When the Mountains Stop Warming the Plains: Anomalous Winter and Spring Cooling in Southeastern Alberta Linked to Reduced Chinook Activity

Abstract

ABSTRACT Winter and spring surface air temperatures across North America show near-ubiquitous warming over the past 75+  years in both station observations and reanalysis datasets. Embedded within this broad pattern, however, is a region of ∼220,000 km² in southeastern Alberta that exhibits persistent spring and, to a lesser extent, winter cooling and/or lack of warming, representing one of the few multi-decadal cold anomalies in continental North America. We integrate multiple lines of evidence, including ERA5 and ERA5-Land reanalyses, Environment and Climate Change Canada station observations, and a physically based chinook (föhn) detection algorithm applied to hourly ERA5-Land surface air temperature fields, to examine whether long-term changes in chinook frequency and warmth signal are associated with this anomaly. Cooling anomaly characterization, station–reanalysis comparisons, snow water equivalent trend analyses, and upper-air diagnostics collectively reveal a consistent multi-decadal signal. While long-term warming is evident over 1950–2025, the period 1980–2025 shows spring cooling of up to −0.29°C decade−¹ and a weaker winter signal (−0.09°C decade−¹) across southeastern Alberta. ERA5-Land chinook statistics indicate a statistically significant decline in winter chinook frequency (−1.13% chinook hours decade−¹) alongside a modest reduction in chinook warming (−0.017°C decade−¹). Upper-air diagnostics reveal weakened westerlies, enhanced meridional flow, and increased winter blocking since 1950, consistent with evolving large-scale circulation patterns linked to Arctic warming. Taken together, the results point to a role for chinook dynamics in the observed regional cooling, acting in concert with evolving snowpack conditions and broader circulation shifts. Reductions in meridional temperature gradients (baroclinicity) associated with Arctic amplification may contribute to weakened zonal flow, modulating cold-season chinook frequency. These findings highlight the role of mesoscale chinook (föhn) processes in shaping regional climate expression and underscore the importance of incorporating evolving wind regimes into regional climate variability and attribution analyses.