"Lapse Rate" - Finding the temperature at elevation

[jman]

So I just learned something interesting and maybe some of you already know this fact about geography, but there is a formula out there called the "lapse rate". You may have experienced this as you hike/climb up in elevation, the temperature decreases. But what this "lapse rate" means is that you could find out the approximate temperature of the summit of a mountain before you ascend it (without having to Google it, or have some sort of remote sensing GIS to tell you what that temp I). This should become part of your Hiking 101. And I'm here to help you with that. :)

Geographers use something what is called the "lapse rate". Lapse meaning change. And there is a formula that you can use (it's easy to memorize) to find out the approximate temperature.
The ICAO (International Civil Aviation Organization) says that for every 1000ft in elevation gain, the temperature will change +/- 3.56 degrees Fahrenheit. And this formula goes up to 36,090 ft (11 km). And from 11 km to 20 km (60,000ft+) the temperature in that zone is a steady -56.5 degrees.

So how is this practical to a simple hiker like me? Here's a scenario:

I currently live in Kaysville, Utah. The elevation of my house is approximately 4350 ft.
And there is a mountain summit that I frequently visit on a summer basis, called Francis Peak (aka "the radar towers") located just to the East of my house. It's elevation is 9560.
So lets say that I start hiking at a temperature of 80 degrees F, and I am wanting to know what the approximate temp is at the peak currently.

You subtract the elevation of the Peak from your current elevation. 9560-4350= 5210 ft in elevation change. And knowing that for every 1000 feet that it is going to have a 3.56 degree change, the math is simple and something you can do in your head.

For the sake of simplicity, I'm going to round down the 5210 feet to 5000 ft and round down the 3.56 to 3. So that means 3 x 5 = 15 degree change.

So while it is 80 degrees F at my house, that means the approximate temperature at the peak (at this current moment in time) will be 80 F - 15F (the adiabatic lapse rate), which equals 65 degrees F.


Of course, there are other factors to consider such as 1) is there a temperature inversion going on? 2) is there any wind? If so, factor in the "wind chill", 3) as you hike, will the temperature stay the same (like in Hawaii for example) or will it continue to rise to reach its daily maximum temp?

So take the above with a grain of salt, and you can have an approximate temp for your destination.

Conversely, the opposite can happen if you are on the rim of the Grand Canyon, for example, and you are descending thousands of feet down into the canyon. Then, of course, the temperature will rise approx. 3 degrees for every 1000 ft in elevation that is loss.

Further reading on Lapse Rate on Wikipedia (https://en.wikipedia.org/wiki/Lapse_rate).

[Bootboy]

I grew up just using 5F as a rule of thumb.

I believe that the rate is actually greater in the Grand Canyon due to topographic proclivities. The temp difference between north rim and canyon bottom is way more than the 18 the 3.6 rule cites on a hot summer day. Rim to floor can be 40° different


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[jman]

I think you are right but to a point. The lapse rate is the rule across the world (fun fact: even Venus has the same lapse rate) but the other factors (rock type, soil type, no evapotranspiration) all contribute to the extra heat or loss of heat. And in an extreme place like the Grand Canyon, you will see added degrees to the lapse rate.



But for the practical/amateur hiker - 3.5 degree for every 1000ft, keeps it nice and easy.


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[Bootboy]

Right, I didn't intend to contradict you. That rule of thumb has certainly served me well.

Just pointing out that there are exceptions


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[Scott P]

But for the practical/amateur hiker - 3.5 degree for every 1000ft, keeps it nice and easy.

That is a good rule of thumb as far as annual temperatures go, but be aware that it works better on a slope, rather than comparing mountain top to valley floor locations.

Also be aware that it is not consistent throughout the year. For Utah, a good rule of thumb is 2 degrees per thousand feet in winter and up to 5 degrees per thousand feet in summer. The temperature drops more quickly in summer as you rise in elevation than it does in winter. The same is true in the Grand Canyon.

Anyway, here are some figures used to point this out.

1981-2010 average January temperature in Salt Lake City (elevation 4250 feet) = 29.5
1981-2010 average January temperature at Alta (elevation 8710 feet) = 22.5

January change from Salt Lake City to Alta = 7.0 degrees over 4460 feet = 1.6 degree change for each 1,000 feet of elevation change.

1981-2010 average July temperature in Salt Lake City (elevation 4250 feet) = 78.7
1981-2010 average July temperature at Alta (elevation 8710 feet) = 60.7

July change from Salt Lake City to Alta = 18.0 degrees over 4460 feet = 4.0 degrees change for each 1,000 feet of elevation change.

1981-2010 average January temperature at Phantom Ranch (elevation 2570 feet) = 46.9
1981-2010 average January temperature at North Rim Grand Canyon (elevation 8410 feet) = 27.7

January change from Phantom Ranch to North Rim Grand Canyon = 19.2 degrees over 5840 feet = 3.3 degree change for each 1,000 feet of elevation change.

1990-2010 average July temperature in Phantom Ranch (elevation 2570 feet) = 90.3
1990-2010 average July temperature at South Rim Grand Canyon (elevation 8410 feet) = 63.1

July change from Phantom Ranch to North Rim Grand Canyon = 27.5 degrees over 5840 feet = 4.7 degree change for each 1,000 feet of elevation change.

If you are hiking in the mountains above Salt Lake (or anywhere else in the Rockies), it must also be pointed out that day time temperature swings are less on a slope or mountain top then they are on the valley floor. In July, for example, the average difference between the high and low in Salt Lake City is 27.9 degrees. At the summit of Mount Baldy, at 11,068 feet and above Alta, the average change in July is only 15 degrees, so mountain tops have a lot less variation if temperatures than the valley floors do.

Of course wind-chills are usually present in the high mountains as well.

As a general rule in Utah though, 2 degrees per 1000 feet works well in winter and 5 degrees per thousand feet works pretty well in summer, especially for day time temperatures.

[Doc Foster]

It is not so much that their is a seasonal difference in the adiabatic lapse rate, but it is determined by the humidity of the air and whether or not the air is saturated (clouds forming or raining).
There is a dry adiabatic lapse rate and a wet or saturated adiabatic lapse rate. I used to teach this to my high school students in the 80's to explain cloud formation, cooler temperatures on mountain tops as well as orographic cooling and the rain shadow effect of mountain ranges. Thanks for bringing back those fond memories.
This may help some - https://www.youtube.com/watch?v=ObnWb7yspxA

[Doc Foster]

[QUOTE=jman;583615



But for the practical/amateur hiker - 3.5 degree for every 1000ft, keeps it nice and easy.


Sent from my iPhone using Tapatalk[/QUOTE] YES, nice and easy to remember and calculate!

[jman]

YES, nice and easy to remember and calculate!

From what I have gathered, this same principle applies to other planets as well that have an atmosphere - Venus, Mars, etc.


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[Scott P]

It is not so much that their is a seasonal difference in the adiabatic lapse rate, but it is determined by the humidity of the air and whether or not the air is saturated (clouds forming or raining).

Although a factor, it's a lot more than that, especially out West.

In winter, valley bottoms are subject to cold air pooling, radiative cooling, and inversions, which do not affect mountain tops. Also, since mountain tops are generally windier locations than the valley floors, extreme radiative/cold air pooling does not occur (the cold temperatures are caused solely by the pressure change rather than cold air sinks caused by dense air "hugging" the ground). The mountains also experience seasonal lag due to snow cover and other reasons.

The above are prime reasons that 5F drop per thousand feet for summer daytime temperature and 2F drop per thousand feet for winter daytime temperatures is a good rule of thumb in locations such as Utah. It will be a lot more accurate than using the 3.5 degrees per thousand feet.

In areas that experience Chinook Winds or Foens, such as the eastern front of the Rockies, the seasonal differences in lapse rates are less pronounced, though seasonal lag is still present, sometimes on a larger scale.

Unfortunately, night time temperatures are harder to predict with changes in elevation. Record lows are actually significantly lower in mountain valleys than on the mountain tops. For example in Colorado, the two weather stations at above 14,000 feet have never recorded temperatures below -40. The mountain valleys have recorded temperatures significantly colder than that and at lower elevations. The same is true in Utah, though there aren't as many mountain top weather stations. Even at Alta though, the record low is significantly warmer than that of places such as Green River or Hanksville. Lapse rates really only work well with daytime temperatures, at least when comparing mountain tops with valley floors. In areas with good wind drainage, radiative cooling isn't as much a factor, so lapse rates are easier to streamline.