Telemetry temp. vs snow surface temp.

When I was camping on Mazama Ridge this past weekend I noticed something that has me wondering. Both Friday-Saturday and Saturday-Sunday nights were quite cold at our camp at ~5700 ft. Full liter bottles of water left outside the tent froze extensively each night - about half of the water was frozen by morning. Both nights were very clear and there's no doubt that a lot of radiational cooling was going on. The Paradise telemetry, however, indicated overnight lows of 36 and 37 degrees, respectively. So is it possible that the Paradise telemetry station's temperature measurement is taken at a height above the snow that might not always accurately reflect the true temperature right near the snow surface, and thus the actual snow surface conditions?

Hi Charles.  I don't know the exact requirements, but AFAIK official temperatures are taken at a specified height off the ground.  There are other requirements as well: shade, for example.  I assume that this accounts for the fact that although telemetry has reported above freezing temperatures in our neighborhood mountains for weeks (last below-freezing temperature was registered ten days ago!), we still managed to ski 1700 feet of dry powder at more or less the same elevation last Sunday.  This is pretty common, right into late spring.  <br><br>Edit to add: I also assume that some temperature stations are better shaded than others, judging by the fact that the three different reports from the Mt. Baker area (ski resort, WA DOT and NWAC) sometimes differ by as much as 15 degrees during the day, but tend to agree pretty closely at night.

The Paradise temperature instrument is about 27 feet above the ground, which unfortunately is about the same distance above the snow surface this season. &gt;<br><br>It is on a tower to keep it out of the snow during normal winters. It also is not shaded, but it is in a white shield to minimize sun effects. Perhaps it is measuring warmer than normal temps at night as it is farther above the snow surface than normal? ???

You did pretty good Larry. The ground gets heated and cools primarily by radiation - it absorbs solar radiation from the sun, and emits radiation back to space. It is much more efficient at absorbing and emitting radiation than the air. On a calm, clear day the sun will heat the ground strongly. Without any wind, it will heat up quickly and be a few degrees warmer than the air 20 ft above say as there is not an efficient way to transfer heat from the ground to the air (diffusion is not efficient). At night, it will cool much more rapidly than the air above and be a few degrees cooler. If there is any wind, then heat can be transfered much more efficiently between ground and air through mixing. The coldest nights in Seattle are those clear, calm winter nights when the warmer air above cannot get mixed down (you will often see the NWS forecasters stress about the forcasted lows in this situation in the discussion - any wind or lack there of can make a big difference in temps).<br><br>Here's a good illustration of this link. This is an archived model forecast from Friday morning from somewhere in Puget Sound (Kosmos,WA? dunno where that is, but somewhere in south sound, inland away from the water). The red line is temperature. Click on loop at the top and notice how during the day the ground is warmer than the air above, and at night is colder. I'm not sure how long the link will work, probably a few weeks.

Thanks for the replies. That loop is pretty dramatic in showing the near-ground effect (once I figured out how to interpret it). I guess this just illustrates another grain of salt to take when browsing the telemetry data.