The downside is that things can be very busy at this time of year and if you want to avoid the crowds you should consider a different time. The period from April to September sees regular rainfall, but it tends to be short heavy storms here, rather than long drizzly days.
Zurich is an excellent place for those who enjoy snowy cold winter conditions. The snow begins here in November and can continue right through until April. Temperatures rarely get far above zero at this time, so you’ll need to be prepared with plenty of warm clothes.