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Abstract Recent decades have seen record-high temperatures on the Antarctic Peninsula (AP) due to combined atmospheric rivers (ARs) and föhn warming. While ARs frequently enhance föhn, not all events cause surface warming over the entire Larsen C Ice Shelf (LCIS). Using high-resolution Polar WRF simulations, we examine the relationship between ARs and föhn over the AP during austral summers and identify four distinct AR shapes associated with föhn-induced surface warming over the LCIS: zonal-perpendicular, zonal-like, convex, and concave. Zonal-like ARs associated with coupled low-high-pressure systems and convex ARs linked to blocking highs produce strong föhn warming across the entire LCIS, primarily affecting its northern and southern sectors, respectively. In contrast, zonal-perpendicular and concave ARs generate moderate-to-weak warming, owing to either weaker AR intensity or AR curvature. Although downward shortwave radiation dominates surface warming, enhanced moisture suppresses its increase from föhn-induced cloud clearance while enhancing downward longwave radiation near mountain gaps. Sensible heat flux also contributes substantially along the mountain foothills. As ARs intensify under climate change, their interaction with föhn over the AP can critically influence the future stability of coastal ice shelves. 

Abstract Since the late 1990s, summer surface melt across ice shelves in the Ross-Amundsen Sea sector of West Antarctica increased significantly, as demonstrated by satellite measurements and MetUM simulations. This contrasts with the period from 1979 to the late 1990s, which witnessed a decreasing summer melt trend driven by the positive trend in Southern Annular Mode. The increase in summer melt since the late 1990s is linked to an increase in geopotential height and intensified anticyclonic blocking along coastal West Antarctica, which strengthened northerly winds over the Ross-Amundsen Sea sector, leading to enhanced advection of warm, marine air. Our analysis reveals a strong connection between summer melt indices and sea surface temperatures in the South Pacific Convergence Zone during this period. Moreover, increased summer precipitation in South Pacific Convergence Zone since the late 1990s strengthened the Rossby wave teleconnection toward West Antarctica, contributing to enhanced blocking along the coastal region. This is consistent with the transition of the Interdecadal Pacific Oscillation to its negative phase. 

Abstract The 5-year (2024 - 2028) World Meteorological Organization’s (WMO) World Weather Research Programme (WWRP) Polar Coupled Analysis and Prediction for Services (PCAPS) project aims to accelerate research on environmental forecasting and services in the Arctic and Antarctic regions. As climate change intensifies, rapid transformations in the polar regions have complex impacts on local and global socio-ecological systems, exacerbating existing challenges for residents and operators. PCAPS focuses on enhancing forecast actionability, impact, and fidelity through a multifaceted approach of user engagement, model and service improvements, and impact studies. Key outcomes will include support for improved predictions of small-scale processes, enhanced understanding of observing systems and of the utility of Artificial Intelligence / Machine Learning (AI/ML) applications, contributions toward the development of a tiered surface observing network, and strengthened cooperation between users, operational centres, and researchers. PCAPS explores approaches to improve forecasts for sea ice, surface wind, visibility, and other key variables, which are essential for developing salient forecasting services that can enhance operational and environmental safety in extreme polar environments. Through collaborations between social and physical scientists, PCAPS also assesses decision-making, risk perceptions, and interactions between forecasters, service providers, and users, including Indigenous communities, and considers political, legal, and economic implications of information delivery. PCAPS is expected to inform WMO’s contribution to the fifth International Polar Year (2032-2033), support WMO Strategic Objectives, and build upon previous initiatives such as the Polar Prediction Project. 

Abstract Atmospheric rivers are episodic events that can advect relatively large quantities of moisture to Antarctica, contributing to both disproportionate precipitation and melting events. The Year of Polar Prediction, an international effort to improve weather prediction over the southern polar region, presents an opportunity to study the clouds and precipitation associated with winter atmospheric river events. This study uses enhanced surface, profile, and remote‐sensing observations from the Antarctic Peninsula (AP) during a Targeted Observing Period around 16 May 2022, when an event occurred with local warming similar to a warm front. We compare regional atmospheric simulations with the polar‐optimized version of the Weather Research and Forecasting Model to various in situ and remote‐sensing observations. The study emphasizes data from three stations: Escudero, Vernadsky, and Rothera. Mixed‐phase clouds were simulated at the three stations, with the precipitation being primarily rain at Escudero and primarily snow at Vernadsky and Rothera. The model produced reasonable simulations of the clouds and precipitation. Furthermore, modeled longwave cloud forcing at Escudero had small errors compared to observed values. A sensitivity test enhancing secondary ice production indicates mixed‐phase cloud sensitivity to the Hallett‐Mossop process, especially at Rothera. 

Abstract The Year of Polar Prediction (YOPP), an international research initiative organized by the World Meteorological Organization’s (WMO) World Weather Research Program from 2013 to 2022, aimed to markedly enhance environmental prediction capabilities in the polar regions and beyond, particularly in the context of a rapidly changing climate. YOPP achieved this through a concerted effort in observation, modeling, verification, user engagement, and educational activities. This article offers a comprehensive overview of YOPP’s key outcomes and impacts, using a dual approach that merges qualitative success stories with quantitative metrics. Scientifically, the focus is on the role of polar observations in improving prediction accuracy, enhanced understanding of processes to support model development, advancements in forecast verification, particularly in sea ice prediction, an improved understanding of the interconnections between polar and midlatitude regions, and effective user engagement. This paper also discusses how these scientific discoveries have been converted into practical applications, emphasizing the route from science to services. Additionally, it summarizes the education, communication, outreach, and coordination efforts employed to maximize YOPP’s impact. Finally, the article provides a series of recommendations for future research, informed by the insights gained from YOPP’s experiences and recent radical developments in technology. Significance StatementThe Year of Polar Prediction (YOPP) was a landmark initiative aimed at enhancing our ability to predict environmental changes in the polar regions, areas that are increasingly affected by climate change. By integrating global efforts in observation, modeling, and data analysis, YOPP has significantly contributed to improve the accuracy of weather and climate forecasts in these critical zones, and beyond. These advancements matter because they provide crucial insights into polar processes along with their remote impacts, enhance global prediction models, and inform stakeholders about predictive capabilities. The project’s focus on user engagement and education ensures that these scientific achievements translate into practical benefits. The collaborative spirit of YOPP exemplifies how international scientific cooperation can address some of the most pressing environmental challenges of our time. 

Abstract Clouds and radiation play an important role in warming events over the Southern Ocean (SO). Here we evaluate European Center for Medium‐Range Weather Forecasts Reanalysis version 5 (ERA5) and Polar Weather Research Forecast (PWRF) output through comparison to surface‐based measurements of clouds, radiation, and the atmospheric state over the SO during 2017–2023 at Escudero Station (62.2°S, 58.97°W) on King George Island. ERA5 mean monthly downward shortwave (DSW) radiative fluxes are found to be 38–50 W m⁻²higher than observations in summer, whereas ERA5 mean monthly downward longwave (DLW) is biased by −18 to −22 W m⁻²in summer and −16 W m⁻²on average over the year. Comparisons of temperature, humidity, and lowest‐cloud base heights between ERA5 and observations rule these factors out as large contributors to the DLW flux biases. The similarity between observed DLW cloud forcing distributions for atmospheric columns containing low‐level liquid and ice‐only clouds suggests limited influence of cloud phase errors on DLW biases. Thus the most likely explanation for DLW flux biases in ERA5 is underestimated cloud optical depth, which is also consistent with DSW flux biases. Similar biases in ERA5 are found during atmospheric river (AR) events. By contrast, PWRF flux bias magnitudes are much smaller during AR events (−12 W m⁻²for DSW and −2 W m⁻²for DLW). After bias correction, ERA5 monthly average net cloud forcing over 2017–2023 is found to be a minimum of −107 W m⁻²in January and a maximum of 65 W m⁻²in June. 

Abstract Clouds play an important role in the Southern Ocean and Antarctic surface energy balance via their radiative effects and in surface mass balance via precipitation formation. Here, we use measurements at Escudero Station (62.2°S, 58.97°W) on King George Island, north of the Antarctic Peninsula, to characterize clouds and their effects on the surface incoming radiation between 2017 and 2023. These measurements are unique providing 7 years of simultaneous cloud and radiation measurements, including year‐round observations. Cloud measurements using a mini micropulse lidar showed that clouds are present 96% of the time with persistent low‐level supercooled liquid‐containing clouds: 86% of the lowest cloud bases are within the first 1 km. Liquid was present about 80% of the time, and most liquid was supercooled: cloud‐base temperatures were below 0°C for 82% of atmospheric columns classified as liquid‐containing. Combining pyranometer and pyrgeometer measurements with clear‐sky radiative transfer modeling, we find that the downward cloud radiative forcing is negative during October–March and positive during April–September. For clouds with base temperatures below 260 K, downward longwave cloud forcing is found to be lower for ice‐only clouds than for liquid‐containing clouds; however, at warmer temperatures, both ice‐only and liquid‐containing clouds exhibited similar radiative forcing. During strong atmospheric river (AR) events, when long corridors of moisture bring heat and precipitation, surface temperatures are found to be positively correlated with downward shortwave (DSW) cloud forcing in summer, indicating that weaker DSW cloud forcing is linked to higher summertime surface temperatures. 

Abstract The Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) held seven targeted observing periods (TOPs) during the 2022 austral winter to enhance atmospheric predictability over the Southern Ocean and Antarctica. The TOPs of 5–10-day duration each featured the release of additional radiosonde balloons, more than doubling the routine sounding program at the 24 participating stations run by 14 nations, together with process-oriented observations at selected sites. These extra sounding data are evaluated for their impact on forecast skill via data denial experiments with the goal of refining the observing system to improve numerical weather prediction for winter conditions. Extensive observations focusing on clouds and precipitation primarily during atmospheric river (AR) events are being applied to refine model microphysical parameterizations for the ubiquitous mixed-phase clouds that frequently impact coastal Antarctica. Process studies are being facilitated by high-time-resolution series of observations and forecast model output via the YOPP Model Intercomparison and Improvement Project (YOPPsiteMIIP). Parallel investigations are broadening the scope and impact of the YOPP-SH winter TOPs. Studies of the Antarctic tourist industry’s use of weather services show the scope for much greater awareness of the availability of forecast products and the skill they exhibit. The Sea Ice Prediction Network South (SIPN South) analysis of predictions of the sea ice growth period reveals that the forecast skill is superior to the sea ice retreat phase. 

Abstract The Antarctica Peninsula (AP) has experienced more frequent and intense surface melting recently, jeopardizing the stability of ice shelves and ultimately leading to ice loss. Among the key phenomena that can initiate surface melting are atmospheric rivers (ARs) and leeside foehn; the combined impact of ARs and foehn led to moderate surface warming over the AP in December 2018 and record‐breaking surface melting in February 2022. Focusing on the more intense 2022 case, this study uses high‐resolution Polar WRF simulations with advanced model configurations, Reference Elevation Model of Antarctica topography, and observed surface albedo to better understand the relationship between ARs and foehn and their impacts on surface warming. With an intense AR (AR3) intrusion during the 2022 event, weak low‐level blocking and heavy orographic precipitation on the upwind side resulted in latent heat release, which led to a more deep‐foehn like case. On the leeside, sensible heat flux associated with the foehn magnitude was the major driver during the night and the secondary contributor during the day due to a stationary orographic gravity wave. Downward shortwave radiation was enhanced via cloud clearance and dominated surface melting during the daytime, especially after the peak of the AR/foehn events. However, due to the complex terrain of the AP, ARs can complicate the foehn event by transporting extra moisture to the leeside via gap flows. During the peak of the 2022 foehn warming, cloud formation on the leeside hampered the downward shortwave radiation and slightly increased the downward longwave radiation.