<blockquote>
  <p>Is there a correlation between temperature and cloud, during the night?</p>
</blockquote>

<p>Very much so. It's called radiative cooling. Three factors come into play: cloudiness, relative humidity, and windiness. Nighttime radiative cooling is greatest under clear skies, low relative humidity, and light or no winds. The temperature drop (in degrees per hour) can be a factor of more than four greater under conditions of clear skies, low humidity, and light winds compared to that under conditions of thick low clouds and high relative humidity. That increased cooling can make for a significant temperature drop on a long winter night.</p>

CC BY-SA 3.0
2015-01-09T17:09:59.310Z
Four degrees per hour is pretty significant! Here's a resource you might want to point to that backs up your answer: http://www.sjsu.edu/faculty/watkins/cloudiness.htm
Adam Davis
CC BY-SA 3.0
2015-01-09T17:19:39.843Z
"four degrees" isn't unambiguous. Do you mean four kelvin?
410 gone
CC BY-SA 3.0
2015-01-09T18:26:49.820Z
Whether radiative cooling is largest under low or now wind depends on the perspective.  When measuring temperature in a valley it's certainly true.  When measuring outgoing longwave radiation from space, I can't think why it would be.
gerrit
CC BY-SA 3.0
2015-01-09T18:55:53.913Z
@gerrit Cooling usually refers to change in temperature. Wind speed does not affect the radiative flux itself.
milancurcic
CC BY-SA 3.0
2015-01-09T19:16:33.923Z
@gerrit - A marked nighttime temperature inversion sets up under conditions of clear skies, low humidity, and no wind at all, and this grows in height throughout the night. Surface temperature can be 6C cooler than air 1000 meters above the surface by the end of the night. With light winds, there is some turbulent mixing of the cooler air below and warmer air above. The cooling isn't as strong. The inversion never sets up with even stronger winds. In this case, turbulent cooling dominates over radiative cooling.
David Hammen
CC BY-SA 3.0
2015-01-10T03:33:20.007Z
Aren't winter temperatures at higher lattitudes (day or night) associated with high pressure systems generally colder than those with low pressure systems? And high pressure systems tend to be clear. So in addition to the radiative cooling, is there a reason associated with the weather patterns? I suppose some of this could be a chicken and egg issue.
haresfur
CC BY-SA 3.0
2015-01-21T10:28:49.120Z
Thanks for this David! I have check on [radiative cooling on wikipedia](https://en.wikipedia.org/wiki/Radiative_cooling#Radiative_cooling_on_Earth.27s_surface_at_night)and I think I understood it the wrong way. It's seems that the clouds stops the "warmth" (or rather the coldness) of the deep night sky rather than the clouds reflecting the warmth accumulated by the earth during the day (cf. th explanation of the experience with the paper in the link above).
MagTun
CC BY-SA 3.0
2015-01-09T17:03:11.120Z
2015-01-09T17:03:11.120Z
David Hammen
<p>I have noticed this winter that nights without clouds (especially when the 12h before the night where not cloudy) were way colder than the cloudy ones. </p>

<p>It makes sense to me because the clouds can reflect the heat (infrared?) earth have accumulated during the day rather than loosing it into the atmosphere (like a kind of blanket). But I could be "swayed" by a confirmation bias here, so here is my question:</p>

<p>Is there a correlation between temperature and cloud, <strong>during the night</strong>?</p>

CC BY-SA 3.0
2015-01-09T16:17:32.317Z
@AdamDavis - Insignificant? No. It can be extremely significant.
David Hammen
<meteorology><temperature><clouds>
Are cloudy nights warmer than nights without clouds?
MagTun
# Are cloudy nights warmer than nights without clouds?

(Asked by: username_0 on 2015-01-09)

I have noticed this winter that nights without clouds (especially when the 12h before the night where not cloudy) were way colder than the cloudy ones.

It makes sense to me because the clouds can reflect the heat (infrared?) earth have accumulated during the day rather than loosing it into the atmosphere (like a kind of blanket). But I could be "swayed" by a confirmation bias here, so here is my question:

Is there a correlation between temperature and cloud, **during the night**?

**Tags:** meteorology, temperature, clouds

> **Comments:**
> **username_1**: @username_2 - Insignificant? No. It can be extremely significant.  

---

## 1 answers

### Answer by username_1 on 2015-01-09. Score: 16 | Accepted answer

> Is there a correlation between temperature and cloud, during the night?

Very much so. It's called radiative cooling. Three factors come into play: cloudiness, relative humidity, and windiness. Nighttime radiative cooling is greatest under clear skies, low relative humidity, and light or no winds. The temperature drop (in degrees per hour) can be a factor of more than four greater under conditions of clear skies, low humidity, and light winds compared to that under conditions of thick low clouds and high relative humidity. That increased cooling can make for a significant temperature drop on a long winter night.

> **Comments:**
> **username_2**: Four degrees per hour is pretty significant! Here's a resource you might want to point to that backs up your answer: http://www.sjsu.edu/faculty/watkins/cloudiness.htm  
> **username_3**: "four degrees" isn't unambiguous. Do you mean four kelvin?  
> **username_4**: Whether radiative cooling is largest under low or now wind depends on the perspective.  When measuring temperature in a valley it's certainly true.  When measuring outgoing longwave radiation from space, I can't think why it would be.  
> **username_5**: @username_4 Cooling usually refers to change in temperature. Wind speed does not affect the radiative flux itself.  
> **username_1**: @username_4 - A marked nighttime temperature inversion sets up under conditions of clear skies, low humidity, and no wind at all, and this grows in height throughout the night. Surface temperature can be 6C cooler than air 1000 meters above the surface by the end of the night. With light winds, there is some turbulent mixing of the cooler air below and warmer air above. The cooling isn't as strong. The inversion never sets up with even stronger winds. In this case, turbulent cooling dominates over radiative cooling.  
> **username_6**: Aren't winter temperatures at higher lattitudes (day or night) associated with high pressure systems generally colder than those with low pressure systems? And high pressure systems tend to be clear. So in addition to the radiative cooling, is there a reason associated with the weather patterns? I suppose some of this could be a chicken and egg issue.  
> **username_0**: Thanks for this username_1! I have check on [radiative cooling on wikipedia](https://en.wikipedia.org/wiki/Radiative_cooling#Radiative_cooling_on_Earth.27s_surface_at_night)and I think I understood it the wrong way. It's seems that the clouds stops the "warmth" (or rather the coldness) of the deep night sky rather than the clouds reflecting the warmth accumulated by the earth during the day (cf. th explanation of the experience with the paper in the link above).  

---

