Global climatology and trends in modeled Storm Prediction Center (SPC) risk categories

Over the last decades, the NOAA Storm Prediction Center has developed a unique technique of predicting severe convective storm hazards by issuing so-called convective outlooks. Over time, those products have gained recognition and proved to be an effective tool in informing the general public about possible hazards associated with severe convective storms. Following the SPC idea, similar solutions have also been used in other regions of the world (e.g., ESTOFEX, PREVOTS). SPC outlooks translate the probability of occurrence of large hail, severe wind and tornadoes over the period of 24h into specific risk level categories, which since 2014 involve: (level 0) thunderstorm, (level 1) marginal, (level 2) slight, (level 3) enhanced, (level 4) moderate, and (level 5) high. In this work, we employ ERA5 reanalysis data between 1960 and 2024 (3h steps at 0.25 deg grid), and ASTORP models (Automated Severe Thunderstorm Outlooks from the thundeR Package) to construct a preliminary global climatology and trends of convective hazard probabilities corresponding to specific SPC risk categories. By doing this, we want to address two main aspects. Globally, the United States has the most comprehensive severe storm dataset, which may suggest that environments favoring extreme storms are the most frequent in this country. First, we test this hypothesis by comparing the modeled frequency of SPC risk categories between different parts of the world to determine how globally unique severe storm environments are in the United States. Second, we explore how the frequency of modeled SPC risk categories and specific severe storm hazards changed over time on the global scale, also in the context of a warming climate and with a special focus on densely populated areas. Our preliminary results indicate that while a frequency of situations resulting in non-severe or marginally severe thunderstorms has decreased over time, we observed an increase in the environments associated with particularly large probabilities for the occurrence of severe and significant severe convective hazards.