Yes, surprisingly, high humidity can contribute to snowmelt, even in winter. While it might seem counterintuitive, humid, cloudy days can actually warm the snowpack and increase the likelihood of melting.
How Humidity Affects Snowmelt:
While factors like air temperature and sunlight are commonly associated with snowmelt, humidity plays a significant role through several mechanisms:
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Increased Downward Longwave Radiation: High humidity indicates a higher concentration of water vapor in the atmosphere. Water vapor is a good absorber and emitter of longwave radiation (heat). Humid air emits more longwave radiation back towards the earth's surface, including the snowpack. This increased radiation can warm the snow from above.
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Reduced Evaporation: Snow can sublimate (go directly from solid to gas) and evaporate, processes that cool the snowpack as they require energy. High humidity reduces the rate of evaporation and sublimation because the air is already saturated with water vapor. This allows the snowpack to retain more of its energy.
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Cloud Cover Association: High humidity often accompanies cloudy conditions. While clouds block direct sunlight (which would melt the snow), they also trap outgoing longwave radiation from the surface, creating a warming blanket effect. This is particularly effective on humid days.
Winter vs. Spring Melt
It's important to differentiate between winter and spring snowmelt:
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Winter Melt: During winter, the overall energy balance is typically negative (more energy is lost than gained). High humidity's effect might be enough to cause some surface melting, but it usually won't lead to widespread snowpack loss. The more critical impact in winter is preventing snowpack growth. The article referenced highlights that humid, cloudy winter days can prevent the snowpack from growing at its expected rate, setting the stage for faster melting in the spring.
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Spring Melt: As temperatures rise in spring, the energy balance shifts to positive. Humidity then exacerbates melting by further reducing evaporative cooling and increasing incoming radiation.
In Summary:
High humidity, especially when combined with cloud cover, can warm the snowpack, reduce evaporative cooling, and ultimately contribute to snowmelt. While this effect might be minor during winter, it can prevent snowpack growth and become a significant factor in accelerating melting in spring.
