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chickencoupe1

Warm air temps with freezing dew point.

9 years ago

Anyone know how this happens? This occured at 11:30am yesterday.

Here's the local mesoreading.

Comments (2)

  • 9 years ago
    last modified: 9 years ago

    I don't know what you saw, Bon, because the Mesonet data linked shows the most current data, not what you saw at one point in time.

    Air temperature is just the measurement of the energy contained in the various gases that make up the air. I believe it is independent of dewpoint.

    Dewpoint is the temperature to which the air must be cooled in order to be fully moisture-saturated (100% relative humidity).

    You get precipitation (dew, rain, snow, whatever....or frost if the temperatures are low enough, in which case I guess the dew point really becomes the frost point) when the dew point and the air temperature are the same, or are very close to being the same. The closer the air temperature and the dewpoint are to the same number, the more likely it is that precipitation will form.

    So, if you were looking at data that showed a dewpoint of 31, that means that the air temperature would have to drop to 31 in order for precipitation to occur, technically speaking. If the air temperature were 50 or 70 or whatever while the dewpoint was 31, then the air is too warm for the air to achieve full saturation and it is too warm for precipitation to occur.

    The air temperature always is higher than the dewpoint, as far as I know, although perhaps a meteorologist could tell you of special circumstances where the dewpoint might get higher than the air temperatures. If that is possible, I've never heard of it occurring but weather and climate are complex.

    I watch my dewpoints on nights when air the temperatures might drop down below freezing or very close to freezing. Depending on what the dewpoint is, air temperatures in the mid- to upper 30s might be a little worth worrying about, or not at all. It just depends on what the dewpoint is at the same time. Dewpoints rise and fall throughout the day and don't remain static.

    Our local TV met usually mentions the dewpoint in his forecast discussions, indicting what they are and how they are going to influence whether we see frost or dew or rain overnight or nothing at all. Usually if the air temperature is going to fall close to the dewpoint at night and we also are going to be close to having freezing temperatures, he alerts gardeners to the fact that we will be seeing a situation that is potentially bad news for warm-season plants. It is all iffy, of course, so he usually words his warning to say something like "so, patchy frost might be possible" and if it is more likely in one part or another of the viewing area, he might say it is more likely further east or north or whatever. Or, if his concern is more with low-lying microclimates that tend to cool off more than the surrounding area, he'll even say that---usually by saying "so patchy frost might be possible in the usual colder, low-lying locations" and then folks, like me, who live in one of those usually colder, lower-lying locations know to be a bit more vigilant.

    Hope this helps.

    Dawn

    chickencoupe thanked Okiedawn OK Zone 7
  • 9 years ago

    Okay. I think I understand. Probably means it's really dry.