Category Archives: Weather & Sky

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)

Quiz: Where Is The Largest Desert on Earth?

Rippled sand of Sharjah Desert, UAE (photo from Wikimedia Commons)

Quiz! Where is the largest desert on Earth? What continent is it on?

By “largest” I mean square miles. By “desert” I mean …

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid.

Wikipedia entry for Desert

Did you know that the majority of deserts are not composed of sand dunes?

To get you in the mood, here are photos of deserts around the world.

The road to Mar Musa, Syria (photo from Wikimedia Commons)
Gobi Desert, Mongolia, in autumn (photo from Wikimedia Commons)
Valle de la Muerte, Atacama Desert, Chile (photo from Wikimedia Commons)
Arizona National Scenic Trail (photo from Wikimedia Commons)

Leave a comment with your answer. I’ll post the answer later today (see below).

Click here for a map (By the way, this map includes the answer but it doesn’t look that way!)

ANSWER: Antarctica! In fact both poles are deserts. The Antarctica Polar Desert is 5.5. million square miles, the Arctic Polar Desert is 5.4 million sq mi and the Sahara is 3.5 million sq mi. Read more about the largest deserts at

Snow surface at Dome C Station, Antarctica (photo from Wikimedia Commons)

Why is it a desert? Because the air is so dry. As the Dan Satterfield explains in Scientific Facts That Are Not True:

It cannot be too cold to snow some. It can be too cold to snow a lot. As air gets colder, it can hold less moisture. This is why the Antarctic is the greatest desert on Earth. It’s drier in many places than the Sahara! Climate change is expected to cause more snow in polar regions, not less. Now you know why. (warmer air means it can snow more)

— Wild Wild Science Blog: Scientific Facts That Are Not True

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

It’s Raining Rocks

Raining rocks and lava (photo of Krakatua eruption 2008, Wikimedia Commons)

In case you missed it last week …

Back in 2018 astronomers discovered a planet 200 light-years away and five times the size of Earth. K2-141b is a lava planet so close to its sun that its rotation and orbit are in lock step; the same side always faces the sun. It also moves really fast completing an orbit in only 0.28 days. Earth’s orbit takes a year. On K2-141b a “year” lasts 6.7 hours!

Artist’s rendering of a lava planet (image from Wikimedia Commons)

All of this was so intriguing that astronomers from York University, McGill University, and the Indian Institute of Science Education and Research decided to model K2-141b’s atmosphere. Published in the Monthly Notices of the Royal Astronomical Society, their report attracted attention because K2-141b is so unbelievably hellish. For instance:

The planet rains rocks, has an enormous lava ocean over 60 miles deep, and winds whip across its surface at speeds more than four times the speed of sound. And, because of how the small planet moves around its sun, one part of it experiences permanent daylight and reaches temperatures up to 5,432 degrees Fahrenheit, while the other side exists in permanent darkness, and temperatures drop to negative-328 degrees.

The Cut: Astronomers Discover … Earth?? by Madeleine Aggeler

Put all that together and you get a place hot enough to evaporate rock, windy enough to transport the evaporated minerals rapidly to the other side of the planet, and cold enough on the dark side for minerals to condense quickly and fall as a rain of rocks!

Oh fun. K2-141b is more hellish than Dante’s Seventh Circle of Hell.

There are a few — mercifully few — places on Earth where it rains rocks. The eruption of Krakatua, above, is one of them.

Read more at Wikipedia and at The Cut: Astronomers Discover…Earth??

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

The Largest Jack O’ Lantern

Jack O’ Lanterns face off (photo from Wikimedia Commons)

30 October 2020

Halloween is almost here. Who has the largest jack o’ lantern?

Two pumpkins in Jersey would like to win the honor. They’re nearly as wide as a picnic table.

They would lose to this 905.5 pound pumpkin from Ohio. Even if scooped out it would break the picnic table.

No squash can match the Ericsson Globe in Stockholm, Sweden when dressed for Halloween. At 360 feet in diameter it’s wider than a football field, the largest jack o’ lantern in the world.

Ericsson Globe arena in Halloween costume, Stockholm, Sweden, 2014 (photo from Wikimedia Commons)

However, the universe wins the prize for size. The Jack O’ Lantern nebula is a cosmic cloud of radiation and particles emitted by a huge star 15-20 times heavier than our sun. This 2019 animation from NASA/JPL-Caltech shows why it’s called The Jack O’ Lantern.


Jack O’ Lantern nebula animation from NASA/JPL-Caltech via Wikimedia Commons

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

p.s. Betty Rowland reports there’s a 1,179 pound pumpkin in Aspinwall raising money for Project Bundle Up. Here are her photos.

1,179 pound jack o’ lantern in Aspinwall, PA, 30 Oct 2020 (photo by Betty Rowland)
1,179 pound jack o’ lantern in Aspinwall, PA, 30 Oct 2020 (photo by Betty Rowland)

Hurricanes and Smoke

23 October 2020, 9:10a: Satellite shows Hurricane Epsilon near Bermuda and smoke from Colorado’s East Troublesome Wildfire crossing the Atlantic (image from GOES East, crop+description from Yale Climate Connections)

2020 has been a prolific year for heat, fires and hurricanes.

Last month was the hottest September on record, dangerous western wildfires have been burning since late July, and the Atlantic has had so many storms that the National Hurricane Center ran out of English alphabet letters and began naming storms using the Greek alphabet.

On Friday, 23 October 2020, Yale Climate Connections reported that a weather disturbance in the Caribbean is likely to become the sixth Greek alphabet storm, Zeta. That’s number 32. In the report they included an intriguing GOES EAST satellite image, above, with this explanation.

Smoke from Colorado’s second largest fire on record, the 170,000-acre East Troublesome Fire, was carried by the jet stream to the northeast of Hurricane Epsilon (upper right of image).

Yale Climate Connections: Disturbance in the western Caribbean likely to become Tropical Storm Zeta

As this moment Colorado’s East Troublesome Wildfire is burning through Rocky Mountain National Park and threatening Estes Park (click here for video). I’m not surprised the smoke showed up near a hurricane.

See more reports at Yale Climate Connections:

(image from GOES East cropped by Yale Climate Connections)

Nature’s Bird Food and Other October Delights

Rose hips, Frick Park, 3 October 2020 (photo by Kate St. John)

This October there are plentiful fruits and seeds for migrating birds in Pittsburgh. Virginia creeper, porcelain berry, and rose hips (above) provide food for cedar waxwings and robins.

Pine siskins invaded southwestern Pennsylvania this week! Many of you are reporting them at your backyard feeders while natural food sources, such as arborvitae, have created pine siskin hotspots. Siskins force open the cones with their sharp beaks and pick out the seeds.

These arborvitae cones were on the ground at a pine siskin hotspot. Three stages are pictured: Top = Spent cones as much as one year old, Middle = Opened cones that were emptied by pine siskins, Bottom = a mix of closed, opened and spent cones.

Arborvitae cones that fell on N Dithridge Street thanks to pine siskins, 9 Oct 2020 (photo by Kate St. John)

The huge acorn crop in Schenley Park is attracting many blue jays, squirrels and chipmunks. Here’s what the ground looks like below the oaks at Bartlett Shelter.

Many, many acorns, Bartlett Shelter Schenley Park, 7 Oct 2020 (photo by Kate St. John)

In other delights October trees, sky and shadows are spectacular.

Fall colors, Schenley Park, 7 Oct 2020 (photo by Kate St. John)
Long shadows, Schenley Park, 7 Oct 2020 (photo by Kate St. John)
Fall color in Frick Park, 6 Oct 2020 (photo by Kate St. John)
Dead hickory points to the moon, 8 Oct 2020 (photo by Kate St. John)

It’s a good time to be outdoors.

(photos by Kate St. John)

Signs of Fall

Sun rays on a misty morning in Schenley Park, 8 Sept 2020 (photo by Kate St. John)

20 September 2020

Fall is in the air in Pittsburgh as sun rays peek through autumn mist in Schenley Park.

Below, though the large ash trees have died of emerald ash borer the small ones still put out leaves that turn unique colors. These are on their way from yellow to lavender.

White ash leaves turn a variety of colors in fall, Schenley Park, 18 Sept 2020 (photo by Kate St. John)

Teasel flower heads (dipsacus sp.) have dried, leaving the husk that’s a “natural comb for cleaning, aligning and raising the nap on fabrics, particularly wool.” It’s hard to imagine holding this prickly husk to do the job. Use gloves, of course.

All summer we noticed curly dock (Rumex crispus) leaves and not the flowers. Now our attention is reversed because the seeds have turned a rich brown. The stalk is ugly, however the seeds are fascinating up close, each one surrounded by the calyx that produced them. The papery wings allow them to float on water and fly a bit in the wind.

Curly dock, gone to seed, Schenley Park, 17 Sept 2020 (photo by Kate St. John)

The most obvious sign of fall is the temperature. 43 degrees F at dawn today. Speaking of gloves, you’ll need them when you go birding in the morning.

(photos by Kate St. John)

Smoke Gets In Our Eyes

Late afternoon sun looks pink in Pittsburgh, 14 Sept 2020 (photo by Jonathan Nadle)

16 September 2020

This week’s spooky sunsets and hazy skies in eastern North America are due to smoke from the massive wildfires in Washington, Oregon and California. The smoke is so intense that it’s dispersing across the continent and across the Atlantic, causing haze in Europe.

Near sunset on Monday 14 September the sun was a strange shade of pink in Pittsburgh, captured above in true color by Jonathan Nadle.

We can’t see the smoke coming but the satellites do, blowing eastward in two paths on Tuesday 15 September: one over the Northern Plains and Great Lakes, the other over Nebraska to Kentucky and Virginia.

It’s also blowing west over the Pacific, shown here on Friday 11 September.

The haze is inconvenient for us but truly hazardous on the West Coast. The dark brown colors on the map below are the worst air quality in the world. The air is so bad that people are leaving the area. I know of at least one person who’s fleeing from San Francisco to Pittsburgh.

screenshot of AirNow air quality map, 16 Sept 2020

By now the fires cover 4.5 million acres, an area so large that it’s hard to imagine. To help you visualize it The Guardian has created an interactive map comparing the fire acreage to well known cities and your own hometown — click here or on the tiny screenshot below. NOTE: The comparison below is for New York City. I compared the fire acreage to Pittsburgh and found it would run from approximately I-80 to the PA-West Virginia line!

Meanwhile the sunsets are still creepy.

Strange sun at sunset in Pittsburgh (filtered), 15 September 2020 (photo by Jonathan Nadle)

None of us are immune to this huge effect of climate change. Smoke gets in our eyes.

UPDATE: Janet Campagna, who lives in California, remarked that the days are much cooler because the sun can’t get through the smoke. This reminded me of the volcanic winter which results from smoke in the atmosphere after giant volcanic eruptions such as Krakatoa in 1883 and Mount Pinatubo in 1991.

(photos by Jonathan Nadle, screenshot of AirNow map from, screenshot of article from The Guardian)

La Niña This Winter

Average location of the jet stream and typical temperature and precipitation impacts during La Niña winter over North America. (Map by Fiona Martin for NOAA

Pittsburgh will be warmer this winter because the Pacific Ocean’s “skin” is colder than usual at the equator. This ocean change is called La Niña.

During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3 to 5 °C (5.4 to 9 °F). It persists for at least five months.

definition of La Niña, Wikipedia

Here’s what the sea surface temperature looks like in this anomaly map from November 2007. Blue is colder than normal, orange is warmer.

Seas surface temperature during La Niña in Nov 2007 (map from Wikimedia Commons)

La Niña affects weather worldwide, causing “more rain than average through Indonesia, drier weather in southeastern China” and a variety of colder/warmer and wetter/drier effects in North America as shown on the map at top.

Pittsburgh will be affected but it won’t be extreme.

Check out these December-January-February 2020-21 predictions for the continental U.S.

3-month Temperature Anomaly Outlook for Dec-Jan-Feb 2020-21 (map from NWS Climate Prediction Center)
3-month Precipiation Anomaly Outlook for Dec-Jan-Feb 2020-21 (map from NWS Climate Prediction Center)

The Gulf Coast is really going to feel it!

(maps from NOAA and National Weather Service. Click on the captions to see the originals)

Avoiding Hurricane Laura

U.S. Doppler Weather Radar, 26 Aug 2020, 9:48pm EDT (from National Weather Service)

27 August 2020

Last night two hours after sunset bird migration was intense over the southeastern United States. The birds showed up as blue blobs on Doppler weather radar but there was a noticeable gap over Louisiana, southern Mississippi and southeastern Alabama. The birds were avoiding Hurricane Laura.

This National Weather Service radar map from 26 Aug 2020, 9:48pm EDT shows where the birds won’t go. (I’ve added a pink line to illustrate their self-imposed boundary.) I believe the small blue blob south of the pink line –at Jackson, Mississippi — is a sign of birds leaving for safer locations.

Humans were urged to leave too because of the coming storm surge, 20 feet high, as illustrated in the Weather Channel video below.

As of this writing (27 Aug 2020, 6am) about 150 people chose to stay home in the path of the storm.

Birds don’t have our brains but they know to avoid Hurricane Laura.

(maps from National Weather Service, click on the captions to see the originals; embedded tweet from The Weather Channel)