Mountain cold pockets

There are a few days a year when the air is so clear, dry, and still that localized pockets of cold air can remain entrenched in the Wasatch anywhere the sun doesn't shine.  Today was such a day.

Just have a look at some of the MesoWest observations this afternoon.  At Alta, it's 20F at the top of the Collins chair, but a frigid 8F in Collins Gulch and 12F at the base.

The conditions are ideal for these cold pockets to persist through the day.  We had a calm, clear, dry night last night, so strong cold pools developed.  We are near the winter solstice, so the sun angle is very low.  Today the winds were light and the dewpoint very low, which enables the snow surface to remain very cold anywhere it is shady. Without much of a breeze to stir things up, we're just not going to mix out these cold pockets.

Just to highlight how dry it is, check out the dewpoints on Mount Baldy.  They dropped below 0F at around 10 PM last night, and were near or below -20F after midnight.

Mountain weather observers report limited surface hoar formation last night, despite the clear cold conditions, and perhaps these very dry dewpoints offer a partial explanation.  There simply wasn't much vapor in the atmosphere for deposition onto the snowpack.