Oct 17 2012

Like A Cork

Published by under Weather & Sky

We’re in for some interesting weather though it probably won’t look as dramatic as the cold front pictured above.

Last night the National Weather Service Pittsburgh forecast discussion said, “Showers becoming likely daytime Thursday with the passage of a mature occluding cold front. NAM model profiles show the cold frontal passage can also be accompanied by wind gusts up to 30 mph.”

I had never heard of an occluding front let alone a mature one (obviously, I haven’t been paying attention), so I had to look it up.

Occluded means blocked or stopped up.  An occluding cold front is one that overtakes a warm front, jamming it in a wedge between the cold air ahead of the warm front and the new cold air mass overtaking it.  The warm air has nowhere to go but up.  Cold air floods in and the warm air rides atop it like a cork on water.

It looks like this — before and after — as the cold front approaches from the left, catches up to the warm front and forces it up.  (Technically this drawing shows a “cold occlusion.”)

The practical result is that we had cold air early this week, warm air today (the warm front), and cold air tomorrow.  The weather map shows the actual occlusion will track north of us.

The forecast also said, “As what often occurs with these maturing systems there can be a dry slot passage Thursday night before the ensuing cold upper low passes eastward through the upper Ohio Valley Friday.”  So it will be dry on Friday.

The cork will rise tomorrow.

(photo from Wikimedia Commons of a cold front moving rapidly along the Rappahannock River. Occlusion diagram from Wikimedia Commons. Click on the images to see the originals.)

p.s. 10/17, 6:23 pm, Thursday’s forecast more includes the possibility of a severe thunderstorm & Friday has a chance of showers. Things change all the time!

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Oct 16 2012


Published by under Musings & News,Trees

On Saturday while hiking with KTA in the Quehanna Wild Area we encountered an area of low vegetation and waist-high stumps. The only trees were those growing on top of stumps like the one pictured above. These were not live sprouts from the old stumps.  They were all different species.

It was an oddly barren place where tree regeneration was prevented unless the seedlings were nurtured in the core of a stump.  Here’s a Wikimedia photo by Ruhrfisch, taken in the same area.


The stumps were white pines, felled a hundred years ago.  State Foresters wondered how old the trees were when cut so they studied stumps with intact rings and discovered that they were all the same age –  200 years old.  Something had caused the area to regrow from scratch around 1700.

And they were all cut down at once at the turn of the last century.  Loggers clear-cut the entire state, each tree felled by two men with a cross-cut saw.  When they were done Pennsylvania looked like this (Tioga County, 1914):


It took a long time to recover from this damage.  The clear-cuts were ravaged by fires and erosion.  During the Great Depression some areas were replanted by the Civilian Conservation Corps.  In other places the land is still challenged.

And so we have a few barren reminders of the time when Pennsylvania exploited trees.


(photo of a tree growing on a stump by Kate St. John, other photos from Wikimedia Commons — click on those photos to see their originals)

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Oct 15 2012

Free For All

The scientific literature calls ring-billed gulls opportunistic omnivores or as the gulls themselves would say:

“We’ll eat anything and we’ll snatch it from anybody.”

Early this month Shawn Collins photographed this behavior when a gull caught some bread at Pymatuning Spillway.

The chase was on.

He was nearly overrun by the gang when …  ooops!  he dropped a big chunk!

The bread fell free for all of them.

The result was a free-for-all. ;-)

(photo by Shawn Collins)

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Oct 14 2012

Ash Leaves

This is one of the things I’m going to miss when all the ash trees have died.

In autumn ash leaves turn yellow, orange and lavender.  Often, all of the colors are on the same leaf.  No other tree is quite as beautiful.

Fall won’t look the same when the ashes are gone.

(photo by Kate St. John)

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Oct 13 2012

Best View In The Parking Lot?

Published by under Mammals

October’s a good time to take in fall foliage and the autumn activities of Pennsylvania’s wildlife.

If your travels take you to Elk County, stop by the Visitor Center on Winslow Hill Road in Benezette to see Pennsylvania’s elk.

You might get lucky and find them in the parking lot, as Paul Staniszewski did above.

On the other hand, elk are pretty busy right now and more likely to be in their natural setting.  This is their mating season.

Click here for Elk Country information and here for Paul’s guide to photographing elk … when they’re not in the parking lot.

(photo by Paul Staniszewski)


p.s. Today I’m hiking at the Quehanna Wild Area in nearby Clearfield County. The fall foliage is colorful but it is *cold*! The growing season just ended with 23 degrees this morning.

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Oct 12 2012

Green Rivers

Published by under Weather & Sky

From the ground auroras look like sheets of light.  From high above the Earth they look like shining green rivers.

Click on the image above to watch an aurora over the Indian Ocean as seen from the International Space Station.

Way cool, huh?

(image from NASA)

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Oct 11 2012

How’s The Water?

Southwestern Pennsylvania’s waterways are scenic but in many places the water is bad.  This photo of the notch where Stony Run meets the Conemaugh River is a case in point.  See the orange tinge on the river bottom?  That’s bad water from abandoned mine drainage.

How prevalent is bad water in our area?

PittsburghTODAY recently published a map of non-attaining waterways in southwestern Pennsylvania.  Using Department of Environmental Protection data, the yellow lines show where water quality is compromised by abandoned mine drainage, agricultural runoff, sewage, and other causes.  The good water is blue.

Even in this thumbnail it’s easy to see that most of Allegheny County has bad surface water while most of Greene County is good.  The white space in the middle of Allegheny County is the City of Pittsburgh where the streams were buried as the city was built.  Click on the image to see the large map at PittsburghTODAY and drill in for a close-up.

The region’s bad water affects both our quality of life and the natural world.  Where water’s impaired aquatic life is poor, there are fewer fish, fewer birds, fewer mammals and bad water for us to drink.

So why is a lot of the map yellow?  It’s the legacy of coal.

During the heyday of deep mining in the early 1900′s Pennsylvania had weak or non-existent environmental laws and the state did not collect money from industry for clean up of the inevitable abandoned mine drainage.  Pennsylvania eventually enacted laws to prevent new damage but there’s no money to turn all of the yellow lines into blue.

One would hope that Pennsylvania learned from this history but in my opinion (not necessarily the opinion of WQED) our state has not.  Though damage is predictable from new industrial threats like Marcellus shale, the state still begins with weak laws, suffers new damage, then changes the laws after the damage is done.  (Click here for an example.)

So… how’s the water?

(photo by Tim Vechter; map from PittsburghTODAY.org.  Click on the map to see the details)

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Oct 10 2012

They’re Baaaaack!

Published by under Crows, Ravens

Pittsburgh’s crows are back!

The winter flock is building.  Hundreds gathered last evening near Bigelow Boulevard at Craig Street.  As sunlight faded in the western sky they left to roost  … where?

This morning Tony Bledsoe dodged the “rain” from their roost in the trees near Clapp Hall.  His guess at the size of the flock?  500.   And this is just the beginning.   By November they’ll build to a crescendo of crows.

Where do they gather at dusk?  Leave a comment with the news … or tweet me the location of Pittsburgh’s crow flock @KStJBirdblog  (hashtag #pghcrows)


(photo of hooded crows in Denmark, by Jens Rost via Wikimedia Commons. Click on the photo to see the original.)

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Oct 10 2012

Making Waves

Published by under Weather & Sky

These rare Kelvin-Helmholtz clouds look like waves on the ocean.

In fact they are breaking waves generated by the same fluid dynamics that creates wind-driven waves on water.

Both are caused by Kelvin-Helmholtz instability which occurs at the boundary where two fluids flow by each other at different speeds or densities.  The air above these clouds is moving faster left-to-right than the air below them.  The boundary is very turbulent and becomes more so when the waves break.

Kelvin-Helmholz instability can be described mathematically and its effect plotted over time.  This silent video by VanjaZ shows a yellow fluid on top flowing faster than the black fluid on the bottom.  Talk about turbulence!


We rarely see K-H clouds because the atmosphere has to be just right to make them stand alone. The curling waves disappear in seconds, wiped out by chaos as soon as they break.

(photo by GrahamUK on Wikimedia Commons; video by VanjaZ on YouTube)

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Oct 09 2012

How Stakes Hurt Trees

Every day on my way to work I pass this unusual tree in Schenley Park.  It was planted with care, probably more than 40 years ago, when stakes were provided to stabilize the young tree.

But the stakes were never removed.  The tree grew and grew.  The trunk had nowhere to go except outward.  Slowly it engulfed the stakes.

Now this tree’s in a world of hurt.  The rubber guide and wires disappeared long ago.  The stake on the right is still outside the trunk but only a short length of wire is visible (below).


The other stake is completely surrounded.  Its top is inside the trunk.

And now the stakes can never be removed.  Though they’ve created a weakness in the trunk, they’re the only support the tree has at that spot so they have to stay.  The damage is done.

It’s too late to save this tree, but you can help others.  Examine staked trees to make sure the guides are not girdling the trunk.  Remove the stakes 1 to 2 years after planting.

For more information see Bartlett’s plant health guide for newly planted trees.

(photos by Kate St. John)


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