Foothills Winter Weather Patterns
Warm before the storm. That was Saturday’s weather. 50°F by 9:30 am and mild all day. It was a good day to get outside for a while and we went for a short hike. But, as predicted, the clouds moved in with a cold front and it was snowing by 9 pm dropping just an inch of snow on my deck, with temps dipping into the teens overnight. Sunday warmed again but will move to more snow arriving early Tuesday. Sunday evening’s high wind event heralded the incoming weather. Not a big storm week, but definitely winter returns along with temperatures dropping into the teens and even to 0° and lower as the system moves back out pulling the warm air away with it.
If you grew up in Colorado or have been here many decades, these patterns are well known to you and that’s just how the weather works. If you are new to the area, enticed by either milder winters (Colorado winters are amazing compared to Minnesota where I grew up), or are intrigued by the idea of simply having some snow, understanding how the mountains affect the weather patterns can help to make sense of the wild swings in Foothills weather. Consider this a simple ‘skipping stone’ across some main weather concepts.
Let’s start with some topography. Taking our place at the south end of the Rocky Mountains, which extend from Northern Canada to New Mexico, 59 of our mountain peaks are 14ers and another 830 peaks are 11K feet and higher. This longitudinal wall catches jet stream winds moving from west to east, causing them to roll back and drop the Pacific moisture on the western side of the higher peaks. Yay, skiing! On the eastern side of this wall, the foothills, less wind and moisture make it through and create a ‘shadow’ area where less moisture and warmer temperatures remain a consistent pattern. If you’ve heard the phrase that we are ‘in the shadow of Mount Evans’, this is what that means. Many of our snowfall amounts are under six inches and there is notable melting between storms.
The Pacific moisture is a common pattern - until it’s not.
Colorado can have a range of wind temps, cold and warm fronts from the west certainly, but also storm activity in Gulf of Mexico can push moisture into the state up from the south and east. As this sometimes powerful air flow from the Gulf moves in, the moisture then hits the mountains from the East causing it to roll back as an upslope event which can dump massive amounts of snow on the Foothills and Front Range. Recent memory storms include 2003 when Conifer received over 6 FEET of snow (higher in some areas) and Rollinsville (Southwest of Boulder) saw 87 inches. In 2021, a storm system brought an initial dump of 27 inches to our driveway in Bailey, and then an additional 8-10 inches every few days for weeks after that. I stopped counting after about 110 inches from March 14th on. So, while our big snowblower doesn’t get used often, when we need it, we need it!
Then, the Pacific moisture pattern returned and it all melted.
Of course, there’s far more to it all than this. Wind flows over and around the peaks creating complex waves of wind and moisture events that keep things interesting about living here. Some valley temperatures can bottom out with sinking cold air masses making for some of the coldest places in the country. Open areas within the high country such as South Park can receive hurricane-force winds and bitter temps as cold fronts push through. Downslope winds such as the warm Chinook or cold Bora create wind events that can bring down trees and power lines.
Thankfully, we have great technology in place now that can provide warning and perspective on our upcoming weather events. Watching wind maps like on windy.com can be mesmerizing and give a better understanding of how air flow over and around our peaks will affect the weather at our doorstep. What’s your favorite weather resource?
Sources:
- https://climate.colostate.edu/climate_long.html
- https://www.accuweather.com/en/weather-news/what-are-chinook-winds/339761
- https://waterknowledge.colostate.edu/climate/
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