The alps are often dry through Jan and Feb...the heaviest snowfall typically comes in April. It has snowed 80+cm at 3000m in Chamonix in the last 4 days, so there is snow accumulating now, despite the somewhat dry conditions over the last few weeks. Even in very dry years like 2003, the Matterhorn was not in "summer condition" by May. And I'd be willing to make a sizable wager that it will not be this year either. Of course, the Hornli ridge can be climbed at any time and is descended routinely by people making winter and spring ascents of the N face. But I believe we're discussing typical "in season" conditions when relative novices can make the ascent and the rock is generally dry. Of course, anything is possible. But I wouldn't plan a trip weeks or months in advance, hoping to make an ascent in May. I'd say there's about a 1% chance.