Dewpoint, not Relative Humidity, the accurate measure

Yes and no. I think saturated air in the upper 60s might feel worse than a warm afternoon that is 90/72...that cool, clammy stuff doesn't do it for me.

Tedrick P wrote:

Yes and no. I think saturated air in the upper 60s might feel worse than a warm afternoon that is 90/72...that cool, clammy stuff doesn't do it for me.

You're wrong. You'll sweat so much more on that 90/72 day, and that sweat will go nowhere.

I'd kill to train in the desert than in this South Carolinian sauna where the dew point rarely dips below 73. Makes me want to vomit.

Don't forget about the sun. If it's sunny, 80s, dp 70, it's hell. If it's cloudy with the same, it's not nearly as bad. 90s with dp 50-60 isn't too bad. So far this season my most grueling runs have been temps in the mid-upper 80s, dp in the 65-75 range and sunny.

Alan

I got an email from a friend in the southeast who said the temperature that day during a rce was in the upper 80's with the humidity over 90%. That would mean the dewpoint was well into the 80's. Impossible.

What probably happend is he look at the current conditions in the morning when the dewpoint was 70 and the temp around 72 (which would be a relative humidity in the 90% range) and extrapolated that figure to the afternoon. of course neither the dewpoint nor the absolute humidity went down, The temperature just went up, lowering the "relative" humidity. I have heard people say that it is most humid in the morning, basing that on looking at the relative humidity. Hogwash, if the dewpoint remains the same all day. Sure, the clothes on your clothes line will dry more slowly in higher relative humidities (to a point) but the absolute measure of moisture in the air is the dewpoint.

So for my run this AM

81°F

Humidity: 79 %

Barometer: 29.83" (1009.7 mb)

Dewpoint: 74°F

Heat Index: 86°F

Visibility: 10.00 mi.

It's entirely possible to get a dewpoint as high as 82-83F in the Southeast during the worst part of August.

Those kinds of days are the reason why I plan on August being my light recovery month every year.

You are correct. The most humid cities in the US are in WA state. They have low dewpoints though. Lower than 50.

The weather channel data at 3:36 PM in Fairburn, Georgia ( About seven miles south of the Atlanta airport ) was:

Temp-86

Dewpoint-74

Feels like-93

and don't be fooled that the desert is always dry....monsoon season can get sticky in these parts. In fact last year Phoenix had a week where its dew point was higher than that of Miami. Sure, many times its a dry heat (though 110+ sucks anyway you slice it!) but many folks are surprised when they visit in late July and August that the air feels sticky and muggy just like the Southeast.

desert dweller wrote:

and don't be fooled that the desert is always dry....monsoon season can get sticky in these parts. In fact last year Phoenix had a week where its dew point was higher than that of Miami. Sure, many times its a dry heat (though 110+ sucks anyway you slice it!) but many folks are surprised when they visit in late July and August that the air feels sticky and muggy just like the Southeast.

...and don't be fooled by anonymous posters with erroneous facts and creative imaginations.

I can only find ONE DAY last Summer (July 31) in which the dew point in Phoenix exceeded the dew point in Miami. On that day the dew point spiked for 2 hours in the immediate aftermath of a thunderstorm, then dropped right back down to 70 as it had been all day.

Perhaps you were comparing to Miami,ARIZONA?

Phoenix, a city in which the average daily high is 15-20 degrees warmer than Miami, had exactly 14 days in which the dew point climbed above 70. Unlike Miami, the nighttime dew points in Phoenix drops like a rock. The nighttime DPs on those 14 days: 61,64,66,62,61,62,61,62,65,62,63,66,53,59. The average DPs in Phoenix for June, July and August is 33, 56, and 61, respectively. Make no mistake about it - it's the dry heat.

By contrast, Miami (FL), the Summertime temperature and dew points are predictable and consistent: high temps in the low 90s. High DP: 75, low DP: 70. For the Summer of 2007, there were only 3 days in which the high DP dropped below 73 - all of them in late September! Phoenix had only 6 days where the dew point ever made it to 73.

Phoenix

Miami

I remember a similiar thread in which Malmo explained the difference between dew point and relative humidity. It was in relation to th World XC chanps in Mombasa Kenya.

It was really informative with plenty of links and statistics.

An interesting topic no doubt, especially in these oppresive summer months.

BTW, how is the humdity where you live. Here in Eugene, Oregon it's dry. The humidity is not noticeable and never a problem. It rains alot, but it cools down when it does, so it's not muggy and sticky like in high humid areas of the world.

Des Arc, Arkansas - today at 7pm.

Temp: 98

Dew Point: 78

Heat Index: 115

That's about as unpleasant as you'll find in the lower 48. Summers in Arkansas I used to run at 2-3AM and would still find heat indices over 90.

Springfield, IL - 90 degrees, DP 83, Heat Index 113. Corn just keeps vomiting water vapor day and night. Can't wait for Wednesday...

Just ran with a temperature of 95 and a dew point of 78. F'ing sucks.

I look at wet-bulb globe temperature on NWS website and their guidance as relevant.