In reply to Rampikino:
I've been the end of March the last few years and it's generally been good with no significant loss of climbing time due to weather but it does come down to luck.
At the sub Font7A grades I climb I wouldn't be too worried by May temperatures either.
If you are looking for nice weather to do a bit of climbing go in May and are not too worried about pulling on 8A slopers.
I go in March to kick start the season when the difference between Glasgow and Paris weather is generally significant.