Category Archives: Weather & Sky

Is It Spring Yet?

Honeysuckle leaves in the City of Pittsburgh, 16 March 2019 (photo by Kate St. John)

20 March 2019

Today is the astronomical First Day of Spring when the sun crosses the celestial equator at 5:58pm EDT. But is it Spring yet? It depends on where you live.

The USA National Phenology Network tracks spring across the continental U.S. based on first leaf out conditions for honeysuckle (Lonerica) and first bloom conditions for lilacs (Syringa vulgaris). The plants are non-native, and honeysuckle is invasive, but they make good indicators because they’re early responders to springtime warmth.

Monday’s animated Spring Leaf Index (18 March 2019) shows that leaf out was ahead of schedule through late February but fell behind in northern Virginia, the southern Great Plains, and the Pacific Northwest when cold weather hit in early March.

Spring Leaf Index as of 18 March 2019 (animation from USA NPN)

According to the model, spring hasn’t reached Pittsburgh yet but I’m conducting my own Leaf Out Survey in my neighborhood. I took the honeysuckle photos below on 11 March and 16 March 2019. Both were cold days after a spurt of exceptionally warm weather. The tiny leaves on the right show the effect of 77 degrees F on March 14!

Honeysuckle leaf out, City of Pittsburgh, 11 March and 16 March 2019 (photos by Kate St. John)

Do you have leaves in your neighborhood yet? Is spring on time?

Follow spring’s progress at the USA National Phenology Network. For blooming times click here for the latest Spring Bloom map.

(animated map from the USA National Phenology Network. photos by Kate St. John)

What Will Our Climate Feel Like in 60 Years?

Clouds in hot summer (Creative Commons license on Flickr)

We know our climate is changing compared to 30 years ago because we see obvious signs:

Science predicted this more than a generation ago, but most of us couldn’t imagine how it would feel. Now that we’ve seen 30 years of change and more is in store, we’re anxious to know what our climate will be like in the future.

Matt Fitzpatrick and his colleagues at the University of Maryland Center for Environmental Science have answered this question by visualizing the future on an interactive map. Their study analyzes 540 cities in the U.S. and Canada, mapping their predicted climate in the 2080s to an existing climate today.

I tried out the map for myself at I looked up Pittsburgh, PA of course and got the answer shown in the screenshot below.

It shows that Pittsburgh’s 2080 climate will feel like Jonesboro, Arkansas does today. Jonesboro is 665 miles away from here, near Memphis, Tennessee. (Click on the image to see the website. Use website controls to see more complex answers.)

What will Pittsburgh’s climate feel like in 60 years? (screenshot of climate prediction at

The map bubbles explain: Our winters will be 10.8F warmer and 46.8% wetter. Our summers will be 10F warmer and 17.6% drier.

Let’s compare current to future using graphs. Pittsburgh’s current climate averages are shown below from U.S. Climate Data.

Sixty years from now our average winter lows will barely reach freezing. July and August average highs will be 93+ degrees F but watch out for the highest highs. August record temperatures in Jonesboro are all above 103oF!

Graph comparing current average high/low temperatures by month to 2080 prediction, Pittsburgh, with 100+ degrees maximum (graph by Kate St. John using current averages, adding UMCES prediction)

Our precipitation will be really different. We’ll go from a fairly steady 3 inches of rainfall per month to a rainy season in November-to-May and a dry season June-to-October. This might resemble California’s wet (flood) and dry (fire) seasons.

Graph comparing current average rainall by month to 2080 prediction for Pittsburgh (graph by Kate St. John using current averages, adding UMCES prediction)

Try the app for yourself at

We’re in for a wild ride.

For more information read about the study here at University of Maryland Center for Environmental Science.

(credits: Cloud photo from Flickr, Creative Commons license. Map screenshot from Pittsburgh current climate graph from U.S. Climate Data. Graphs of Pittsburgh’s future temperature and rainfall by Kate St. John. Click on the captions to see the originals)

Zooming Past Jupiter

What is it like to get close to Jupiter?

In this NASA video a robotic spacecraft called Juno makes its sixteenth fly-by (Perijove) since arriving in mid-2016. Its closest approach is almost dizzying. I feel better when the spacecraft zooms away and we see the swirling clouds.

Did you notice that Jupiter is on the sound track, too? The fourth movement of Gustav Holst’s The Planets is called Jupiter, The Bringer of Jollity. Listen to the entire majestic movement here.

This video was featured on NASA’s Astronomy Picture of the Day on 5 February 2019.


Glaze ice on a Japanese maple (photo from Wikimedia Commons)

An article about ice on a very icy day, 8oF and falling.

Considering how often the temperature has fluctuated in Pittsburgh this winter I’m surprised we haven’t seen more glaze ice.

Glaze ice is the name for the icy coating caused by freezing rain or freezing drizzle. If the accumulation is small, the effect is beautiful and the electricity stays on. The photo above from Wikimedia Commons is more beautiful than my own below.

Glaze ice on a tree, overcast sky, Pittsburgh (photo by Kate St. John)

When glaze ice is 1/4 inch thick or more the Weather Service calls it an ice storm. A quarter of an inch doesn’t sound like much but it’s so heavy that it weighs down the trees and they fall on power lines, streets, parked cars and houses. Power lines and power towers can fall, too. According to Wikipedia, “just one quarter of an inch of ice accumulation can add about 500 pounds (230 kg) of weight per [power] line span.” No wonder things come crashing down.

In January 1998 I wasn’t in Maine for the Great Ice Storm but I remember its results quite vividly. We visited central Maine in September and there were still broken trees everywhere. Folks who lived through it said they were without power for weeks. Everyone was stuck near home — couldn’t drive anywhere — so the radio stations connected people by announcing supplies and requests for help. Everyone pulled together.

The Great Ice Storm of January 1998 was even worse in upstate New York and Canada. Here are four photos from NOAA.

Effects of the Great Ice Storm of 1998 (photos from 10th Anniversary, NOAA)
Great Ice Storm of 1998 in upstate New York (photos from 10th Anniversary, NOAA)

Pretty as glaze ice is, I’m glad to do without it.

(photo credits: Japanese maple glaze ice from Wikimedia Commons, glaze ice in Pittsburgh by Kate St. John, photos of the Great Ice Storm of 1998 from NOAA, 10th Anniversary. click on the captions to see the originals)

Clouds Foretell Changing Weather

  • clouds (photo by Kate St. John)

Let’s appreciate clouds. Tuesday January 22 was an especially good day for it.

After a beautiful red sunrise the sky cleared enough to reveal thin, wavy clouds flowing overhead. The National Weather Service said these clouds were at 11,000 feet — “alto” height, not cirrus height — but they really looked like this cirrocumulus undulatus photo at the International Cloud Atlas. Notice the feathery details in the photos above. (The four slides show two in normal color and two enhanced for contrast).

Cirrus clouds indicate a change in the weather. So did the red sunrise, photographed by Dan Dasynich. “Red sky at morn, sailors forewarn.”

Dawn in Pittsburgh area, 22 Jan 2019 (photo by Dan Dasynich)

Almost clear on Tuesday we had rainy, foggy weather the next day. The clouds told us it was coming.

(slideshow photos by Kate St. John, sunrise by Dan Dasynich)

Wobbly Jet Stream, Arctic Air

Low temperature forecast maps, 27 Jan to 2 Feb 2019, from National Weather Service as of 27 Jan 2019, 5:30a.

Remember how cold it was in January 2014? It’s been five years since we saw extremely cold weather but the jet stream is wobbling again and we’re going to see a smack of subzero temperatures this week. The maps show this week’s forecast lows described by the National Weather Service:

Bitter cold temperatures will give way to a potentially record breaking push of Arctic air this week. Wind chills as low as -40 or colder can be expected across the Northern Plains and Great Lakes. In addition, wide swaths of heavy snow can be expected across the area. This system will push east and south early this week with much below normal temperatures and wintry precipitation.

National Weather Service, 27 Jan 2019, 5am

Crazy as it seems, extreme cold is a sign of climate change. Here’s an explanation from my Polar Vortex article of January 2014:

“In the good old days before climate change, the winter polar vortex in the northern hemisphere was generally well behaved.  It was a persistent, strong, cold, low pressure zone surrounding the polar high at roughly the same latitude around the globe.  The strong winds kept the jet stream in line.  Nobody got too hot or too cold.

“But now as the Earth gets hotter hot air from the troposphere is forced into the stratosphere and disrupts the polar vortex. The vortex weakens, becomes disorganized, and can collapse into smaller pieces.  Its winds weaken and the jet stream flaps like a flag in the breeze, as shown in (c) below.”

Jet stream Rossby waves (graphic from Wikimedia Commons)
Jet stream Rossby waves (graphic from Wikimedia Commons)
  • (a) Strong polar vortex (blue) keeps jet stream (pink) at same latitude.
  • (b) Polar vortex weakens
  • (c) Weak vortex lets the jet stream range widely north and south.

Get ready! Arctic air is on its way.

(forecast maps from the National Weather Service. jet stream diagram from Wikimedia Commons; click on the captions to see the originals)

The 100th Meridian Is Moving East

North Dakota, riparian wildlife habitat (photo from USDA)

The 100th Meridian West is an imaginary line on the map that happens to mark the climate divide between the humid east and arid west in North America. Or rather, it used to. The rainfall divide is moving east.

Extending from the North to South Poles, the 100th runs longitudinally in the U.S. from North Dakota through Texas.

The 100th meridian is on the upright border of Oklahoma and Texas (image from Wikimedia Commons)

Its coincidence with the rainfall divide was first documented in 1877 by John Wesley Powell who found during his explorations in the Great Plains that the 100th was a visible boundary. Locations to the east of the 100th received 20+ inches of annual rainfall, the west received less.

20 inches is a key number for agriculture and human population. It determines what you can grow, whether you have to irrigate and, thus, how many people can live there. Powell saw the line and told Congress it had implications for settlement of the western plains. Congress didn’t heed him but …

This 2014 map of U.S. Population by County shows that it played out as Powell expected. You can see the rainfall divide in population density. People choose to live where there’s water.

U.S. population by county, 2014 (map from US Forest Service)

You can also see the line from outer space. I’ve marked the 100th (approximately) on this satellite photo of Nebraska. The landscape is deep green to the east though not uniform.

Satellite photo of Nebraska shows it is drier west of the 100th (photo from Wikimedia Commons)

Nowadays the 100th is no longer the rainfall divide.

A study by Columbia University meteorologists found that the aridity line has shifted 140 miles east and is now statistically located at the 98th meridian. Climate change will move it even further as warming evaporates moisture in the northern plains and alters rainfall in the south.

In a hundred years the aridity mark may be firmly inside Minnesota, Iowa and Missouri. Aridity decreases the amount of agriculture and will probably change the population. People choose to live where there’s water.

John Wesley Powell’s “100th meridian” is moving east.

This article was inspired by Yale Climate Connections. Read more here in Yale Environment 360, 11 April 2018.

(photos from USDA, USFS and Wikimedia Commons; click on the captions to see the originals)

It’s Time To Appreciate Clouds!

Wrinkled clouds in Pittsburgh, 7 Jan 2019

A week ago, 7 Jan 2019, the National Weather Service said the sky was clear at Pittsburgh International Airport but I have proof that at that moment it was overcast in the East End.

Not only was it overcast but the clouds were doing something special near the Cathedral of Learning. See that wrinkle? Is that undulation? Or is it the beginning of an asperitas formation?

Asperitas clouds are newly named, the first formation to be added to the International Cloud Atlas in 66 years. They were proposed by the Cloud Appreciation Society in 2009 and accepted in 2017. The atlas goes back to 1896 so this is a big deal.

This video of asperitas clouds in Tenerife, featured by the Cloud Appreciation Society, shows how fascinating these clouds can be.

Thick clouds say “Pittsburgh in winter” all over them. Stratus (low) and altostratus (mid-level) are our specialty but we also have altocumulus undulatus, cumulus fractus and sometimes even mammatus. Click to see what they look like.

Yes, we have overcast skies (tell me about it!) but there are cool things above us if we just take the time to look. Watch the video to get in the mood (exciting background music!).

C’mon, Pittsburgh, it’s time to appreciate clouds!

(photo by Kate St. John, video from on YouTube)

p.s. Did you know that clouds have a genus and species? At the bottom of this webpage is a cloud diagram that shows genus by height. Explore the International Cloud Atlas.

p.p.s. The sun is at the top edge of my photograph. Do you see it?

Diamond Dust

Here’s a form of ice we’re unlikely to see in Pittsburgh because our weather is rarely cold enough and it’s often overcast.

Diamond dust is clear-sky precipitation that looks like tiny diamonds in the air, falling through a ground-level cloud. The conditions for producing diamond dust are very specific:

  • The temperature has to be well below freezing — best at -13F or lower.
  • The cloud must be made of ice. It’s not a freezing fog that started wet and turned icy.
  • The cloud is in a clear sky and the sun is shining. That’s how you see the diamonds.

The best place to find diamond dust is in Antarctica where it falls 316 days of the year. Otherwise you have to be in the right place at the right time. Bundle up!

Bonus Question: Diamond dust is not associated with a pogonip. What’s a pogonip?

(video “Diamond Dust in Bellevue Washington” from Wikimedia Commons; click here to see the original)