Major HYSPLIT Update Improves the Nation’s Public Safety

On December 6, 2022, a major new version of HYSPLIT was fully implemented to provide new operational tools to weather forecasters at the National Weather Service. HYSPLIT is the pre-eminent model, developed and updated by NOAA’s Air Resources Laboratory, that has been used for tracking hazardous and toxic emissions from industrial, transportation, and nuclear accidents, smoke from wildfires and prescribed fires, ash from volcanic eruptions and dust from dust storms. Among its new capabilities is an expanded and enhanced capability for volcanic ash modeling.

The HYSPLIT model is now entering its third decade in operations, and is used to determine the spatial and temporal distribution of toxic substances emitted to the atmosphere for use by First Responders across the nation. HYSPLIT is utilized by all 122 NWS Weather Forecast Offices as their primary emergency response application for providing weather forecasters with information about the location and extent of hazardous materials that result from hazardous chemical spills, industrial fires, chemical train derailments, the release of nuclear materials, volcanic eruptions, wildfires, prescribed burns, and dust storms. When informed of this new update, the director of NWS, Kenneth Graham, stated that, “As a user of HYSPLIT during spills, leaks, explosions, etc., I can really appreciate this. Thank you for the hard work on this. Amazing!!!”

HYSPLIT is available on a 24/7 basis as a tool to alert communities and first responders across the nation to hazards to allow for both the safe evacuation of people from areas that could be impacted by conditions that are threatening to human life, and also allow first responders to know where to deploy critical mitigation resources in a timely fashion. HYSPLIT is employed in all major public events from sporting events such as the Super Bowl, to key political venues such as the Presidential Inauguration; but it is always available for being called upon at a moment’s notice for a chemical train derailment or large industrial fire.

Volcanic ash is a serious hazard to all aviation interests and can bring a jet aircraft crashing to the ground. NOAA’s two Volcanic Ash Advisory Centers (VAAC), located in Washington and Anchorage, monitor volcanic emissions to alert aircraft of dangerous ash levels within U.S. airspace. They use HYSPLIT to model the transport and dispersion of the volcanic ash cloud and produce volcanic ash advisories (VAAs) for aviation users. An expanded volcanic ash forecasting capability allows analysts at the VAACs to generate probabilistic forecasts which express a range of possible outcomes, and will allow the aviation sector to use this information in risk-based approaches to flight planning. The new HYSPLIT products will also provide higher vertical resolution and better indicate concentrations of ash at various heights. Overall, these features will lead to better warnings for the entire flying public – both domestically and internationally.

Comments from NOAA’s VAAC operators have been positive on the improvements offered by this version of HYSPLIT. One Washington VAAC operator noted: “There is a high degree of uncertainty in volcanic ash dispersion modeling and an ensemble approach will assist in reducing that uncertainty and should lead to overall improvements in forecasting and warning product verification compared to a single deterministic model approach.” NOAA’s Anchorage VAAC operators also noted that “we do not currently have a capability to produce volcanic ash products based on specific ash thresholds, and the work done for HYSPLIT is our path toward meeting these requirements.”

The recent volcanic eruptions of Mauna Loa and Kilauea in Hawaii has demonstrated the great utility that HYSPLIT has for ensuring public safety. The ashfall predictions generated by HYSPLIT were key to the Ashfall Advisory issued by the NWS’ Honolulu Weather Forecast Office for the entire state on Nov 28, 2022; in this advisory, the public was alerted to where volcanic ash could expected only one hour after the eruption at Mauna Loa. ARL’s research is improving volcanic ash dispersion forecasts by providing state-of-the-art capabilities to operations at the NWS and ultimately, public safety is the motivation for the research that underlies the continued improvements in HYSPLIT, now embodied in this latest version implemented in early December 2022.