<p>I'm not an expert, but my understanding is that you need moisture/humidity <strong>and</strong>  nuclei around which water droplets can form. </p>

<p>I remember seeing a demonstration many years ago that showed this. There was a box about 12" per side with one side a rubber sheet and a few sides glass or plastic. They pulled the rubber sheet out (lowering the pressure) and nothing. They then lit and blew out a match inside the chamber. Closed the door, pulled the rubber sheet, viola a little cloud.</p>

<p>The soot provided the nuclei for the water droplets. </p>

CC BY-SA 4.0
2018-06-25T17:46:11.063Z
So you are suggesting that regardless of the pressure if there is no moisture you would get no clouds? I'll check the humidity level for that day.
a.m.
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2018-06-25T18:06:21.417Z
It seems unlikely to have clouds in the complete absence of moisture. As I looked into this a little further, temperature also plays a role in this dynamic. And I find myself quickly out of my depth. Hopefully someone with more complete knowledge will respond.
Tim Nevins
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2018-06-25T15:52:50.890Z
2018-06-25T15:52:50.890Z
Tim Nevins
<p>My understanding is that low pressure is usually associated with cloudy skies, however in the last week I observed a day that had low pressure reading but no clouds. Is this possible or did I perhaps read the barometer wrong?</p>

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2018-06-25T14:37:34.143Z
Low pressure is a relative minima in pressure, so if you don't have any other readings than your own, you can't say that it is low pressure. Also, do you know if it was MSLP (i.e. corrected to sea level) or if it hasn't been corrected for altitude.
BarocliniCplusplus
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2018-06-25T15:15:19.983Z
I believe it is. The data I have describes it as "The sea-level air pressure in millibars."
a.m.
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2018-06-25T19:45:44.113Z
It is perfectly possible to have low pressure areas without clouds.  For instance, here in the US Great Basin, it's possible to go months without significant cloud cover.
jamesqf
<meteorology><weather-forecasting>
Can you have a low pressure with no clouds?
a.m.
# Can you have a low pressure with no clouds?

(Asked by: username_0 on 2018-06-25)

My understanding is that low pressure is usually associated with cloudy skies, however in the last week I observed a day that had low pressure reading but no clouds. Is this possible or did I perhaps read the barometer wrong?

**Tags:** meteorology, weather-forecasting

> **Comments:**
> **username_1**: Low pressure is a relative minima in pressure, so if you don't have any other readings than your own, you can't say that it is low pressure. Also, do you know if it was MSLP (i.e. corrected to sea level) or if it hasn't been corrected for altitude.  
> **username_0**: I believe it is. The data I have describes it as "The sea-level air pressure in millibars."  
> **username_2**: It is perfectly possible to have low pressure areas without clouds.  For instance, here in the US Great Basin, it's possible to go months without significant cloud cover.  

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## 1 answers

### Answer by username_3 on 2018-06-25. Score: 1

I'm not an expert, but my understanding is that you need moisture/humidity **and** nuclei around which water droplets can form.

I remember seeing a demonstration many years ago that showed this. There was a box about 12" per side with one side a rubber sheet and a few sides glass or plastic. They pulled the rubber sheet out (lowering the pressure) and nothing. They then lit and blew out a match inside the chamber. Closed the door, pulled the rubber sheet, viola a little cloud.

The soot provided the nuclei for the water droplets.

> **Comments:**
> **username_0**: So you are suggesting that regardless of the pressure if there is no moisture you would get no clouds? I'll check the humidity level for that day.  
> **username_3**: It seems unlikely to have clouds in the complete absence of moisture. As I looked into this a little further, temperature also plays a role in this dynamic. And I find myself quickly out of my depth. Hopefully someone with more complete knowledge will respond.  

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