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Complex terrain features—in particular, environmental conditions, high population density and potential socio-economic damage—make the Trans-Mexican Volcanic Belt (TMVB) of particular interest regarding the study of deep convection and related severe weather. In this research, 10 years of Moderate-Resolution Imaging Spectroradiometer (MODIS) cloud observations are combined with Climate Hazards Group Infrared Precipitation with Station (CHIRPS) rainfall data to characterize the spatio-temporal distribution of deep convective clouds (DCCs) and their relationship to extreme precipitation. From monthly distributions, wet and dry phases are identified for cloud fraction, deep convective cloud frequency and convective precipitation. For both DCC and extreme precipitation events, the highest frequencies align just over the higher elevations of the TMVB. A clear relationship between DCCs and terrain features, indicating the important role of orography in the development of convective systems, is noticed. For three sub-regions, the observed distributions of deep convective cloud and extreme precipitation events are assessed in more detail. Each sub-region exhibits different local conditions, including terrain features, and are known to be influenced differently by emerging moisture fluxes from the Gulf of Mexico and the Pacific Ocean. The observed distinct spatio-temporal variabilities provide the first insights into the physical processes that control the convective development in the study area. A signal of the midsummer drought in Mexico (i.e., “canícula”) is recognized using MODIS monthly mean cloud observations.

Tornadoes are extreme meteorological phenomena that can produce significant damage. The Mexican territory is prone to tornadogenesis; however, these phenomena are poorly studied in the country, and several characteristics of their behavior are unknown. We analyzed the spatiotemporal distribution of tornadoes and waterspouts in Mexico (2000-2020) and compared them with potentially severe convective environments. The updated climatology consists of 378 tornado and 99 waterspout reports and is the product of previous research and recent documentation obtained from official and non-official sources. Given the significant influence of population density on the distribution of tornado reports and the lack of meteorological instrumentation for severe weather monitoring, we used the ERA5 dataset to complement the documentary data by computing potentially severe convective environments. The results show an increasing trend in tornado reports, from an annual average of 12 (2000-2012) to 44 (2015-2020). Tornadoes are mainly documented along the Trans-Mexican Volcanic Belt in central Mexico, while waterspouts are reported in the central and southern portions of the Pacific Ocean and the Yucatán Peninsula. The tornado season spans from May through August, while waterspouts are common during June. Tornadic activity is most frequent between 15:00 and 21:00 h local time (20:00-02:00 h UTC). The results obtained from the reanalysis data indicate favorable conditions for severe storm development in northeastern and northwestern Mexico during late spring and summer. These regions coincide with those where significant tornadoes and supercell storms have been previously documented. The computed covariates based on convective available potential energy and wind shear allowed the identification of regions vulnerable to the impact of diverse severe storm manifestations (e.g. tornadoes) and the coverage of areas without documentary information.

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Tornadoes are violent and destructive natural phenomena that occur on a local scale in most regions around the world. Severe storms occasionally lead to the formation of mesocyclones, whose direction or sense of rotation is often determined by the Coriolis force, among other factors. In the Northern Hemisphere, more than 99% of all tornadoes rotate anticlockwise. The present research shows that, in topographically complex regions, tornadoes have a different probability of rotating clockwise or anticlockwise. Our ongoing research programme on tornadoes in Mexico has shown that the number of tornadoes is significantly higher than previously thought. About 40% of all tornadoes occur in the complex topographic region of the Trans-Mexican Volcanic Belt. Data collected (from Internet videos) on the rotation of tornadoes formed in this region showed that about 50% of them rotated in a clockwise direction, contradicting tornado statistics for most of North America. Time series of the helicity parameter showed that tornadoes formed in topographically complex areas exhibited different behaviours compared to those formed in plains that are related with supercell systems.