Thanks folks...I follow Al's blog. Was hoping there was better insider info. I'll stand by.
A-Basin's seasonal goal is to run full ops until the first Monday in June. This is the official target closing date and would be the 4th this season.
@SkiNurse kindly provided a visual of one of the two seasons in the last 40 years or so (according to Al) where A-Basin did not make it to June
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Zuma is usually closed by Memorial Day or maybe a week sooner because of melt at the lift base and snow too soft to get the cats back out. Pali and East Wall usually close by mid-May due to wet slab slide risk. A-Basin is the site of a long term continental snowpack avalanche study due at least in part to an inbounds avy fatality on Pali - they have sensors that measure water running under the snowpack. It can go from winter like we just had to closure in just a few days at this point if temps really spike, and there are sometimes reopenings if it cools again, but that's only if there was an early closing. They have not tried to reopen later in May recently.
From there, A-Basin does "extension weekends" in June (Fri-Sun) provided they can keep Lenawee Face to High Noon open for top to bottom skiing that includes Lake Reveal.
There has been at least one extension weekend since 2013, and just one has been typical recently. High Noon gets a little ugly by the end, but those late weekends are awesome. It goes very fast - they can lose 4" a day. From last year:
May 21 - Zuma Bowl
June 10 - Lenawee Face
June 10 - looking back to High Noon, last run