Recently buried surface hoar

We rode snowmobiles near the Rubicon Trail today, and explored some of the peaks within the open riding area both to the north and south of the trail. Although conditions were still excellent on cold slopes, both today's and previous tree bombs were something to watch out for, especially at lower elevations. Warm slopes were still rideable but getting wet at the surface. On many cold slopes without much tree cover, large surface hoar was easily observable on the surface. But on other similar slopes, I didn't see the expected surface hoar, so I put my hands and shovel into the snow in several places and found it buried under an inch of yesterday's snow. It seems yesterday's snow was quite localized, and I couldn't figure out a pattern based on aspect and elevation. Some cold slopes had surface hoar on the surface, and others had it under an inch of yesterday's snow.

Pic 1: No mistaking the large surface hoar here, so this area must not have received new snow yesterday.

Pic 2: No surface hoar on the surface, but reaching barely below the surface I pulled out several large surface hoar crystals.

Pic 3: Using my shovel to provide contrast behind the snow, the newly buried surface hoar was intact in the many places I looked.