You can count on it being WET... hahaha
I usually plan a few trips there, but those trips tend to be later in the summer due to the natural fact it has soooo much water constantly running down it all the time. I did go out there in Oct the year before last to see the upper portion completely covered in thick ICE sheets as well... So my guess would be June thru Oct is when me and my buddies will be heading there quite often.