<p>I think you're mixing two things together. There are generally 2 processes that correlate low temperatures during and after a snowfall, but they are separated. These are both based on physical laws but also on my personal experience :)</p>
<p>First of all, during a strong snowfall (the same usually does not happen for light snowfall) the snowflakes have to fall through different layers to finally arrive at the surface. If the temperature at the surface is not extremely low (and this is the case for most mid-latitudes snowfalls) most of the snowflakes will melt, at least partially, when falling. This melting process is what causes a sudden drop of temperature that can be observed during strong snowfall.</p>
<p>To observe this you need to get temperature data with high sampling (at least 5 minutes) because the process is really fast and hourly observations will not capture it. Plus, it is not always visible because it really depends on the temperature you have at the beginning of the snowfall. If you're starting from 1/2°C, you'd see a strong drop to values close to 0. If you're already starting from temperatures close to 0 or negative probably you won't see a change at all.</p>
<p>Atmospheric vertical profilers can also catpure snow melting and associated temperature drops, but this kind of data is obviously hard to find.</p>
<p>Second, the process of surface cooling after a snowfall is mostly related to radiative balance. In fact, after a strong snowfall usually the sky clears up (this is because again in mid-latitudes strong snowfall are associated with cold fronts moving in and bringing dry and cold air from the north). This enhances surface cooling because there are no clouds reflecting the infrared radiation irradiated towards the sky. Snow (especially when fresh) is really effective in radiate energy, way more than bare soil, and that's why the surface temperature decreases rapidly. Also, during the day, snow reflects a lot of incoming solar radiation, preventing the surface from heating up. If the snow persists for many days this process amplifies and can lead to surface thermal inversions. There are some other processes causing cooling at the surface, like snow sublimation and snow melting.</p>

CC BY-SA 4.0
2024-01-18T16:40:04.847Z
The white surface is NOT effective in radiating energy. The black is. You mixed radiating and reflecting capabilities. White reflects but does not radiate, and vice versa. So, the snow surface saves energy, in the ground and the snow itself.
Gangnus
CC BY-SA 4.0
2024-01-18T20:50:51.723Z
The fact that the snow is "white" does NOT mean it cannot radiate: we're talking about thermal infrared spectrum so the snow radiates proportionally to its temperature and emissivity (Stefan-Boltzmann). As snow has a higher emissivity than bare soil it can emit more efficiently heat. You mention that snow is a good insulator, and this is another factor hindering surface warming because the heat coming from the soil does not reach the air but stays in the snowpack. There are other secondary effects like latent heat and a higher thermal mass that causes an additional cooling effect.
Droid
CC BY-SA 4.0
2024-01-18T20:51:28.763Z
There are many papers describing these effects, you won't have a hard time finding sources otherwise I'd be happy to send it to you ;)
Droid
CC BY-SA 4.0
2024-01-18T20:54:20.200Z
I have to say, though, the biggest impact on surface temperature may be just a side-effect of a snowfall, in the sense that, as I said before, such processes are associated with cold air advection which brings also really dry and clean air, a medium that is ideal to irradiate heat. So eventually the biggest factors enhancing surface cooling are the shortwave reflection during the day and the enhanced cooling due to drier air. All the rest is likely secondary
Droid
CC BY-SA 4.0
2024-01-19T13:21:12.450Z
But at any rate, please, correct that: "Snow (especially when fresh) is really effective in radiate energy". It is absolute nonsense. It is effective in *reflecting*, not  *radiating*
Gangnus
CC BY-SA 4.0
2024-01-19T16:51:15.283Z
I don't understand why you get so angry about people asking question, that's the whole point of this stack exchange. The OP maybe has no deep knowledge of atmospheric science and was just curious. There's no need to address people in such a negative way. You can leave a comment to improve the question or downvote it, there's no need to use bad words.
Droid
CC BY-SA 4.0
2024-01-19T16:55:07.333Z
Regarding the other fact I already explained to you what it means that it radiates more efficiently: it has a higher emissivity than bare soil so it radiates more efficiently than it. There's nothing to discuss about this, and you'll find this in many articles and papers.
The fact that it is efficient in reflecting it's a different story: you're talking about short-wave and I'm talking about long-wave infrared radiation.
Droid
CC BY-SA 4.0
2024-01-19T16:55:10.083Z
Regarding the winter day duration obviously it depends where you are on the planet. But still here we're talking about a difference between bare soil and snow, so of course IN THE SAME ATMOSPHERIC CONDITIONS, the second one would reflect more radiation.
Droid
CC BY-SA 4.0
2024-01-20T01:10:17.093Z
Yes, for the reflection. But in winter in extended areas, the reflection is unimportant at all.
Gangnus
CC BY-SA 4.0
2024-01-21T01:24:55.890Z
**Comments have been [moved to chat](https://chat.stackexchange.com/rooms/150989/discussion-on-answer-by-droid-colder-after-snow); please do not continue the discussion here.** Before posting a comment below this one, please review the [purposes of comments](/help/privileges/comment). Comments that do not request clarification or suggest improvements usually belong as an [answer](/help/how-to-answer), on [meta], or in [chat]. Comments continuing discussion may be removed.
f.thorpe
CC BY-SA 4.0
2024-01-17T10:04:05.553Z
2024-01-17T10:04:05.553Z
Droid
<p>The aftermath of a snowfall can also cause a cooling near the surface, if an air mass moves in that's warm enough to melt the snow. The snow indeed starts to melt, thereby absorbing the latent heat required to do so and cooling the otherwise warmer air near the surface. If, as often happens during the winter, the warmer air also brings in a dew point above 0°C/32°F, then this near-surface cooling can lead to water vapor condensation and thus induce fog.</p>

CC BY-SA 4.0
2024-01-26T14:18:48.170Z
2024-02-24T08:01:41.893Z
2024-02-24T08:01:41.893Z
Oscar Lanzi
<p>I had a physics professor that said that it becomes colder after snow because heat from the air is absorbed by the snow as it melts.</p>
<p>This makes sense to me in that the snow should lower the temperature from what it would have been had the snow not been on the ground because the phase change of the snow should absorb ambient heat, but it does not make sense to me in that the ambient temperature should be lower than when it was snowing in an absolute sense, because the temperature would have to be &gt; 0 C for the snow to melt and the snow would have to have been falling at a temperature &lt; 0 C.</p>
<p>Does anyone know if temperature is lower following snow than it is during snow and if it is lower whether my professor got the mechanism wrong? Or, if there is something that I'm not accounting for?</p>
<p>Alternatively, does anyone know of good atmospheric data in the United States that I could use to confirm or disprove the correlation? (I would need temperature, precipitation, and whether it was snowing or not - more granular the better - I have strong python / data science skills and could do the confirmation myself).</p>

CC BY-SA 4.0
2024-01-18T16:53:48.770Z
I am afraid, the sentence of your prof, as you remember it, lacks concretization. 
 
 - Are we talking about the daytime under sunlight? (what effect is more important? - radiation or reflection of the surface?)
 - Is the temperature above zero, close to it, or deep below? (Does the snow melt at all or melt in some moments?)
 - What is meant by "after snow" - after the snowfall stops, or after the snow cover melts?
Gangnus
CC BY-SA 4.0
2024-01-18T16:53:54.240Z
- What is the wetness of the air? In Eastern Europe the weather with snowfall is warm and wet, the snow falls at temperatures of about +3- -5C. And the clouds fleeing means sunny and frosty high-pressure weather comes. On the contrary, in the dry areas, for example in inner Finland, the snow easily falls at -15C. And after the snowing clouds flow away, the sunshine comes and the temperature rises.
Gangnus
CC BY-SA 4.0
2024-01-18T19:29:23.167Z
So, it is impossible to answer to such undefined question.
Gangnus
CC BY-SA 4.0
2024-01-20T16:07:17.910Z
"It has a higher *infrared* (Droid was talking about it) emissivity than bare soil" YES. Please read Section 7 of the article that you can find at: doi: 10.1098/rsta.2018.0161
To demonstrate the contrary, please convince me that infrared emissivity of bare soil is above the one of snow, which is 0.98-0.99, and I would be very happy to change my idea. As Droid mentioned, color and emissivity in the IR are totally unrelated.
Husky
<temperature><precipitation><snow>
colder after snow
Campbell Hutcheson
# colder after snow

(Asked by: username_0 on 2024-01-17)

I had a physics professor that said that it becomes colder after snow because heat from the air is absorbed by the snow as it melts.

This makes sense to me in that the snow should lower the temperature from what it would have been had the snow not been on the ground because the phase change of the snow should absorb ambient heat, but it does not make sense to me in that the ambient temperature should be lower than when it was snowing in an absolute sense, because the temperature would have to be > 0 C for the snow to melt and the snow would have to have been falling at a temperature < 0 C.

Does anyone know if temperature is lower following snow than it is during snow and if it is lower whether my professor got the mechanism wrong? Or, if there is something that I'm not accounting for?

Alternatively, does anyone know of good atmospheric data in the United States that I could use to confirm or disprove the correlation? (I would need temperature, precipitation, and whether it was snowing or not - more granular the better - I have strong python / data science skills and could do the confirmation myself).

**Tags:** temperature, precipitation, snow

> **Comments:**
> **username_1**: I am afraid, the sentence of your prof, as you remember it, lacks concretization.     - Are we talking about the daytime under sunlight? (what effect is more important? - radiation or reflection of the surface?)  - Is the temperature above zero, close to it, or deep below? (Does the snow melt at all or melt in some moments?)  - What is meant by "after snow" - after the snowfall stops, or after the snow cover melts?  
> **username_1**: - What is the wetness of the air? In Eastern Europe the weather with snowfall is warm and wet, the snow falls at temperatures of about +3- -5C. And the clouds fleeing means sunny and frosty high-pressure weather comes. On the contrary, in the dry areas, for example in inner Finland, the snow easily falls at -15C. And after the snowing clouds flow away, the sunshine comes and the temperature rises.  
> **username_1**: So, it is impossible to answer to such undefined question.  
> **username_2**: "It has a higher *infrared* (username_3 was talking about it) emissivity than bare soil" YES. Please read Section 7 of the article that you can find at: doi: 10.1098/rsta.2018.0161 To demonstrate the contrary, please convince me that infrared emissivity of bare soil is above the one of snow, which is 0.98-0.99, and I would be very happy to change my idea. As username_3 mentioned, color and emissivity in the IR are totally unrelated.  

---

## 2 answers

### Answer by username_3 on 2024-01-17. Score: 4 | Accepted answer

I think you're mixing two things together. There are generally 2 processes that correlate low temperatures during and after a snowfall, but they are separated. These are both based on physical laws but also on my personal experience :)

First of all, during a strong snowfall (the same usually does not happen for light snowfall) the snowflakes have to fall through different layers to finally arrive at the surface. If the temperature at the surface is not extremely low (and this is the case for most mid-latitudes snowfalls) most of the snowflakes will melt, at least partially, when falling. This melting process is what causes a sudden drop of temperature that can be observed during strong snowfall.

To observe this you need to get temperature data with high sampling (at least 5 minutes) because the process is really fast and hourly observations will not capture it. Plus, it is not always visible because it really depends on the temperature you have at the beginning of the snowfall. If you're starting from 1/2°C, you'd see a strong drop to values close to 0. If you're already starting from temperatures close to 0 or negative probably you won't see a change at all.

Atmospheric vertical profilers can also catpure snow melting and associated temperature drops, but this kind of data is obviously hard to find.

Second, the process of surface cooling after a snowfall is mostly related to radiative balance. In fact, after a strong snowfall usually the sky clears up (this is because again in mid-latitudes strong snowfall are associated with cold fronts moving in and bringing dry and cold air from the north). This enhances surface cooling because there are no clouds reflecting the infrared radiation irradiated towards the sky. Snow (especially when fresh) is really effective in radiate energy, way more than bare soil, and that's why the surface temperature decreases rapidly. Also, during the day, snow reflects a lot of incoming solar radiation, preventing the surface from heating up. If the snow persists for many days this process amplifies and can lead to surface thermal inversions. There are some other processes causing cooling at the surface, like snow sublimation and snow melting.

> **Comments:**
> **username_1**: The white surface is NOT effective in radiating energy. The black is. You mixed radiating and reflecting capabilities. White reflects but does not radiate, and vice versa. So, the snow surface saves energy, in the ground and the snow itself.  
> **username_3**: The fact that the snow is "white" does NOT mean it cannot radiate: we're talking about thermal infrared spectrum so the snow radiates proportionally to its temperature and emissivity (Stefan-Boltzmann). As snow has a higher emissivity than bare soil it can emit more efficiently heat. You mention that snow is a good insulator, and this is another factor hindering surface warming because the heat coming from the soil does not reach the air but stays in the snowpack. There are other secondary effects like latent heat and a higher thermal mass that causes an additional cooling effect.  
> **username_3**: There are many papers describing these effects, you won't have a hard time finding sources otherwise I'd be happy to send it to you ;)  
> **username_3**: I have to say, though, the biggest impact on surface temperature may be just a side-effect of a snowfall, in the sense that, as I said before, such processes are associated with cold air advection which brings also really dry and clean air, a medium that is ideal to irradiate heat. So eventually the biggest factors enhancing surface cooling are the shortwave reflection during the day and the enhanced cooling due to drier air. All the rest is likely secondary  
> **username_1**: But at any rate, please, correct that: "Snow (especially when fresh) is really effective in radiate energy". It is absolute nonsense. It is effective in *reflecting*, not  *radiating*  
> **username_3**: I don't understand why you get so angry about people asking question, that's the whole point of this stack exchange. The OP maybe has no deep knowledge of atmospheric science and was just curious. There's no need to address people in such a negative way. You can leave a comment to improve the question or downvote it, there's no need to use bad words.  
> **username_3**: Regarding the other fact I already explained to you what it means that it radiates more efficiently: it has a higher emissivity than bare soil so it radiates more efficiently than it. There's nothing to discuss about this, and you'll find this in many articles and papers. The fact that it is efficient in reflecting it's a different story: you're talking about short-wave and I'm talking about long-wave infrared radiation.  
> **username_3**: Regarding the winter day duration obviously it depends where you are on the planet. But still here we're talking about a difference between bare soil and snow, so of course IN THE SAME ATMOSPHERIC CONDITIONS, the second one would reflect more radiation.  
> **username_1**: Yes, for the reflection. But in winter in extended areas, the reflection is unimportant at all.  
> **username_4**: **Comments have been [moved to chat](https://chat.stackexchange.com/rooms/150989/discussion-on-answer-by-username_3-colder-after-snow); please do not continue the discussion here.** Before posting a comment below this one, please review the [purposes of comments](/help/privileges/comment). Comments that do not request clarification or suggest improvements usually belong as an [answer](/help/how-to-answer), on [meta], or in [chat]. Comments continuing discussion may be removed.  

---

### Answer by username_5 on 2024-01-26. Score: 3

The aftermath of a snowfall can also cause a cooling near the surface, if an air mass moves in that's warm enough to melt the snow. The snow indeed starts to melt, thereby absorbing the latent heat required to do so and cooling the otherwise warmer air near the surface. If, as often happens during the winter, the warmer air also brings in a dew point above 0°C/32°F, then this near-surface cooling can lead to water vapor condensation and thus induce fog.


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