Re: July temps at higher elevations in Yosemite

I'll bet this has been asked numerous times, but I tried a few different searches and struck out.

I found a listing on the NPS website for the typical high and low temps for each month in Yosemite Valley, but didn't see any thing with average temps at the higher elevations. We'll be taking a backpacking trip in mid to late July and I'm trying to figure out what is the best temperature rating for the sleeping bag I need to buy. We'll spend the first night camping in the valley then up to the north rim at Yosemite Falls and work our way around the valley clockwise coming back in at Happy Isles. Our highest night will probably be in the May Lake area which looks to be a little over 9000 feet. Is a 30 degree bag going to be too warm? I'm planning to be in a 3 season tent with an open top (rain permitting) if that makes any difference.

thanks

Personally, I _always_ take a 20 degree bag into the Sierra in the summer (I have a 40, 20, and 0 bag). At 30...99 times out of 100 it'd probably be fine, particularly at the altitude you mention, and particularly in late July (I'd typically say that late July is the only frost-free period, but I have seen (rare) frost then).

Another way to look at it:

you lose three degrees of temperature for every 1,000 feet you gain in elevation. If you are camping 4,000 higher than Yosemite Valley, you can take those temps and subtract 12 degrees.

Or you can see what the weather is going to do and make the decision a few days before you start.

We use 20 degree bags most of the time...and often sleep with them open and flopping.

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Or just read a good mystery novel set in the Sierra; https://www.amazon.com/Danger-Falling-Rocks-Paul-Wagner/dp/0984884963



Edited 1 time(s). Last edit at 01/17/2012 07:55PM by balzaccom.

It sounds like you are assuming summer up there is the same as summer everywhere lower elevation. 20 degree setup is my summer Sierra habit. Depending upon weather patterns and topography you can easily wake up to a good frost, or light snowfall, any time in summer. I won't go anywhere without at least an emergency poncho, either.

You can be warmer at night by not camping in the bottoms of canyons along waterways - of course, most established sites are there. Cold flows downhill and pools at the bottom. But while it can make a perceptible difference, it's still quite cold at higher elevations where sleeping in the valley camps can mean 50-60F at night. One guy actually left his sleeping bag in the car after not needing it in the valley -- the following night with only two thousand feet of gain he froze and begged an emergency blanket from someone. Extreme example, but it was largely due to having camp near the river in the bottom of a canyon. Elevation alone doesn't account for a 15+ degree drop in temp - it was changing weather and topography.

Balza & almost covered it perfectly. 3 degrees for every 1000 feet. I have a 30 degree marmot bag and a 0 degree marmot. By june I'm usually on the 30 degree bag. That being said, you do have to check the forecast before you go out. Also, what type of pad you have can add or subtract temperature to your bag.

My two dollars worth:

first of all... a quite brillant person said this many moons ago:
http://yosemitenews.info/forum/read.php?1,7957,7970#msg-7970

In direct response to your question:
NO, a 30 degree bag will not be too warm.

What exactly you buy should factor in how often you think you will actually
use the bag and where you will use it. A very nice down 25 degree
bag will be light and with a nice pair of lightweight long johns will
afford you 3 season camping anywhere in the Sierra.
As for the snow talk in July... take that out of your equation.
Just assume it will get near freezing at night and you'll be fine.
I've used a 30 bag just about everywhere in Yosemite in July and August.
If you are not planning on going often perhaps you should look into
renting one from a place like REI?
Also since you are buying... I'm assuming you haven't backpacked in
Yosemite... and you may be in for a rude awakening.

Have fun... the meter is up

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Camped in Tuolume Meadows last summer, mid July. Was a LOT colder than I expected, below freezing at night. A 20 degree bag is a good idea.

Ok, I'll be looking for 20-30 degree bag. I was thinking that with an average July low of 55 in the valley and 3 degrees per 1000 feet that a 40 degree bag might be good enough up to 9000 feet, but I'd rather remove layers than be cold.

I didn't know that REI rented equipment so I'm definitely going to check that out. This discussion has also opened my eyes to the realization that I'm going to have to carry heavier cloths than I originally thought for those nights sitting around camp.

thanks

Regarding that cooling rate...don't have a URL but I'll reference "Weathering the WIlderness", Reifsnyder, pub. Sierra Club: 3 F/1000 is the wet adiabatic cooling rate (meaning, its raining and/or snowing). The dry adiabatic rate is 5.5 F/1000. But, as others noted, things vary based upon microclimates (cold air drains down into meadows).

There are many days in Tuolumne Meadows or higher where you can be in a t-shirt during the day and be perfectly comfortable. I've been at 11K to 12K that way, although it feels a bit weird because you're baking on the sun side, and freezing on the shadow side. It averages out to be comfortable.

One thing you have to experience to believe, when the sun goes down, the temperature plummets LIKE A ROCK! BAMM! You go from t-shirt to 3 layers of jacket in 45 minutes.

I have a 3 point something lb mummy bag with a hood that's supposed to be 30deg when your head isn't in the hood, and 20deg when it's IN the hood. It's never completely failed me, although there's been a few nights where I never really got comfortable. However on the really cold nights I usually have every bit of clothing and jackets on me while I'm in the bag to keep myself warm. I either sleep cold, or the bag isn't really a 20deg bag.

And that leads to a big factor in this. There's a HUGE variation between people as to what they need in a sleeping bag to keep them warm. There's also no standard to how the manufactures rate their bags. Two people can have the the same bag on the same night, with one person freezing and the other person toasty. Next you can have the same person sleep two nights in two different 20deg bags, one night freezing and the next toasty. It's not an exact science.

One tip, make sure you have a good pad between you and the ground. You can lose a lot of heat that way. I've woken up in the middle of the night from the cold because I'd rolled off the pad. I have an old foam pad. foam, not air mattress!

I would definitely recommend a 20 degree bag. Temperatures in Yosemite at high elevation can vary tremendously. The summer of 2011 was unseasonably mild. I've seen it be 18 degrees at 9,000 feet in Yosemite in July at night and I've also seen it be 70 degrees at the same location and date in a different year.

Here's a few plots from TUM - Tuolumne Meadows.
Air Temperature for Month of July from the Odd years 2001-2011:


I'll let you draw your own conclusion.

As for extra clothes. Since I go a couple of times a year... I have settled on a poofy jacket and poofy pants.
The ones I have are Marmut Zeus and Western Mountaineering Flash Pants.
I take them year round. The jacket gets put into a custom pillow case 99.9% of the time... and the pants get kicked down
to keep my feets toasty. Pants can also be used to keep ye old thighs and knees a bit warmer if the down gets
moved a bit in the sleepy bag. A nice fleece pullover and fleece pants would do the trick too.
Anyway, just rent the stuff you need from REI.
You asked about xcountry route on another board... and I answer you... but with this question I would
change that respond to something like:
"Since it seems you haven't done a lot of backpacking... just play it by ear... more than likely you'll want to stay on the trail."

Have fun

Bird out

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20 degree bag highly recommended for TM. Take an extra blanket too.

Worst part is having to get up to take a pee.
brrrrrrrrrrrr.......