In reply to alps_p: just to update people on conditions.. I called the Guides office in Zermatt.
Has been snowing for a while + largest snowfall expected tonight.
According to the guides office, Thursday is about the earliest one could think of attempting the Matterhorn, and that is on the assumption that it doesn't snow heavily tonight. If it does (and it's likely as per the forecast), then there won't be conditions for the whole of next week.