BSK?

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MUP
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BSK?

Post by MUP »

BSK wrote:Looks like we'll get a bit of a break from the heat over the weekend, with cooler and slightly drier air. An even more dramatic break in the weather will occur with a second front coming through on the following Monday, with Monday through Wednesday the having much drier air.

What temp swing are you seeing for the first, and the second fronts?
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Re: BSK?

Post by BSK »

It isn't so much temperature change (although there will be a drop of about 6-7 degrees). It is the drying of the air that will make the biggest difference in felt temperature. In fact, the "feels like" temperatures will be lower than the actual air temperature because of the drier air. In addition, morning low temps will fall into the low 60s and even possibly the high 50s because less moisture in the air allows temperatures to fall farther at night (not as much moisture to hold the heat in during the night).

In stead of low to mid 70 dew point temperatures (which is the measure of the amount of moisture in the air), the dew points could fall to the mid to upper 50s by early next week.
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Re: BSK?

Post by MUP »

Oh music to my ears! This may be my opportunity to get out on the mtn and make a tcam run and not end up drenched in sweat when I get back!
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Re: BSK?

Post by BSK »

Long-range models indicate backdoor fronts--fronts coming down from the north or northeast--will make several appearances over the next two weeks. These backdoor fronts may not drop the daily high temperatures that much, but they will bring in drier air. And drier air makes a huge differences in "felt" temperature. Plus they allow lower temps at night so mornings start cooler.
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Re: BSK?

Post by MUP »

If only those fronts would continue to drop from the North as they apparently did a few years ago. The year we had temps drop into the 40's during July I believe it was, and it was fairly often too if I remember correctly, wow, that was a VERY comfortable summer!
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Re: BSK?

Post by sdw »

Just walked out to check my pool water and add chemicals if necessary. Instantly sweating. It's 91% humidity here. Image
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Re: BSK?

Post by BSK »

sdw wrote:Just walked out to check my pool water and add chemicals if necessary. Instantly sweating. It's 91% humidity here.
You make an important point I'm always stressing to people. The relative humidity is relative. In essence, it is relative to the temperature. Warmer air can hold more moisture than cooler air, so even if the amount of moisture in the air stays the same throughout the day (the dew point temp stays the same), the relative humidity drops dramatically during the peak heat of the day, and rises dramatically during the cooler temps at night, yet the felt humidity stays the same. That's why I always stress for people to look at the dew point temperature instead of the relative humidity for assessing how humid it feels. For the life of me, I can't understand why TV meteorologists continue to provide the relative humidity numbers. They're basically meaningless. It is the dew point temperature that actually tells you how humid it is. In your example sdw, the dew point is 71, which is very humid. Any dew point above 70 degrees is extremely humid. At 75 degrees it is truly oppressive. Dew points in New Orleans or some of the Deep South swamplands in mid-summer can get as high as 80-82 degrees, which is truly gagging. Basically, the air starts feel humid when the dew point gets 60 or above.
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Re: BSK?

Post by BSK »

MUP,

Models have changed a bit this morning, suggesting drier air this weekend, and especially Monday. A slight return to more humid air Tuesday and Wednesday, but a major dry front coming in which could bring in extremely dry air (for this time of year) Thursday through Saturday of next week. The models are suggest dew points down into the upper 40s, but I think that is too aggressive. I would think mid 50s dew points are more reasonable for that period late next week, which for this time of year would feel quite pleasant.
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BSK?

Post by sdw »

I've been learning about dew point from your posts. I figured I might get a whipping from you if I didn't include something showing the dew point too Am I correct in figuring, from your explanation, the closer the dew point is to the temperature, the more miserable it will be? And thank you for the explanation! I'm beginning to understand it better. Also, had the dew point been 74 (same as temp) would it have been foggy?
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Re: BSK?

Post by sdw »

BSK would not run with this dew point.
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Re: BSK?

Post by MUP »

I'm all for "unseasonably" cool temps in the summer! Whether it's real time temps or "felt" temps, the cooler the better!
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Re: BSK?

Post by BSK »

MUP wrote:I'm all for "unseasonably" cool temps in the summer! Whether it's real time temps or "felt" temps, the cooler the better!
Unfortunately for me, the models are now backing off on that much drier air late next week for Middle TN. Now they are indicating that backdoor front will only dry the air for East TN but not Middle or West TN.

Next real break I see for all of TN is far in the future--potentially the 4th of July weekend.
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Re: BSK?

Post by BSK »

sdw wrote:I've been learning about dew point from your posts. I figured I might get a whipping from you if I didn't include something showing the dew point too Image Am I correct in figuring, from your explanation, the closer the dew point is to the temperature, the more miserable it will be? And thank you for the explanation! I'm beginning to understand it better. Also, had the dew point been 74 (same as temp) would it have been foggy?
How close the dew point temp and air temp are is what drives the relative humidity. When the two are close the relative humidity gets close to 100%. But 100% relative humidity at 40 degrees is very different than 100% at 75 degrees. One is humid to the feel and the other isn't. That's why the actual dew point temp is so important to how humid it feels. Cooler air can't hold as much moisture as warmer air. The dew point temperature is the temperature the air would have to decrease to before the air is completely saturated (100% relative humidity) and water vapor begins to condense on objects (morning dew) or actually form a cloud (fog). That's why fog usually forms in the morning. The temperature fell during the night until it reached the dew point temperature and the water vapor in the air condenses to form a cloud at the ground we call fog. Once the sun rises, the air warms above the dew point temperature, and the liquid water droplets that make the cloud visible evaporate back into invisible vapor and the fog vanishes, literally into thin air (although it's still there in the form of invisible water vapor).

So it is the dew point temperature that tells you how humid it feels, not the relative humidity. Again, you can have 100% relative humidity at 20 degrees (air temp of 20 and dew point of 20), yet that will NOT feel humid! At the same time you can have a relative humidity of only 53% that will feel exceptionally oppressive because the air temp is 95 degrees and the dew point of 75 degrees. It is the 75 degree dew point that tells you how humid it is. The two relative humidity values are so different--100% at 20 degrees versus 53% at 95 degrees--because warm air can hold so much more water vapor than cold air. 95 degree air can hold a massive amount of water vapor. 20 degree air cannot.

In fact, what normally occurs in the summer is that the dew point temperature doesn't change during the day, but obviously the air temperature does, climbing during the day and falling at night. This causes the relative humidity NUMBER to fall dramatically during the middle of the day but rise to near saturation (near 100%) at night. The hot mid-day air could hold much more moisture than the cooler night-time temps, hence the lower mid-day relative humidity. Yet the amount of moisture in the air, and the "felt" humidity, isn't changing day or night. When we get up in the morning and watch the morning news, it's common to see a morning temp of 75 with a dew point of 73, which makes the relative humidity 94%. However, if you were to check mid-day, when the air temp has risen to 98 degrees, that same dew point of 73 (and same "felt" humidity) produce a much lower relative humidity of only 45% because 98 degree air could hold so much more moisture. The "relative humidity" number is literally the percent of maximum moisture the air is currently holding (percent of maximum). Yet "felt" humidity is the amount of moisture actually in the air, and that is numerically represented by the dew point temperature.
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Re: BSK?

Post by BSK »

sdw wrote:BSK would not run with this dew point.
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Actually I ran 3 1/2 miles yesterday morning with a dew point of 72 degrees. It was not a pleasant run, and my body was in overheat shutdown mode by 3 1/2 miles, but I did it!

Through a lot of trial-and-error, I've found that with a dew point of 75 or higher I cannot run at all without rapidly overheating. With a dew point between 70 and 74 I can run about 3 miles before overheating. Dew points 65-69, I can get in 5 miles before overheating. 60-64 about 7 miles. Below 60 I'm good for any distance.
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Re: BSK?

Post by sdw »

Thanks again for the explanation.
All the running you do is impressive. I need to start working on being a little more fit and healthy. Only way I could run 3 1/2 miles is if something was chasing me. Not sure I could then.
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Re: BSK?

Post by BSK »

sdw wrote:Thanks again for the explanation.
All the running you do is impressive. I need to start working on being a little more fit and healthy. Only way I could run 3 1/2 miles is if something was chasing me. Not sure I could then.
I only started running two years ago. At the time, I couldn't run for 60 seconds without being so winded I would have to stop. Now I can run non-stop for 3 hours. When I first started, I though I was NEVER going to get any better. Each incremental gain seemed like agony. But if a person will keep at it, especially through the earliest days--which truly are the toughest--the gains begin to accelerate. Getting to the point I could run for 30 minutes without stopping was by far the hardest part. That took two months of working at it almost every day. After that, the rest came much easier. Basically the breakthrough comes once you can run for 3 miles without stopping. That took three months. But after that I was adding a mile every week. It took three months to go from 60 seconds of running to 3 miles of running, but only 6 weeks to go from 3 miles to 9 miles non-stop.
"Know where you stand and stand there" Jesuit Father Daniel Berrigan

"It is useless to attempt to reason a man out of a thing he was never reasoned into" Jonathan Swift
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