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41 votes

Why would it be drier indoors during the winter vs the summer?

The only physics you need to know is that if the temperature is higher the air† can hold more water vapour (the gaseous phase of water). Cool molecules don't have enough energy to free themselves from ...
Matt Hall's user avatar
  • 11k
17 votes

Why does warm air "hold" more moisture?

Saying that warm air "holds" more moisture is technically incorrect, but is a common colloquialism. Let's break it down to the technicalities. Let's consider a glass of water with a vacuum (no air) ...
BarocliniCplusplus's user avatar
15 votes
Accepted

Why (actually) is the night sky so bright in the city? How far up is that happening?

What's actually happening is scattering of light, both off of aerosol particles and nitrogen and oxygen molecules. For a review of quantitative models of light pollution as a function of distance ...
DavePhD's user avatar
  • 5,962
14 votes

Why would it be drier indoors during the winter vs the summer?

Because cooling air tends to take out moisture, while heating air doesn't change the actual moisture levels. When air gets colder, it can't "hold" as much water vapor (lower saturation vapor ...
JeopardyTempest's user avatar
11 votes

Why would it be drier indoors during the winter vs the summer?

A psychrometric chart is very useful for those kind of calculations. There is a lot of information and the chart looks overwhelming at first. You can click on the charts to see a larger version. 35°...
Eric Duminil's user avatar
11 votes

Is "humidity" the quantifiable metric for mugginess?

Relative humidity is just about the most over-used, relatively useless measure of moisture there is. It's just how full the air is, based upon what it can hold, in moisture. Warm air holds more ...
JeopardyTempest's user avatar
10 votes

How do the pros measure humidity?

The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with ...
M Juckes's user avatar
  • 772
9 votes
Accepted

How to calculate relative humidity from temperature, dew point, and pressure?

You can refer to this question for more detail on the origin of this formula (based on the Magnus approximation), but if you do some algebra to the expression there for dew point ($TD$) as function of ...
Camilo Rada's user avatar
  • 17.7k
8 votes

Why do anticyclones bring clear skies in summertime?

Why anticyclones are also called areas of high pressure Let's call anticyclones areas of high pressure. Areas of high pressure (anticyclones), pull air towards the earth's surface. The increase in ...
G. Gip's user avatar
  • 772
8 votes

Why does warm air "hold" more moisture?

The water molecule is just another molecule in the atmosphere - except that it's triatomic, whereas 99.97% of the dry atmosphere is monatomic (Argon) and diatomic (Oxygen and Nitrogen). It's also ...
rchuso's user avatar
  • 151
8 votes
Accepted

Relative Humidity approximation from Dew Point and Temperature

The equation for relative humidity is $$RH=100\times \frac{e}{e_s(T)}=100\times \frac{e_s(T_d)}{e_s(T)} \tag{1}$$ Where $T_d$ is the dewpoint temperature and $T$ is the temperature, $e$ is the water ...
BarocliniCplusplus's user avatar
7 votes

What the humidity metric is hiding?

Weather services rarely state the absolute humidity because it is not easy to determine. Instead, they state the relative humidity. Absolute humidity is the mass of water vapor divided by the mass ...
Fred's user avatar
  • 24.7k
7 votes

How is relative humidity determined from a wet and dry bulb readings?

Edit: 1 May 2021 The following procedure uses the less accurate method from page 455 onward from the scanned sections of the book pictured below, from the original answer. The procedure is a ...
Fred's user avatar
  • 24.7k
6 votes

Why does warm air "hold" more moisture?

What is the deep physics or chemistry reason this happens? In one word, entropy. In a thousand words (i.e., a picture), Source: Wikipedia article on Phase Diagram The above is a phase diagram of ...
David Hammen's user avatar
  • 23.7k
6 votes

How do the pros measure humidity?

We use something like an Onset HOBO electronic sensor. They've got logging (and in some cases, networking) built in. They'll typically log both temperature and relative humidity at regular intervals ...
410 gone's user avatar
  • 4,080
5 votes
Accepted

Is it hotter in different places with the same air temperature?

A temperature is a temperature but the effect of that temperature is not always the same. Some things that add to our perception include sun intensity, wind, humidity, and simply what we are used to. ...
dlb's user avatar
  • 626
5 votes

Is it hotter in different places with the same air temperature?

While perceptions about the climate can have an effect on how we react to our environment, Guangdong and Minnesota are fundamentally different climates altogether. Using the Koppen-Geiger climate ...
Trevor J. Smith's user avatar
5 votes
Accepted

How to predict when contrails are likely to form over a specific location using public data?

As described here, condensation of cloud particles (i.e., contrail formation) will occur if the mixing between hot and moist exhaust from an aircraft engine and ambient environmental air results in ...
dplmmr's user avatar
  • 1,144
5 votes
Accepted

What is the difference between surface specific humidity and surface relative humidity?

Let's put it a different way: Specific humidity is how much actual water (vapor) is in the air. More warmth tends to mean more evaporation. Warming air also raises the limit of how much water it can ...
JeopardyTempest's user avatar
5 votes

Is "humidity" the quantifiable metric for mugginess?

There are a number of things going on here. One is microclimate. The data for Houston most likely comes from Houston Intercontinental Airport (IAH), which is 70 miles from the Gulf Coast. Travel ten ...
David Hammen's user avatar
  • 23.7k
5 votes
Accepted

How to convert specific humidity ERA5 in kg/kg to g/kg or mm/day?

The specific humidity of ERA5 data is kg/kg, but some articles work with this variable in g/kg. How can I convert this? Conversion from kg/kg to g/kg is as simple as multiplying by 1000. Or to ...
alex_danielssen's user avatar
5 votes

At 100% relative humidity, why does the air still feels dry?

Humans cannot directly sense humidity since we lack the sensory neurons for that specific purpose. Therefore our sensation of, say, relative humidity in the air is always a combination of different ...
Jpe61's user avatar
  • 184
4 votes
Accepted

How does humidity vary with height in the Earth's atmosphere?

Humidity strongly varies as a function of time and space, which is why standard atmospheres like CIRA may choose to omit it at all. It simply doesn't make sense to include an “average” humidity ...
gerrit's user avatar
  • 11.7k
4 votes
Accepted

Why does relative humidity seem to correlate with high temperature (at least where I live)?

In coastal New Jersey, relative humidity is maximal in the early fall when the ocean temperature is warmest, and minimal in early spring when the ocean is coldest. However, the monthly variation is ...
DavePhD's user avatar
  • 5,962
4 votes

Why does relative humidity drop if I open the window in winter? What about the temperature drop?

Let's do this with accurate equations. We know how to calculate the saturated water vapour pressure for temperature $T$: $$e_s(T)=e_{s0}e^{\frac{h_i}{R_w}(\frac{1}{T_{s0}}-\frac{1}{T})}=610\text{ Pa} \...
User123's user avatar
  • 638
4 votes
Accepted

What Pa level should I use when looking at Relative Humidity data from CMIP6 models?

What Pa level should I use... That really depends what you're trying to do with it. Is this data just missing near the surface? The pressure level 1 hur data in ...
Deditos's user avatar
  • 3,960
3 votes

How would I use data to find specific humidity and mixing ratio?

The online calculator is giving you the specific humidity, which at a relative humidity of 43% is 43% of the saturation specific humidity at that temperature. Reading from the chart, a rough ...
alnilam's user avatar
  • 31
3 votes
Accepted

How to calculate humidity using outside temperature and outside relative humidity?

You can easily achieve that assuming that there is no sources of water vapour inside, so the absolute humidity (mass of water per volume of air), remains constant. This excerpt from my undergrad tesis ...
Camilo Rada's user avatar
  • 17.7k
3 votes
Accepted

Is there a name for these "pouring" clouds?

The term used by the American Meteorological Society is orographic fog. A perhaps more descriptive name is "orographic waterfall cloud". Prevailing winds can force air to flow upwards over rising ...
David Hammen's user avatar
  • 23.7k
3 votes

Mild climate, low-humidity city all year round

Low humidity means nowhere near the coast or near any large lakes. Warm winter temperatures without being too hot in summer means tropical high elevation or lower latitude inland sub-tropical. Parts ...
Gordon Stanger's user avatar

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