Study: Denver’s flurries fall above freezing temps
The Denver Post
A true Coloradan knows a warm, sunny day followed by fat snowflakes just comes with the territory, but it turns out there’s more to the state’s weather anomalies than good socialmedia griping material.
Factors like a region’s elevation and proximity to coastlines help explain why flakes collect on car windshields as the dashboard below proclaims a toasty 40 degrees — above the commonly known 32 degree threshold that separates rain and snow.
A recently published University of Colorado Boulder study found coastal areas have a cooler threshold for rain while mountainous terrain is likelier to get powder with temperatures above freezing.
“In Denver, Colorado, it might be 40 degrees and snowing,” said Noah Molotch, director of the Center for Water, Earth Science and Technology at CU and co-author of the study. “But in Charleston, South Carolina, it could be 28 degrees and raining. This study shows these fine-grain differences on a hemispherelevel scale for the first time.”
Knowing that variables like elevation, relative humidity and surface play an important role in rain or snow prediction could change the future of climate and land surface modeling globally.
This discovery could be particularly valuable in the United States, which has the most rain-snow variability of any country included in the study. The study compiled nearly 18 million precipitation observations spanning more than 100 countries and four continents.
The last few snowstorms in the Denver area, Monday into Tuesday, and March 18 into March 19, also including one that passed through late Wednesday afternoon, have had flakes flying down at 36 degrees, said Natalie Sullivan, a meteorologist with the National Weather Service in Boulder.
A snowflake forms high up in a cloud where temperatures are well below freezing, said weather service meteorologist Kyle Fredin.
Whether the flake stays fluffy or liquefies into rain is simply a race against time, making higher elevations more likely to bust out the snow boots than their lower-terrain counterparts.
Snow also can drag cool air down with it, keeping it intact as it falls.
“It’s almost like standing by traffic,” Fredin said. “You would feel the air of those cars go by you, and there would be a net flow with those cars. There’s a volume of air recycling.”
Spring snow such as the storms Colorado has experienced as of late are considered to be most unpredictable since, often, winter temperatures fall below the standard freezing mark to begin with.
“When it comes to March and April, that’s when we have to worry about precipitation type,” Fredin said. “Is it going to be just a few degrees too warm or too cold to predict?”
While a correct precipitation prediction could make life more convenient for those wondering whether to pack an umbrella or earmuffs, the repercussions go beyond commute and outfit preparation.
Precipitation forecasts impact water management, “especially in droughtstricken areas of the American West,” according to the CU study. Snowfall provides water storage for an estimated one billion worldwide while the same amount of rain-on-snow events could raise the risk of flooding.
“With less snowfall, snow water equivalent decreases, snowmelt occurs earlier, and streamflow reduces,” read an explanation of the CU study. “Further, experts predict more rainfall relative to snowfall and more rain-on-snow events in the future, which increase flood risks. Thus, it is with increasing importance that meteorologists improve forecasting for rain versus snow events.”