The big crowds don't hit the Black Hills and Yellowstone until mid-June. And fair warning: Despite what others have said about the Black Hills being fine in April -- I've lived here (just west of Black Hills) for 43 years, and late April snow storms are NORMAL! Big ones! Very true that the weather might be warm, even possibly dry, but there's always a real threat of BIG snow storms throughout April. I'm talking several feet! In Yellowstone they come even later. FWIW, April is my least favorite weather month of the year in Wyoming -- wind, clouds, rain, sleet, snow, and (more) wind. And all this without benefit of leaves on the trees! ;)
America's Snowiest Places#5: Lead, S.D.
Snow stats
Average yearly snow: 201.4"
Population (2000 census): 3,124
Snowiest month: March (35")
Snowiest day: 52" (3/14/1973)
Record depth: 73" (3/1/1998)
Quick question: Name a region with a reputation for heavy snow? Did you answer the Rockies? New England? The Great Lakes snowbelts? Cascades or Sierra? Alaska? I'll bet the Black Hills of South Dakota wasn't one of your answers. But it should be.
Lead (pronounced LEED), and its sister city, Deadwood, are in the northern Black Hills. North winds circulating around powerful Plains storm systems are lifted by the hills, wringing out prolific snow totals well over 10" three to four days a year, on average.
An incredible 5-day snowstorm once dumped over 112" in Lead in late February/early March 1998. That's over 9 feet or more than double the average annual snowfall in Denver... in one snowstorm!
What other location in the U.S. averages over 20" of snow... in six different months (November through April)? Two spring months, March (35") and April (34"), are Lead's snowiest months!
How many places average almost 1" of snow... wait for it... in June? There was once 10" of snow on the ground on June 2!