I saw this trick on rec.juggling. It is a shape distortion of the Shower so that the thrown balls trace a Cascade pattern.
Juggle a shower, one hand only makes cascade throws over to the other side so I'll call it the 'throwing' hand. The other catches the cascade throws & feeds them back into the throwing hand so I'll call it the 'feeding' hand. Throughout the trick the two hands either throw or feed, only the shape of the pattern changes.
Continue juggling a shower & pick a ball. Instead of cascading it to the other side, throw it up on the same side of the pattern so that it will fall on the outside of the throwing hand. Make a cascade throw & feed the next ball into the throwing hand as normal, but continue the feeding motion so that your feeding hand passes underneath the throwing hand to snag the vertical throw with an Under the arm catch. As soon as you have caught the ball bring your feeding hand back, make a cascade throw then feed the ball you caught under the arm straight up into the throwing hand. Practise this move on its own until smooth.
Continue juggling the shower pattern, count out the cascade throws from the throwing hand as they peak & don't look at your feeding hand at all. Make every fourth throw from the throwing hand an outside throw (remember to count the cascade throw made as you reach under to make the under arm catch). Then work on every third, then finally every second.
Once you can make every second throw to the outside, you are juggling a shower cascade. To make the cascade more 'cascade like' juggle the pattern with your throwing hand level with the centre line of your body & really make the outside throws fall level with your hips. This creates a lot of work for your feeding hand & makes the pattern very visual.
Be sure to learn this pattern with both hands as the throwing hand, as switching between shower cascades with both hands using a round or two of The Box or 441 looks very cool. As does catching an outside throw & leaving the feeding hand under the other arm to juggle a Crossed arm cascade.