This past weekend had some pretty cold mornings once again, but the biggest difference between these and what we have been experiencing most of the winter has been the wind. There was very little, if any wind across the state this weekend leading to an almost bearable cold, even though temperatures were in the teens and 20's below zero. This is a little more typical of a Minnesota winter. When the skies clear and the winds calm, the very cold very dense air is allowed to sink to the surface, which in turn drops the temperature. These conditions will lead to the coldest air temperatures on the planet, but will also vary greatly over short distances because of terrain, vegetation, and amount of water. Natural vegetation and valleys will typically have the coldest temperatures, but if you are in the metro, you often stay relatively warm because of what we call "the urban heat island effect." The urban heat island effect is a warming phenomenon in major metropolitan areas because of a massive amount of concrete, asphalt, roofing, and many other man made materials that typically hold in more heat than grass, trees, and the ground otherwise would. This is far more predominant in the warmer months, but can still have a pretty good effect on clear and calm nights when temperatures can really plummet in open areas. What is very interesting to note, is often times heavy snow cover will negate this effect all together because large amounts of snow hold cold temperatures very well, but for whatever reason, this didn't happen over the weekend, even with perfect conditions. Here is a screen capture of temperatures at 7am Sunday morning across the metro area. This shows all types of reporting stations from the National Weather Service stations, to CoCoRas, Snotel, and a couple of other networks.
Not all of these temperatures are reliable because of software errors, broken systems, and other unseen devices, so I crossed those numbers off. Take note of the temperatures in the heart of the city, generally in the -6 or -7 range. But if you get out into the burbs or even open country, you see temperatures are much colder. Elk River reports -15 with Buffalo at -14, and even Jordan at -12. Also take note of the river valleys with Northfield sitting at -12 which is solely because of elevation. I hope this gives you an interesting perspective on just how much different temperatures can be over a very small area.