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Humidity myths/other science-y tidbits

June 29, 2010

If you live in TN, or even the southeast at all, you know damn well that it’s been hot and humid as hell lately. The entire southeast has been a sauna for several weeks in a row. You always hear people say stuff like, “man, it’s 90 degrees and 90% humidity out there!” Anyone with half a brain knows that’s a VAST exaggeration, but honestly the concept of humidity is a rather confusing one, and even some meteorologists don’t explain it very well. I’m not going to attempt to fully explain it because it’s already been done quite well at this Cincinnati meteorologist’s website. Please click through that link if you want a very detailed, but still in layman’s terms, explanation. Read on if you want my extremely condensed version.

Basically, in terms of actually knowing how much water vapor is in the air, relative humidity sucks. In order to really know how humid it is, and how uncomfortable you will be, look at the dew point. The dew point is simply the temperature at which the water vapor in the air will begin to condense. The higher the dew point, the more H2O is in the air. According to most charts that I’ve found, dew points in the 40-50 degree range feel very dry, like you would feel in a desert… Dew points between 50-60 degrees generally feel comfortable, dew points between 60-70 degrees are generally uncomfortable, and dew points 70+ degrees are utterly oppressive. Yesterday afternoon our dew point in Nashville was hovering around 70-72 degrees. Relative humidity takes into account the air temperature as well as the dew point, and the relationship between temperature and RH is inverse. That means that as the air temp goes up, the RH goes down. Of course the relationship between dew point and RH is converse. Again, if you want a really good, albeit long explanation then visit this website. Fortunately, TN is in for a bit of a relief from the oppressive conditions we’ve been enduring. Cold fronts during the summertime aren’t exactly “cold” though they do normally bring slightly cooler temps, but the main thing they usually bring is a drier airmass. The typical summer weather pattern in the southeast US often involves hot and humid air from the Gulf of Mexico being blown northward across the southeastern states, creating the conditions we’ve been experiencing the past few weeks. Sometimes, however, an airmass that originates over the northern US and Canada will make its way southward. That’s exactly what’s happening today, and the dew point is already falling (this morning it was 68, and right now at lunchtime it’s all the way down to 61!). This airmass is drier because it originated over a large area of land, rather than water. All forecast I’ve seen are in agreement that the dry weather will persist for at least a week, if not more, though the temps will creep back up into the 90s by this weekend. But 90 degree temps with a dew point of 60 is hella better than 90/70!

I must mention a couple of science news tidbits that pinged my radar today and yesterday…

The Obama Administration has announced a new national policy for aerospace that supports and guides the plans for NASA that were announced back in February. This is more of an over-arching “this is where we’re headed” type of policy, and it needed to be implemented to be in line with Obama’s NASA plans. Again, I fully agree with his desire to cancel the Constellation program, rely on the private space industry for low-earth orbit, and focus NASA on exploring beyond the moon. With this new policy, NASA basically has no choice but to use the plan unveiled in February. Hopefully this will get some of the opponents of Obama’s plan in Congress to STFU. But that’s probably a pipe dream. (Via Space.com)

The Large Hadron Collider in Geneva continues to creep closer and closer to its final goal of having the most intense proton collisions ever. Right now, Fermilab still holds the record for highest beam intensity, but the LHC just set a new record for overall number of proton collisions. It will be several more years before they have the LHC running at full capacity, but I have no doubt it will pay off. (Via Discovery News)

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2 Responses to “Humidity myths/other science-y tidbits”


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