November 17, 2025

ARL’s HYSPLIT model is a vital operational model that can track and forecast the release of hazardous airborne materials. This is valuable for emergency managers trying to determine areas most at risk during an event and to efficiently and effectively place response efforts. During the recent 43-day government shutdown, full HYSPLIT support was suspended,  however the HYSPLIT modeling team continued to respond to high-priority issues.

All 122 of the National Weather Services’s (NWS) Weather Forecast Offices (WFO) use a NWS purpose-built version of HYSPLIT. ARL is frequently called upon by the WFOs for various support questions and model support. During the shutdown, several critical issues for NWS operations were identified. On November 5 the WFO in Billings, MT reported an outage of the trajectories component of the model. A HYSPLIT team member was recalled to duty and quickly identified and fixed the root cause of the outage. Full system recovery took about 20 hours, during this time the team member monitored the process and made necessary adjustments.

Other WFO issues fielded by the HYSPLIT team during the shutdown included the WFO in Melbourne, FL that asked for an application programming interface to be created to access the NWS HYSPLIT model. This identifier is a unique identifier that the WFO in Melbourne needed to access HYSPLIT services remotely. Additionally, the WFO in Hastings, NE requested more options for nuclear detonation simulations above 45 kilotons, which the modeling team is working to provide.

Emergency managers around the country continued to need HYSPLIT trajectories to address different emergency situations during the shutdown. For example, last week the WFO in Central IL provided a HYSPLIT run to Logan County Emergency Management for leak of anhydrous ammonia near Cornfield, IL. Anhydrous ammonia is a dangerous chemical used as a fertilizer and must be kept in pressurized tanks. A broken hose caused the release from two 1,000 gallon tanks. The Logan County Sheriff’s office issued shelter-in-place orders which they credited to NOAA. They later issued a press release thanking the WFO for providing the HYSPLIT run so quickly, stating it “allowed responders to make informed decisions throughout the evolving situation.” 

The Indiana Department of Homeland Security requested a HYSPLIT run for UPS Flight 2976 which caught on fire and crashed at take-off at Louisville Muhammad Ali International Airport on November 4. Multiple explosions stemming from this accident stretched out an estimated quarter of a mile from the crash affecting a Ford assembly plant and several other businesses. As a result of the HYSPLIT run, a shelter-in-place was ordered for two thirds of Jefferson County to protect citizens from hazardous airborne gases and chemicals.

A local emergency manager contacted the WFO in Chicago on October 30 after an explosion at a dairy farm near Fair Oaks, IN released hydrogen sulfide. Hydrogen sulfide gas is highly toxic to people and animals and extremely flammable and prone to exploding. Once it begins burning, it creates other toxic gases such as sulfur dioxide. HYSPLIT trajectories provided to the emergency manager helped them to evacuate residents in the path of the hazardous plume.

ARL’s HYSPLIT modeling team supported the 2025 World Cup this summer with multiple simulations and is actively involved in planning for the 2026 World Cup. Planning during the shutdown continued, so several ARL scientists were brought in from furlough on October 16 and November 6 to meet with the World Cup Specialized Services and Tools team. ARL provided important information about the HYSPLIT emergency response support during the 2025 Club World Cup and the kinds of products that could be produced for the 2026 World Cup.

Additionally during the shutdown, ARL scientists worked with the NWS Senior Duty Meteorologist and corresponding Canadian personnel to plan for an important World Meteorological Organization Regional Specialized Meteorological Center (RSMC) exercise that will be held tomorrow, in case the shutdown was still in effect. Tomorrow’s exercise is a formal biannual exercise led by Washington RSMC and Montreal RSMC requiring ARL expertise and contributions.

ARL’s contributions to emergency response, national security and public safety are vital resources to other agencies and the public. During the government shutdown, ARL staff continued to respond to critical issues to ensure the NWS, emergency response teams and other organizations had the accurate information and access they needed.