Do I need sleeping bag in yellowstone?

I'm going to yellowstone on 1st August and I wonder if I need sleeping bag. We drive Ford mustang and as you may be aware the boot is really small therefore I try to spare some space.
I don't want to take sleeping bags but Mrs keeps telling me it's going to be cold over there even in august. What do you people think?

Throw it in the back seat, better off than being cold. Low temp. Average for Yellowstone Lake is high 30's low 40's. Sounds like you'll need a sleeping bag if you're in a tent!

Yes. I live at 9,600 feet and establish base camps at 12,000 feet in the mountains during summer. During winter, spring, and fall, I sleep in a 0-degree down sleeping bag. In summer, I switch to my 15-degree down sleeping bag. I also pack my down jacket and a layer of fleece. I'm also prepared to boil water to fill bottles that I put in my sleeping bag for additional warmth.

Yes, it can get down to freezing overnight in August in Yellowstone. In fact, I have awakened in the morning to find snow on my tent there in late Summer. Decent sleeping bags pack down small enough that they should fit in the trunk of any car. You will also need sleeping mats or air mattresses. You can't just sleep on the ground.

Yes you will need a sleeping bag. Get one rated for 15* and pack for any weather condition. One year I left home it was 90* got to camp it was 45* and in the night it snowed 6" weather is un predictable.

Toss this from the returning seat, superior down compared to staying wintry. Small temp. Typical with regard to Yellowstone Sea is usually excessive 30's low forties. Feels like you may need a slumbering tote if you're inside a tent!

No. Y'all know where the value is.
Sleep in the Mustang. Its natural for you
and the engine to turn over several times
each night to warm each other up. Birds
of a feather fly together at Yellowstone.