Abstract This study examines the mesoscale structure and evolution of a polar low associated with a marine cold-air outbreak (MCAO) on 2 April 2024 over the Norwegian Sea. As part of the Cold-Air Outbreak Experiment in the Subarctic Region (CAESAR), the National Science Foundation National Center for Atmospheric Research C-130 aircraft equipped with an array of in situ and remote sensing instrumentation, including profiling radars and lidars, traversed this polar low five times, yielding detailed vertical transects of clouds and precipitation. This polar low was rather shallow and formed in the wake (not at the leading edge) of an MCAO. Observations and output from an operational convection-permitting model reveal that the polar low developed in the lee of an island, Svalbard, under deep northerly flow that roughly aligned with surface-driven baroclinicity. The polar low was marked by a region of surface-driven, mostly open-cellular precipitating convection, and a separate region of deeper stratiform clouds driven by moist-isentropic ascent in an area of suppressed surface heat fluxes. The confluence of a cold air mass from the northeast, only briefly exposed to open water, with a more mature, warmer MCAO air mass with a deeper well-mixed boundary layer previously exposed to high surface heat fluxes over the Fram Strait led to convergent, cyclonically sheared boundaries with enhanced convection. These convergent boundaries emerged as cyclonic potential vorticity streamers generated frictionally by Svalbard’s terrain, became more intense by diabatic heating in clouds, and were transported downstream into the polar low. Significance Statement Polar lows are small, intense cyclones that may cause havoc with maritime transport and may bring strong winds and heavy snowfall to coastal areas. While they are most common across the far northern Atlantic Ocean, they also occur over other high-latitude oceans. Their predictability is hampered not only by the lack of measurements at high latitudes but also by a poor understanding of their vertical structure. An airborne field campaign was conducted in early 2024 to better understand clouds in marine cold-air outbreaks, including polar lows. This study combines profiling radar and lidar data collected aboard an aircraft with operational high-resolution model data to unveil fine-scale cloud and precipitation structures of a polar low in unprecedented detail.

Abstract Polar Lows are intense weather systems that drive strong exchanges of momentum, heat, and moisture between the atmosphere and ocean, potentially affecting ocean conditions. However, their small scale and short duration make them poorly represented in climate numerical models. Here, we use sensitivity experiments to assess the impacts of Polar Lows on the global ocean. Their effects vary regionally, depending on both Polar Low frequency and ocean structure. In the Northeast Atlantic, wind associated with Polar Lows enhances oceanic heat loss and vertical mixing, while precipitation has a minor opposing effect. In the Labrador and Irminger Seas, both wind and precipitation contribute similarly to horizontal heat transport, and their opposing effects largely cancel, reducing the net impact. In the Southern Hemisphere, despite frequent Polar Lows, strong background winds minimize their influence. These findings highlight regional variability in Polar Low impacts and offer insights for improving their representation in climate models.

Abstract. Polar Mesoscale Cyclones (PMCs), particularly their intense subset known as Polar Lows (PLs), characterized by short lifespans of 3–36 h and horizontal scales below 1000 km, pose significant hazards to polar maritime activities due to extreme winds exceeding 15 m s−1 and wave heights surpassing 11 m. These intense weather systems play a critical role in modulating sea-ice dynamics and ocean-atmosphere heat exchange. However, current understanding remains constrained by sparse observational records and an overreliance on single data sources (e.g., remote sensing or reanalysis). To address these gaps, this study presents the Integrated Multi-source Polar Mesoscale Cyclone Tracks (IMPMCT) dataset, a comprehensive 24-year (2001–2024) record of wintertime (November–April) PMCs for the Nordic Seas. The IMPMCT dataset was created by combining vortex-tracking algorithms applied to ERA5 reanalysis data with a deep learning-based method for detecting cyclonic cloud features in Advanced Very High-Resolution Radiometer (AVHRR) infrared imagery. It also incorporates near-surface wind data from Advanced Scatterometer (ASCAT) and Quick Scatterometer (QuikSCAT) measurements. The dataset contains 1110 vortex tracks, 16 001 cyclonic cloud features including length, width, position and morphological characteristics (spiral/comma shape), and 4472 wind speed records (wind vector imagery and cyclone maximum winds). Corresponding ERA5-derived hourly vortex tracks are also provided, including 850 hPa vorticity and proximate sea-level pressure minima. Validation demonstrates statistical agreement with existing PLs track datasets while providing more complete cyclone life cycle trajectories, more intuitive cloud imagery visualization, and a richer set of parameters compared to previous datasets. As the most comprehensive PMCs archive for the Nordic Seas, the IMPMCT dataset provides fundamental data for advancing our understanding of the genesis and intensification mechanisms, enables the development of enhanced monitoring and early warning systems, supports the validation and refinement of polar numerical weather prediction models, and facilitates improved risk assessment and safety protocols for maritime operations. The dataset is available at https://doi.org/10.5281/zenodo.17142448 (Fang and Ding, 2025).

Abstract The genesis and intensification mechanisms of polar lows (PLs) are investigated using an idealized baroclinic wave in a channel model with the Navy’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). The model setup is composed of a baroclinic jet with environmental conditions based on observations of marine cold-air outbreaks, namely, low environmental static stability and an ice–ocean boundary with a discrete step in surface temperature. Interestingly, the model is not initialized with a finite amplitude disturbance to perturb the baroclinic jet stream but instead relies on surface fluxes to indirectly initiate genesis. For this specific setup, the PL genesis is found to depend upon the development of a deep sloping boundary layer induced by the strong surface sensible heat flux as air flows across the ice–ocean boundary. The steep slope in the boundary layer top leads to a zonal temperature gradient that drives the development of a meridional wind perturbation. This perturbation disturbs the zonal jet stream and leads to growth through baroclinic instability. The sensitivity of the intensification to processes and dynamics is investigated by exploring the parameter space in various simulations, further demonstrating the importance of the boundary layer development on not only PL genesis but also its intensification. Furthermore, simulations with weak baroclinicity, strong static stability or the absence of surface sensible heat flux was found to result in very weak or no PL development.

Abstract. Cyclonic storms resembling tropical cyclones are sometimes observed well outside the tropics. These include medicanes, polar lows, subtropical cyclones, Kona storms, and possibly some cases of Australian East Coast Lows. Their structural similarity to tropical cyclones lies in their tight, nearly axisymmetric inner cores, eyes, and spiral bands. Previous studies of these phenomena suggest that they are partly and sometimes wholly driven by surface enthalpy fluxes, as with tropical cyclones. Here we show, through a series of case studies, that many of these non-tropical cyclones have morphologies and structures that resemble each other and also closely match those of tropical transitioning cyclones, with the important distinction that the potential intensity that supports them is not present in the pre-storm environment but rather is locally generated in the course of their development. We therefore propose to call these storms CYClones from Locally Originating Potential intensity (CYCLOPs). We emphasize that mature CYCLOPs are essentially the same as tropical cyclones but their development requires substantial modification of their thermodynamic environment on short time scales. Like their tropical cousins, the rapid development and strong winds of CYCLOPs pose a significant threat and forecast challenge for islands and coastal regions, and the effects of climate change on them should be considered.

ABSTRACTPolar lows (PLs) are intense maritime mesoscale cyclones that often form during marine cold air outbreaks. The objective of this study is to determine the atmospheric model horizontal resolution needed to correctly represent PLs for climate modelling. Three simulations have been conducted with the Weather Research and Forecasting (WRF) model using grid spacings of 50, 25 and 12.5 km. PLs have been tracked using a combination of objective and subjective tracking methods. The number of PLs detected in each simulation increases, and their average equivalent radius decreases, as the model resolution increases. A comparison against three PL track climatologies shows that the hit rate increases with increasing resolution of the atmospheric model. The lifetime maxima of the area‐maximum 10‐m wind speed and area‐average surface sensible heat fluxes associated with PLs are on average 12% and 20% larger, respectively, in the higher‐resolution simulations than in the lower‐resolution one. The lifetime maximum of the area‐maximum 1‐h accumulated precipitation is 67% and 133% larger in the 25‐ and 12.5‐km simulations, respectively, than in the lower‐resolution one. We conclude that a better representation of PLs can be obtained by increasing the resolution of atmospheric models from 50 to 25 km, but further increasing the resolution to 12.5 km will not result in a substantial improvement.

Abstract The impacts of initial condition errors on the forecasted intensity and location of two polar lows (PLs) occurring over the Norwegian–Barents Seas region are evaluated by applying the ensemble sensitivity analysis (ESA) to 48-h ECMWF ensemble forecasts valid at the time of the PL maximum intensity. The two PL cases represent opposite ends of the so-called PL spectrum and are chosen based on the observed cloud morphology and large-scale atmospheric conditions. The comma-cloud case is characterized by strong, deep-tropospheric baroclinicity, while the spiraliform case exhibits weaker, low-level baroclinicity. Both cases develop in connection with a marine cold air outbreak and an associated upper-level trough. Our analysis demonstrates the importance of the marine cold air outbreak (MCAO) temperature (based on the upper-level geopotential height) to the intensity of both systems, but the comma-cloud case is more sensitive to the strength of environmental baroclinicity. The forecasted location of both systems is sensitive to the representation of the synoptic-scale circulation, with the positioning of the upper-level trough ultimately determining where the PL forms. Our analysis suggests that the PL location is more predictable than PL intensity, and we show how ensemble prediction might be utilized to understand uncertainty in real-time forecasts of PLs. Significance Statement Polar lows are intense high-latitude cyclones with small spatial scales (∼300 km) and lifetimes on the order of a day. They intensify rapidly and produce hazardous weather conditions that threaten communities and operations in the Arctic, which motivates skillful polar low forecasts. Accurate initial conditions for polar low forecasting are challenging due to sparse observations in the Arctic. In this study, we investigate the relationship between initial condition uncertainty and short-term forecasts of polar low intensity and location. We find strong relationships between the representation of key environmental conditions and forecasts of polar low intensity and location, which may be used to better assess uncertainty in the real-time forecasting of polar lows.

The WIVERN mission promises to deliver the first global observations of the three-dimensional wind field and the associated cloud and precipitation structure in a wide range of atmospheric phenomena, including isolated thunderstorms, tropical cyclones, mid-latitude frontal systems, and polar lows. A critical element in the development of the mission’s wind products is the differentiation between stratiform and convective regions. Convective regions are defined as those where vertical wind velocities exceed 1 m/s. This work introduces CONSTRAINN, a family of U-Net-based neural network models that utilise all of WIVERN observables—including vertical profiles of reflectivity and Doppler velocity, as well as brightness temperatures—to reconstruct convective wind activity within the Earth’s atmosphere. Results show that the retrieved convective/stratiform masks are well reconstructed, with an equitable threat score exceeding 0.6. Ablation experiments further reveal that Doppler velocity signals are the most informative for the reconstruction task.

Abstract Sea surface temperature anomaly (SSTA) associated with mesoscale oceanic processes, which are prevalent throughout the ocean, can significantly influence the atmospheric boundary layer and consequently atmospheric systems. While its influences on tropical and extratropical cyclones have been well-documented, the influence of mesoscale SSTA on polar lows (PLs) remains unexplored. To bridge this knowledge gap, we conducted a series of sensitivity numerical experiments with different SST configurations. The simulation results indicate that, over the lifespan of a PL, SSTA does not significantly influence PL intensity but does enhance latent heat release. On a longer time scale, based on simulations of five winter seasons over the Nordic Sea, we found that the accumulated impact of mesoscale SSTA creates favorable environments for PL intensification, characterized by higher moisture levels and lower static stability. These results highlight the importance of considering high-resolution SST boundary conditions, i.e. resolving mesoscale SST, in climate simulations of PLs.

The Arctic Seas are attractive for shipping, fisheries, and other marine activities due to the abundant resources of the Arctic. The shrinking ice cover allows for the opening of activities in increasingly larger areas of the Arctic. This paper evaluates the possibility of executing all-year complex marine activities, here termed “marine operations”, in the Norwegian Sea and the ice-free part of the Barents Sea. The approach used during the preparation of this review paper is to identify constraints to marine operations so users can be aware of the limitations of performing such operations. The weather conditions in the Norwegian Sea and the Barents Sea are well known, and these seas are considered representative of ice-free or partly ice-free Arctic Seas with considerable marine activities. Similar conditions could be expected for other Arctic Seas during periods without ice cover. Marine operations require safe and stable working conditions for several days. The characteristics of marine operations are discussed, and the particulars of the Norwegian Sea and the Barents Sea physical environments are highlighted. Emphasis is on the wind and wave conditions in unpredictable polar low-pressure situations. Furthermore, situations with fog are discussed. The large uncertainties in forecasting the initiation and the tracks of polar lows represent the main concern for executing marine operations all year. Improvements in forecasting the occurrence and the path of polar lows would extend the weather window when marine operations could be carried out. Discussions of the potential for similar conditions in the wider Arctic Seas during ice-free periods are presented.

Polar lows can pose serious threats to maritime operations and coastal communities in polar regions, especially due to their extreme wind speeds. The accurate and reliable representation of their wind field thus plays a crucial role in forecasting and mitigating the risks associated with this phenomenon. This study aims to evaluate the value of the SAR-based Sentinel-1 Ocean Wind Field product compared to two reanalysis products—regional CARRA and global ERA5—in studying the spatial wind speed distribution of polar lows. A visual comparison of the wind direction and wind speed fields was performed, as well as a brief quantitative analysis of wind speeds. Despite notable differences in spatial resolution, all of the data sources are able to identify the polar lows. However, the SAR-based product remains unmatched in capturing the intricate structure of the wind field. Although CARRA resolves more details than ERA5, it still deviates from the SAR image to a degree that suggests that the difference in spatial resolution is not the only source of disparity between the sources. Both CARRA and ERA5 underestimate the maximum wind speed as compared to the SAR data. Only the SAR data seems capable of providing the information necessary to study the details of the wind field of polar lows.

Abstract Polar lows (PLs) are intense mesoscale cyclones that form over polar oceans during colder months. Characterized by high wind speeds and heavy precipitation, they profoundly impact coastal communities, shipping, and offshore activities. Amid the substantial environmental changes in polar regions due to global warming, PLs are expected to undergo noteworthy transformations. In this study, we investigate the response of PL development in the Barents Sea to climate warming based on two representative PLs. Sensitivity experiments were conducted including the PLs in the present climate and the PLs in a pseudo–global warming scenario projected by the late twenty-first century for Shared Socioeconomic Pathway (SSP) 2-4.5 and SSP 3-7.0 scenarios from phase 6 of the Coupled Model Intercomparison Project (CMIP6). In both warming climate scenarios, there is an anticipated decrease in PL intensity, in terms of the maximum surface wind speed and minimum sea level pressure. Despite the foreseen increase in latent heat release in the future climate, contributing to the enhancement of PL intensity, other primary factors such as decreased baroclinic instability, heightened atmospheric static stability, and reduced overall surface heat fluxes play pivotal roles in the overall decrease in PL intensity in the Barents Sea under warming conditions. The augmentation of surface latent heat flux, however, results in increased precipitation associated with PLs by enhancing the latent heat release. Furthermore, the regional steering flow shifts in the warming climate can influence the trajectory of PLs during their development. Significance Statement Global warming is anticipated to impact cyclone systems worldwide. Polar lows (PLs), intense mesocyclones in polar regions with potential socioeconomic and human life implications, pose uncertainties regarding intensity changes in a warming climate. In this study, we aimed to better understand how PLs over the Barents Sea will respond to the environmental changes in future climate conditions [Shared Socioeconomic Pathway (SSP) 2-4.5 and SSP 3-7.0] by the end of the twenty-first century. Our results find that the intensity of PLs is expected to decrease in the future while there is an expected increase in precipitation associated with PLs in the warming climate. These findings aim to contribute valuable insights for disaster management strategies in the face of evolving climate scenarios.

ABSTRACT Polar lows are small, high-latitude, intense maritime cyclones and frequently have severe impacts on the ocean such as strong winds, high waves and heavy rainfall. They are difficult to observe and forecast due to their short lifetime (<48 hours), small horizontal scales (200 ~ 1000 km), and the sparse synoptic observing network that exists in the subarctic and Arctic oceans. Previous studies have identified and monitored polar lows by visual analysis of visible and thermal infrared imagery from satellites. However, this manual inspection method is subjective, time-consuming and inevitably involves errors in polar low detections. In this study, we present an automatic objective procedure which we demonstrate by detecting polar lows using spaceborne active synthetic aperture radar (SAR) and passive microwave radiometer observations. Based on the marker-controlled watershed segmentation method and the morphological image thinning algorithm, the centre locations of polar lows are determined using RADARSAT-2 and Sentinel-1A high-resolution SAR images and total atmospheric water vapour content fields from radiometers (AMSR2, SSM/I, GMI, and WindSat). Furthermore, the trajectories of polar lows are constructed, using detected centres from multi-temporal SAR and radiometer observations. Polar low detections are confirmed by high surface wind speeds from SAR, scatterometer, and radiometer data, the presence of cloud vortex signatures visible in MODIS, AVHRR, and VIIRS thermal infrared imagery, as well as the difference between the sea surface temperature and the air temperature at 500 hPa. These results show that the proposed methods have potential to automatically detect and track polar lows from multisensor data. We also estimate the characteristic parameters of detected polar lows. The diameters, translation speeds, and distances travelled are 189 km and 225 km, 8 m/s and 4.9 m/s, and 318 km and 263 km, respectively.

Abstract Global deep learning weather prediction models have recently been shown to produce forecasts that rival those from physics-based models run at operational centers. It is unclear whether these models have encoded atmospheric dynamics or simply pattern matching that produces the smallest forecast error. Answering this question is crucial to establishing the utility of these models as tools for basic science. Here, we subject one such model, Pangu-Weather, to a set of four classical dynamical experiments that do not resemble the model training data. Localized perturbations to the model output and the initial conditions are added to steady time-averaged conditions, to assess the propagation speed and structural evolution of signals away from the local source. Perturbing the model physics by adding a steady tropical heat source results in a classical Matsuno–Gill response near the heating and planetary waves that radiate into the extratropics. A localized disturbance on the winter-averaged North Pacific jet stream produces realistic extratropical cyclones and fronts, including the spontaneous emergence of polar lows. Perturbing the 500-hPa height field alone yields adjustment from a state of rest to one of wind–pressure balance over ∼6 h. Localized subtropical low pressure systems produce Atlantic hurricanes, provided the initial amplitude exceeds about 4 hPa, and setting the initial humidity to zero eliminates hurricane development. We conclude that the model encodes realistic physics in all experiments and suggest that it can be used as a tool for rapidly testing a wide range of hypotheses.

Abstract Using two case studies, we analyze the effects of explicitly resolving polar lows in a global climate model (ICON‐Sapphire) with a high resolution of 2.5 km on the upper ocean and sea ice. We aim to understand the mechanism of how polar lows form in a global coupled model and how they interact with the upper ocean and sea ice. When polar lows form at the sea ice edge, they induce marine cold air outbreaks that lead to large heat loss from the ocean. This heat loss contributes to dense water formation in the Iceland and Greenland Seas, which replenishes the climatically important Denmark Strait Overflow Water (DSOW). The high wind speeds of polar lows open leads and polynyas in the sea ice cover, such as the Sirius Water Polynya in northeastern Greenland. Heat loss in polynyas is compensated for by the formation of new ice, and the rejected brine densifies the water on the Greenland shelf. In the Labrador Sea, polar lows intensify cold air outbreaks from the sea ice and rapidly deepen the ocean mixed layer. Resolving polar lows and kinematic features in the sea ice improves the realism of climate models, in particular the surface heat loss and the dense water formation in (sub)polar oceans.

Abstract Strong surface winds induced by polar lows (PLs) may affect the upper ocean. However, understanding of the oceanic responses and feedback processes associated with PLs remains insufficient, especially for observations. Using a combined analysis of satellite‐based sea surface temperature (SST) and PL tracking data, we investigated the oceanic response to 380 PL passages over the Nordic Sea occurring between 1999 and 2018. Consequently, two types of oceanic responses—warming and cooling—occurred in 32% and 40% of the total occurrences, respectively. The average magnitude of SST response was approximately ±0.2 K. Significant differences in upward surface turbulent heat flux (THF) between warming and cooling response cases were found, causing a significant difference in the decay rate after maximum PL development. By analyzing changes in the state variables of the THF, we identified two different feedback processes depending on the oceanic warming/cooling response. During a warming (cooling) response, the atmosphere near the surface becomes more unstable (stable), and the turbulence of the marine atmospheric boundary layer increases (decreases), which strengthens (weakens) the ocean surface wind and decreases (increases) temperature and specific humidity. These changes contribute to increasing (decreasing) the upward THF that influences PL development. The differences between these two responses may be caused by the state of the upper ocean layer, including temperature inversion. The analysis of the in situ observations of the upper ocean supports the hypothesis that a warming response occurs when inversion is strong. This study emphasizes the importance of feedback through oceanic responses for understanding and predicting PL.

Abstract Sea spray, originating from wave breaking under high wind conditions, can significantly affect turbulent heat fluxes at the air–sea interface. Even though polar lows (PLs) can become extreme weather features with gale‐force wind, the impact of sea spray on their development has rarely been investigated and is not considered in operational forecast models. In this study, the impact of sea spray on the development of two PLs over the Barents Sea is studied based on sensitivity experiments with an atmosphere–wave coupled model, where the spray‐mediated heat fluxes are parameterized. The results show that the impact of sea‐spray‐mediated heat fluxes on PL development is sensitive to the surface wind speed. In the case of the stronger PL, the higher surface wind speed results in significantly higher spray‐mediated heat fluxes. Consequently, these spray‐mediated heat fluxes intensify the convection and diabatic heating of the PL, resulting in its intensification. In comparison, the case with a weaker PL experiences less sea spray production and lower spray‐mediated heat fluxes due to its weaker surface wind speeds. Overall, we find that spray‐mediated sensible heat fluxes play an important role in the development of PLs, while the latent heat fluxes induced by sea spray have a relatively minor impact.

Abstract Several warm‐core cyclones in the Mediterranean, which were analyzed in the literature, are studied using ERA5 reanalysis, to identify the environment where they develop and distinguish tropical‐like cyclones from non‐tropical warm‐core cyclones. Initially, the cyclone phase space is analyzed to distinguish the cyclones that have a symmetrical deep warm core. Subsequently, the temporal evolution of several parameters is considered, including the distance between the area of maximum tangential wind speed and the cyclone center. Some differences are observed between the cyclones analyzed: one category of cyclones develops in areas of moderate‐low baroclinicity and intense convective processes, as occurs in tropical cyclones. Another group of cyclones develops in a strongly baroclinic environment with weak convective processes and intense vertical wind shear, as occurs in warm seclusions. Two cyclones, showing similarities with polar lows, are also identified.

Abstract The link between weather regimes (WRs) and polar low (PL) activity is examined over the North Atlantic and North Pacific basins. Compared to earlier studies based on limited, regional PL datasets, our study conducts a more complete evaluation of regional WR–PL relationships using an expanded PL climatology. Our findings show that PL activity is increased over the Norwegian and Barents Seas during the Atlantic ridge regime and decreased over the former region during the Scandinavian blocking regime, with negative impacts also stretching to the Irminger Sea. Over the Labrador and Irminger Seas, PL activity is modulated strongest by the North Atlantic Oscillation (NAO), with positive impacts during the positive phase and vice versa. Over the North Pacific, the Arctic low contributes to increased PL activity over most regions, while the opposite is true for the Pacific wave train regime. The variability of PL activity associated with WRs is strongly related to changes in key environmental conditions. In general, regions of enhanced (reduced) PL activity are coincident with anomalous low-level northerly (southerly) flow and reduced (increased) static stability. Further analysis shows that certain persistent WRs can strongly modulate PL activity over some regions, either due to the amplification or propagation of favorable or unfavorable conditions, which cautions the limitation of regarding WRs as stationary patterns. A previously developed PL genesis potential index is shown to represent the observed impacts well, which serves to confirm the robustness of our findings and suggests the potential applicability of WRs to the subseasonal prediction of PLs. Significance Statement Polar lows are intense small-scale (∼300 km) cyclones that form over high-latitude oceanic regions. The hazardous impacts they pose to coastal communities and maritime and air operations in the Arctic motivate their skillful prediction, which remains a major challenge at lead times beyond a few days. In this study, we relate PLs and the key environmental conditions that favor their development to weather regimes, which are recurrent large-scale circulation patterns that can persist for weeks at a time. We find that weather regimes have strong impacts on polar low activity through the modulation of key environmental conditions. These relationships can potentially be utilized in the extended-range prediction of polar lows.

Polar lows (PLs), which are intense maritime polar mesoscale cyclones, are associated with severe weather conditions. Due to their small size and rapid development, PL forecasting remains a challenge. Convection-permitting models are adequate to forecast PLs since, compared to coarser models, they provide a better representation of convection as well as surface and near-surface processes. A PL that formed over the Norwegian Sea on 25 March 2019 was simulated using the convection-permitting Canadian Regional Climate Model version 6 (CRCM6/GEM4, using a grid mesh of 2.5 km) driven by the reanalysis ERA5. The objectives of this study were to quantify the impact of the initial conditions on the simulation of the PL, and to assess the skill of the CRCM6/GEM4 at reproducing the PL. The results show that the skill of the CRCM6/GEM4 at reproducing the PL strongly depends on the initial conditions. Although in all simulations the synoptic environment is favourable for PL development, with a strong low-level temperature gradient and an upper-level through, only the low-level atmospheric fields of three of the simulations lead to PL development through baroclinic instability. The two simulations that best captured the PL represent a PL deeper than the observed one, and they show higher temperature mean bias compared to the other simulations, indicating that the ocean surface fluxes may be too strong. In general, ERA5 has more skill than the simulations at reproducing the observed PL, but the CRCM6/GEM4 simulation with initialisation time closer to the genesis time of the PL reproduces quite well small scale features as low-level baroclinic instability during the PL development phase.