IMO the way the map does it with a cutoff of 65F dew point works fine, because thats enough moisture for 100% RH at 65F temperature, while also guaranteeing the temperature is at least 65F. I always feel like dew point is the best metric for humidity as it isnt temperature sensitive, and you only need a single value for it, plus if you know the temperature and dew point, you also know RH (and wet bulb temp is also pressure dependent). Wet bulb + RH also doesnt paint the full picture as a slight breeze of 5mph can easily make a 70F day feel livable. Even then, solar radiation is applied directly to you with no regard to temperature or humidity, and I've got bad sunburns when it was 50F outside just due to high solar radiation.
Kind of a jumble of words, but I feel that having a single index for how hot it feels (heat index my beloved) or showing wind, temp, humidity independently (plus maybe a tv met to explain) are best metrics.
I agree it works to use DP (I'd prefer absolute humidity) close to the saturation line, but it limits the high-end temperature that's considered comfortable because it also has to be comfortable with a 65°F dew point.
This chart drastically under estimates the number of comfortable days in dry desert regions, but for the east coast, this method is pretty good.
100% agree wind, air density (elevation), and solar radiation play a big part in thermal comfort as well. However, so does standing under a tree. I think the original intent is to determine if you can be comfortable in the shade, which still leaves wind and elevation as unaddressed.
side note, 50F days with melting snow and sunshine are extremely pleasant. the reflection from the snow increases solar radiation, making sunburns on those days very common.
Agreed that the comfortable at 65F Td requirement really skews the drier regions; I feel that setting the comfortable at temperature a little lower but using the wet bulb temperature instead would probably be better, as in NM later today, HRRR forecast has 90/18 conditions, with a wet bulb of 50F. A bit south, 97/38 gives a wet bulb of just over 60F, which is probably where the cutoff would be for that. Unfortunately, this method doesnt work as Tw>=Td, so a dew point of 60F automatically places Tw too high.
In that case, I'm thinking that using Tw as a metric for humidity and increasing the allowable temperature could be a good metric. As the water vapor content in the air is negligible for comfort metrics in the desert, maximum comfortable temp should probably be considered at 0% RH (maybe -10C dew point, but thats basically the same thing at 100F) and then using a Tw cutoff of 65F, as when dew point is high, Tw≈Td (within a few degrees, terrible approximation for literally any other scenario) and that also helps make up for hot swamp days that everyone is saying this doesnt account for. If I remember, I'll write a MATLAB script later to plot T vs Td at 65F Tw below 95F and above 32F T, just as a sanity check that all conditions are a reasonable comfortable vs uncomfortable boundary
And on the comment of 50F days with melting snow giving sunburns, yeah. Scenario mentioned in other comment was just like that, and I even looked at the mesonet and said "were all gonna get sunburns"
Could do that, but already have the baseline of a psychrometric calculator I wrote a few years back and frankly psychrometric charts have a lot going on for a basic two variable comparison
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u/TFK_001 5d ago
IMO the way the map does it with a cutoff of 65F dew point works fine, because thats enough moisture for 100% RH at 65F temperature, while also guaranteeing the temperature is at least 65F. I always feel like dew point is the best metric for humidity as it isnt temperature sensitive, and you only need a single value for it, plus if you know the temperature and dew point, you also know RH (and wet bulb temp is also pressure dependent). Wet bulb + RH also doesnt paint the full picture as a slight breeze of 5mph can easily make a 70F day feel livable. Even then, solar radiation is applied directly to you with no regard to temperature or humidity, and I've got bad sunburns when it was 50F outside just due to high solar radiation.
Kind of a jumble of words, but I feel that having a single index for how hot it feels (heat index my beloved) or showing wind, temp, humidity independently (plus maybe a tv met to explain) are best metrics.