Category Archives: Weather & Sky

It Rimes

Rime scene in Helsinki, Finland (photo from Wikimedia Commons)

We don’t have flowers in December but we do have ice and it comes in many forms.  Here’s the first in a series on ice, starting with my favorite:  Rime.

The word “rime” comes from Old English hrim which meant hoarfrost or a chill mist or fog.  Nowadays hoarfrost and rime are not the same thing. Hoarfrost doesn’t form in fog. To get rime there has to be cold fog or the location has to be in the clouds. For that reason, “Rime shouts, Mountains!”  It’s easy to find rime at high altitudes.

Rime at Jay Peak, Vermont (photo from Wikimedia Commons)

Rime forms when super-cooled water drops (in fog or a cloud) crystallize on cold objectsSoft rime is feathery and so lightweight that it can’t break the trees.  Hard rime is denser and comb-like.  Both are white because they contain trapped air.

Soft rime on a small branch (photo from Wikimedia Commons)

The best part about rime is that it can form in a light wind. When it does it points toward the wind because each new crystal is deposited on the windward side. This is counter-intuitive; it’s the opposite of rain.

What direction did the wind blow through this fence?

Rime on a chainlink fence (photo from Wikimedia Commons)

Rime can even coat snowflakes. Graupel, which looks like hail, is actually a rime-coated snowflake.  I wonder if these pop when you step on them.

Garupel in Elko, NV (photo from Wikimedia Commons)
Graupel in Elko, NV (photo from Wikimedia Commons)

This month is a good time to find rime in the Laurel Highlands. My best experience with it was during an east wind at the Allegheny Front Hawk Watch.  No one else was up there to enjoy it.  It was way too foggy!

Click here to see more rime photos including a “rime doughnut” at Summitpost.

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

Snow On Leaves

Snow on leaves, Schenley Park, 16 Nov 2018 (photo by Kate St. John)

On Thursday it rained. Then it sleeted. Then it snowed in the wee hours of Friday morning, especially north of Pittsburgh.

In the old days most of the trees would be bare by now, but this year many still have leaves.

Ice and snow made the leaves heavy and some of the trees came down, hitting power lines as they fell.  By Friday morning KDKA reported that 65,000 households north and east of the city were without electricity.  No power, no heat, and for those with well water, no water.  It may take until Sunday evening to get all of the power restored..

The City is warmer than surrounding counties so Schenley Park had snow on the leaves, but no ice.

Snow on leaves, Schenley Park, 16 Nov 2018 (photo by Kate St. John)

Here’s what my favorite hillside looked like yesterday. 50% of the trees still have leaves.

Only half of the trees are bare, Schenley Park, 16 Nov 2018 (photo by Kate St. John)

The power failures wouldn’t have been so bad if most of the trees had been bare. 

(photos by Kate St. John)

The Sun Will Rise An Hour Early

Sunrise in Pittsburgh, 13 Nov 2009 (photo by David Fulmer, CC license on Flickr)

The sun will rise an hour early tomorrow in Pittsburgh.

At 2:00am on 4 Nov 2018 the cell networks will push out the new time (1:00am Standard Time) to our mobile phones.  We’ll gain an hour of sleep and will be surprised when the sun sets just after 5pm. Rush hour will start at dusk on Monday.

Now that we’ve passed the autumnal equinox we’re losing daylight every day.  Tomorrow we’ll lose two minutes! 

Sunrise/sunset in Pittsburgh, PA, Nov 3 and 4, 2018 (screenshots from SunDroid)

Meanwhile, birds are unaffected by our trick with clocks and will still cue on daylight.  When the crows show up in Oakland at rush hour, lots of people will be surprised. 

Hundreds pf crows above Bayard (photo by Kate St. John)
Hundreds of crows above Bayard Street  at dusk, 7 Nov 2016 (photo by Kate St. John)

Monday will be the first time people and crows are on the same schedule.  😉

(photo credits: Pittsburgh sunrise by David Fulmer, CC license on Flickr, screenshots of SunDroid app & photo of crows by Kate St. John)

Dew On The Grass

Dew on the grass, early October (photo by Kate St. John)

Sunday morning, 21 Oct 2018:

In early October, warm days and cool clear nights are the perfect combination for dew on the grass.  One of these nights the temperature of the grass will drop below freezing and the dew will form as frost.

Have you had frost in your neighborhood yet? 

Tonight might be the night.

p.s. If the air is below freezing but not humid, the plants freeze without a frost

(photo by Kate St. John)

Outside The Hook Echo

EF1 tornado, Greene County, NC (photo from Wikimedia Commons)

Last week the National Weather Service published an analysis of six of the many tornadoes that hit our area on Tuesday, October 2.  There were 14 tornadoes in Pennsylvania that day!

The most damaging tornado hit a nursing home in Conneautville, PA.  The most unusual one touched down in the Valley Green Road area of Westmoreland County.  NWS Pittsburgh describes what made the Valley Green Road EF1 tornado so interesting:

This tornado was unusual not only for its northward movement in an eastward-moving storm, but especially because it formed on the northern side of the parent thunderstorm, removed from the typical hook echo region.

NWS Damage Surveys for 10/2/2018 tornado event, National Weather Service Pittsburgh

So what is the hook echo region?

According to Wikipedia, “A hook echo is a pendant or hook-shaped weather radar signature as part of some supercell thunderstorms.” describes how it forms: “This “hook-like” feature occurs when the strong counter-clockwise winds circling the mesocyclone (rotating updraft) are strong enough to wrap precipitation around the rain-free updraft area of the storm.”

The annotated radar image below shows the hook at bottom left, curling around the back of the storm with a tornado at the tip. 

Annotated radar image of a violently tornadic classic supercell near Oklahoma City, Oklahoma, USA on 3 May 1999 (image from Wikimedia Commons)

Tornadoes usually form in the hook echo and they move with the storm.  Storm chasers use these facts to find and safely chase tornadoes.

But not at Valley Green Road.  That tornado formed on the north edge and traveled north (See region on the annotated example of an Oklahoma tornado below.)

Supercell radar image from NSSL NOAA, annotated in pink to show northern edge of the storm (image from Severe Weather 101, NSSL NOAA)

Sneaky tornado!  Fortunately it was not very powerful (EF1) and there were only trees in its path.

(photo and hook echo images from Wikimedia Commons. The tornado photo was taken in North Carolina (not in PA); click on the captions to see the originals)


Southeast U.S. radar image, 15 Sept 2018, 5:08 EDT (image from National Weather Service)

Birds can sense when bad weather is coming. If it’s going to be dangerous and they have some lead time they get out of the way.  Hurricane Florence gave them plenty of time to prepare.

Weather radar shows us where it’s raining by detecting objects in the sky.  When masses of birds are on the move they show up on radar, though less intense than steady rain. Flocks of birds look green on radar and are only detected when near radar stations.  Since most birds migrate at night, that’s when to watch.

This radar image from 5:08am on Saturday September 15 shows the rain bands of Hurricane Florence swirling over the Carolinas. Notice that there’s no rain for miles surrounding the circle of the storm but there are intense green blobs southwest of Florence over the Florida panhandle.

Thousands of birds! They’ve heard the news and they’re leaving the area.  Evacuate!

p.s. Read more about birds on radar here and an article about birds escaping storms by flying hundreds of miles out of their way 

(image from National Weather Service)

Rain, Rain Go Away!

In case you haven’t heard, it’s been raining here in Pittsburgh.  A lot! 

This is mostly from the remnant of Tropical Storm Gordon that came ashore in Mississippi on September 4 and arrived here September 8.  We were in a drought but now it’s been raining for three days.

Yesterday set a record of 3.73 inches at the National Weather Service in Moon Township but it’s rained even more in the South Hills. Since Friday morning 7.5 inches have fallen at the Allegheny County Airport in West Mifflin (as of 10 Sept 2018, 7:53a). And it’s still raining!

Basements are flooded and roads are closed.  Two screenshots from PennDOT traffic cameras show:

  • On the left, the 10th Street Bypass is flooded and closed (hard to see through the rain-splashed cam).
  • On the right, the I-376 “bathtub” at Stanwix Street hasn’t filled yet but it’s going to, so it’s closed.
screenshots from PennDOT traffic cams at

And the rivers are rising.  Here’s the National Weather Service’s Ohio River prediction for Pittsburgh.  Uh oh!

Ohio River gauge from the NWS Advanced Hydrological Prediction Service

Fortunately our house and street are fine (photo at top) but I feel bad for those who live in the valleys.

Rain, Rain Go Away!

(photo by Kate St. John, PennDOT traffic camera screenshots, Ohio River gauge from the NWS Advanced Hydrological Prediction Service)

Watching The Clouds

Thunderhead forming, Aug 2018 (photo by Kate St. John)

Pittsburgh’s weather had a tropical flavor this month with a chance of thunderstorms predicted every afternoon.

On clear days I could see individual thunderheads form and sometimes hear them rumble in the distance.  This late morning cloud on August 13 had some interesting features. Was it going to rain or thunder?

Two parts to this cloud: cumulo top, nimbus bottom

It was already a two-part cloud: Cumulus is the bright white top, nimbus is the darker lower section.

Cumulus congestus stage

While I watched, two updrafts rapidly pushed moisture higher in the sky. If I’d made a video you would see both columns expanding upward and growing fast. The small cloud on the left dissolved moments after I took this photo. The big one kept growing.

photo retouched to highlight lumpy nimbus area

The nimbus section looked threatening with dark lumpy areas (photo retouched to add contrast).  I’m not sure what the lumps mean but they probably weren’t good.

I watched this cloud as I walked home and, sure enough, it thundered after I took the photo.  Fortunately I was indoors before it rained.

(photos by Kate St. John)

Hurricane Chris In Newfoundland

Hurricane Chris at Branch, Newfoundland (screenshot from video by Chris Mooney)
Hurricane Chris at Branch, Newfoundland (screenshot from video by Chris Mooney)

What happens when a hurricane hits Newfoundland?  I found out last week when Hurricane Chris came to eastern Newfoundland while I was there on a birding trip.

The cold waters of the North Atlantic usually take the fangs out of hurricanes before they hit Atlantic Canada and so it was with Hurricane Chris.  Before the storm we asked some Newfoundlanders about it and they said it wouldn’t be bad. “We won’t even take in the lawn furniture for this one.”

By Thursday morning, 12 July 2018, Chris was downgraded from hurricane strength to a post-tropical cyclone — from winds greater than 74 mph (119 kph) to winds less than 40 mph (64 kph).

Nonetheless, it was forecast to hit Cape Race around 8pm on Thursday with sustained winds of 35 mph (56 kph) while dumping 3-4 inches of rain (75-100 mm) near Terra Nova National Park.  The map below shows both locations with purple pins:  “Cape Race, Day 4” on the south shore and “Terra Nova, Day 6” in the north.

Our birding schedule meshed perfectly with the hurricane’s timing.  We left Trepassey near Cape Race on Thursday morning and were sleeping in Clarenville by the time bad weather hit the Avalon Peninsula Thursday night.

Along the way we experienced the calm before the storm — hot and windless.  On the Maine coast I’ve heard this called The Hurricane’s Breath because it is so unusual.

When the post-tropical cyclone crossed Cape Race Thursday night its maximum sustained winds were 40 miles per hour (67 km/h) with gusts up to 54 mph (87 km/h).  Meanwhile about 3 inches (76 mm) of rain fell near Terra Nova.

So what did it look like on the south coast of Newfoundland when the storm was at its peak?  Chris Mooney, a park interpretation technician at Cape St. Mary’s Ecological Reserve, took these videos from his home in Branch, NL on Thursday evening.

Posted by Chris Mooney from the town of Branch, 7/12/2018 at 9:02pm. (Click the speaker icon to turn on the sound.)

… and posted at 9:24pm

Chris remarked that salt spray had already coated his windows so much that he couldn’t see out of them.

And what about the nesting birds on the rock? “We’ll lose a few chicks for sure.”

Fortunately the remnant of Hurricane Chris was a relatively mild storm.  When a real hurricane hits Newfoundland it’s devastating.  Click here to read about Hurricane Igor in September 2010, the strongest hurricane ever to hit the island.


(videos and screenshot by Chris Mooney via Facebook)