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Old 03-13-2014, 09:42 AM
 
Location: Pueblo - Colorado's Second City
12,259 posts, read 24,361,938 times
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Quote:
Originally Posted by phetaroi View Post
Thank you Littlekw.

It's all about orographic precipitation. And yes, all of the Front Range is in the rain shadow.
Especially Pueblo as not only do we sit in the shadow of the mountains west of us we sit in the shadow of the Palmer divide/ Monument Hill.
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Old 03-13-2014, 09:44 AM
 
8,317 posts, read 29,367,714 times
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Quote:
Originally Posted by phetaroi View Post
Thank you Littlekw.

It's all about orographic precipitation. And yes, all of the Front Range is in the rain shadow.
Well, that is not entirely accurate. During winter, that is absolutely true because most storms that affect Colorado come from the Pacific. That air mass, though dried considerably by passing over the Sierra Nevada and/or Cascade Mountains (and the large arid area between there and Colorado) still has sufficient moisture to drop much of it when it is orographically lifted by the Rockies--and that falls mostly on the Western Slope. An exception, especially in late winter and spring, is when a powerful low pressure system skirts along the Colorado/New Mexico border (the famed "Trinidad Low"). That type of system can fetch copious amounts of moisture from the Gulf of Mexico and slam it against the Front Range in those storied "upslope storms." They occur much less frequently than the Pacific winter storms, but can pack a huge punch. Colorado's record snowfall from a single storm occurred west of Boulder--on the Eastern Slope--from one of these storms.

In late spring and summer, the westerly winds from the Pacific die back considerably, while, at the same time, the Bermuda High begins it enlargement and westward expansion. During that period, orographic precipitation favors the Eastern Slope, arriving from the Gulf of Mexico to the southeast of Colorado. That is why May and June are typically the wettest months on the Eastern Slope and, in southwestern Colorado, are the driest months. The Eastern Slope will continue to get some orographic precipitation in July and August (typically, some of the most individually severe thunderstorms occur then), but the focus shifts more to the south and west during those months. That is the famed Southwest Monsoon, caused when the Bermuda High expands far enough westward that its winds fetch moisture from both the Gulf of Mexico and the Gulf of California and slam it into the Southwest, including all of south-central and southwestern Colorado, regularly as far north as I-70, and occasionally as far north as Canada.

The Bermuda High usually retreats eastward by mid to late September, and the Pacific airflow begins to strengthen, once again favoring orographic precipitation on the Western Slope, usually more heavily affecting northwest Colorado more regularly in the early part of winter and the southern areas more in January and February.

In any case, Colorado, being so far removed from the sources of its moisture--the Gulf of Mexico, Gulf of California, and the Pacific--it only takes small variations of airflow and winds at those sources to dramatically affect how much moisture reaches Colorado. That is why Colorado is so subject to wild fluctuations in precipitation from year-to-year--a characteristic of Colorado climate that coping with becomes more and more difficult with increasing population and water demands.
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Old 03-13-2014, 10:00 AM
 
26,116 posts, read 48,720,528 times
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Another factor adding understandable confusion to precipitation calculations is the differing measurements of "rainfall" and "snowfall."

Within the past decade Colorado has had winters where Gunnison got over 500 inches of snowfall, so much so that they ran out of convenient places to stack it all up to keep the streets open. Converting inches of snowfall to inches of rainfall isn't easy or all that exact as the moisture content varies from storm to storm and probably within the same storms.

IIRC prior discussion on here, many ski resort areas typically get 300-500 inches of snow per year (that's why they're ski resorts, eh).

I've never heard of Boulder or any other Front Range area getting clobbered like that with snowfall, though a freak summer storm along the Front Range can inundate an area with deadly amounts of rainfall in a short time (as happened just last summer to the Boulder area).

If people want to split hairs and fuss with each other over all this and go to extremes to prove each other wrong then that's their choice to waste their time doing that. When it gets out of hand I'll do what moderators usually do which is to close the thread and if needed issue infractions. Meanwhile, can't we all just get along?

But to answer the OP's basic question it seems to boil down to a simple answer that weather patterns are insanely varied in and around the mountains of Colorado which causes precipitation patterns to vary greatly due to geography and it is what it is. That's the Cliff's Notes answer the OP was looking for.
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Old 03-13-2014, 11:37 AM
 
Location: Bend, OR
3,296 posts, read 9,652,928 times
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Quote:
Originally Posted by jazzlover View Post
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.
We all misread. I just wasn't sure if I was truly missing something other than the obvious. I am not a weather expert by any stretch of the imagination, so I am glad to have your insight.

Quote:
Originally Posted by Colorado Rambler View Post
^^^

Hmmm... I only clicked on jl's first link, but I got the same numbers as he did from the charts?
My point wasn't to refute what Jazzlover said, but clearly the numbers are not what he wrote. The annual rainfall was correct, but that's only part of the picture. The annual snowfall is the big difference (and makes sense IMO). In the first link that was given, Boulder's annual precip is 18.3" and annual snowfall is 73.2". Boulder, Colorado Travel Weather Averages (Weatherbase) Whereas Aspen's annual precip is 17.3" (so less rain than Boulder) but the annual snowfall is 134.2". Aspen, Colorado Travel Weather Averages (Weatherbase)
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Old 03-13-2014, 11:52 AM
 
Location: CO/UT/AZ/NM Catch me if you can!
6,926 posts, read 6,888,435 times
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Quote:
Originally Posted by delta07 View Post

My point wasn't to refute what Jazzlover said, but clearly the numbers are not what he wrote. The annual rainfall was correct, but that's only part of the picture. The annual snowfall is the big difference (and makes sense IMO). In the first link that was given, Boulder's annual precip is 18.3" and annual snowfall is 73.2". Boulder, Colorado Travel Weather Averages (Weatherbase) Whereas Aspen's annual precip is 17.3" (so less rain than Boulder) but the annual snowfall is 134.2". Aspen, Colorado Travel Weather Averages (Weatherbase)
Yeah, I was tired last night and only glanced at the rainfall amounts - didn't take the snowfall into consideration at all. As others have noted, the question of local climate is not so simple as it might seem to a novice observer. I also think Aspen is greener due to the influx of wealthy tourists with dollar bills falling out of their pockets.
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Old 03-13-2014, 11:58 AM
 
Location: Bend, OR
3,296 posts, read 9,652,928 times
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Quote:
Originally Posted by Colorado Rambler View Post
Yeah, I was tired last night and only glanced at the rainfall amounts - didn't take the snowfall into consideration at all. As others have noted, the question of local climate is not so simple as it might seem to a novice observer. I also think Aspen is greener due to the influx of wealthy tourists with dollar bills falling out of their pockets.
Bwaahhh!!! Could be.

Yes, I definitely think Colorado weather and precipitation patterns are not easily explained or summed up by a one size fits all answer. My own years spent in Colorado, especially when I working in the field daily during my Forest Service years, will tell you that the monsoons and whether they actually produce precip in a given year (or arrive at all), can drastically change this picture.
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Old 03-13-2014, 02:31 PM
 
8,317 posts, read 29,367,714 times
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The greatest misconception about Colorado climate is that it is "wet." About the wettest location in the state is Wolf Creek Pass in far southern Colorado, where a combination of high elevation, along with a favorable location to intercept both Pacific moisture in winter and Southwest Monsoon precipitation in mid to late summer gives it an annual average precipitation of 42.5". That is nearly double what many locales in Colorado receive--even many mountain locations, and nearly SIX TIMES as much as Manassa in the San Luis Valley only about 60 or so air miles from Wolf Creek gets.

Now, consider that most places in the United States east of the 100th Meridian typically get over 30" of annual precipitation and Colorado's overall aridity comes into focus.

Mike is also absolutely right about water content in snow. A "typical" benchmark is 1" of liquid precipitation in 10" of snow, but many a Colorado snow event may only have half that water content in an inch of snow. Snow on the ground does not always translate into equivalent water for soil, runoff, and plants, either. In a warm, windy winter like a fair part of southern Colorado is having this winter, a lot of snow may just "sublimate"--evaporating directly into the air without going through the liquid stage, without inuring any benefit by melting into the ground.
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Old 03-13-2014, 08:37 PM
 
Location: Pikes Peak Region
481 posts, read 1,293,186 times
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By the way, Jazzlover, you brought up some points on meteorology and micro-climates in the state that I never heard of. I appreciate that, I have new things to research now. I like this thread, I'm learning quite a bit more about my home. Thanks!
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Old 03-13-2014, 10:11 PM
 
Location: Littleton, CO
3,158 posts, read 6,087,874 times
Reputation: 5619
Quote:
Originally Posted by delta07 View Post
My point wasn't to refute what Jazzlover said, but clearly the numbers are not what he wrote. The annual rainfall was correct, but that's only part of the picture. The annual snowfall is the big difference (and makes sense IMO). In the first link that was given, Boulder's annual precip is 18.3" and annual snowfall is 73.2". Boulder, Colorado Travel Weather Averages (Weatherbase) Whereas Aspen's annual precip is 17.3" (so less rain than Boulder) but the annual snowfall is 134.2". Aspen, Colorado Travel Weather Averages (Weatherbase)
Quote:
Originally Posted by Colorado Rambler View Post
Yeah, I was tired last night and only glanced at the rainfall amounts - didn't take the snowfall into consideration at all. As others have noted, the question of local climate is not so simple as it might seem to a novice observer. I also think Aspen is greener due to the influx of wealthy tourists with dollar bills falling out of their pockets.
I feel the need to point something out here:

These cities don't get 17 - 18 inches of rain plus 73/134 inches of snow; the 17-18" of precipitation is all the water they get over the average year. The water content of the snow is included in the 17-18" figure.

That said, one reason not stated here is the fact that Aspen's precipitation is more evenly spread out than Boulder's is. Aspen's monthly precipitation averages between 1" and 1.8". About half of that total is in the form of snow which starts about October and continues through March. As the snow melts, it soaks into the ground starting in April and continues through June allowing the grasses and flowers in the meadows to sprout and grow. The second half of the precipitation is in the form of rain from May through September. Combine this with the much lower temperatures in Aspen (Aspen averages less than one day above 90 degrees each year), and you realize that Aspen does not have the same evaporation that Boulder has.

Boulder's precipitation is much different. Boulder's monthly averages are between 0.5" and 3.1" -- much more hit and miss. It experiences much less snow than Aspen does and what snow does fall is quickly melted. In April and May, Boulder gets the greatest amount of its precipitation, so things start out green, but the summer months combine for only 5" of precipitation. Combine little rain with 44 days (avg) above 90 degrees and you get a brown landscape.
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Old 03-13-2014, 10:30 PM
 
66 posts, read 102,420 times
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just to clarify...jazz said that he has seen aspen dry and boulder green some years. Generally speaking, is my observation here accurate 19/20 years? That is Aspen being significantly greener than brownish Boulder?
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