Increasing variability in seasonal snow poses growing uncertainty about the length of ski seasons, impacting New Zealand’s small club ski fields that have a long and valued history of recreational activity. Integrating observational data sourced from historical ski patrol records collected at the Craigieburn Valley (CV) ski area, regional and globally gridded climate data, and synoptic weather types enables this study to disentangle the atmospheric controls on inter-annual snow variability from changes in longer-term trends in climate that impact seasonal snow in the Craigieburn Range.

Despite a significant increase in the mean annual air temperature of New Zealand from 1991 to 2019, there is no evidence of a significant warming trend in the Virtual Climate Station Network (VCSN) data at a ridgetop elevation (1520 m a.s.l.) on the Craigieburn Range. The mean annual temperature at this elevation is 4.7 °C, while precipitation averages 1544 mm, with 78% estimated to fall as rain and 22% as snow. During the ski season (July to September), 55% of precipitation is estimated to fall as rain, and 45% as snow, with the proportion of snowfall varying between 22% and 83%. Air temperatures during the majority of precipitation events range between 1 and 5 °C annually and -1 to 1 °C during the ski season, underscoring the sensitivity of snow versus rain-bearing storms in winter to small changes in air temperature.

Ski patrol observations at the base of the CV ski area (1265 m) show that the winter snowline persists at this elevation in the current climate, with the mean snow depth equal to 39 cm over the 29-year study period. However, the observations reveal a small but statistically significant decrease in the mean snow depth by 1.3 cm per year, which if projected linearly, indicates that the snowline will reside above the ski field base by 2045. Conversely, there is no significant trend in the total amount of seasonal snowfall over the study period. Between 1991 and 2019, half of the total snowfall is accounted for by large and extreme snowfall events (>15 cm) during one-fifth of days where it snowed. Seasons that experience more of these events tend to have higher seasonal snowfall and mean snow depth. A synoptic weather typing approach commonly used in New Zealand, known as Kidson types, shows that the snow-bearing Kidson types are T and TSW, while H is the most frequent Kidson type over all seasons. Analysis of the three established regimes (trough, zonal, and blocking) shows a slight increase in the blocking regime over the study period and a statistically significant increase in the Kidson type HE, which favours higher air temperatures that are not conducive to snowfall. If this persists in the future it will likely enhance the loss of seasonal snow in the high elevation areas of the Craigieburn Range.