Category Archives: Weather & Sky

La Niña This Winter

Weather & Sky
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 Climate.gov)

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

Migration, Water and Shore, Weather & Sky
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)

Why Are The Rivers Full When Rainfall Is Low?

Water and Shore, Weather & Sky
Monongahela River running high even though there’s a drought, 8 Aug 2020 (photo by Kate St. John)

In this 8 August 2020 photo, the Monongahela River is full near the Homestead Grays Bridge, yet rainfall since June 1 is down 2-4 inches in the Monongahela watershed and the ground was bone dry at that time. This got me thinking … How could the river be full when we’re nearly in a drought? The abundance of water is deceiving.

Ever since Europeans arrived in western Pennsylvania they’ve worked to make our rivers more navigable. In the early 1800s these efforts barely made a dent, especially in late summer when the dry season turned the rivers into shallow pools and rivulets. The Lewis & Clark Expedition coped with this after they left Pittsburgh a month later than planned. Embarking on 31 August 1803 the Ohio was so low that the expedition had to push and drag their laden keelboat over many shoals. It took them a week to reach Wheeling. (read more here).

Keelboats and flatboat on Ohio River, early 1800s (image from Wikimedia Commons)

In 1824 Congress authorized the U.S. Army Corps of Engineers to get involved and the navigation improvements became permanent. By 1929 locks and dams had transformed all three rivers into chains of lakes. (read more at From Rivers to Lakes: Engineering Pittsburgh’s Three Rivers)

Braddock Lock and Dam on Monongahela River, 2017 (photo from Wikimedia Commons)

Because of the “lakes” we have lots of river traffic, making the Port of Pittsburgh the 15th largest port in the U.S. when measured in domestic trade. On the Mon River the trade seems to be mostly coal.

Coal barge and pleasure boat on the Monongahela River (photo from Wikimedia Commons)

The river is full when rainfall is low because the water is controlled for navigation.

Oh well.

p.s. Some people say the dams are for flood control but the locks and dams don’t perform that service. As Rob Protz points out, the flood control dams are very different. (See the Conemaugh River Dam.) Even with those dams in place we still get floods, though perhaps less frequently.

At the edge of the Mon River at Duck Hollow, 17 Feb 2018, 9:30am
The Mon River flooding the parking lot at Duck Hollow, 17 Feb 2018, 9:30am

August Flowers, Spotty Rain

Plants & Fungi, Schenley Park, Weather & Sky
Tansy at the meadow at Frick Park, 14 Aug 2020 (photo by Kate St. John)

This week brought a profusion of August flowers and very localized rain.

Above, tansy’s rayless flower heads look like daisies without petals. Tansy (Tanacetum vulgare) has only one kind of flower — the small yellow ones in the central disk. Daisies have two kinds — the central disk plus white flower rays.

Below, cup plant (Silphium perfoliatum) is blooming in Schenley Park showing off the cupped leaves that give it its name.

Cup plant, Schenley Park, 10 Aug 2020 (photo by Kate St. John)
Leaves join at the stem to make a cup on cup plant, Schenley Park, 10 Aug 2020 (photo by Kate St. John)

Spotted knapweed (Centaurea stoebe) is invasive but the flower sure is pretty.

Spotted knapweed, Frick Park meadow, 14 Aug 2020 (photo by Kate St. John)

Asiatic dayflower (Commelina communis) can be invasive, too, though the flower lasts only a day.

Asiatic dayflower, Duck Hollow, 8 Aug 2020 (photo by Kate St. John)

This week brought rain to our new home north of Schenley Park and continuing drought just south of here. At home on 11 August it rained so hard that a bug took shelter on our window. Its location 70 feet off the ground explains why chimney swifts fly so high.

A bug took shelter from the rain at our new home north of Schenley, 11 Aug 2020 (photo by Kate St. John)

While the bug was avoiding rain north of Schenley, no rain fell in the park just a mile away.

There’s still a drought in Schenley Park, 12 Aug 2020 (photo by Kate St. John)

It’s a very localized drought.

(photos by Kate St. John)

Are We In a Drought?

Weather & Sky
United States Drought Monitor (screenshot from droughtmonitor.unl.edu)

2 August 2020

It’s been so dry in western Pennsylvania this summer that we find ourselves wishing for rain. Yesterday some areas were lucky. It rained 0.61 inches at Pittsburgh’s airport but not throughout the region. Precipitation is still down -2.24 inches since June 1. Are we in a drought?

The US. Drought Monitor map (28 July 2020 above) shows drought conditions and severity across the country. Pale orange in southwestern Pennsylvania indicates areas of Moderate Drought with short-term impacts (“S“). Yellow is Abnormally Dry.

The map above changes quickly if it rains heavily one day. The Drought Severity Index (Long Term Palmer) map, below, charts prolonged abnormal dryness or wetness and matches what gardeners and farmers are dealing with. Southwestern PA has felt like it’s in a drought and, yes, according to the Palmer Index the situation is Severe. (Black on the map is missing data.)

Long Term Palmer Drought Severity Index, 25 July 2020 (map from NOAA)

Our situation in Pennsylvania is mild, though. The real concern is out West where the Drought Monitor is bright red (Extreme Drought) with long term impacts (“L“) and the Palmer Index is dark orange.

West Texas is suffering the double whammy of rampant COVID-19 + extreme drought. Today’s a good day to count our blessings in southwestern Pennsylvania.

(maps from US. Drought Monitor and Drought Severity Index)

Sunrise On The Longest Day

Books & Events, Weather & Sky
Summer solstice sun rises over the Heel Stone at Stonehenge, 2005 (photo from Wikimedia Commons)

20 June 2020

Today the summer solstice arrives in Pittsburgh at 5:43pm EDT giving us this year’s longest daylight of 15 hours 3 minutes and 54 seconds(*).

If you were tracking the sun’s location at sunrise you would see why “solstice” means “sun stands still” for it rises at nearly the same place for a day or two before it heads south again.

Stonehenge near Salisbury, England is the perfect place to watch this happen as the sun rises over the Heel Stone on the summer solstice.

Some of the crowd at Stonehenge sunrise, 2005 (photo from Wikimedia Commons)

Normally huge crowds gather at Stonehenge to watch this phenomenon but English Heritage has canceled the 2020 celebrations and is urging people to stay away because of COVID-19.

Fortunately we can all watch sunrise at Stonehenge via live stream on the English Heritage Facebook page. Tune in on Sunday June 21 at 4:52 am British Summer Time, which is Saturday 11:52 pm Eastern Daylight Time.

Night owls in Pittsburgh don’t have to get up early to watch sunrise on the longest day.

(*) Pittsburgh’s 20 June sunrise was at 5:49am, sunset at 8:53pm.

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

Despite The Cold, An Early Spring

Climate Change, Phenology, Plants & Fungi, Weather & Sky
Honeysuckle buds March 2019 vs Feb 2020 (photos by Kate St. John)

Except for a 10 degree cold snap in the last 24 hours, we’re having an early Spring.

So far this year temperatures in Pittsburgh have been 10-34 degrees above normal a third of the time. January 11 was 34 degrees above normal at 71 degrees F.

Honeysuckle bushes responded by leafing out. Last Monday (10 February 2020) I found open honeysuckle buds in my neighborhood. I took a similar photo last year on 11 March 2019 but it was whole month later and the buds were not as open.

According to the USA National Phenology Network, Spring is three weeks ahead of schedule in the southeastern US:

Spring leaf out has arrived in the Southeast, over three weeks earlier than a long-term average (1981-2010) in some locations. Charlottesville, VA is 24 days early, Knoxville, TN is 20 days early, and Nashville, TN is 18 days early.

— Status of Spring USANPN.org

Here’s what it looks like on the map as of 14 February 2020.

Spring Leaf Index as of 14 Feb 2020 (animation from USA National Phenology Network)

Despite the cold, today will warm to almost 40 degrees in Pittsburgh and to 52 by Tuesday. I think we’ll still have an early Spring.

(photos by Kate St. John, map from USANPN.org)

Moonglade

Beyond Bounds, Weather & Sky
Moon and Jupiter reflected on Brofjorden, Sweden (photo from Wikimedia Commons)

When the moon is bright, the sky is clear, and the wind is calm the moon’s reflection makes a path on the water.

In Sweden where this photo was taken the word for the moon’s path is mångata or “moon street.”

In English we have a name for it, though the word is rarely used: Moonglade.

(photo from Wikimedia Commons; click on the caption to see the original)

Space Junk May Collide Over Pittsburgh Tonight

Musings & News, Weather & Sky
Space junk collision (screenshot from PBS Be Smart video)

Wednesday, 29 January 2020:

Chances are it won’t happen but …

Tonight at around 6:39pm two defunct satellites that are still in orbit have a 1% (or less) chance of colliding 900km (560 miles) above Pittsburgh. They’ll be traveling toward each other at 32,880 mph!

If they don’t collide, everyone who has anything to do with satellites will breathe a sigh of relief because there will be that much less out-of-control space junk for their own satellites to hit.

If they do collide they won’t hurt us. At best we’ll see a few shooting stars as the bits burn up in Earth’s atmosphere. But we probably won’t see anything because Pittsburgh’s cloud cover will be 40% at that point. Check out the Clear Dark Sky chart for the forecast (screenshot below).

screenshot of Pittsburgh Clear Dark Sky chart for 29 Jan 2020 (from cleardarksky.com)

Here’s the original collision prediction from LeoLabs, an outfit in California that tracks space junk and potential collisions.

See KDKA’s announcement with video.

And here’s a more in depth article from Forbes Magazine.

In the meantime, LeoLabs revised their estimate to a pass distance of 13-87 meters and a 1 in 1000 chance of collision.

I’ll bet we won’t see any stars tonight.

(screenshot of space junk collision from PBS Be Smart video; click on the caption to see the original video)

UPDATE on 31 January 2020: No, they didn’t hit but they came mighty close. Analysis by LeoLabs at The IRAS / GGSE 4 Close Approach.

On Vortex Street

Musings & News, Weather & Sky
Clouds on the lee side of Guadalupe Island, Mexico, 24 May 2017 (image from NASA’s Landsat satellite)

What do these photos and video have in common?

Smokestacks at Proserpine Mill, Jan 2012 (photo from Wikimedia Commons)

humming sound of wind in the wires (turn up speakers)

Answer: All three indicate the presence of — or potential for — a von Kármán vortex street.

When you’re in the neighborhood, this street is a fluid dynamic place. Learn more in this vintage article as we go Walking Down Vortex Street. (click the link)

(photos NASA and Wikimedia Commons; click on the captions to see the originals. video by Megan Lewis on YouTube)