Category Archives: Weather & Sky

How To Make Ice in the Desert

A piece of ice (photo from Wikimedia Commons)

6 January 2021

The desert dips below freezing on winter nights but if you want ice in the summer, how do you get it? This is a story of human innovation using natural processes.

In the 17th century BCE the Persians (Iranians) figured out how to make ice in the desert and store it through long hot summers. They used this method for 3,600+ years until electric refrigeration replaced it in the 20th century.

Though water is scarce in Iran, the method works well because the air is so dry. The process requires many steps: deliver water, make ice, store ice and keep it cool.

Deliver water to the ice-making location: The Persians built underground water channels called qanats to deliver water from uphill wells to the downhill population. Water in the qanat does not evaporate in the sun and stays cooler because it’s underground.

Cross section of Persian underground water channel called qanat (diagram from Wikimedia Commons )

Make ice: To make ice the Persians built plaza-like ponds, shaded by a high wall, where the shallow water froze on winter nights. Collecting the ice before sunrise, they stored it in the ice house (dome in the background). Here are two photos of the same ice plaza no longer in use. People give it a sense of scale.

Store the ice: The ice house, called a yakhchal, stored ice underground, where conditions are naturally cooler, and protected it with an insulated dome. The hole at the top of the dome allowed hot air to escape.

Ice house in Iran, exterior (photo from Wikimedia Commons)
Ice house in Iran, interior top of the dome (photo from Wikimedia Commons)

Keep the ice cool: The ice was kept cool using natural ventilation to draw in cold air and remove hot air. Windcatcher towers in some towns were quite ornate.

Here’s a video that puts it all together.

Very cool!

(photos from Wikimedia Commons; click on the captions to see the originals)

Not Much To Show For a Gray Week

Unusual clouds at sunrise, 30 December 2020 (photo by Kate St. John)

2 January 2021

Since last Sunday Pittsburgh has been warm, wet and overcast except for a single sunny day, 29 December, which I largely spent indoors (foolish me!). I don’t have much to show for a gray week.

The next morning, 30 December, dawned with thin ragged clouds, a tantalizing end to sunshine.

On New Year’s Eve I took a three hour walk in Schenley Park and stopped to look for the Pitt peregrines. There’s a peregrine perched on this building. Can you see it?

There’s a peregrine on this building. Can you see it? Pittsburgh, 31 Dec 2020, 11:43am (photo by Kate St. John)

Zoomed in, the peregrine is on the right hand leaf-stem. Morela matches the building.

Peregrine falcon on the leaf-stem, 31 Dec 2020 (photo by Kate St. John)

Later she spent an hour at the nestbox.

Morela at the nestbox, 31 Dec 2020, 2:20pm (photo from the National Aviary snapshot camera at Univ of Pittsburgh)
Morela preening at the nestbox, 31 Dec 2020, 2:34pm (photo from the National Aviary snapshot camera at Univ of Pittsburgh)

New Year’s Day 2021 was a washout. No photos. No peregrines. (I tried to find them. no luck) It rained most of the day.

(photos by Kate St. John)

The Sun Stood Still Before Sunrise

Sunrise (photo by Fir0002/Flagstaffotos via Wikimedia Commons)

21 December 2020

Today is one of two days per year when the sun stands still.

By the time you read this article the December solstice has already happened. The sun paused over the Tropic of Capricorn at 10:02 UTC, the same moment everywhere on Earth. In Pittsburgh it occurred at 5:02am local time, more than two and a half hours before sunrise.

If you wanted to experience sunrise and the December solstice simultaneously the best place would have been Georgetown, Guyana where the sun rose at 5:59am and the solstice occurred 3 minutes later at 6:02am local time (GYT). It’s too late to do that this year but 2021 is a possibility. By then we hope to travel safely thanks to the COVID-19 vaccine.

The good news for now is that the days are already getting longer in Pittsburgh. Tomorrow will be 3 seconds longer than today.

(photo by Fir0002/Flagstaffotos via Wikimedia Commons; click on the caption to see the original)

p.s. I am old enough that… I cannot think of Guyana without remembering the Jonestown, Guyana massacre orchestrated by cult leader Jim Jones on 18 November 1978. 918 people died in the mass murder-suicide. It is the origin of the phrase “Drinking the Kool-Aid.”

More Than Nine Inches

City lights glow on the snow and clouds, Pittsburgh at dawn 17 Dec 2020 (photo by Kate St. John)

18 December 2020

It began snowing here in Pittsburgh on Wednesday morning, 16 December 2020, and didn’t stop for 17.5 hours. By 7:30 the next morning there were 9.25 inches of snow in Oakland. City lights glowed against the snow and clouds.

9.25″ of snow in Oakland, 17 Dec 2020, 7:30am (photo by Kate St. John)

Yesterday I took a long walk to Pitt’s campus, Carnegie Library and Schenley Park to appreciate the beauty. Here are a few of the scenes I encountered.

Red Euonymus leaves peek out of the snow, Univ of Pittsburgh, 17 Dec 2020 (photo by Kate St. John)
White trees frame the Cathedral of Learning, 17 Dec 2020 (photo by Kate St. John)
Bach, Shakespeare, and Dippy wear snowy blankets at Carnegie Museum, 17 Dec 2020 (photo by Richard St. John)
This meadow near Schenley’s Westinghouse Fountain offers seeds for sparrows and juncos, 17 Dec 2020 (photo by Kate St. John)
Sweetgum seed balls wear snowy caps, 17 Dec 2020 (photo by Kate St. John)

On my way home I found one of Santa’s elves near the Library!

Santa’s elf or fire hydrant? 17 Dec 2020 (photo by Kate St. John)

Though the snow didn’t melt it did compress in 24 hours. Here are two snapshots of the Pitt peregrine nestbox at 7:30am on Thurs 17 Dec and Fri 18 Dec. Though there is still a lot of snow it is not as daunting, even if it hasn’t been shoveled.

No peregrines visited the nest yesterday but I know they are present. I saw Morela perched on a gargoyle.

UPDATE 18 Dec 2020, 4:08pm: Morela examines the snow.

(photos by Kate St. John; statues photo by Richard St. John)

The Great Conjunction of Jupiter and Saturn, Dec 21

Saturn and Jupiter converging, 11 December 2020 (photo by Steve Gosser)

16 December 2020

An event of astronomical proportions will happen on Monday 21 December 2020 when two bright planets — Jupiter and Saturn — converge in the night sky, visible just after sunset.

A “conjunction” occurs when two astronomical bodies appear close to each other as seen from Earth. This one is called “Great” because it involves the two largest planets, Jupiter and Saturn.

A Great Conjunction happens every 20 years but this one is rare, as NASA explains:

It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this “great conjunction.”

NASA: The Great Conjunction of Jupiter and Saturn

When Steve Gosser took the photo above on Friday 11 December the two planets had not yet converged but you can see Saturn’s rings at top left and Jupiter with four moons at bottom right (the fourth moon is faint in the bottom right corner).

See the Great Conjunction yourself using NASA’s sky map

Location of the Great Conjunction in the sky, 21 Dec 2020 (illustration by NASA/JPL-Caltech)

.. and check these websites for the cloud forecast at sunset in your area.

Sunset in Pittsburgh is at 4:57pm on 21 December. Unfortunately our sky will be overcast that evening.

Learn more in this video. Get an astronomy app at this link:

(photo by Steve Gosser, sky map from NASA/JPL-Caltech)

Picture Of The Week

Merlin eating a junco at sunset, 7 Dec 2020, Schenley Park golf course (photo by Kate St. John)

12 December 2020

If you follow me on Facebook or Twitter you’ve seen my best photo of the week, perhaps for the whole year, with only a brief description: Merlin eating a junco at sunset, Schenley Park golf course, 7 December 2020. Here’s the back story.

This week Pittsburgh suffered through six days in a row of unrelenting overcast “Pittsburgh Gray” skies. During that period there was only one moment when the sun made an appearance and I was determined to be outdoors with a big view of the sky when it happened: The Gleam At Sunset on Monday December 7.

During winter Pittsburgh often has overcast skies all day and clear skies at night. When the transition happens at sunset you can see clear sky approaching from Ohio but it will arrive too late to enjoy the sun. We have 10 minutes of happy sunshine and then it’s dark. The Gleam At Sunset.

The Gleam at Sunset, 30 Jan 2016 (photo by Kate St. John)

A gleam was predicted for Monday so I walked to Schenley Park golf course to reach high open ground. The sky started to clear. The sunset was going to be beautiful.

Passing through Fezziwig Grove, I began to think about the merlin(s) that visit the golf course in winter. As I scanned the dead snags a merlin flew in with prey, a dark-eyed junco. My cellphone is not a robust camera so I positioned myself for the merlin silhouette.

I was lucky to photograph both: a merlin and The Gleam at Sunset.

(photos by Kate St. John)

Tarballs in the Himalayas

Mt Everest, Himalayas (photo from Wikimedia Commons)

9 December 2020

Every November air pollution spikes in India as farmers in the Punjab burn their fields in preparation for the next crop. Because the practice causes terrible air pollution it was outlawed in 2015, but small farmers cannot afford to buy the machines needed to clear the fields so the practice continues year after year.

Burning stubble to clear the fields, Nov 2011, Punjab, India (photo from Wikimedia Commons)

When the stubble burns Delhi is smothered in dangerous air pollution. The smoke from thousands of fires swirls high in the atmosphere and can be seen from satellites.

Smoke from agricultural fires (red dots) swirls toward the Himalayas, Nov 2013, NASA MODIS satellite (photo from Wikimedia Commons)

Meanwhile glaciers in the Himalayas have been retreating for the past decade. Scientists wondered if atmospheric carbon air pollution, landing on the white ice, was a factor in their warming. A team led by Yuan Q placed air pollution monitors in remote locations on the northern side of the Himalayas. Their report, published by the American Chemical Society on 4 November 2020, found an amazing thing:

Using electron microscopy, the researchers unexpectedly found that about 28% of the thousands of particles in the air samples from the Himalayan research station were tarballs, and the percentage increased on days with elevated levels of pollution. Brown carbon ‘tarballs’ detected in Himalayan atmosphere , 4 Nov 2020

Microscopic tarballs form from brown carbon in the smoke of organic fires — in this case, stubble burning. They are so lightweight that they travel far, rising over the Himalayas to deposit on the other side. Their dark color absorbs sunlight and causes the glaciers to melt faster.

How smoke transforms to brown carbon tarballs in the Himalayas (CREDIT: ACS / Environmental Science & Technology Letters, graphic embedded from SciTechDaily news)

Stubble burning is a persistent annual problem in India as shown in the 2018 video from France 24 below.

Dec 2018: Crop burning crisis: India chokes as farmers set fields on fire, France 24 News

As India’s government provides community-shared machines for clearing stubble, the burning will come to an end. Will it be soon enough for the glaciers? Probably not.

Read more in this 4 Nov 2020 press release from Brown carbon ‘tarballs’ detected in Himalayan atmosphere

(photos from Wikimedia Commons, chart embedded from; click on the captions to see the originals)

The study is here: Yuan Q et al. Evidence for Large Amounts of Brown Carbonaceous Tarballs in the Himalayan Atmosphere. Environmental Science & Technology Letters. Published 4 November 2020.

Pittsburgh Gray

6 December 2020

The National Weather Service forecast for Pittsburgh is:

Today Cloudy, with a high near 35. Northwest wind around 6 mph.

— National Weather Forecast for Pittsburgh, PA, 6 December 2020 at 7am

Cloudy? Nope. Overcast! Here’s what it looks like in my neighborhood at 7:30a.m.

Sky looking southeast, Pittsburgh, 6 December 2020, 7:33am (photo by Kate St. John)
Looking south, Pittsburgh, 6 Dec 2020, 7:33am (photo by Kate St. John)
Looking north, Pittsburgh, 6 Dec 2020, 7:32am (photo by Kate St. John)

We call this Pittsburgh Gray.

(photos by Kate St. John)

p.s. It is hard to keep a positive attitude when the sky looks like this and our hospitals are overwhelmed with COVID patients. Hang in there! Take a walk. Sit among the birds.

Scenes Of The Week

  • Red leaves at Duck Hollow, 29 Nov 2020 (photo by Kate St. John)

5 December 2020

Here’s a visual portrait of the past week, from a warm day at Duck Hollow on 29 November, to snow on 1 December, and yesterday’s awesome sky at Moraine State Park.

(photos by John English and Kate St. John)

Clouds Radiate Heat

Night sky photo from Wikimedia Commons, arrows and text added

Now that the weather is colder here’s something to ponder: Why is it warmer on a cloudy night?

Some people say it’s warmer because clouds act like a blanket to hold in the heat but that’s not scientifically true.

Clouds are not holding in heat. They are emitting it!

Clouds absorb heat during the day just as the earth does. When the temperature falls clouds emit heat in all directions including downward to us below. Their warmth can be just enough to keep us above freezing.

On a clear night there is nothing to warm us so we have frost in the morning.

Did you know you can avoid frost on your windshield if you park beneath a tree on clear, near-freezing nights? The tree is emitting heat, too. No frost in the morning.

Either it is very cold in this picture or the car was not parked under a tree.

Frost on a car windshield, London (photo from Wikimedia Commons)

Read more about cloud blankets and other scientific “facts” that aren’t true at Dan Satterfield’s Wild Wild Science Journal.

(photos from Wikimedia Commons; click on the captions to see the originals)