How much cooler than in the valley?

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njlinderer
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How much cooler than in the valley?

Postby njlinderer » Sun May 31, 2009 8:38 am

Question:
Lets say it is 36 degrees in Breckenridge overnight. Do you think that is cool enough to freeze a few thousand feet up in the mountains (Cristo Couloir is what I'm hoping will freeze this weekend)? Specifically, is there a rule of thumb regarding subtracting degrees as you gain altitude? Thanks!
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Re: How much cooler than in the valley?

Postby highpilgrim » Sun May 31, 2009 8:49 am

general rule is about 3 degrees per K. But weather and air movement patterns affect the temps beyond the norm. And I should have said geography; see Scott's post) Remember the Cristo is east facing and will get very early sunhit...

Breck is about 9600 feet, base of the Cristo about 11500?, about 2k difference or 6 degrees = right at freezing. Sounds close to me. There are a bunch of people living in around Breck on this site. Bill is one. Ask them what they think about the whether the Cristo is in or not...
Last edited by highpilgrim on Sun May 31, 2009 10:12 am, edited 2 times in total.
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Re: How much cooler than in the valley?

Postby Scott P » Sun May 31, 2009 9:38 am

Specifically, is there a rule of thumb regarding subtracting degrees as you gain altitude?


In Colorado and on a slope or ridge and in summer, daytime temperatures drop 5 degrees per thousand feet.

Valley floors and night temperatures are different and harder to predict. High basins will get usually colder at night than the higher mountain tops.

For example, according to historical data, in summer Breckenridge itself is actually slightly colder at night than Fremont Pass which is at 11,360 feet and near Quandary Peak, so it might not be any colder in the couloir than in Breckenridge.

Also keep in mind that consolidated snow can get hard even if the temperature doesn't quite drop to freezing. Also keep in mind that official temperatures are taken several feet off the ground and with snowcover, it can still freeze at ground level even if the official air temperature is 36.

Anyway, at this time of year and with an early start and early return, most of the time you should be OK with the snow. Just try and be done before the air really starts heating up (9-10 am depending on sunhit, exposure, day, etc.).
Last edited by Scott P on Sun May 31, 2009 9:57 am, edited 1 time in total.
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Re: How much cooler than in the valley?

Postby Prairie Native » Sun May 31, 2009 9:54 am

Something I noticed last year: It was a hot day previous to the morning we climbed, everything was 3-4 feet of slush it only dropped down into the mid to upper 30s and everything froze VERY solid somehow. I was pretty blown away.
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Re: How much cooler than in the valley?

Postby highpilgrim » Sun May 31, 2009 10:17 am

[quote="Scott P"

In Colorado and on a slope or ridge and in summer, daytime temperatures drop 5 degrees per thousand feet.

Thanks for clarifying this Scott. I had always held that 3 degrees per 1000 feet was the number, and didn't even consider that might be degrees celsius. 3 degrees C = 5.4 degrees F. Your number is right if you're talking F, which is what I was doing.
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Re: How much cooler than in the valley?

Postby Scott P » Sun May 31, 2009 10:37 am

I had always held that 3 degrees per 1000 feet was the number


Actually 3 degrees F (actually between 3-3.5) per 1000 feet is the correct number for the decrease in average annual temperature of a location (and usually only works really well on a slope). It’s also not consistent throughout the year. As mentioned, in summer it is closer to 5 degrees in the daytime, but in winter on average it is closer to 2 degrees per thousand feet. Summer and winter are completely different. Even the 5 summer and 2 winter doesn’t work when comparing slopes or ridges to valley floors, especially at night (and most especially if the locations are susceptible to temperature inversions or radiative cooling).

To see what I’m talking about, compare Fraser with Berthoud Pass.

Berthoud Pass is at 11,315 feet. Fraser is at 8560 feet and a few miles to the north. Compare night time temperatures at both locations:

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?cobert

http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?cofras

Keep in mind that Fraser is 2755 feet lower (and is almost always colder at night except for on cloudy nights).

Unfortunately, the 3 or 5 and 2 generalization doesn't work at all for comparing nighttime temperatures of a valley vs. slope. The 5 and 2 works when when comparing slope temperatures, especially in the day. On a slope it's not that bad for comparing night temperatures, but is usually not accurate when comparing valleys or basins (such as Breckenridge) to a slope (such as on Quandary Peak). The only exception would be if it was cloudy all night in which case it should come out fairly close. Luckily day temps are easier to predict, but unfortuantely when you want to know if something freezes at night, nightime is what you want.

I would guess that it is likely that a few thousand feet above Breckenridge (Breck is at about 9600 feet), it wouldn't be any colder at night than in the valley itself. You would probably have to get closer to 12,000 feet on a slope before the nights would likely get colder on a slope (such as the couloir) than in the valley bottoms surrounding the peaks.
Last edited by Scott P on Sun May 31, 2009 10:51 am, edited 1 time in total.
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Re: How much cooler than in the valley?

Postby highpilgrim » Sun May 31, 2009 10:47 am

Thank for the info Scott.

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Re: How much cooler than in the valley?

Postby Scott P » Sun May 31, 2009 10:52 am

How come you're stuck inside today?


Leaving for church in a few minutes. :D
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Re: How much cooler than in the valley?

Postby joe4186 » Sun May 31, 2009 2:37 pm

bill also has some links to point forecasts for all the peaks, the one for Quandary is at 13,674
http://friendsofcaic.org/


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