Núñez Ocasio, Kelly M., Erin M Dougherty, Lulin Xue, Zachary L Moon, Antonio Ruiz Núñez, Monica A Morrison, Kwesi T Quagraine, Ye Mu, Carlos Martinez, and Veeshan Narinesingh, et al., April 2026: Advancing weather and climate science in Mesoamerica and the Caribbean: A novel regional multiweek convection-permitting simulation. Bulletin of the American Meteorological Society, 107(4), DOI:10.1175/BAMS-D-25-0023.1E836–E852. Abstract
Understanding the weather and climate of Mesoamerica and the Caribbean remains challenging due to complex hydroclimate interactions, limited observations, and poor representation of regional processes in global models. We introduce the Mesoamerica Affinity Group (MAAG), a National Science Foundation (NSF) National Center for Atmospheric Research (NCAR) and community initiative that fosters research collaboration to advance weather and climate science, develop convection-permitting datasets, and promote knowledge exchange. MAAG’s first major contribution is a 2-week convection-permitting simulation of Hurricane Maria (2017) using Model for Prediction Across Scales–Atmosphere (MPAS-A), featuring a novel regional 15- to 3-km variable-resolution mesh over the region. Initial evaluation shows that MPAS-A captures key features like precipitation patterns, the intertropical convergence zone, and low-level jets. Some biases remain, particularly in enhanced land convection and slight deviations in Maria’s track. This novel dataset, now publicly available through NCAR’s Data Archive, supports studies of other extreme events and mesoscale convective systems active during the same period. It offers a valuable resource for the research community. MAAG is a new but rapidly growing initiative achieving notable milestones in a short time. It serves as a collaborative platform for codesigning high-resolution modeling experiments aimed at producing actionable weather and climate information. We invite the community to join MAAG, explore this initial dataset, and advance regional weather and climate research.
Wang, Lei, Jian Lu, Melissa L Breeden, Gang Chen, Stephanie A Henderson, Veeshan Narinesingh, Isla Simpson, Tim Woollings, Yanjun Hu, and Sandro W Lubis, March 2026: Gaps and ways forward in atmospheric blocking and extreme weather research. Nature Communications, 17, 2873, DOI:10.1038/s41467-026-70487-z. Abstract
Atmospheric blocking often results in significant weather extremes and associated impacts such as heatwaves, droughts, wildfires, cold spells, and floods in mid-latitude regions. However, the physical processes behind blocking and associated extreme weather events are not well understood, hampering prediction and decision-making for mitigation and adaptation. Further, numerical models often struggle to simulate the frequency, duration, and geographic distribution of atmospheric blocking events. Here, we provide an overview of blocking-related weather extremes and impacts, as well as of our current understanding of the key physical processes. We identify knowledge gaps and current challenges and provide our perspective on potential ways forward.
We examine the intensity, duration, and physical drivers of Northern Hemisphere summer heat extremes in observations, reanalyses, CMIP6 models, and prescribed sea surface temperature (SST) simulations representing historical- and future-projected climates. Extremes are defined using a 90th percentile anomaly defined relative to a 29-day × 11-yr running mean to examine how the tail of temperature anomaly distributions changes in projections. Models generally capture the observed regional variations of intensity and duration. The magnitude of 90th percentile temperature anomalies shows a generally positive meridional gradient with some zonal variation but with warm biases over eastern India and southern North America. Both the reanalysis and climate model simulations exhibit positive biases in the duration of heat extremes in regions where the lowest model level temperature budget shows that diabatic effects dominate: Mexico extending through Central America, northeastern South America, and India. By investigating both prescribed SST forced by observations and coupled ocean simulations, heat extreme biases do not seem to be SST driven. In the warming simulations, projections under medium [shared socioeconomic pathway (SSP) 2–4.5] and high emission (SSP5–8.5) scenarios for late twenty-first century demonstrate sign change agreement for more intense anomalies over the Southeast United States, the Sahel and central Africa, and polar regions, along with weaker anomalies over Greenland brought on by melting ice. In terms of duration, the models have lesser agreement, likely due to internal variability, but nonetheless project increased duration over Northwest and Southeast United States and a reduction in northwest Canada and northern Africa.
Coupled ocean and prescribed sea surface temperature (SST) experiments are performed to investigate the drivers of Northern Hemisphere (NH) midlatitude winter circulation and blocking changes in warmer climates. In coupled experiments, a historical simulation is compared to a simulation following an end of the twenty-first-century shared socioeconomic pathway (SSP5-8.5) emission scenario. The SSP5-8.5 simulation yields poleward-shifted jets and an enhanced stationary wave pattern compared to the historical simulation. In terms of blocking, a reduction is found across North America and over the Pacific Ocean with the suggestion of more blocking over parts of Eurasia. Separately, prescribed SST experiments are performed decomposing the SSP5-8.5 SST response into a uniform warming component plus a spatially dependent change in SST pattern. SSP5-8.5 changes in circulation are primarily driven by a uniform warming of SST. Uniform warming is also found to account for most of the SSP5-8.5 blocking reduction over North America and the Pacific Ocean, but not over Eurasia. El Niño–like changes to the SST pattern also yield less blocking over the Pacific and North America. However, adding the responses of uniform and pattern experiments yields a nonlinear overreduction of blocking compared to the SSP5-8.5 experiment. Regional analyses of block energetics suggest that much of the reductions in blocking in warming simulations are driven by decreased baroclinic conversion in some regions and enhanced dissipation from diabatic sources in others.
Narinesingh, Veeshan, James F Booth, and Yi Ming, January 2023: Northern hemisphere heat extremes in a warmer climate: More probable but less colocated with blocking. Geophysical Research Letters, 50(2), DOI:10.1029/2022GL101211. Abstract
This work uses reanalysis and NOAA Geophysical Fluid Dynamics Laboratory's Coupled Model Intercomparison Project 6 model, CM4, to investigate the colocation of heat extremes and atmospheric blocking in the current climate and an end of 21st century, extreme-emissions projection. In the present day, the colocation of heat events and blocking is greatest for the strongest heat events. Block-heat extreme colocation is found to be less prevalent over ocean than land, exhibiting regional variation throughout the Northern Hemisphere. Over North America, colocation is greatest near the northwestern and northeastern coasts, minimizing near the center; over Eurasia, colocation is most prevalent in northern regions. In an RCP 8.5 projection, the historical 90th percentile temperature decreases to 0–70th percentile, depending on the region. This is primarily driven by mean state warming. Blocking is found to decrease along with the colocation of blocking and heat extremes, suggesting that in some regions, the mechanisms driving heat extremes will change in future climates.
White, Rachel H., Sam Anderson, James F Booth, Ginni Braich, Christina Draeger, Cuiyi Fei, Christopher D G Harley, Sarah B Henderson, Matthias Jakob, Carie-Ann Lau, Lualawi Mareshet Admasu, Veeshan Narinesingh, Christopher Rodell, Eliott Roocroft, Kate R Weinberger, and Greg West, February 2023: The unprecedented Pacific Northwest heatwave of June 2021. Nature Communications, 14, 727, DOI:10.1038/s41467-023-36289-3. Abstract
In late June 2021 a heatwave of unprecedented magnitude impacted the Pacific Northwest region of Canada and the United States. Many locations broke all-time maximum temperature records by more than 5 °C, and the Canadian national temperature record was broken by 4.6 °C, with a new record temperature of 49.6 °C. Here, we provide a comprehensive summary of this event and its impacts. Upstream diabatic heating played a key role in the magnitude of this anomaly. Weather forecasts provided advanced notice of the event, while sub-seasonal forecasts showed an increased likelihood of a heat extreme with lead times of 10-20 days. The impacts of this event were catastrophic, including hundreds of attributable deaths across the Pacific Northwest, mass-mortalities of marine life, reduced crop and fruit yields, river flooding from rapid snow and glacier melt, and a substantial increase in wildfires—the latter contributing to landslides in the months following. These impacts provide examples we can learn from and a vivid depiction of how climate change can be so devastating.
This study examines the climatology and dynamics of atmospheric blocking, and the general circulation features that influence blocks in GFDL’s atmosphere-only (AM4) and coupled atmosphere–ocean (CM4) comprehensive models. We compare AM4 and CM4 with reanalysis, focusing on winter in the Northern Hemisphere. Both models generate the correct blocking climatology and planetary-scale signatures of the stationary wave. However, at regional scales some biases exist. In the eastern Pacific and over western North America, both models generate excessive blocking frequency and too strong of a stationary wave. In the Atlantic, the models generate too little blocking and a weakened stationary wave. A block-centered compositing analysis of block-onset dynamics reveals that the models 1) produce realistic patterns of high-frequency (1–6-day) eddy forcing and 2) capture the notable differences in the 500-hPa geopotential height field between Pacific and Atlantic blocking. However, the models fail to reproduce stronger wave activity flux convergence in the Atlantic compared to the Pacific. Overall, biases in the blocking climatology in terms of location, frequency, duration, and area are quite similar between AM4 and CM4 despite the models having large differences in sea surface temperatures and climatological zonal circulation. This could suggest that other factors could be more dominant in generating blocking biases for these GCMs.
Many fundamental questions remain about the roles and effects of stationary forcing on atmospheric blocking. As such, this work utilizes an idealized moist general circulation model (GCM) to investigate atmospheric blocking in terms of dynamics, geographical location, and duration. The model is first configured as an aquaplanet, then orography is added in separate integrations. Block-centered composites of wave activity fluxes and height show that blocks in the aquaplanet undergo a realistic dynamical evolution when compared to reanalysis. Blocks in the aquaplanet are also found to have similar life cycles to blocks in model integrations with orography. These results affirm the usefulness of both zonally symmetric and asymmetric idealized model configurations for studying blocking. Adding orography to the model leads to an increase in blocking. This mirrors what is observed when comparing the Northern Hemisphere (NH) and Southern Hemisphere (SH), where the NH contains more orography and thus more blocking. As the prescribed mountain height increases, so do the magnitude and size of climatological stationary waves, resulting in more blocking overall. Increases in blocking, however, are not spatially uniform. Orography is found to induce regions of enhanced block frequency just upstream of mountains, near high pressure anomalies in the stationary waves, which is poleward of climatological minima in upper-level zonal wind, while block frequency minima and jet maxima occur eastward of the wave trough. This result matches what is observed near the Rocky Mountains. Finally, an analysis of block duration suggests blocks generated near stationary wave maxima last slightly longer than blocks that form far from or without orography. Overall, the results of this work help to explain some of the observed similarities and differences in blocking between the NH and SH and emphasize the importance of general circulation features in setting where blocks most frequently occur.
