Article from wunderground.com
Brian Donegan
Published: December 28, 2018
Snow was not in the forecast, which isn’t surprising given the mild temperatures and the rarity of wintry precipitation in Las Vegas.
“I would never forecast snow at 50 degrees,” Ashley Wolf, meteorologist at the National Weather Service office in Las Vegas, told the Las Vegas Review-Journal.
The last time a trace of snow was reported at McCarran International Airport was Christmas Day 2015, according to NWS records. The last measurable snow (at least 0.1 inches) there was on Dec. 17, 2008, when 3.6 inches was observed.
What caused this unexpected snowfall in Las Vegas on Thursday?
“We had cold air aloft mixed with very dry air,” NWS-Las Vegas said in a tweet. “This resulted in a wet-bulb temperature in the mid- to upper 30s in parts of the Valley, resulting in frozen precipitation.”
The wet-bulb temperature is the lowest temperature that evaporating water can reach in the air. Evaporation is a cooling process, so the more evaporation that takes place, the colder the air can become. Drier air is able to be cooled faster.
In Thursday’s case, temperatures in the clouds were below freezing, allowing the precipitation to begin as snow. The clouds were situated at a relatively low altitude, so with those wet-bulb temperatures in the mid- to upper 30s, the snow did not have enough time to turn to rain before reaching the ground despite the 50-degree temperatures.
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Featured image: Las Vegas Review Journal
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