hey folks, thanks for your replies.
the rear tires passed the penny test before i left for LA.
i was definitely driving for the conditions, sometimes going less than 50. it was just frustrating having SUVs and pickups blow by me doing 70 or better. i live in texas, i should be used to knuckleheads going too fast.
i always try to avoid taking my car out in the rain. however, it is a daily driver. so, sometimes i can't avoid it. (it is garaged on both ends of the commute though.) the few times i've driven in the rain here at home, i haven't had any trouble maintaining freeway speeds and feeling safe. nostalgia for LA must have made me forget how bad the roads and weather can be.
i think i'll check the ball joints just to be safe. but, the shimmy only happened in those adverse conditions.