For Eugene, Oregon, Accuweather predicts some snow for early this morning, accumulating to about an inch, and on Monday night more snow, possibly accumulating to between two and four inches. ( I seriously doubt that will happen, because rain and snow are becoming mere memories. We’re already some months into yet another dismal rain year, which is even worse considering the rain deficit since the new year).
Anyhow, at the same time this (probably imaginary) snow is being predicted, the actual temperature is expected to stay above freezing, though the “real-feel” temp is much cooler. Obviously, a raindrop or snowflake can’t feel anything. On the other hand, blowing on things does have a real cooling affect on them. You can cool down hot coffee or soup that way, as the moving air draws heat away from the hot liquid.
I’m in Portland, and it’s snowing as I write this. According to my watch it’s 34F, and Siri is saying it’s 36F. So, while I can’t get into specifics (not being a meteorologist), I’d be inclined to say the answer is yes.
There can be snow if it’s above freezing at ground level, but I think the wind makes it less likely. Blowing warmer air on something heats it up faster, for the same reason that blowing cooler air on coffee or soup will cool it down faster.
The water can freeze at altitude (less than 0°C), with temperature cooler than on ground (4 or 5°C). Than when the snow had fallen, it takes time to heat and melt if the temperature is slightly above freezing level and the snow is a good insulator, so can form a blanket on the ground, and further snow will land on snow cooler than the ground.
And the feel temperature depend of humidity/evaporation, so definitely will help snow.
Also humidity plays a factor, at least in snow making at ski resorts and it is possible to make (poor quality) snow at 39F at/near 0% humidity due to evaporative cooling.
Doesn’t have diddly to do with the “real feel” temperature. The snowflakes form up higher, and it has to be below freezing in order for them to form, but can be significantly warmer at ground level when you step out of the house and say “Hey, it’s snowing”. ETA: actually FrenchDunadan explained it better. And I guess I’m wrong about the irrelevance of the “real feel” since humidity is a factor.
“Real feel” is based on human experience and how fast a 98.6°F object that generates heat to maintain that temperature loses heat in a given set of conditions (assuming we’re talking about winter). The reason blowing on things has a cooling effect is it speeds up the heat transfer, meaning how fast the warmer object reaches the temperature of the cooler air. However, blowing 34°F air on water that is 40°F will never make that water colder than 34°F no matter how hard it blows. (This ignores effects of radiated heat and evaporative cooling, but I don’t think that effect is large for the situation we’re talking about.)
Also as mentioned, multiple conditions have to occur to get snow on the ground and the air temperature at ground level might not even be the most important factor. Snow forms way up high.
Yes. I assume “real feel” is what we in the Great White North refer to as wind chill. You’d lose X calories per minute at this temperature A° in a still air environment - so if it’s warmer B° but windier, you still lose the same X calories per minute. Hence, the wind chill is usually expressed as a “equivalent to…” temperature.
(Although Environment Canada anso wants tu use WCI* = wind chill index, kg⋅cal/m2/h that nobody understands.)
Snow forms at higher altitudes. The standard for adiabatic cooling (approximate, it varies with humidity) is about 5°F/1000ft of altitude, so it’s very easy to be, say, 35°F, warmer than freezing, and still have snow since it would be below freezing over 1000 feet higher in the clouds. Keep in mind it takes a lot of heat to turn ice to water at the same temperature (See how long ice cubes last in a cold drink?). It also depends- ground temperature may be warm enough to melt the snow, or the amount accumulating may cool the ground so snow stops melting and accumulates.
Here in Canada we’ve seen all sorts of conditions. Every possible one that involves snow. Toronto just had snow thunderstorms.
They use the term “real feel” for two separate things, and yes, one of those is wind chill. The other is for warmer weather, when the humidity is high enough that it becomes noticeably uncomfortable; the term “heat index” is sometimes also used for that effect.
And, as others have mentioned, wind chill / “real feel” isn’t going to be the factor that comes into play in the OP’s question.
At a temperature at ground level that’s just above freezing, as the OP described, the air temperature at cloud level will be well below freezing (as @md-2000 describes), and certainly cold enough to produce snow when it starts to precipitate from the cloud. The question becomes, is the temperature in the air between the clouds and the ground cold enough for those snowflakes to stay in snowflake form all the way down, or if they’ll melt on the way down.
It’s absolutely possible for the air temperature at ground level to be above freezing, but for snow to be hitting the ground, if it’s cold enough aloft.
We got only a very small amount of snow this year, which isn’t unusual. But what little we did have was the finest powder I’ve ever seen. I’d always imagined that snow had to fall in easily visible flakes, but these grains of powder were all but invisible. You could hold your hand out and feel the tiny pinpricks of cold without being able to see the flakes landing.
It’s roughly 3° colder per 1000’ of elevation* so it’ll start out as snow & remain so all the way to the surface as long as it’s cold enough for most of the ride down. It it’s too warm it’ll change to rain…or sleet or
Generally, you can have inversions where you get a layer of warm over a colder layer.
We get ice fog a lot in Calgary. The weather services sometimes just refer to it as ice crystals. Poor visibility, and a very fine dust accumulates everywhere. Often comes with some cool optical effects such as light pillars.
I watched it snow for an hour and a half this morning when the temperature was between 34 and 36 degrees. The flakes kept hitting the ground and melting immediately on all the paved surfaces. Finally, it turned to a light rain and melted every trace of snow right before my other household members got up. I’m not sure they’d have believed me if I hadn’t taken a picture.
True, though in most situations in which “wind chill” is a thing, the air is likely to feel dry to us humans, in the absolute, as cold air simply can’t hold much water vapor.
It can also depend on ground cover snow. If it’s snowing while the temp is just above freezing, due to wind chill, etc, whether snow actually accumulates may depend on whether there’s already a build up on the ground.
A few inches old dense, heavy snow, then covered with ice from freezing rainfall, sitting on the ground, will mean that ANY snowfall, even during light over zero temps, will accumulate.
When, in fact, without that existing ground cover snow, any such snow fall would melt on contact with the ground. So zero accumulation in those circumstances.
I have often wondered, if it’s 30 degrees out with a wind chill factor of 15, does it take more fuel to heat a building than if it were 30 degrees with no wind?
The exterior of the building won’t get any colder than 30; wind chill is a measure that describes what it feels like to a human to be in those conditions, and reflects the fact that wind will cool you more quickly than still air, so it feels colder to you. Wind can’t cool an object to a temperature that’s any lower than the actual (still) air temperature. But, what wind can do to an object is cool it off more rapidly than still air would (though it won’t cool it to any cooler than the still air temperature).
In the scenario you describe, there might be a couple of reasons why it would take more fuel to warm a building on a cold, windy day or night:
The heating system doesn’t just heat up the air inside the building; it also heats the walls, ceiling, etc., and some of that heat will work its way out to the exterior surfaces of the building, heating it up somewhat. If there’s wind, that’ll work to cool off the exterior more than still air would, and thus, the interior walls and ceiling might be a little colder than in still air. That might have a net effect of making the rooms cooler, and requiring more heating.
If the building has older windows, leaky doors, etc., which let in cold air, then if there’s wind, that might make the problem worse, and thus, again, require more fuel for heating.