Snow on the rose, Pittsburgh, 2 Dec 2025 (photo by Kate St. John)
6 December 2025
As I mentioned on Thursday, Pittsburgh isn’t usually this cold in early December and certainly not for long. But ever since it snowed Tuesday morning the temperature has not ventured above freezing, though it will finally do so later today.
On Monday it was comfortably above freezing when I saw sun shining through yellow-green willow leaves at the Beaver River in Rochester, PA.
Willow with green and yellow leaves, Rochester, PA, 1 Dec 2025 (photo by Kate St. John)
On Tuesday all the trees were coated in snow and so was the rose (photo at top). It was hazardous weather for a flower.
Snow covered trees, Cathedral of Learning, overcast sky, Pittsburgh, 2 Dec 2025 (photo by Kate St. John)Snow-covered tree on Pitt’s campus, 2 Dec 2025 (photo by Kate St. John)
On Thursday sun lit Flagstaff Hill before the night turned quite cold.
Snow on Flagstaff Hill, Schenley Park, Pittsburgh, 4 Dec 2025 (photo by Kate St. John)
Today and tomorrow the snow will melt but then we’re heading back into a deep freeze Monday night. Terrible weather for a rose.
Last night the full Cold Moon was big and bright as Jupiter rose in the clear sky over Pittsburgh. These two jewels were visible even among city lights, though they are much more beautiful in the photo from Sweden at top.
In March 2025 Nate Luebbe (@nateinthewild) was north of the Arctic Circle at Vestvågøy island, Norway when he witnessed snowfall with a rainbow (“snowbow”) and the Northern Lights. So many jewels all at once!
This is perhaps the most outrageous thing I've ever captured. A moonbow (rainbow made from moonlight rather than sunlight), with snow (rather than rain) with the northern lights behind it. A Polar Lunar Snowbow? pic.twitter.com/vRsPHqYf27
— Nateinthewild | Nate Luebbe (@nateinthewild) March 3, 2025
Sometimes a satellite photobombs the natural jewels. The satellite here was not too intrusive on the Moon and Venus.
But satellites can quickly become space junk when they outlive their useful lives or accidentally fall out of orbit. The falconcam at Cromer Church in Cromer, Norwich, UK captured an amazing blaze of space junk upon reentry in February 2025. Wait for 10 seconds for the space junk to appear!
The AMC-21 satellite will become space junk some day. Launched in 2008, it uses the C band to transmit broadcast television. It was expected to last 15 years — until 2023 — but it’s still running. SES-21 was launched in 2022 to take over AMC-21’s job.
The term Polar Vortex came into popular use about 12 years ago when Earth’s normally well behaved jet stream went wobbly and forced arctic air into the continental U.S. The high temperature map on 6 January 2014 indicated -20°F in Minnesota!
U.S. maximum temperature map for January 6, 2014 (graphic from NOAA)
This week forecasters are talking “Polar Vortex” because the jet stream is wobbling again and we’re seeing the same effect. The slideshow at top is our low temperature series for today through next Tuesday 9 December. Pittsburgh’s highs will be below normal, hovering just above and below freezing.
It was much much colder in January 2014 but the difference this year is that it’s happening sooner, in some places setting temperature records for early December. And it repeats with very cold lows in Pittsburgh on the 4th & 5th, not so bad on 6th & 7th, and back again on 8th & 9th.
Lake Erie is the shallowest of the Great Lakes and can be very calm, but when the wind kicks up in November the waves start crashing and the lake reveals its hidden treasures.
On the day before Thanksgiving the wind blew steadily from the west-southwest at 25-30 mph, gusting to 50 mph in Ohio.
After that the wind died down and the lake sloshed back and forth like a bathtub. This effect is called a seiche. You can see this on the lake level graph, rising and falling stepwise after the high water mark.
Late afternoon light, Schenley Park, 23 Nov 2025 (photo by Kate St. John)
29 November 2025
This week I’ve spent a lot of time in the car for family Thanksgiving visits so I don’t have a lot of photos to show. Mostly pictures of the sky.
Sunset in Pittsburgh, 23 Nov 2025 (photo by Kate St. John)Sunset in Pittsburgh, 23 Nov 2025 (photo by Kate St. John)
We spent some time in Virginia Beach where there has not been a killing frost so flowers like this henbit deadnettle (Lamium amplexicaule) were still blooming.
Henbit deadnettle, Virginia Beach, 27 Nov 2025 (photo by Kate St. John)
On the bay shore boardwalk at First Landing State Park I found a lot of fallen acorns.
Acorn from a sand live oak, First Landing State Park, Virginia Beach, 27 Nov 2025 (photo by Kate St.John)
They are similar to southern live oaks but are very likely the sand live oak (Quercus geminata) that grows in sand and is commonly cultivated. It’s a good bet the trees were planted on the dunes. The leaves look like this.
Freezing fog made weather history yesterday when the National Weather Service in Pittsburgh issued its first ever freezing fog advisory. The advisory was issued for Westmoreland, Indiana, Armstrong, Butler, Lawrence, Clarion, Venango and Forest counties until 9 a.m, 20 November. The southwest corner of the state, including Pittsburgh, was unaffected.
This historical record may seem odd if you’ve ever been to Somerset County in winter, especially on the Turnpike. I myself have been in freezing fog at the Allegheny Front Hawk Watch (yup, no birds), but Somerset County is in the State College forecast area so they get to predict freezing fog.
The cool thing about freezing fog is that in a wind it forms rime ice, shaped like needles, on the windward side of twigs and branches. Check out the vintage article, below, about rime ice, but before you go you’ll want to watch this video from Mount Washington Observatory in New Hampshire, the Bad Weather Capital of the World. Amazing!
Frost in Pittsburgh on 4 Nov 2021 (photo by Kate St. John)
4 November 2025
Four years ago today I took a photo of frost because it was so late that year.
Though Pittsburgh’s killing frost date officially ranges from October 20 to 22, it was so warm in 2021 that we had no killing frost until early November when low temperatures were in the upper 20s for five days. The growing season ended abruptly.
This year, vegetation in my “urban heat island” neighborhood is still in good shape so we’ve had no killing frost here even though there was a freeze warning on 9 October (not!) and the temperature dipped to 31°F at the airport on 27 October.
I’ve marked this NWS graph of Pittsburgh temperatures last month with yellow on 9 October (we did not freeze at all) and a red box on 26 October (the one day that fell below freezing at the airport).
Because of the urban heat island effect, Pittsburgh’s growing season between frost dates could be mapped in micro climates with a warmer zone in the city and colder pockets in the creek valleys.
This graph was drawn with summer temperatures; I added October/November low temperatures to give you an idea of the variation in first frost.
Sunrise in Pittsburgh, 19 October 2025 (photo by Kate St. John)
25 October 2025
Vibrant reds and oranges graced the sky and the forest in Pittsburgh this week.
Our region is in the midst of an oak-hickory forest so red-colored leaves can be scarce. Oaks turn dark red after most other trees are bare and hickories turn yellow, so I look forward to the moment when our few sugar maples turn red. It happened this week in Schenley Park, as you can see below.
Fall color on maples in Schenley Park, 23 Oct 2025 (photo by Kate St. John)Fall color on maples in Schenley Park, 23 Oct 2025 (photo by Kate St. John)Fall color along the Lower Trail at Schenley Park. Notice that it’s yellow. 20 Oct 2025 (photo by Kate St. John)Fall color on maples in Schenley Park, 23 Oct 2025 (photo by Kate St. John)Sunlight breaks through the background; fall color in Schenley Park, 23 Oct 2025 (photo by Kate St. John)
Two deer browsed near Schenley’s Upper Trail. One is already in her gray winter coat but so close to the trail that her camouflage didn’t matter. I would have missed the other deer (yellow arrow) except that it moved.
Two deer browsing in Schenley Park near the Upper Trail, 20 Oct 2025 (photo by Kate St. John)
Cold temperatures have ended this year’s spotted lanternflies so I was surprised to see one on the Panther Hollow Bridge. The air was so cold that didn’t move as I approached. Hah! I see you.
Spotted lanternfly, Schenley Park, 20 Oct 2025 (photo by Kate St. John)
p.s. Mary Kate reminded me that sweetgum trees are very pretty in the fall. I’ll try to get some pictures this coming week.
Though Pittsburgh’s air has improved since the Smoky City days, we still have heavy industry and unhealthy air too frequently. The rotten egg smell of sulfur lingers when there’s a temperature inversion, and since Pittsburgh averages 157 inversion days per year it’s likely there’s bad air somewhere here almost half the time. But not everyone smells it. It depends on where the plume goes, and that depends on the surface wind or lack thereof.
This two minute video explains how it works showing air movements on 10 December 2020. Back then the Cheswick power plant (orange plume) was still in operation; it closed on 31 March 2022.
To whet your appetite for the PlumePGH website, here are still shots from a recent bad air day on Saturday 4 October 2025. A screenshot of the SmellPGH map on 4 October shows that the air was really awful and a lot of people noticed it.
We think of hurricanes as very dangerous and very devastating but there’s a pigeon-sized seabird, the Desertas petrel (Pterodroma deserta), who nests during hurricane season because it chases hurricanes to feed its chick.
High on a rocky plateau [on Bugio Island], one small nocturnal seabird is nestled in its burrow, where far below waves lap gently against the cliffs. In the blackness of night, it senses a storm brewing 1,000 miles (1609km) from the coast of Morocco.
Bugio Island is well situated for chasing hurricanes, all of which are born as tropical depressions off the coast of Africa, travel west to the Americas, then swing north.
When scientists put data trackers on Desertas petrels and tracked them for five years, 2015-2019, they found:
Desertas petrels make some of the longest foraging trips ever recorded in any species – traveling as far as 12,000km (7,460 miles) over deep, pelagic waters – all the way from Africa, to the New England coast and back again.
Unlike most seabirds who circumnavigate hurricanes or try to stay inside the eye of the storm, the Desertas petrel actively chases hurricanes, braves incredible winds, and captures food churned to the ocean’s surface in the wake of the hurricane.
They put themselves exactly in the right place at the right time to be run over by a hurricane.
