"Free Air Freezing Level": Useful for predicting temperatures?

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OneSpeed
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"Free Air Freezing Level": Useful for predicting temperatures?

Post by OneSpeed » September 25th, 2020, 9:42 am

I'm sure there's no really specific answer to this one, but I can still learn something.

I'm looking to backpack at Mount Adams next week, and the forecast says "free air freezing level" at 16,000 feet. If I'm camping at 5,000 feet, is there some rough calculation as to what the temp will be in camp?

A little online research seems to imply 3 degrees per thousand feet, but that's crazy. 32 degrees at 16K + 3 degrees per thousand feet (33 degrees) = 65 degrees at 5K. I think not?

Also, if it's 16,000 day and night ... shouldn't that change when the sun goes down?

Forecast for Trout Lake Monday night is a low of 43, so presumably up at 5K on the mountain it will be somewhere between 32 and 43 -- which is good enough for general predictions, but I still wonder if there's some way to translate freezing level to some rough estimate "camp temp" from "free air freezing level."

This is the forecast I'm looking at.

pcg
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by pcg » September 25th, 2020, 10:47 am

Can't answer your question, but I would just refer to this...
https://www.mountain-forecast.com/peaks ... casts/3741

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adamschneider
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by adamschneider » September 25th, 2020, 10:49 am

Good question. But I doubt there's a foolproof formula, because 16,000' is pretty much the highest it ever gets around here, and I have a feeling the nighttime temperature at the end of September with a FAFL of 16k is NOT going to be the same as it would have been in July.

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mjirving
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by mjirving » September 25th, 2020, 11:00 am

Another method is to go to weather.gov and browse on the map to your camping site and click on it to get a localized forecast to the GPS location. I’m not sure how they do it, I guess it would be an algorithm off the local weather stations based on altitude and such? I find it to be reasonably accurate.

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retired jerry
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by retired jerry » September 25th, 2020, 11:14 am

yeah, weather.gov

https://forecast.weather.gov/MapClick.p ... 25Br2hKjIU

low temps between 45 and 50 F at 5900 feet elevation

good idea, I was thinking about that too

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Don Nelsen
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by Don Nelsen » September 25th, 2020, 1:38 pm

Using free air temperature to calculate a ground temperature doesn't take into consideration the effect of proximity to the ground. In the day, the sun warms the ground and near the ground it will be warmer than the standard lapse rate (3.5/1,000'). At night, the proximity to the ground works the other way, cooling the air lower than the rate would indicate. Then there's inversions to consider. Throw in cloud cover, wind velocity and even humidity and it gets really complicated to figure out with any degree of accuracy.
"Everything works in the planning stage".

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OneSpeed
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by OneSpeed » September 25th, 2020, 3:20 pm

Excellent resources, thanks! Didn't realize how specific they can get at weather.gov, and had never even heard of mountain-forecast.com. See, I knew I would learn something!

And Don, thanks for the reminder that the stand 3.5/1K' is for on the ground!

Paul

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retired jerry
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by retired jerry » September 25th, 2020, 3:39 pm

with weather.gov you can get the forecast for a specific spot, but it just gives you the forecast for a square area about 1/2 mile square

it says what the elevation is for that square

if that is different than the exact spot you're going, you can select a slightly different square that's closer to the elevation you're actually going

small difference

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drm
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Re: "Free Air Freezing Level": Useful for predicting temperatures?

Post by drm » September 26th, 2020, 8:01 am

The short answer is no because the atmosphere has layers and boundaries in it - think of inversions. And so the temp at some upper altitude doesn't take into consideration those various layers and boundaries.

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