In reply to jack_44:
I don't know whether last spring was typical but actually conditions were pretty optimal in mid-March following a cold Feb.
Also, judging by your profile you're probably going to want to hit some tufa? Last spring these were seeping throughout Feb, making March a better option. And the steeper sectors tend to offer more shade options anyway, if it does start to get too warm to climb in the sun.
Post edited at 15:50