Badlands & Custer SP. Difference in June vs August?

WOW.
Please let me help about weather and crowds in the Black Hills.
June is our wet month with higher humidity, showers to rains that may last an hour or 2 early in the month, tending to occasional local T' storms later, say about the 3-4 weeks. July to early August is our challenging time where temps may reach 97f, a day or two in the higher elevations, localized t'storms may produce hail or damaging winds. These are brief and spotty.

Temperatures in late June range from the mid 80s to high 60s days to 50s to high 30s nights.Extremely changeable.
August is more stable and dryer with a lower chance of severe weather. Temps after Sturgis Rally time vary from high 80s to mid 60s days, 50s to low 40s nights.
ALERT There is no normal
Please do not let this scare you. what i've described are rare events that are fleeting, even memorable. Any local will help you know what tomorrow will bring.
Enjoy!

A couple things to remember. Custer State Park requires an admission fee, but it isn't expensive. The National Parks pass doesn't work there. Also, if you want to see the buffalo in August, go early morning or late afternoon. They hide from the sun in the trees during the day. Their fur coats are permanent.
Also, there are several wild burros that call Custer SP home. They are the relatives of the burros that the prospectors brought with them during the gold rush days.
The park asks that you don't feed them, but the burros have quite a scam going. One stands in the middle of the road to block traffic and the others go from car to car begging for food. I assume they take turns blocking traffic. If you must, take carrots with LONG green tops. The burros don't have very good eyesight but they have sharp teeth.

We stayed the week after Sturgis this summer at Beaver Lake Campgorund in Custer. The weather was great on the way there the temps were over 100 driving thru SD.I would have traded hot weather than all the fires we had to dodge the next few weeks

We were in that area this past summer in late June and early July and it was perfect.
We did the Badlands for two days, Mount Rushmore on July 3 ( second busiest day of the year), Deadwoods, Sturgis,Custer State park and the needles Highway.
We saw Buffalo roaming along the side of the highway and lots of elk and deer as well.
We visited devils Tower on our previous visit 14 years ago.
All great things to see.

"If it were me I wouldn't hesitate to go in June rather than August. August is usually very hot while June is very pleasant. No comparison. Late August will be a bit cooler but still can be very hot and humid. Late June can be getting pretty warm but is almost sure to be much nicer than late August. "

I agree. With the prairies greening up the temps still relatively cool your stay will be much more comfortable in June. August is hot, even in the Hills, but especially in the Bad Lands.
FWIW - We really don't have a lot good to say about the Bad Lands. Do the loop and take pictures because there are some interesting formations, but we had people come into CSP when we were there talking about spending a week there. A couple or three hour drive through is all I can see it taking.

Had the same question about going to Banff/Jasper. Have done that area of SD in both early June and late August. Weather was actually similar in nature-late August had less kids. Critter babies in June are small-racks in August are bigger. Ya pays your money ya takes your choice.

double post

June will have cooler weather, but late August is not bad. Too early for the fall color on the trees, though. That comes in Sept.
Either way, if you want to stay in Custer State Park, make reservations as early as you possibly can because that park is very popular and with great reasons.
We will be making our reservations for the buffalo roundup almost a year in advance this year.

I live in the Black Hills, and either would work. Just be sure to understand, early June we can still get snow, but by late June, you should be safe.

In June, the hardwoods will be green, and most likely in late August too. If you heard an elk bugle, I would be shocked. If you want to see elk, make sure and drive through Wind Cave NP. Take road #5, and keep a close watch. We see elk every time we drive that road. The bison in Custer State Park have traces of cattle DNA, as do most herds. The bison in Wind Cave have no cattle DNA. Just so you know, you can not tell the difference between them by looking at them. You will see as many bison here as you will at Yellowstone, but with very little traffic.

Also, it is unusual for it to be over about 30% humidity here.

We were there in August and I don't remember it being overly hot.