A new study published in Nature highlights how atmospheric rivers (ARs), powerful streams of water vapor in the atmosphere, could disrupt dreams of a white Christmas for many this year by bringing unseasonably warm temperatures to mid-latitude regions. These atmospheric phenomena, previously known for their role in transporting moisture, are now shown to have a significant impact on global near-surface air temperatures, creating heat anomalies that make traditional winter weather less predictable.
Atmospheric rivers act as highways of moisture, carrying water from the subtropics to regions further north. They are critical for precipitation and water resources in many parts of the world. However, the study by Serena R. Scholz and Juan M. Lora reveals that ARs also transport heat, which can result in temperature anomalies of 5–10°C above average during their occurrence. This heat transfer is caused by an increase in both sensible heat flux (heat moving through the air) and downwelling long-wave radiation (heat radiated back to the surface from the atmosphere), driven by the moisture-laden air these rivers carry.
The implications are stark: in seasons with more frequent AR events, mid-latitude regions often experience warmer-than-average winters. On an hourly scale, the study found that over 70% of extreme warm-temperature anomalies occur during AR events in large parts of these regions. This means that the same weather systems responsible for replenishing water supplies may also bring about unexpected heat spikes, which can disrupt traditional winter patterns, including the likelihood of snowfall.
For those hoping for snow this holiday season, ARs could mean rain instead, as these warm and moist weather systems reduce the chances of freezing conditions. The heat anomalies tied to ARs also contribute to compound heatwaves—events where moisture and heat combine to create unusually warm weather, even during times typically associated with colder conditions.
The study underscores the broader role of ARs in global energy transport, highlighting how these phenomena influence air temperatures across a range of timescales. Scientists believe that including AR data in weather models could enhance the ability to predict certain extreme heat events. This could prove crucial as the planet continues to grapple with climate change, which amplifies the intensity and frequency of such phenomena.
As the holiday season approaches, meteorologists are keeping a close eye on atmospheric rivers and their potential to derail traditional winter weather. While snow lovers may need to adjust their expectations, the findings also serve as a reminder of how interconnected atmospheric processes are and the importance of understanding their influence on global weather patterns.