Why It Dumps

What does Coolio’s line “Gotta gotta get up to get down” have to do with 2-3 inch-per-hour snowfall rates during the latest western storm?
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What does Coolio’s line “Gotta gotta get up to get down” have to do with 2-3 inch-per-hour snowfall rates during the latest western storm? Everything, actually. But first, let’s set the stage.

A major snowstorm rolled across most of the western US mountains on Sunday and Monday, leaving FEET of snow (24” in Jackson Hole, 13”+ in Aspen, and multiple more feet in Oregon and Washington). The storm was large and had tons of moisture, so the flakes were flying for many days which helped to up the totals.

The leading edge of the storm produced some of the highest snowfall rates, which closed roads and brought a twinkle to the eyes of most skiers as they eyed nearby hills that turned from brown to white in a matter of minutes. This heavy rate of snow – known to most as “dumping” or “nuking” when it’s 2-3”/hr - is the subject of today’s CSI-type investigation. Let’s focus on Colorado during the morning of Monday, October 25th where 5-7” fell in some spots in just three hours.

When I give talks about the science behind snow, I explain it all with one line: “Snow happens when moist air gets high.” Nope, this is not a political statement; it’s actually meteorology 101.

When air rises, it cools and the moisture in the air condenses into either rain drops or snow flakes. Luckily, there are many ways for air to rise and thus to produce snow.

  • Jet Stream: This fast-moving “river of air” at about 30,000ft helps to “lift” the air below it (through a bunch of messy math and physics…just take my word for it).

    Cold Front: As heavy and dense cold air pushes along the ground, it forces lighter and warmer air ahead of it to rise.
  • Mountains: When air hits a mountain, it is forced to rise to get over the obstacle.

Monday morning’s snowfall took advantage of all three of these methods to make moist air get high, but the cold front really provided the extra “oomph”. The radar image below from 6:30am actually shows the cold front moving from northwest-to-southeast across Colorado (click here for the radar movie):

So like Coolio prophesized, the moist air does ‘gotta gotta get up’ so that it can ‘get down’ as snow flakes and provide us smiles all winter long. In fact, I can’t wait any longer…it’s time to go skiing and take advantage of the pre-Halloween blizzard, which is hopefully just one of many more to come.

Meteorologist Joel Gratz is the creator of http://www.ColoradoPowderForecast.com and is based in Boulder, CO.

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