Rain can significantly accelerate snow melt, adding approximately 1.25 inches of melt to what would occur naturally on a 50-degree day that would otherwise melt 2-4 inches.
Here's a breakdown of how rain influences snow melt:
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Additional Melting Power: Rainwater, especially if warmer than the snowpack, transfers heat to the snow, causing it to melt more quickly than air temperature alone. The cited reference indicates an extra 1.25 inches of melt with rain on a day where air temperature alone would melt 2-4 inches.
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Temperature Dependence: The impact of rain on snowmelt is most pronounced when air temperatures are cooler. As air temperatures rise, the contribution of rain to snowmelt becomes relatively less significant because the warmer air itself contributes more to melting.
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Factors Affecting Melt Rate: Several variables impact how quickly rain melts snow, including:
- Air Temperature: Higher air temperatures accelerate both rain-induced and natural snowmelt.
- Rainfall Intensity: Heavier rainfall delivers more heat to the snowpack, increasing the melt rate.
- Snowpack Temperature: A snowpack already near its melting point (32°F or 0°C) will melt faster with rain than a colder snowpack.
- Snow Density: Denser snow contains more mass and therefore requires more energy (heat) to melt.
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Example Scenario: On a dry day with a temperature of 50°F (10°C), approximately 2-4 inches of snow might melt. If an inch of rain falls on the same day, the total snowmelt could increase by an additional 1.25 inches.
In summary, rain enhances snowmelt by transferring heat, with the effect being more pronounced at lower air temperatures. The actual melt rate depends on several interacting factors.
