Why is aspen/carbondale so much more green/lush than Boulder? (Steamboat Springs: coop, school)

[allyvip]

Can anyone give me the cliff notes biology/geology on why Boulder is so brown and aspen area is so green?

[Josseppie]

Aspen is in the mountains so they get more rain and snow.

[jazzlover]

Very different precipitation patterns. Boulder is Eastern Slope--while it gets a fair amount of snow in winter, it also gets strong Chinook winds that actually can evaporate a lot of the winter moisture before it can soak into the ground. Aspen and Carbondale are Western Slope--the snow they get in winter tends to stay around and soak in. Boulder can be lush green in early summer because May and June are two of the wettest months of the year in a normal year. Boulder tends to dry out in late July and August. Aspen and Carbondale usually have enough ground moisture carry over from winter to keep them greenish during the somewhat dry months of June and early July. By mid-July through August, both Aspen and Carbondale are far enough south to be influenced by moisture from the Southwest Monsoon. Areas farther south in south-central and southwestern Colorado are even more influenced by the Southwest Monsoon pattern--typically being very dry from mid-May until mid-July, then getting most of their warm season moisture in the following six weeks from mid-July to the end of August.

Wildfire danger follows the same pattern--northern areas and much of the Eastern Slope of Colorado can tend to have more wildfire problems in a normal year in the latter half of summer, the southern and western areas more in early summer. The last few years have been relatively abnormal in most areas of Colorado, both in winter and summer precipitation patterns, however. And, yes, in my many decades of following Colorado climate and weather, I've seen years when Boulder was as green as Ireland and Aspen brown as hell in summer. People unfamiliar with Colorado climate just don't understand that it is highly variable from year to year, and can be abnormally dry in one area and abnormally wet in another area of the state at the same time. This winter is a great example--northern Colorado has been above normal in snowfall in many areas, while much of southern Colorado has been below normal and still mired in long-term drought.

Josseppie is absolutely incorrect above: Aspen gets 17.3" of precipitation in an average year, Boulder gets 18.3". Glenwood Springs (the closest cooperative weather station to Carbondale) gets even less--16.4". Boulder also gets more snow than either Glenwood or Aspen--73.2" in an average winter. That data can be easily accessed at www.weatherbase.com or http://www.wrcc.dri.edu/coopmap/ .

[Josseppie]

I am correct. You have to look at the mountains around aspen as they make the city look green and they get more rain and snow.

[delta07]

Originally Posted by jazzlover

Very different precipitation patterns. Boulder is Eastern Slope--while it gets a fair amount of snow in winter, it also gets strong Chinook winds that actually can evaporate a lot of the winter moisture before it can soak into the ground. Aspen and Carbondale are Western Slope--the snow they get in winter tends to stay around and soak in. Boulder can be lush green in early summer because May and June are two of the wettest months of the year in a normal year. Boulder tends to dry out in late July and August. Aspen and Carbondale usually have enough ground moisture carry over from winter to keep them greenish during the somewhat dry months of June and early July. By mid-July through August, both Aspen and Carbondale are far enough south to be influenced by moisture from the Southwest Monsoon. Areas farther south in south-central and southwestern Colorado are even more influenced by the Southwest Monsoon pattern--typically being very dry from mid-May until mid-July, then getting most of their warm season moisture in the following six weeks from mid-July to the end of August.

Wildfire danger follows the same pattern--northern areas and much of the Eastern Slope of Colorado can tend to have more wildfire problems in a normal year in the latter half of summer, the southern and western areas more in early summer. The last few years have been relatively abnormal in most areas of Colorado, both in winter and summer precipitation patterns, however. And, yes, in my many decades of following Colorado climate and weather, I've seen years when Boulder was as green as Ireland and Aspen brown as hell in summer. People unfamiliar with Colorado climate just don't understand that it is highly variable from year to year, and can be abnormally dry in one area and abnormally wet in another area of the state at the same time. This winter is a great example--northern Colorado has been above normal in snowfall in many areas, while much of southern Colorado has been below normal and still mired in long-term drought.

Josseppie is absolutely incorrect above: Aspen gets 17.3" of precipitation in an average year, Boulder gets 18.3". Glenwood Springs (the closest cooperative weather station to Carbondale) gets even less--16.4". Boulder also gets more snow than either Glenwood or Aspen--73.2" in an average winter. That data can be easily accessed at Travel Weather Averages (Weatherbase) or US COOP Station Map .

Great summary of the climate patterns. However, your point regarding Josseppie isn't correct in using your own references. I checked both Aspen & Boulder, because I was very surprised. Aspen, does in fact get more rainfall and snowfall than Boulder. What am I missing?

[jazzlover]

Originally Posted by delta07

Great summary of the climate patterns. However, your point regarding Josseppie isn't correct in using your own references. I checked both Aspen & Boulder, because I was very surprised. Aspen, does in fact get more rainfall and snowfall than Boulder. What am I missing?

Well, I will humbly eat my crow. Aspen does get more snowfall than Boulder--I misread some averages in the data. However, Aspen still does not get as much total precipitation as Boulder according to Weatherbase. However, Aspen gets more if one looks at the WRCC data. Weatherbase uses 30 years of data, while WRCC uses longer data streams, but some out of date. The Aspen station WRCC uses ceased reporting in 1979. Weatherbase does not enumerate what 30 year average it uses.

Typical of many areas of Colorado, valley locations in western Colorado often get less warm season precipitation than locales on the Front Range, and must rely on melting winter snowpack to keep things green through the summer. Since temperatures (and thus evaporation) are lower in the higher western valleys (like Aspen), they may stay greener in summer even though they get less warm season precipitation. Another factor is that they valley floors in western Colorado are generally irrigated--either naturally sub-irrigated, or man-irrigated in summer. That doe not happen in many foothills locations on the Front Range. The plants there have to survive on natural soil moisture and rainfall.

Yet another factor, especially comparing the northern areas of western Colorado and the central and southern areas of western Colorado is the predominant forestation. In the northern areas, lodgepole forests (that are dying from the pine beetle) don't look as "wet" or green as the aspen/mixed conifer forests commonly found at the same elevation regime farther south.

The OP wanted a "Cliff notes" answer and there really isn't one. A lot of factors and variations come into play--even more so in the last few years as the Colorado climate has been much more variable than in a number of the prior years.

[Colorado Rambler]

^^^

Hmmm... I only clicked on jl's first link, but I got the same numbers as he did from the charts? One thing I noticed was the difference in over-all average temperature for July in Boulder vs Aspen. Aspen's average July temp is a cool 63.5 F while Boulder's is a somewhat balmier 72 F. Seems to me that the higher July temp in Boulder would also result in higher rates of evaporation and plant transpiration than in Aspen since cooler air generally carries less water vapor than warm. My guess is that one reason may be that the soils in Boulder lose moisture more quickly than those in Aspen, leaving Aspen to remain green while Boulder turns brown.

And that's my story and I'm sticking it to it!

[bluescreen73]

To gloss over what's been said even more, it's all about location, location, location. Go to New Castle 40 miles NW of Aspen as the crow flies and you're in desert.

Same kind of scenario with Craig and Steamboat Springs. 40 miles and a climate zone apart from each other.

[Littlekw]

Rain Shadow - Windows to the Universe

Rain shadow effect. The Continental Divide acts as a barrier so the west side tends to get more precipitation than the east side. Same with the Sierra Nevadas and Cascades. At least that what they taught us in school.

[phetaroi]

Originally Posted by Littlekw

Rain Shadow - Windows to the Universe

Rain shadow effect. The Continental Divide acts as a barrier so the west side tends to get more precipitation than the east side. Same with the Sierra Nevadas and Cascades. At least that what they taught us in school.

Thank you Littlekw.

It's all about orographic precipitation. And yes, all of the Front Range is in the rain shadow.