Topic: Min temps few degrees off with Daytime FARS

[rockncola]

Hi all.

It's winter here and something I'm noticing is that on cold, calm nights/mornings my station is often 2-3C warmer than the official stations around me. I can also confirm this as I've taken a temperature gauge out to the station's location itself, left it there for some time and it also reads cooler than the station itself which is sitting right next to it. I've tried calibrating it down to the correct temperature but that just leads to daytime temperatures running way too cool. My question is what could be causing this and how might I go about fixing it?

Thanks.

[johnd]

My guess is that your station is recording correctly. If you just left a separate thermometer in the open air on a clear night then of course it will read lower than true air temperature because of radiation effects.

What height is your station's temp sensor - is it the recommended 1.2m? If not then it will record non-standard temps on a radiation night.

[ValentineWeather]

Everywhere is the same with warmer locations like the top of a hill or ridge at night and then you have drainage areas where calm unmixed cooler air drains to lower areas. As John said for any exposed thermometer, not in a protective shield, radiational cooling will occur with calm wind and clear sky.

Good examples are frost on grass or frost over the exposed windshield in the morning but actual air temperature never reaches freezing at thermometer height.

[rockncola]

Guys, you were exactly right. I happened to find a few unofficial stations not far from me (in town) and they've all been recording very similar temps to mine. It seems to be mainly the airport stations recording the colder temps on cool, still nights.