[gb]

There is no "typical Cascade nighttime summer temperatures", as it varies with the weather and the location. I think, as a couple have said, you need to look at the forecast temperatures for the particular period and location you are thinking of hiking. Use telemetry and point forecasts - the latter come from tools like the University of Washington MM5 forecast model (12km). I use that and look specifically at 850 MB (5000') and 700 MB (10,000' - especially for the Rockies where it is higher) https://a.atmos.washington.edu/wrfrt/gfsinit.html and then interpolate at 4F (2C) per thousand feet - the actually number is 5F for a dry atmosphere and 3F for a moist one. Another tool is the ZSE freezing level plots from the NWS. https://www.weather.gov/zse/FreezingLevelMap Freezing levels above 12,000' give generally very warm temperatures. Interpolate downward as above. But realize, also, that location and time of year make a lot of difference; as much as the weather. Late July through mid-August are generally the warmest and nights can be pretty warm under a strong dome of High Pressure, especially then. Until early July it can be still cool/cold at elevation, and nights can get very chilly - mid-teens and 20's in colder basins by latter September. Think also location. Nighttime temperatures on a ridge can be warm, while those near a stream, near a glacier or snowfield, or in a basin will be much cooler - perhaps 20 degrees difference at times. The answer with respect to clothing and sleeping bags is to have a good feeling for particular conditions and then to select a bag in the appropriate range. I have a 50 degree bag that I seldom use, a bag that is about 28 degrees, and a 20 degree bag. The weight difference is not great; it is mainly bulk that determines your pack size.

[Cyclopath]

It's a very good idea to check the forecast before you leave but the question was about what sleeping bag to buy for a trip several weeks out so you really have to rely on generalizations for that.

[Das Boot]

Hi OP....get a 32F bag. You will be happiest. I have tried 45F, 40F and while those work you will have to wear warm clothes.

[Randito]

One additional note -- An aspect of the Quilt + down hoody + warm pants approach that I appreciate is that it makes hanging out in the evening and getting going in the early morning more comfortable.

[olderthanIusedtobe]

Maybe I missed it, but I haven't seen a sleeping pad mentioned in the thread. That might be even more important than the sleeping bag. Something to insulate you from your body heat seeping out into the ground. I don't know what the latest and greatest is. I use an old Thermarest, there are probably lighter and better options now.

[Cyclopath]

The previous two posts have a lot of (probably hard won) wisdom.

[InFlight]

[Navy salad]

[thunderhead]

Obviously it depends but a good mountain rule of thumb is it can drop to freezing any time anywhere, and that the great volcanoes can drop far below freezing.

[Cyclopath]

[Randito]

On the issue of sleeping pads there is also a huge range of options. When I was in my 20's the 1 inch thick thermarest pads were consider a luxury compared to ensolite and blue foam pads. Recently I did a short section of the AT in NY and was impressed with the 4 inch thick air mattress that a thru hiker in her late '70s was using. I haven't found a 4 incher that is light enough in my book -- But I did find a 3 incher that is acceptable to carry. For me the key to comfort on thicker air matress is to avoid inflating the pad too much. If you blow it up hard -- all the extra thickness doesn't do much -- it ends up like sleeping on a hard futon. The key is to inflate it enough so that your rump (or hip if you are a side sleeper) is suspended just an inch or so above the ground. Thin foam mats offer plenty of insulation. But unless one does yoga frequently thicker air pads improve sleep quality that is impared by lack of flexibility.

[forest gnome]

Ya well if that's a backpacking bag I'll eat my hat... Lets take a pole and see how many experiencied backpackers (not car campers) would try to keep the wife happy with that one Another tip is a THIN foam pad from the foam shop...we have paid 16$ and u can cut 2 out of it....we allso use them on top of our big ages airmatts...ok I actally Hav a neo air

[Cyclopath]

[forest gnome]

YA ...PREPARE TO FREEZE YAR ASSESSMENT OFF..sometimes... DAM AUTO CORRECT....ASSES...NOT ASSEMENTS...

[xrp]