The Gleam at Sunset, Pittsburgh, 2 Feb 2021 (photo by Kate St. John)
18 December 2022
Often in winter Pittsburgh has overcast skies all day and clear skies at night. When the transition happens at sunset we see clear sky approaching from the west but it arrives too late for us to enjoy the sun. We have 10 minutes of sunshine and then it’s dark. I call this The Gleam At Sunset.
Why does this happen so often? Does Ohio have lovely weather all day that only reaches us at night?
Gleam at sunset, Downtown Pittsburgh in the distance, 2016 (photo by Kate St. John)
Pittsburgh is well known for overcast skies in winter but you may be surprised where the clouds come from.
Lake Erie plays an extensive role in our cloud cover and, as long as it isn’t frozen over during the winter, it serves as a local moisture source that plagues the region with clouds. … Most places have clear blue skies after a cold front passage, but when we have northerly flow off of the lake we have cloud cover.”
Buffalo, New York has Lake Effect Snow. I like to think that Pittsburgh has “Lake Effect Clouds.”
Mixing and the Boundary Layer
When the air is well mixed (wind and/or rising warm air, falling cold air) it creates a defined line between the clouds and the rest of us below. In winter and early spring this mixing happens while the air is heated during the day.
During the winter and early spring, often times we observe a well-mixed boundary layer (we call this boundary layer coupling). When the atmosphere is coupled/mixed, the top of that mixing height is where we observe a cloud base [i.e. the bottom of the overcast deck]. You may even feel gusty wind during the day that supports the notion of a mixed atmosphere, when strong wind aloft is transported to the surface through this means.
The cloud base remains well defined while the air is mixing. It falls apart when the mixing stops at sunset.
At night, wind gusts typically subside as the surface cools and the atmosphere becomes decoupled again in tandem with sunset / loss of daytime heating. At decoupling you may lose your mixing height and essentially dissolve your cloud cover.
Rising moon reflected in the Monongahela River at Duck Hollow, 5 Dec 2022, 4:23pm (photo by Kate St. John)
10 December 2022
In December daylight is in short supply and the skies are often gray so clouds have a big effect on our mood in Pittsburgh. This week ranged from brilliantly sunny to thick overcast, from exhilarating to subdued (depressed?) depending on the variable clouds.
Above, on the miraculously clear afternoon of 5 December the moon rose over still water at Duck Hollow. Below, a line of clouds at sunrise painted the sky red on 2 December.
Sunrise in Pittsburgh, 2 Dec 2022, 7:16am (photo by Kate St. John)
The next day I was scouting for crows on Mt. Washington when crepuscular rays peeked through the clouds at sunset. Do you see the crows? They’re tiny black dots in the sky.
Crepuscular rays at sunset with crows in flight to Mt Washington’s “Saddle,” 3 Dec 2022, 4:42pm (photo by Kate St. John)
The clouds were so low on 6 December that fog engulfed the top of the Cathedral of Learning. Morela came down to Heinz Chapel’s scaffolding to look for birds in the nearby trees. Do you see her in the middle of the photo?
Peregrine on Heinz Chapel scaffolding, 6 Dec 2022, 12:39pm (photo by Kate St. John)
Last night’s clouds partially obscured the waning moon while moonlight made a colorful halo.
Moon halo, 9 Dec 2022, 7:57pm (photo by Kate St. John)
Today we’re back to overcast skies with 85% to 96% cloud cover for the next two days. Alas. No variation until Tuesday.
Ranking the states by average percentage of land in drought, 2000-to-March-2021 (original map from Wikimedia Commons colored by Kate St. John)
27 November 2022
The western U.S. has always been drier than the east but as climate change heats up the planet, drought has become more prevalent. NOAA’s quarterly weather outlooks now include a 3-month drought prediction along with temperature and precipitation forecasts. Some places are more likely to experience drought than others. Which states are more likely? Which are least?
The graphic above is based on Stacker’s article, States With the Worst Droughts, that ranks states by average percentage of land in drought from 2000 to March 2021. Listing the states in order, I grouped them in 10s with darkest Orange indicating the top ten drought states and darkest Green for the 10 wettest. (White = the middle 10)
The top state for drought is Arizona. No surprise; it’s a desert.
The state with the least drought is Ohio!
Georgia and South Carolina stand alone with a lot more drought than their neighbors. Their drought ranking is like Kansas.
Hawaii (dark orange) and Alaska (dark green) are at opposite extremes.
As climate change continues to unfold human populations will migrate from less habitable to more habitable locations. In the U.S. we can expect people to move west to northeast in the coming century — from more drought to less.
Burning bush leaf and fruit, 15 Nov 2022 (photo by Kate St. John)
19 November 2022
On Tuesday morning, 15 November, I found beautiful fruits on my walk in the neighborhood: Red berries on invasive burning bush (Euonymus alatus), purple berries on native American Beautyberry (Callicarpa americana), and dusty blue fruit on invasive English ivy (Hedera helix).
American beautyberry, 15 Nov 2022 (photo by Kate St. John)English ivy berries, 15 Nov 2022 (photo by Kate St. John)
It began to snow so I hurried home and was glad I was indoors when it came down fast. It looks peaceful in slow motion at the end of this video.
The snow stuck to the grass, parked cars, and the Pitt peregrine nest …
Snow on the Pitt peregrine nest, 15 November 2022, 2:15pm
… then melted overnight as the temperature rose and low clouds moved in.
Low clouds at 8pm, 15 Nov 2022 (photo by Kate St. John)
By Friday most leaves were gone and the only green shrubs in Schenley Park were invasive plants: Bush honeysuckle in this view …
Scene in Schenley Park, 18 Nov 2022. The green shrubs are invasive honeysuckle (photo by Kate St. John)
… and bamboo near the railroad tracks.
Scene in Schenley Park, 18 Nov 2022. The green shrubs are invasive bamboo (photo by Kate St. John)
Tonight the temperature will drop to 19 degrees for a very cold start to the new week. Brrrrr!
Last weekend Chris Randall @ultrapeakschris tweeted a video of a shadowy figure walking in step with him in the fog. At first he thought it was another person. Instead it was a Brocken specter with a faint rainbow halo called a glory.
Spooky!
My first Brocken Spectre. Creepy to see it out the corner of my eye and think it was someone else moving pic.twitter.com/j38PhwGZqE
Wikipedia describes: A Brocken spectre is the magnified shadow of an observer cast in mid air upon any type of cloud opposite a strong light source (such as the sun). If the cloud consists of backscattered water droplets, a bright area and halo-like rainbow rings called a glory can be seen around the head or apperature silhouette. The phenomenon was named for Brocken Peak in Germany where it frequently occurs.
Sometimes the specter appears to hover in the sky like an angel as did this one with a triple glory that appeared to a mountain climbing team in Tajikistan.
And finally, you can create a Brocken specter in nighttime fog if you work at it. The caption on this photo says: “On an exceptionally foggy night, I parked my car at one end of the parking lot, facing into the lot, and covered one headlight with a floor mat. Standing before the uncovered light, I photographed the shadow that I was thus casting into the fog : a Brocken spectre.”
Far, far away at the edge of our solar system there’s a spherical cloud of icy objects with an inner cloud like a bicycle spoke reaching toward the Sun. No one’s ever seen it. It’s the home of comets.
The Oort cloud is the theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years). It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud.
Long-period comets (which take more than 200 years to orbit the Sun) probably come from the Oort Cloud, which is sometimes described as a “cometary reservoir.””
Hale-Bopp is out there with the planetesimals, minute planets believed to be composed of cosmic dust grains that accumulated with many others under gravitation to form a planet.
(photos and illustrations from Wikimedia Commons; click on the captions to see the originals)
p.s. an AU is an Astronomical Unit = the distance from Earth to Sun in one Julian year (365.25 days).
Total lunar eclipse, digiscoped through Pittsburgh city lights and haze, 8 Nov 2022 (photo by Kate St. John)
8 November 2022
This week southwestern Pennsylvania witnessed many atmospheric effects from clear skies to troubled clouds, rainbows and a total lunar eclipse. Here are the stories behind six pictures.
Total lunar eclipse, 8 Nov 2022, 5:29am, photo through my birding scope. The sky was hazy and I am terrible at digi-scoping so by the time I got a decent shot of the moon it was leaving my view. But you get the idea.
Atmospheric optics around the sun, 5 Nov 2022, 9:20am, Yellow Creek State Park, PA. Ice crystals in the clouds produced two sun dogs, a 22 degree halo, and a circumzenithal arc (upside down rainbow at top). Click on the links to read about each phenomenon.
Ice crystals in the clouds produce two sun dogs, a 22 degree halo, and a circumzenithal arc, Yellow Creek State Park, 5 November 2022 (photo by Kate St. John)
Layers of troubled clouds, 5 Nov 2022, 5:45pm: Later that same day two layers of clouds raced overhead in gusty wind. The lower layer threatened rain at the horizon while the upper layer glowed in sunlight.
Lower clouds threaten rain at the horizon while upper clouds catch sunlight, 5 Nov 2022 (photo by Kate St. John)
Light mist over the Monongahela River at Duck Hollow, 3 Nov 2022, 10am.
Haze over the Monongahela River at Duck Hollow, 3 Nov 2022 (photo by Kate St. John)
Rainbow over Pittsburgh, 6 Nov 2022, 1pm: On Sunday I hiked at Hays Woods with Linda Roth (in foreground) and the 40 Acres AKA Hays Woods Enthusiasts. We got caught in a brief downpour but there was a Big Sky reward: a beautiful rainbow.
Rainbow as seen from Hays Woods, Pittsburgh, 6 Nov 2022 (photo by Kate St. John)
The sky glows before sunrise on a clear day, 7 Nov 2022, 6:27am.
Sunrise in Pittsburgh, 28 October 2022 (photo by Kate St. John)
29 October 2022
Fall color was brilliant this week, especially at sunrise.
Bright red was gone from our hillsides as the maples faded but other leaves took up the slack in yellow and orange. Below:
Bottlebrush buckeyes are yellow in Schenley Park.
Japanese knotweed is yellow-orange at Duck Hollow.
Blue-green porcelain berries were eagerly eaten by migrating robins.
Red honeysuckle berries attracted cardinals and house finches.
Confused flowers! Forsythia bloomed along the Nine Mile Run Trail even though its leaves were a deep purple-red.
Red oaks are red-orange in Schenley Park.
Bottlebrush buckeye leaves turn yellow in Schenley Park, 25 October 2022 (photo by Kate St. John)
Fall color, Japanese knotweed, Duck Hollow, 27 October 2022 (photo by Kate St. John)
Porcelain berry fruit, Nine Mile Run Trail, 27 October 2022 (photo by Kate St. John)Honeysuckle fruit, Nine Mile Run Trail, 27 October 2022 (photo by Kate St. John)Forsythia blooming in late October, NMR Trail, 27 October 2022 (photo by Kate St. John)Fall color, Schenley Park from Panther Hollow Bridge, 25 October 2022 (photo by Kate St. John)
Wispy contrails over Pittsburgh, 15 Oct 2022, 1:40pm (photo by Kate St. John)
22 October 2022
Pittsburgh skies put on a show in mid October.
On the 15th feathery contrails were pushed by high winds at 30,000 feet. We could not see them at dawn because of the lumpy clouds.
Sunrise with clouds, 15 Oct 2022, 7:20am (photo by Kate St. John)
The next day the wind dropped, a temperature inversion set in, and rotten-egg smog gathered in the Monongahela Valley, below.
Inversion shows pollution from US Steel trapped in the Mon Valley, US Steel’s Edgar Thompson Works and Kennywood in the distance, 16 October 2022, 9am (photo by Kate St. John)
Temperature inversions are typical in October and November when warm air above traps cold air at the ground, filling the valleys with haze or fog. In Pittsburgh the pollution from US Steel Clairton Coke Works is also trapped, intensifying the rotten egg smell of hydrogen sulfide (H2S) in the Monongahela Valley.
Weather or not, US Steel Clairton always emits these pollutants. The 16th’s stinky haze capped more than ten days of unusually terrible air pollution from USS Clairton(*). Here’s how bad it was: How Bad has Air Quality Been? H2S Was Below PA Standard For Only 3 Hours This Week. (Note: H2S level is supposed to be below the standard to keep our air clean.)
The air smelled better October 17-20 including on this beautiful morning of October 20.
Sunrise, almost clear, 20 October 2022 (photo by Kate St. John)
Yesterday’s pollution was pretty bad. Hoping for better air.
(*) US Steel’s Clairton Coke Works is the largest coking facility in the U.S., baking coal to make coke for steel production. Coking removes coal’s impurities by turning them into gases including stinky hydrogen sulfide (H2S). In March 2022 Allegheny County Health Department reported that “Based on all available data and resources, H2S exceedances that occurred at the Liberty site during the period of Jan. 1, 2020, through March 1, 2022, can be attributed entirely to emissions originating at US Steel’s Clairton coking facility.”
