated, one-hour averages of concentrations that were posted online and refreshed every hour giving the WFO easy and continuous access to the forecasts.

Building on last year’s work, ARL is working with multiple WFOs across the country to prepare for the World Cup games this year. With 11 U.S. cities, each with its own requirements, unique customization by the HYSPLIT modeling team is needed to ensure WFOs can get the specific forecasts officials in each location want before and during the games.