A similar thing happened to us a few years ago riding motos in that area. Dropped into the west side of Cathedral Valley with a huge storm right on our tails, we could see it coming for miles. At the time they said it was a 100yr storm, the same system caused serious flooding on the front range when it reached Colorado, The desert is the last place you want to be in a storm when the nearest pavement is 20mi away. Luckily we were able to stay in front of the worst of it. Same can't be said for a German Tourist we helped that didn't speak any english.
Here we are trying to communicate with the guy (grey shirt) by drawing pictures in the dirt.
That's the storm we're running from in the background. The entire area was impassable about an hour after we get through. Luckily the arroyos weren't flowing much yet or we'd have spent the night out there.
Here's our campsite at Goblin, and a view of more heavy rain on the way. It was quite a show. This was after coming through Canyonlands the day before and almost getting washed off the road in a flash flood. We spent the night on the side of the road, and woke up in a mogul field of mud. I'd go back to Utah in a heartbeat! One of our favorite places