Use data from nearby PWS in aggregate from both Wundermap and MODIS. Check for a DOT and USF weather station as well. I’m assuming this has something to do with frozen surfaces, so you also should have your friend cross reference those temps with shadowing because a 39° air temp in the sun can still be 30° at the surface in a spot that would have been shaded all day.
You're so far gone that you're suggesting June 15th snow isn't an extreme, you're insane dude. I lived in la pine in June 2008 and it did not snow, the latest I've seen snow in la pine/sunriver was May 25th 2012 when we got over an inch.