Lowest Temps

[zonachris]

So the adrenaline is pumping, i leave happy isles Thurs for a week trek on the JMT. Given that happy isles is 4000 elevation, with a high low temp of 80/55 during my trip... how much should I subtract from the low when adding 5000 - 6000 elevation? Is it going to drop below 30 at night? I'm prepping for 20 degrees but not sure I'm over planning.

[balzaccom]

The general rule is that the temperature drops about 3 degrees F. for every 1000 feet you climb...so you can do the math. But if the lows at Happy Isles re in the 50's, You will have to get up to about 10,000 feet to worry about frost...

[zonachris]

thanks Balzaccom

[oakroscoe]

Balza is dead on. You'll be fine. I wish I had taken my 30 degree bag instead of my 0 degree bag last week when I was in yosemite.

[AlmostThere]

Temps are variable - I just got back from an overnight at 9000 ft and we had frost when we woke. My buddies were cold all night because they were guessing it wouldn't be so cold in June and brought 40 degree bags. I was fine with my down quilt rated at 25F. We went from 50F temps in the valley (backpackers campground) to near freezing at LYV last year when we did Half Dome as an overnight trip.

I would take a 20 degree bag, to be safe and to offset any variance in the rating of the bag. Some bags are labeled optimistically.

[bill-e-g]

It got down to 26 near TM Sat. night.

If you have a 20 then bring it. Bring some fleece too.
I had my 30 and fleece and was ok but that was only 1 night.
If I was doing JMT now I'd bring my 15.
So far it's been a wierd year weather-wise. I wouldn't chance it.

[zonachris]

Thanks all. I'm bringing my 15 degree bag and layers. It sounds like that should be enough.