This is what I posted when someone was freaking out that the Birkie might start at 35 degrees (slightly updated):

The snow pack is cold and it won’t be too windy. Except for some south-facing hills (almost always downhills) and maybe the lake and a couple of fields, ambient of temperatures of 33 degrees will not warm the snow as the cold snowpack will radiate out cold air to the surface. These are 2m air temperatures, meaning 2 meters above the surface.

The Korteloppet may transform the snow, but 12+ hours in the low 20s overnight will freeze it right up and there’s a lot of powder down there to till back together. But the model output statistics, which tend to do a better job with high and low temperatures, show it going up to near 40 on Friday, and then in the 12 to 14 range overnight, and I would not be surprised if those verified during the day on the warm end and overnight on the cold side if the surface winds decouple from upper level winds and there is even a couple hours of radiational cooling. Temperatures at 8 a.m. on Birkie Day may actually vary significantly across the course, but should even out by 10 or 11. The models are mostly in agreement that it should be down around 20. There are sort of two camps: one which is clear and calm and gets down into the teens and then up into the 30s, and another which keeps temperatures warmer overnight with some cloud cover, but the clouds keep it cooler on Saturday.

In either case, I would not expect most of the course to be anything but cold and frozen until about noon.

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