Hi there,
I'm in almost exactly the same position as you. Me & my friend will be arriving in St. Jean on Monday, March 26th. I emailed Orisson to ask if they had availability however I received a reply from the owner who said he didn't know if he'd be open & it depended on the weather & I should phone him the day before.
I was thinking that if I arrive in St. Jean at a reasonable time I might start off straight away & head up to Huntto (assuming it's open) as it's only 5km away and shouldn't take too long to get to. It'll also make the next day's hike to Roncesvalles that bit shorter.
I've no idea about the snow but the weather for next week doesn't look too bad so hopefully I'll be able to get some idea of the weather for when I arrive later this week. I'd check with the Pilgrim's office in St. Jean first though.
May well catch up with you somewhere along the way.
Have a good one.
Regards,
Dave