Snow Assessments

WMO GCW Snow Assessment for Winter 2024-2025, Northern Hemisphere and Regional Aspects

Compiled by K. Luojus and the WMO Global Cryosphere Watch Snow Watch Team
September 2025

Northern Hemisphere Continental Snow Cover Extent: 2024/2025 Snow Season Update

David A. Robinson & Thomas W. Estilow; Rutgers University, Piscataway, New Jersey, USA

SSnow cover extent (SCE) over Northern Hemisphere (NH) lands for the August 2024–July 2025 period averaged 23.9 million sq. km. This is 1.0 million sq. km. less than the 1991-2020 mean and 1.1 million sq. km below the full period of record mean (Table 1). Thus, this recent snow season ranks as having the 56th most extensive (3rd least extensive) cover in the 58-year period of record. Monthly SCE during the season ranged from 45.5 million sq. km. in February 2025 to 2.6 million sq. km. in August 2024. North America (NA) annual SCE ranked 50th most extensive in 58 years and Eurasia (EUR) 53rd most extensive.

One table and three figures are presented to depict SCE this past season compared to normal. As is typically the case, there was little snow cover over NH lands (except for Greenland, part of NA) in August or September (Table 1, Figure 1). EUR cover was somewhat above normal in September, however SCE in this month is dominated by NA cover, thus the NH ranked below normal. The EUR and NA rankings changed little in October, however by this point in the season EUR cover begin to dominate, thus the NH ranking was close to normal. SCE conditions were close to normal over both continents in November, falling below normal on both accounts in December. This resulted in a ranking of 46th most extensive out of 58 years evaluated. This early winter pattern of low SCE continued in January, with EUR at a near-record ranking 57th most extensive, thus the NH ranking 55th most extensive. SCE increased to EUR and NA values close to long-term means in February. This resurgence did not persist, with March and April SCE close to record lows, including EUR at 56th most extensive in April. The snow year concluded with May-July NH SCE extents ranking between the 44th and 47th most extensive. Looking more closely at SCE in comparison to long-term means and extremes, weekly and monthly variability is evident (Figure 1). Overall, weekly NH cover increased at close to a mean pace during the fall. Notable weekly SCE swings occurred during the winter months, with a record minimum SCE in late January. This was prior to the short-lived February rebound that was quickly followed by the melt season advancing earlier than normal.

Standardized monthly NH SCE anomalies for the 2024/2025 season were generated using Z-scores, with results shown in Figure 2. Results show close to normal scores in fall before the occurrence of extreme negative scores in December and January and later in March and April. Figure 3 shows that by the end of the current snow year the 12-month running NH SCE mean is at a minimum not seen since 2007 and before then not since the late 1980s and early 1990s.

SCE is calculated at the Rutgers Global Snow Lab (GSL) from daily SCE maps produced by meteorologists at the US National Ice Center, who rely primarily on visible satellite imagery to construct the maps. Maps depicting daily, weekly, and monthly conditions, anomalies, and climatologies may be viewed at the GSL website (https://snowcover.org).

Northern Hemisphere Terrestrial Snow Mass, winter 2024-2025

Kari Luojus¹, Patricia de Rosnay², Ewan Pinnington² and Vincent Vionnet³, ¹Finnish Meteorological Institute, Finland; ²ECMWF, UK; ³Environment and Climate Change Canada, Canada

The WMO GCW Snow Watch expert team has developed several trackers for the cryosphere. Terrestrial snow cover is tracked in regard to snow cover extent and water equivalent of snow cover (SWE) based on satellite data and complemented by model-based information and in-situ snow depth measurements. The trackers provide a quick look at the current state of the cryosphere relative to the mean state of the last 2-3 decades.

The FMI/GCW SWE Tracker is a product of the Finnish Meteorological Institute (FMI), based on ESA Snow CCI SWE. It was developed in collaboration with the GCW Snow Watch expert team. This tracker illustrates the current Northern Hemisphere snow water equivalent relative to the long-term mean and variability. The input data consist mainly of satellite-based passive microwave radiometer data, which is combined with ground-based observations in an assimilation framework (Luojus et al. 2021). The methodology based on passive microwave observations is not able to track snow conditions for the mountains, thus they are omitted from this analysis.

The FMI tracker indicated relatively average snow mass for the Northern Hemisphere during winter 2024-2025. Notably the early accumulation season was below average, but late snow season showed slightly above average snow conditions. The anomalies for winter 2024-2025 during the peak snow season were well within the standard deviation of the 30-year baseline time series for 1982-2012, as seen in Figure 4.

The Environment and Climate Change Canada (ECCC) GCW Snow Water Equivalent Tracker provides an estimate of current Northern Hemisphere SWE relative to the 1998-2011 period. It is based on the Canadian Meteorological Centre operational daily snow depth analysis with SWE estimated using a density look-up table (Brasnett, 1999; Brown and Mote, 2009; Brown et al., 2010). The CMC analysis uses real-time surface snow depth observations and model-derived information to estimate snow over the entire Northern Hemisphere land, including mountain regions. It is not a satellite-derived product.

According to the ECCC SWE Tracker, the Northern Hemisphere experienced SWE conditions that were somewhat higher than typical throughout the 2024-2025 winter season (Figure 5). This excess snow mass was primarily concentrated across Eurasia (Figure 6), where SWE values exceeded the normal range by just over one standard deviation compared to the 23-year reference period from 1988-2011. Meanwhile, North America showed SWE levels that generally stayed within one standard deviation of the long-term average for the same 1988-2011 baseline period (Figure 7).

The ECMWF ERA-5 based NH SWE tracker is shown in Figure 8. It relies on a global reanalysis using model and data assimilation (Hersbach et al., 2020). The SWE tracker is computed for the NH, excluding glaciers areas and Greenland icesheet. It indicates average snow mass for most of the winter 2024-2025 compared to the reference period 2004-2024, with slightly below average snow mass during the peak snow season.

Two of the trackers (FMI/ECMWF) indicate average or slightly below average snow conditions over the Northern Hemisphere domain, while one tracker (ECCC) estimates somewhat above average snow conditions. The differences between the trackers are due to their differences in estimating snow masses. As a conclusion, the overall Northern Hemisphere snow mass does not yet appear to decline in a similar rapid fashion as the spring-time snow cover extent, but we tend to observe a larger variation in year-to-year conditions and between Eurasia and North America.

The snow season in the Northern Hemisphere mountains, 2024-2025

Simon Gascoin, Centre d'études spatiales de la biosphère (Cesbio), France

Figure 9 shows a map of the 01 April snow water equivalent (SWE) anomaly in mountains based on ERA5-Land. On 1st April in the Northern hemisphere mountains, there was a widespread negative SWE anomaly in European mountains and the Caucasus, especially at lower elevation but a positive anomaly in the Scandinavian Mountains. There was close to normal SWE in Arctic mountains ranges of America and Asia, contrasted patterns of positive and negative anomalies in Western North America and close to normal SWE in the High Mountain Asia, with a negative anomaly in the western ranges. The negative anomaly in European mountains is in line with other regional assessments that have been seen.

This section is a contribution to Global Cryosphere Watch from the joint body on mountain snow cover of the International Association of Cryospheric Sciences.

Regional Snow Assessments, Winter 2024-2025

Assessment of the snow-covered area in the central Andes of Argentina and Chile during the first half of the 2025 winter season

Leandro Cara¹, Mariano Masiokas¹, Ricardo Villalba¹, René Garreaud², Duncan Christie², ¹Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT CONICET Mendoza, Argentina; ²Center for Climate and Resilience Research (CR), Santiago, Chile

The snow that accumulates each winter in the Andes between ca. 28° and 37°S (Figure 10A-B) represents a crucial water resource for most human activities in central Chile and central-western Argentina. This snow regulates the flows of mountain rivers, allows the existence of glaciers, and provides water for recharging the aquifers used in the populated lowland areas on both sides of the Andes. Since 2010 the accumulation of snow in this region has declined substantially, resulting in an extended dry period (locally known as the “Megadrought”) that is unprecedented in the instrumental record.

Daily 2000-2025 MODIS snow-covered area (SCA) data from the study area show that during the winter of 2023 (April-October; Figure 10C), the overall snow extent was markedly negative to the north of ca. 33°S, and less negative further south. The 2024 winter season showed a more uniform pattern with above-average SCA anomalies for most of the region (Figure 10D).

Figure 11 below shows daily SCA time series for 2025, aggregated for the basins on both sides of the continental divide (a limit which coincides here with the international border between Chile and Argentina). Three main snow events can be identified during the current winter season (in late May, late June, and early August), which increased the SCA values to around the long-term mean conditions on the Chilean basins. In contrast, on the Argentinean side, the SCA has remained near or below the 25th percentile for most of the winter.

Monitoring the SCA variations during the remaining winter and early-spring months will remain highly relevant given the region’s strong dependence on snowmelt for most human activities. In the absence of new snowstorms, the Argentinean basins in particular will experience another year with water shortages that will accrue the ongoing water crisis.

Assessment of the snow cover in the Third Pole region

Lijuan Ma, National Climate Center, China Meteorological Administration, Beijing, China

In winter of 2024/2025 (DJF), the snow cover extent (SCE) in the Third Pole region was 1348.9×103 km2, which was near the average value (1340.2×103 km2) for the period of 2005-2020. However, within the season, monthly SCE was not always near the normal. In December 2024, it was 10.4% above normal, reaching 1312.8×10³ km², while in January and February 2025, they were 3.7% and 5.9% below normal, respectively, with areas of 1413.8×10³ km² and 1317.2×10³ km². SCE in January reached the second least since 2005.

Spatially, the number of snow cover days (NSCD) in this season exceeded 80 days in the western part of its core area (TPCR, region within black contour denoted in figures), where most NSCD was around 10-20 days higher than normal. In the northern and eastern TPCR where there were large NSCD, with more than 20 days of positive anomalies dominated the region. In contrast, the middle and south part of TPCR where NSCD is less than 10 days, the negative anomalies dominated (Figure 12). In December, the positive anomalies of the NSCD occurred mainly in the mountain areas of the northeastern Third Pole region, exceeding 15 days in most of them. In January, the amplitude of those positive anomalies became smaller than those in December, while the negative anomalies in the east-central part of the TPCR extended to the middle part, compared to that in December. Meanwhile, in the western Third Pole Region, outside of the TPCR, less than normal NSCD newly occurred, which contributed to an overall negative anomaly in January. When it came to February, the areas with positive anomalies further shrunk and some had turned to negative. It is worth noting that the normal to positive anomalies in the western TPCR in December and January had turned to normal by February and a piece of negative anomalies popped up in middle of the southern TPCR. These changes collectively contributed to the larger negative anomaly in February than that in January (Figure 13).

Central Asia Snow Cover Assessment 2024-2025

Joel Fiddes^1,2, Beatrice Marti³, Andrey Yakovlev³, Tobias Siegfried³, ¹WSL Institute for Snow and Avalanche Research SLF; ²Mountain Futures GmbH; ³hydrosolutions GmbH

The winter 2024-25 saw the second operational season of the regional snow tracker Snowmapper a collaboration between the Swiss Agency for Development and Cooperation funded projects “CROMO-ADAPT” and “SAPPHIRE”. This near-real time tracker is forced by ERA5T and IFS 10-day forecast that is downscaled to 500m and then forces a physically based snow model. Results are presented against a 24-year climatology (1999-2023) to assess anomalous conditions. Please refer to Fiddes et al. 2019 for further details on the model chain. Monitoring results from season 2024-2025 are presented below.

Syr Darya: The 2024-2025 season showed anomalously low snow conditions in the Sry Darya basin. After a normal start to the season in autumn and early winter (Sept 2024 - Dec 2024), a dry winter led to reduced snow accumulation through to March 2025. Peak SWE was around 20% less than the long-term norm value. Moreover, an exceptional warm spring led to rapid melt during the spring ablation period. This season the 5th percentile value of the long-term climatology (indicated by grey shading) was passed by the middle of May with a value of 12 mm, this value was reached 1 month in advance of the norm. Impacts on water availability, soil moisture and impacts on the agricultural sector have been widely reported in the region.

Amu Darya Basin: The 2024-2025 season in the Amu Darya basin after a promising early winter was again extremely dry during winter leading to low peak SWE values similar to previous low of season 2023-24. While last season was bolstered by heavy spring precipitation, this season saw extremely high spring temperatures (as in Sry Darya basin) which led to rapid melt of the snowpack. This season the 5th percentile value of the long-term climatology (indicated by grey shading) was passed mid may with a value of 41mm, this value was reached 1month in advance of the norm value, as seen also in the Sry Darya basin.

Snowmapper is available at: https://snowmapper.ch/mcass-dashboard.

The snow season in the Swiss Alps 2024-2025

Christoph Marty, WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland

Snow depth in the Swiss Alps (elevation > 500 m) was evaluated based on modeled 1 km gridded data available since the hydrological year 1962 (1961/1962). These data were provided by MeteoSwiss and SLF. Snow depth in the Swiss Alps in the 2024/2025 season was slightly below until January and then clearly below average during the remaining months (Figure 17). The reason for this evolution was a wide-spread drought during the winter months which caused well below average snow amounts also at elevations above 2000 m a.s.l. Annual snow depth anomalies since 1962 (Figure 18) demonstrate the winter 2024/2025 was about 30 % lower for the October to May period than the current climate (1991-2020).

References

Brasnett, B. 1999. A global analysis of snow depth for numerical weather prediction, Journal of Applied Meteorology 38:726-740.

Brown, R., Derksen, C., and Wang, L. (2010), A multi-data set analysis of variability and change in Arctic spring snow cover extent, 1967–2008, J. Geophys. Res., 115, D16111, doi:10.1029/2010JD013975.

Brown, R. D., and P. W. Mote, 2009: The Response of Northern Hemisphere Snow Cover to a Changing Climate. J. Climate, 22, 2124–2145, https://doi.org/10.1175/2008JCLI2665.1.

Estilow, T. W., A.H. Young, and D.A. Robinson, 2015: A long-term Northern Hemisphere snow cover extent data record for climate studies and monitoring. Earth Syst. Sci. Data, 7, 137–142, doi:10.5194/essd-7-137-2015.

Fiddes, Joel, Kristoffer Aalstad, and Sebastian Westermann. 2019. “Hyper-Resolution Ensemble-Based Snow Reanalysis in Mountain Regions Using Clustering.” Hydrology and Earth System Sciences 23: 4717–36.

Helfrich, S. R., D. McNamara, B. H. Ramsay, T. Baldwin, and T. Kasheta, 2007: Enhancements to, and forthcoming developments to the Interactive Multisensor Snow and Ice Mapping System (IMS), Hydrological Processes 21: 12, 1576-1586. doi:10.1002/hyp.6720.

Luojus, K., Pulliainen, J., Takala, M., Lemmetyinen, J., Moisander, M., Mortimer, C., Derksen, C., Hiltunen, M., Smolander, T., Ikonen, J., Cohen, J., Veijola, K., and Venäläinen, P.: "GlobSnow v3.0 Northern Hemisphere snow water equivalent dataset". Scientific Data 8, 163 (2021). https://doi.org/10.1038/s41597-021-00939-2.