Messaging and Decision Support Challenges Highlighted by a Heat Index-Induced Fatality in Palo Duro Canyon

Every year, dozens of visitors in Palo Duro Canyon (PDC) succumb to heat, requiring rescue and medical services. Some of these casualties are fatal, as was the case on 21 June 2023 when a teenage boy attempted to hike on a dangerously hot afternoon. This fatality occurred despite the fact that the trails were closed in response to a Heat Advisory issued by the National Weather Service earlier that day. The advisory-based trail closures are a new initiative taken by Palo Duro Canyon State Park (PDCSP) to reduce heat related casualties. However, as this case shows, even more work needs to be done to help prevent tragedies such as these.

From an operational forecast and warning perspective, work has been done in recent years to improve awareness of extreme heat within the canyon. These efforts have included the installment of West Texas Mesonet sites around the canyon, and field campaigns to study the localized temperature extremes that occur there. Effective messaging of the heat impacts in the canyon can be complex given the fact that conditions in nearby population centers (on the adjacent Plains) are cooler and the impacts are minimal. In 2018, NWS Amarillo created a special forecast zone which allowed for the issuance of advisories and warnings specific to PDCSP. This greatly improved the ability to message the threat of extreme heat in PDCSP even when surrounding areas were expected to stay below Heat Advisory thresholds, and has allowed park service administrators to make informed decisions on canyon access and trail closures to improve public safety. The 21 June case was unique because of the high level of uncertainty with respect to surface temperature and dew point. The end result was that the maximum temperature was lower than advertised in official deterministic forecasts, less than the 105 degree advisory threshold, but the dew point was higher, resulting in a dangerously high heat index value of 111 degrees. Forecasters' use of probabilistic information and anticipation of potential impacts resulted in the issuance of an impact-based Heat Advisory despite the fact that there was a high degree of uncertainty in the forecast.

This presentation will demonstrate how probabilistic and impact-based decision support can mitigate forecast uncertainties such as these. We will also take a look at dryline interactions within the PDC system, as even high resolution convection allowing models (CAMs) cannot reliably show the small scale terrain influences of the canyon. For instance, dew points on the canyon floor ranged between 68 and 76 degrees F during the afternoon of 21 June, but observations on the rim indicated dew points mixing into the low 40s. These terrain influences produced very localized dangerous heat on the floor of PDC, while more climatological conditions prevailed on the surrounding plains. Successfully messaging this impactful variation of extreme conditions presents a significant challenge for operational forecast and warning services.