I'm riding cross country this summer. Starting on the west coast and coming east. What kind of night time temperatures should i expect in desert and mountain areas? The plan is to head through SW Idaho (desert) and play around on the divide (mountains) for a few days. I originally wanted to go further north and cross the divide around Logan Pass/ Glacier Nat'l park. Basically, I'm trying to decide on a sleeping bag. Would 40+ and a seperate fleece liner for especially cold nights do it?

The adventure cycling maps usually have the temperature averages for the major cities in each section of the route. Another option is to look up some cities on weather.com and check out the temperature averages there.

By "summer" what exactly do you mean?

Canada has a weather archive to refer to: https://www.climate.weatheroffice.ec....s/index_e.html
Maybe the US has one too?

You don't give any actual dates. Exactly when makes a huge difference. Too early and the passes may not even be open. It is easy to find averages for any cities along the way. Do a google search for "climate information" and you will find lots of sites like https://www.wrcc.dri.edu/CLIMATEDATA.html . At the peaks cold is always possible any time of year, but especially before mid June.

in glacier i hit 12" of snow in early august back in 92, so timing does matter

If we take July and August to be the months when you would do your ride I think a 40F or 32F bag would be ample. The low temps for the states on the NT during those months are in the 50s and the record lows seldom fall below 40F. A summer bag with a liner and the option to put on a few layers of clothes will be good. Personally I use a 40F summer sleeping quilt and I've never been cold.

The only problem when using weather sites to figure out an average temperature in mountain areas is they only account for the towns while the passes are often several 1,000 feet higher in elevation. So while it may be 50 degrees in town, it could be 25 degrees just 10 miles away at a higher elevation.

Not sure exactly what you mean by "Northern Tier" since that usually refers to an Adventure Touring route and your proposed route is much further south. The best website for climate normals data is from the Western Regional Climate Center - click on the state, then the community. There are far more choices than most weather sites - so you can find out what it might be like in Stanley, Idaho or Yellowstone Lake.

https://www.wrcc.dri.edu/climsum.html

A word or warning - it sounds like you are from back East. The climate variations in the West are greater both in terms of temperature differences from night to day and weather changes from warm and pleasant to cold and dangerous. Even though Stanley, Idaho is well south of the Northern Tier, it is often the icebox of the lower 48. Spring comes late to the Northern Rockies. You can certainly expect snow in May - even into June. I've seen it snow on July 4th in Jackson, Wyoming. Even if you don't have snow coming down, you will have lots of snow still on the ground in the higher elevations in June since it hasn't had time to melt yet.

If you are starting in mid to late May you should expect temperatures in the low 40s and, occasionally, into the 30s. The AVERAGE low for Yellowstone Lake in June is 32 - that means if gets colder than that about half the time. If you have a 40 degree bag, depending on the make, that often means anything less than 50 is uncomfortable. I'd go 32. You should plan to take glove liners and a fleece earband. These two items take up no space and will warm youconsiderably on chilly mornings - plus you can wear them to bed at night.

Remember - in the West you should always be prepared to sit out a day or two if a late-season snowstorm is on the way. Distances between services and help can be considerable. There is no need to place yourself at risk since these late storms are short and the weather afterwards is always fabulous.

i would use a 20 degree bag. weather at altitude changes fast....when it warms up you can change the way you use the sleeping bag. I'll unzip mine and start using it like a quilt if its too warm at night to get all the way in.

Sorry for the ambiguous first post. I am, in fact, an easterner (baltimore). I'll be starting in late May, when school lets out. Jamawani- thanks for the information. I'm looking into when the passes open and what temps i will encounter. Any suggestions are welcome and much appreciated.

Also, riding across southern Idaho has its problems, too.

It's an easy jog from the TransAm route in Oregon down to Ontario simply by staying on US 26. I've ridden it and it is very pleasant. Across Idaho you have three choices - each with considerations.

1. The more northerly involves heading east thru Emmett via some great hot springs thru Salmon to Challis, then southeast to Arco and over to Rexburg and Driggs. This would be my choice for the best route - although, as I stated earlier, Stanley can be pretty chilly. The Sawtooths are fabulous - as beautiful as any national park. The ride down the Salmon River to Challis is great in early June. (See pix)

2. A middle route involves going thru Boise. The roads into Boise are narrow and congested because of all the urban sprawl, but Boise itself has a fabulous greenway along the Boise River. Then you must get on the interstate for about 20 uphill miles towards Mountain Home before you can get onto paved service roads. From Mtn Home follow US 20 thru Fairfield until you reach Arco and the route above. This ride is pretty exposed - lots of treeless stretches.

3. The southerly route takes you south out of Ontario on OR 201 until you get to Homedale, ID - then following ID 78 thru Murphy to Glenns Ferry. You can follow old US 30 along the bluffs of the Snake River, but it runs out just east of Burley - then you have to get on I-84 for a good chunk before getting to Pocatello. From Pokey you can go either via Idaho Falls on old US 91 then on US 26 to Swan Valley or stay on US 30 to Soda Springs and ID 34 to Alpine. This route is considerably longer.

My vote - northern option - check the weather in Ontario, Oregon.

Late May could be kind of early for a west to east Trans America. Last year it would have been OK, but I am told the passes aren't always open yet. AC says thet McKenzie Pass is usually closed until early July, but Santium Pass is an alternate route there. Hopefully you will have a better idea how the year is shaping up as the trip gets closer.

Last year we did a W to E Trans America starting June 11. I think that W to E makes more sense terrain-wise for several reasons, but you are more likely to have cold weather in the Rockies and hot weather from Kansas through Virginia where the humidity is likely to be bad.

Virginia is brutal for the climbing and we were happy to do it when we had lots of miles of riding in already. The climbs may be relatively short, but they are STEEP. Out west the climbs were really long but seldom more than 7% or so.

FWIW: I am in Baltimore too, Parkville to be more precise. If you are interested in our journal you can see it at:
https://www.crazyguyonabike.com/doc/staehling2007

If I can answer questions about our trip I would be happy to share what I learned. Also I can looks stuff up on the AC maps if you don't have them yet (if you are serious about the trip they are the first thing to buy IMO).

Pete
Edit: Check out the ODOT bulletin from last year on McKenzie Pass. It has some info about what is typical for the pass.
https://www.oregon.gov/ODOT/HWY/REGIO...5-24-07a.shtml

BTW: They open it to bicycles before cars some years and that is pretty cool if you catch it then. If you are too early you can use Santiam Pass which I think is generally open.

Thanks for the input. We'll definitely be cutting it close when it comes to making it through these passes, but our time table kind of demands it and i think it'll be more fun. It looks like my first step is to buy the adventure cycling maps. Over my winter break I'll be lining up all my equipment (surly LHT, assorted other compulsory items...) and finalizing my route. I'll probably go with a 30 degree bag and bring a liner. On especially warm nights at low elevation i might be able to get away with sleeping in some base layers and the liner. If not, i can use the bag as a quilt.

While we liked West to East, if it looks like the passes will be snowed in, you might consider going East to West. The weather is likely to be a lot more comfortable that way.

We liked the West to East route for a few reasons. These included the following:
1. Getting air travel out of the way up front when we could plan the date more easily.
2. Being far away in the beginning of the trip minimizes any desire to back out.
3. Seeing new territory right away.
4. Having a good welcome home at Yorktown more near family and friends.
5. Saving the hardest climbs for late in the trip.

I guess we liked it better for just about everything except the sun in our eyes in the morning and the less comfortable weather.

I think that if I had to leave in May, I would wait until the last minute to buy tickets and be prepared to start in the East if the passes were still badly snowed in.

As far as the sleeping bag... I went with a 30 bag and was OK, but we had abnormally warm weather most of the way. Also we had to do an extra long day to get to lower altitude at one point to keep from freezing. Leaving in May I would be inclined to either take a 20 degree bag or to take layers of clothing that could be worn in the bag.

BTW: We sent stuff like cold weather gear home and had warmer weather stuff sent to us via general delivery. That is a help in being able to adjust the load to the conditions as you go.

Another BTW: We didn't find the prevailing winds thing to actually pan out to be an advantage. In Wyoming we had bad headwinds. and in Eastern Colorado and Kansas there was a side wind that was more in our faces than in our backs. Getting an early start was a big help with this because the winds didn't usually kick up until later in the day.