Kevin Myatt

Latest entries from the Weather Journal blog

• Read the full blog

About Kevin

Kevin Myatt grew up in Arkansas to the tune of tornado sirens and the rhythm of hailstones, aspiring to be a meteorologist before his studies and career were turned to journalism instead. Though he often chases storms, he prefers living in the cooler, more tranquil weather of the Blue Ridge. He moved to Roanoke in 1999 to take a job on the copy desk of The Roanoke Times; writing headlines and editing copy is his principal work for the newspaper today.

Each May, Kevin assists Pulaski County High School / Virginia Tech meteorology instructor Dave Carroll in leading college and high school students to the Plains to observe severe weather firsthand. The accounts of many of his storm chases can be found here on the storm chasing page of his weather blog on roanoke.com.

Kevin was an editor for "Hurricanes and the Middle Atlantic States," a book written by D.C.-area weather enthusiast Rick Schwartz and published by Blue Diamond Books that documents hurricanes striking the mid-Atlantic states since colonial times.

The Weather Journal column began in 2003 and appears on Friday's Virginia section front in The Roanoke Times. The Weather Journal blog began in 2006 and follows weather day-by-day between the larger columns.

Steamy days don't always bring rain

One of the biggest ironies about midsummer weather is that the ground can be parched while the air is soaked.

Humid days are just something we take for granted this time of year, whether we are in a drought or having floods. We might get a couple of days' break from the humidity now and then, but it always comes back.

Geographically, we are situated with warm ocean water to the east and south of us, so any weather pattern bringing winds out of those directions increases our humidity. Evaporation from lakes and rivers adds a little more.

We also have lots of trees that transpire moisture through their leaves. Do not underestimate the contribution vegetation makes to available moisture. Any storm chaser knows that the maturing of cornstalks in the Plains can mean considerably more moisture for thunderstorm development. Our thick mountain forests and other plants act in much the same way.

You might be surprised to learn that a day we would consider brutally humid would probably only have a relative humidity of about 50 percent.

The true measure of the amount of moisture in the air isn't the relative humidity but the dew point. The dew point is the temperature at which the atmosphere would be entirely saturated, or have 100 percent relative humidity. Air can hold more moisture as it gets warmer, so the higher the dew point, the greater the amount of moisture in the air.

Relative humidity represents the percentage of the available space in the air that is filled with moisture. If your gas tank holds 10 gallons and it has nine gallons in it, it is 90 percent full. But if it holds 20 gallons, it is only 45 percent full, even though it is holding the same amount of gas.

A dew point of 62 represents the same amount of moisture in the air whether the temperature is 70 or 100. But at 70 degrees, the humidity would be 76 percent, while at 100, the humidity would only be 29 percent.

On an extremely hot, humid day locally, our temperature might be 95 with a dew point of 75. The relative humidity would be 53 percent.

It probably wouldn't get much hotter than 95 on a day with that much moisture because of the almost inevitable showers and thunderstorms that would develop. Probably about the only way we could have a dew point above 75 would be with a tropical system that would also bring lots of clouds and rain to keep temperatures down.

So, when you hear stories about how the temperature was 100 degrees and the humidity was 80 percent, it's just not true, at least around here. That would require a dew point of 93. Dew points that high have only been recorded a few times anywhere, mostly around the Persian Gulf.

But just because the air has a lot of moisture in it doesn't mean it will end up being squeezed out into rain. That takes a combination of atmospheric events that would lift the moisture into cooler air aloft and condense it into clouds and precipitation.

Daytime heating, if it's not too warm high in the atmosphere to prevent the air from rising, has that effect, but we get only spotty showers and storms. That's why a few of you have had thunderous deluges of rain for a few minutes even as the area as a whole slips deeper and deeper toward drought.

So for most of this week, until a cold front arrives with cooler, drier air for the weekend, most of us will continue to suffer the summer contradiction: steamy air, dusty ground.

Conditions and Storms

• Latest storm warnings and radar from the National Weather Service in Blacksburg
• Ski slopes -- in season, of course
• Road conditions
• Tropical storm updates - 24/7
• Chasing the Wind  - On the road in Tornado Alley

Recent Weather Journals

• 2 Web sites provide fun for weather nerds
• It's warm and dry, but it could be worse
• Summers in the city have trouble topping 100 degrees
• Latest Weather Journals