Home / Backpacking Skills / Will My Sleeping Bag Be Warm Enough? Using Historical Temperature Averages to Plan Camping Gear Needs

Will My Sleeping Bag Be Warm Enough? Using Historical Temperature Averages to Plan Camping Gear Needs

Historical Temperature Tool on Weather Underground
Historical Temperature Tool on Weather Underground

I get a lot of questions from SectionHiker readers asking whether their sleeping bags will be warm enough for their backpacking and camping trips.

For example:

“I’m starting an Appalachian Trail thru-hike in February at Springer Mountain. Will a 20 degree bag be warm enough?”

“My son has to go winter camping with his Boy Scout Troop. We live in Rhode Island. Will his 20 degree bag be warm enough?

It’s not that they don’t trust the temperature ratings of their sleeping bags, which have become¬†quite reliable since US manufacturers adopted temperature rating standards (at the insistence of REI).

The question they’re really asking is what the temperature outside will be on the given date and location for their trip. The answer is to look up historical temperature averages.

Historical Information Detail for mid-Feb on Springer Mountain on the Applachian Trail
Historical Information Detail for mid-Feb on Springer Mountain on the Appalachian Trail

Historical Temperature Averages

You can figure out the expected season temperature for any US location using historical weather information published at Weather Underground (Wunderground.com). I use this tool for planning most of my trips. Go to the Weather Underground website and click on the MORE menu item to access Historical Weather.

For example, you’d type in the name of the closest town to where you plan to start your trip and the date you plan to start. I usually pick that week rather than a specific day and average the temperatures from the past 3-5 years to get a reliable estimated max, mean, and average temperature. I can then mix and match the sleeping insulation I bring on my trip based on these numbers.

Depending on the season, I like to add about 10 degrees of extra warmth to my sleep system in case there’s a cold snap. For example, if the average is 30 degrees, I’ll bring a 20 degree sleeping bag or the equivalent quilt-based system.

EN13537 Temperature Rating Label
EN13537 Temperature Rating Label

Sleeping Bag Temperature Ratings

Sleeping bags temperature ratings assume you will be using an insulating sleeping pad, wearing long underwear, and a warm hat at night. That’s just how the standards work. So don’t skimp on these components of your sleep system.

If you’re a cold sleeper, here are some additional posts about other techniques and information you can use to sleep warmer at night on backpacking and camping trips.

10 comments

  1. There certainly are a lot of variables to consider when deciding whether your sleeping bag will be adequate for conditions. Several years ago, while climbing Aconcagua, I used a Marmot “0” bag. During the three week expedition our team experienced ambient night air temps ranging from +6F down to -21F and we spent many nights with our tents pitched on snow and ice.

    I always slept comfortably and warm in my Marmot bag. During the coldest nights I wore thick socks, a wool hat, liner gloves, and expedition weight long underwear to add insulation. On “warmer” nights, I’d just dress down a bit to remain comfortable.

    Also, IMO, the quality of the bag itself is extremely important. My Marmot “0” bag is very high quality. One of my fellow climbers used another brand bag rated at -20F and he constantly complained of being cold at night.

  2. weatherspark.com is also a great place to get average and extreme temperature information.

  3. It’s worth mentioning that elevation makes a huge difference. Of course, common sense would lead you to believe that everyone knows that. Yet every year people listen to the weather on the news or enter “the name of the closest town” on their computer only to find that the weather up top is much more severe.

  4. Thanks for the tip on WeatherUnderground. I had used it before but didn’t know about the awesome History feature. When I look up my local weather, I am shown dozens of “personal stations”, if I then look up the history for that locale (say the zip code), I am directed to an airport 30 miles away that has quite a different weather pattern than my locale. However, I did find a workaround to this: If I click on a specific PWS (personal weather station) near me, then I can see the data history for that specific station. The history will only go back as far as the PWS has been in use (if it was put up 6 months ago, then I can only see 6 mos of data), but the data is as local as it can get without putting up my own PWS. Pretty cool.

    To find a more local PWS, go to your nearest city and then click the down arrow titled “Change Station” and choose a different station. Then rather than clicking on “History” (which will likely take you to the nearest airport weather station), click on the name of the PWS you just choose. It will be under the city name next to the symbol ((.)) Then you can view historical data for that specific Personal Weather Station. The only caveat of this is I am sure that these PWS systems are not the industrial quality that say, an airport, would use. But with so many PWS in use in a small area, with all of them returning similar figures, I feel confident these are good enough for my uses.

  5. Good tip on historical temperature research. I was looking into buying one of those Kestrel devices as well.

  6. I don’t know about other’s experience, but regarding bag temperature ratings, I’ve not found the new rating system any better than the old. A 15F comfort limit bag will keep me warm (with light long underwear and a hat) down to about 35, Barely. I’m an average middle aged guy. Since my grown daughter has the same experiences, it cannot be just me. I still need to assume one has to add about 20F to the number to make it through the night without waking up looking for something to throw on top, as my legs get too cold. Maybe assume15F difference if I have a coat to throw in top. I am a side sleeper, but use extra padding if I can tote it. Now I am going to experiment with light-weight liners, as that may be the easiest insurance worth toting around, more so than extra pads or coats. I also found that some light weight breathable synthetic on top can make a big difference – such as Frog-Tog raincoat or poncho.

  7. Hi,
    I’ll be taking a winter backpacking weekend class with the AMC in NH next February. They suggest a -20 degree rated bag. At present I only have a RAB Asent 500 24 degree down bag for women, a Therm-a-Rest NeoAir XLite Sleeping Pad, plus a closed cell pad. I also have a thermarest synthetic quilt which I could combine with the bag but I don’t think I’ll get warm enough in a NH February. I will be sleeping in a Hubba Hubba 2 person tent alone.
    We will be out two nights at Cardigan near Bristol. Is there a bag for women to keep me warm? Do I have to go for a -40 rating to ensure I’m warm? I’m sure I can probably rent a bag, but if I want to I’d like to know which one would help me and not break the bank.
    Thanks!
    Jen

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