Despite slow start, climate experts predict strong monsoon season in Colorado
July 20, 2018
Anglers, firefighters, residents and tourists alike have been looking to the Summit skies for the past few weeks, hoping to see signs of the predicted wetter-than-average North American monsoon season. While the rains have not kicked off quite yet, climate experts are still predicting a wet few months that will hopefully put a dent into the statewide drought.
For some areas of the Southwest without snowpack, half the annual rainfall comes from these few monsoon months. To understand why these months are predicted to be so wet, it's helpful to understand how monsoon season works.
The North American monsoon is much weaker than its Asian counterpart. Yet, it works the same way.
From July through September, intense solar heat raises surface temperatures across the Southwest. Hot air rises due to low density and leaves behind areas of low pressure called thermal lows. Winds usually push air from high-pressure systems to low-pressure systems, and this is how moist air from the Gulf of Mexico is pulled into the low-pressure area in and around the Mojave desert.
When that moist air hits the western slopes of the Rockies, it tries to travel up and over the mountains. However, once it hits a certain altitude, the moist air cools and condenses, forming rainclouds and thunderstorms that drop water on the High Country nearly every day during late summer.
Peter Goble, a climatologist for CSU's Colorado Climate Center, said that mountain valley areas like Summit County are especially prone to monsoon rains because of the way mountain peaks essentially act as thunderstorm attractors.
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"At high elevations, mountain peaks warm up faster than the air around it," Goble explained. "That makes them favorable for thunderstorm development. Without those mountain peaks, monsoon season would not be as significant in the mountain valleys."
Goble added that while those rains are welcome across Colorado after a dry winter, people should be aware of some significant dangers.
"This time of year, it's a good idea to be aware of flash flooding," Goble said. "Those thunderstorms rolling off the mountain peaks tend to be quite intense and drop a lot of water in a short amount of time."
Flash floods are a common concern in the High Country during the rainy season as thin, dry mountain soil is often unable to absorb all the water from sudden downpours. The water washes across the surface and collects into gullies and streams within hours, or even minutes, and before you know it there is a wall of water rushing through areas that were bone dry minutes before.
There's an extra danger for people hiking or climbing near mountain peaks: Aside from the additional risk of being struck by lightning, torrential rainfall and flooding can strand people traveling near the top.
"This time of year, it's very important for hikers to be aware of the weather, especially if they're going above the tree line," Goble said. "Hikers should have a plan to go up in the morning and get back down by late morning or early afternoon."
Goble said that the NOAA's Climate Prediction Center is still forecasting a strong monsoon season from late July into October, inviting a welcome calm after a very angry wildfire season.
"With the forecast on track to be wetter than average, I hope people remain a little more optimistic in face of fire danger," Goble said. "It might not make up all these deficits until at least the next snowpack season, but the worst of our fire danger is behind us."