Category Archives: Weather

A tale of two rivers

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Last Friday on my way back to Rome from Huntsville, I stopped at the Little River Falls overlook to see what had happened to the flow since I saw it three days earlier. The river was down, but not very obviously. Here is the picture from a week ago last Tuesday (April 30) and from last Friday (May 3). You can see some differences. More rock is visible to the left in the second figure, but in general they look pretty similar.

Little River Falls, Tuesday, April 30

Little River Falls, Tuesday, April 30

Little River, May 3, 2013

Little River, May 3, 2013

After I got home, Leah and I went into town to eat. We stopped to get a picture of the Oostanaula River. This is a picture of the river Friday afternoon looking downstream from a pedestrian bridge towards the Second Avenue bridge.

Oostanaula River, May 3

Oostanaula River, May 3

Just downstream from the highway bridge there is an old, abandoned railroad bridge and just downstream from that, the Oostanaula flows into the Etowah River to form the Coosa River. Downtown Rome is to the left in this shot; Broad Street crosses the Etowah just up from the confluence of the two rivers. If you boated down the Coosa into Weiss Lake (watch out for the old Mayo’s Lock and Dam, because you have to portage around that), you could find the mouth of the Little River.

The Oostanaula was muddy, but the color was closer to a murky olive than to the red clay it sometimes shows immediately after heavy rain. The Little River was pretty much clear in both of the shots I took.

When I stopped at the Little River on Friday, I met a National Park Service volunteer who had a clipboard with an interesting figure. The figure showed a week-long history of the water flow in the Little River where it empties into Weiss Lake, not very many miles downstream from the waterfall.

Here is a figure I got from the USGS showing the period from just before the weekend of April 27-28, when we got a lot of rain. It includes last weekend, when we got some more rain. I put red diamonds on the chart showing the levels on Tuesday and Friday when I took the pictures. The Y-axis is on a logarithmic scale, which can be hard to read, so I added some additional numbers.

Streamflow on the Little River

Streamflow on the Little River

You can see that the level on Friday, about 450 cubic feet per second, was roughly half what it had been on the Tuesday before. A cubic foot is about 7.5 gallons, so 450 cubic feet per second is about 3375 gallons per second. An olympic pool is about 660,000 gallons according to Wikipedia, so it would take a little over three minutes to fill at that flow. That doesn’t really sound like that much.

The Park Service volunteer showed me a picture of the falls from a few years ago when the flow was about twice the maximum of the April 27-28 weekend, or over 20,000 cubic feet per second. The photo was impressive. He said the record high flow was about twice that number, which would be really impressive, and probably scary from the overlook.

This is a figure showing streamflow for the Oostanuala River for the same period. I think the flow when I took the picture above was probably around 17,000 cubic feet per second.

Streamflow on the Oostanaula River

Streamflow on the Oostanaula River

As I said in the earlier post, the Little River is a short river with a small watershed compared to the Oostanaula River, so it responds quickly to changes in the local rainfall. The Oostanaula itself is about 50 miles long, about the same as the Little River, but it is formed by two other rivers, the Conasauga, about 93 miles long, and the Coosawattee, about 50 miles. The Little River drains an area of about 200 square miles. The total Oostanaula basin is about 2150 square miles, more than 10 times larger. It’s no wonder it takes longer to respond. The tan colored triangles in the plots show the average stream flow for the two rivers. The Oostanaula is about 3000 cubic feet per second on average during this period, while the Little River is around 200 or 300 cubic feet per second, or about one-tenth as much. It seems reasonable that the stream flow is proportional to the area drained.

But there is another interesting difference between the two rivers. The Little River responds very quickly to rain, and then again when the rain stops. You can see how quickly the river flow drops during the week, when there was no rain. It started raining again late Friday and the river flow jumped up again pretty quickly. You can see a period when the rain stopped for a while over the weekend, and then started up again. Compare that to the flow of the Oostanaula. The Oostanaula began to drop after Friday, May 3, but slowly compared to the Little River. It increased again last weekend when it started to rain again. There is a segment with no data for some reason, but you can follow where the curve would be.

One of the interesting things about these figures is how this kind of behavior shows up in other physical systems. Most people have experience with cast-iron frying pans and also with aluminum foil. You know if you fry eggs in a cast-iron pan, the pan will stay hot for quite a while after you take it off the stove. And you probably also know that if you have a pan covered with aluminum foil in a hot oven, you can touch the aluminum foil almost immediately after you take it out of the oven. If you plotted the temperatures against time, the cast-iron pan would look like the Oostanaula, and the aluminum foil would look like the Little River. In my business, we would say the cast-iron pan is thermally massive, and the aluminum foil is thermally lightweight, or thermally responsive. I think it’s pretty cool stuff, but that’s just me.

I plan to keep my camera handy, and if we have some really heavy rain, I’m heading over to the Little River. I want to see just how scary it can get over there.

Signs

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There has been evidence of spring lately. Last Sunday afternoon it was definitive.

Banks of fog in the morning

Banks of fog in the morning

What you see here is drifts of fog in the low spots off to the east from the mountain at sunrise on Sunday morning, March 31. Saturday had been rainy, but during the night the clouds cleared and there was some nice radiative cooling. That cooled air settled in the low spots and the moisture in the humid air condensed. But that’s not a sign of spring; it’s common all year long. It’s what you don’t see here that is actually a definitive sign of astronomical or solar spring. The view off the deck towards town is due east, and the sun is coming up to the left, or north, in this view. On the first day of astronomical spring the sun rose due east, and since it’s too far north to be visible here, it is, by definition, spring, or at least past the vernal equinox. So at least in the solar sense that is proof, but spring comes at different times in different areas, and the location of the sunrise alone doesn’t mean spring is here on the mountain.

Faded daffodils and vinca

Faded daffodils and vinca

The daffodils have bloomed and faded. But daffodils can bloom early, and ours did. The vinca minor, or lesser periwinkle, in the background, blooms year-round. The blooms are more numerous in the spring, but they’re here all year long. So the daffodils and vinca don’t provide reliable evidence.

A hint of green on the mountain

A hint of green on the mountain

A few trees on the mountain are showing some green. We’re later up here than down in the lower elevations. It’s a sign, but not definitive.

Blackberries greening and maples reddening

Blackberries greening and maples reddening

There’s green on the blackberry bushes and red on the maples.

Pine candles

Pine candles

The pines have brought out their candles but they haven’t been lit yet. I have seen, or rather felt, some pollen on the windshield, but nothing like the coat of gritty yellow we get later in the spring. But I have been seeing candles for a while. Not proof.

Dogwood buds

Dogwood buds

The buds have been on the dogwoods since last year, and they aren’t showing signs of opening yet.

I worked in the yard Saturday, and it was warm enough that I had to stop every few minutes to wipe sweat out of my eyes. But we can get 70-degree days in the dead of winter, so that’s not really a definitive sign.

No, the real sign that spring has arrived was something else that got into my eyes: bugs. The bugs were flying around my face, landing in my ears and committing suicide by diving into my eyes. They will pretty much disappear later as the weather gets really hot, but for the time being, they are a really annoying but pretty much definitive sign that spring is here.

The long and the short

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It was cloudy all day Monday, but when we left the hospital that night, it was clear. Not much cooler, but clear enough. The sidewalk was wet and the street looked black and slick. The gravel in our driveway was dark, and water was dripping from the metal roof. It’s easy to understand why people say that dew falls, because the areas under the trees were dry, as if the dew had not fallen through the pine needles. But, of course, dew doesn’t really fall, it condenses on surfaces that have a clear view of the sky. To the infrared eyes of the Earth, a clear night sky is a very cold thing, so the surfaces loses its heat quickly and the moisture in the air condenses on the now-cold surface.

Tuesday morning was still warm. Fog hid everything below the mountain, but we were clear, at least until I took the dogs for a walk.

Zeke and Lucy

Zeke and Lucy

There was a little fog here and there, but it was mostly clear.

Lucy, my mother’s little dog, accompanied Zeke and me. We call her Lucy, Lulu, Lucille, or sometimes Lucifer, but she’s not really a bad dog at all. She has been a true friend and companion for my mother for probably 10 years. We started encouraging Mother to get a dog for company soon after my father died, and eventually she gave in. It’s a funny thing to watch, if you know my mother. She was never a dog person. All our childhood pets had to stay outside, and she never did much more than touch their heads with her fingertips. And now Lucy sleeps on her bed, tucked right up against her back. And she lies on Mother’s lap when Mother reclines and watches NCIS reruns.

Lucy is staying with us until Mother goes home. And then Lucy will go back home with her and keep her back warm until the end.

This is what we call snow

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Sometimes we get a decent amount of snow down here, but if there is even a hint, businesses and schools close and people make runs on the grocery stores for milk and bread. Most of the time, a hint is all it amounts to.

This time we got a little sleet that changed into snow. A little slush accumulated on streets, and there was a light dusting of snow on the fields and forests. It started at about 11 am, and by around noon, most of Huntsville, Al, where I work, was closing down. I was at a meeting on Redstone Arsenal when the word came that the arsenal was closing, supposedly in stages to prevent a traffic jam at the gates. But that plan didn’t really work. As soon as everyone heard that the arsenal, which includes the Marshall Space Flight Center, was closing, they left. There are about six thousand employees at Marshall, and in the thousands on the rest of the base (I’m not sure how many — a lot). Most of them left at the same time. I took this picture with my iPhone while sitting in a line of cars exiting the base. Don’t worry; I wasn’t moving at the time.

This is the worst of it

This is the worst of it — I had to turn on my windshield wipers

That was about the extent of the snow.

If you look closely you can see a line of cars on a cross street. Traffic was backed up a couple of miles trying to get through the gates and off the base. Just on the other side of the gates, the highway crosses I-565, which has five westbound lanes at that point leading out of the city. It was bumper to bumper as far west as I could see. It looked like everyone in the city was leaving. I think it would look about like this if we had been told there was going to be a nuclear strike on the city.

But Huntsville is not a huge city, so the traffic jam was over pretty quick. And so was the snow.