‘Warm Snow’ Falling in Colorado

A new study claims that it snows in Colorado at temperatures so warm the precipitation would fall as rain elsewhere.

The research published by a team from the Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado actually finds that Colorado gets snowfall at some of the warmest temperature on the planet, with snow falling even when temperatures are approaching 4 degrees Celcius.

Keith Jennings, a graduate researcher and lead author of the study, said his team was surprised to find that freezing point at zero degrees Celsius or 32 Fahrenheit was not the key factor in whether precipitation fell as rain or snow, but more where the precipitation was falling.

For snow to form naturally in a cloud the temperature must indeed be at freezing point or lower, but whether a snowflake makes it from cloud to grown as snow or rain depends a lot on the humidity levels in the air below.

The researchers studied nearly 18 million precipitation, temperature, and humidity observations from more than 100 countries on four continents in the Northern Hemisphere.

They found that Colorado’s low humidity meant that snow flakes stayed as snow flakes as they descended even when it was up to 4 degrees Celcius above freezing. The ‘dry snow’ is also Colorado’ signature light powder.

The process is called ‘evaporative cooling’ and is already well understood by Colorado’s snowmakers who are able to create snow with snowmakers in early to mid-Autumn even when the air temperature is above freezing.

The process can work in reverse in other areas of the planet where the air has high humidity.  Here, even if the temperature is below zero, the snow flakes can melt in the high levels of moisture.

The researchers hope that their study will be used in weather and climate forecasting, much of which currently assumes that freezing point is the key factor in snow forming in Colorado.

(Pictured top, Loveland ski area on 3 October, 2017)