Egads, it was cold last weekend! Here in Pittsburgh it was -6 to 11 degrees F, but yesterday things turned around. Sunday (7 Jan.) started at -6oF but warmed to a high of 30. Today will be above freezing and by Thursday the high will be 64oF. That's a swing of 70 degrees in only four days!
The slideshow above shows this in color for January 5, 8, 11 and 12.
I'm not complaining that we're out of the deep freeze but ... this weather is really odd. Why did it get so cold and why is it warming so fast? Why don't we have a moderate winter like we used to?
Crazy as it sounds, it's because the arctic is warming faster than the rest of us. When there's not a big temperature difference between the North Pole and the mid-latitudes (us) the jetstream slows down. When it's sluggish, it wobbles in high amplitude loops that dip as far south as Florida(*).
The video below explains why. I recommend watching it twice; you see more the second time. (My end notes have info on millibars, etc.)
So when a cold loop settles over us, we're really cold and when it moves on we're really hot. It happens quickly in both directions.
Don't put away your winter clothes on Thursday. The forecast says it'll be 5 degrees on Saturday night.
The average air pressure at sea level is 1013.25 millibars = 14.7 pounds.
What's the significance of 500 millibars? The 500 millibar pressure zone is where air pressure is half what it was at sea level, halfway up in the atmosphere. Since air pressure varies as weather systems move above us, the 500mb map is a great diagram of what the weather systems are doing. Here's the air pressure map for Friday 5 Jan 2018 at 1200z (8am). Notice that the pressure lines echo Friday's temperature map above.
On the day before the "bomb cyclone" hit Massachusetts my sister-in-law, Barb Lambdin, sent me two photos of the frozen ocean at West Dennis Beach, Cape Cod. Intrigued by the coming storm, I asked her to take more photos when it hit.
The photo locations are part of the story:
Before the storm: West Dennis Beach on the ocean side.
During the storm: Corporation Beach in the protected middle of the bay shore.
BEFORE THE STORM:
Above, the ocean was so calm on 3 January 2018 that ice had formed in flat sheets and blue-green water ponded on top.
The waves were small and slushy (below). Barb calls them Frozen Margarita waves.
DURING THE STORM:
On 4 January it was too windy and dangerous on the ocean side so Barb went to the bay side at Corporation Beach. The two photos below were taken at high tide.
Keep in mind that this is the calm side of Cape Cod yet the waves are high and about to flood the parking lot. I have never seen waves break at Corporation Beach!
This morning it's 3o F in Pittsburgh with a forecast high of 15o F. Yesterday was just as cold. It's 20 degrees below normal here.
Less than a week ago, on 22 December, the low was 40o with a high of 57o F. It was 19 degrees above normal. To accomplish this temperature swing it rained half an inch on December 23 and froze solid on Christmas Eve night. We had black ice on Christmas Day.
Black ice isn't really black. It just looks that way because it's such a thin, smooth coating of clear ice that the dark pavement shows through.
Technically speaking "black ice" forms when pavement looks dry but its porous surface contains water. When that water freezes it's invisible. So the photo at the top isn't really "black ice" (it was probably laid down by freezing rain) but who can find a photo of something invisible?
Pittsburgh has black ice but we don't have blue ice.
Blue ice is very old ice from the lowest layers of a glacier. It's blue because the weight of the glacier above compressed all the air bubbles out of it. The lack of air makes the ice look blue like sea water.
The computer said, "Those numbers are too high. They must be in error. Throw them out." And so Barrow, Alaska disappeared from the climate analysis database.
Fortunately a lot of people missed Barrow when it was gone. In fact they suspected it might disappear some day because it's so unusual. The error was found quickly and the raw data will be restored.
This month more than a year's worth of temperature data for the northernmost point in the U.S. -- Barrow, or Utqiávik, Alaska (see arrow) -- automatically disappeared from the National Centers for Environmental Information temperature analysis system because it looked so out of whack.
Why would a computer throw away real data?
Computers that collect automated weather data have algorithms that test for wild abnormalities so that instrument errors are isolated (rejected) from the clean data calculations. For instance, when a weather thermometer breaks or goes offline, the temperature is recorded as "zero." When this happens in July in Pittsburgh it's so obviously incorrect that the software rejects it. Algorithms for climate analysis are even more stringent because a change to an instrument's location can look like a trend even though it isn't.
Here's why Barrow looks crazy to a computer. This graph by Derek Arndt at climate.gov shows circles for Barrow's 1979-1999 average monthly temperatures, triangles for 2000-2017. Notice that for most of the year those 20-year averages are pretty close but for October, November and December they're widely different. Computers don't like that!
Barrow is experiencing rapid warming because there's a lot less sea ice than there used to be. When ice crowds the shore in the fall, Barrow gets cold, but now the ice recedes so far in the summer that it takes months longer to reach the town.
Today is the shortest day in the northern hemisphere, the official start of Winter. But don't worry. Spring comes faster than any other season.
Because the Earth doesn't move at a constant speed in its elliptical orbit, the seasons are different lengths. From a warmth perspective, the northern hemisphere is lucky. Our winter is the shortest season.
Winter, December-to-March: 89.0 days from winter solstice to vernal equinox
Spring, March-to-June: 92.8 days from vernal equinox to northern summer solstice
Summer, June-to-September: 93.6 days from the summer solstice to the autumnal equinox
Autumn, September-to-December: 89.8 days from the autumnal equinox to the winter solstice
So after the sun stands still at 4:28pm UTC (Universal Time) -- 11:28am in Pittsburgh -- it'll start its journey northward.
Spring will be here soon.
p.s. Groundhog Day is halfway between the winter solstice and vernal equinox. It's something to look forward to.
Though the ocean will never flood Pittsburgh, I'm still fascinated by the rising sea. (*)
Back in October I wrote about sea level fingerprints, the pattern of tiny elevation changes in sea level caused by uneven gravitational forces around the globe. The highest ocean peaks are in the tropics, the deepest valleys are near melting glaciers. As the land loses mass (ice) its gravitational pull decreases and it stops hugging the ocean to its shore. The water has to go somewhere so it goes to the tropics.
This means that glacial melt affects sea level rise in two ways: (1) It adds water to the ocean that used to be sequestered on land and (2) it alters the sea level fingerprint, lowering the ocean nearby and raising it far away.
If you do the complicated math, you can find out how individual melting glaciers will affect sea level at specific locations.
Last month, scientists at NASA Jet Propulsion Lab did just that when they published a paper in Science Advances and an online tool that illustrates how glaciers will affect 293 coastal cities. Let's take a look at Miami.
Almost half the sea level rise in Miami will be caused by glaciers (47.4% of total sea level rise) and almost half of that will be Greenland's fault (20% of total sea level rise). That's why Greenland is so red in the screenshot above.
The next highest glacial contributor in Miami will be Antarctica (12% of total sea level rise). In the screenshot below you can see that South American glaciers help, too.
In fact, the entire northern hemisphere is endangered by Antarctica's melting ice because it's so far away. Ironically the safest place to be is right next to a melting glacier. Sea level will go down at those sites.
(*) Pittsburgh's Point is 711 feet above sea level. My immediate family lives 10 to 25 feet above sea level in Virginia and Florida.
(screenshots of glacial contribution to sea level rise in Miami from the online tool at NASA Jet Propulsion Lab. On the first screenshot I added a pink circle to highlight Miami. Click on the images to use the online tool.)
You know things are strange when there's an outbreak of 15 tornadoes in Ohio and western Pennsylvania in November.
Just over a week ago, on Sunday November 5, 2017, a cold front passed over the southern Great Lakes and Ohio River Valley. Before the front arrived it was humid and around 70 degrees -- as much as 17 degrees above normal -- so the front's leading edge spawned 15 tornadoes.
The National Weather Service in Cleveland mapped 14 of them in their region. I've added the EF-1 tornado in Calcutta, Ohio just west of Beaver County, PA reported by the National Weather Service in Pittsburgh. Yes, 15 tornadoes!
The tornado in Williamsfield, Ashtabula County, Ohio was one of the strongest, an EF-2 with winds of 127 miles per hour. It cut a swath 7 miles long ending at the western shore of Pymatuning Lake. The damaged house shown above makes me glad I wasn't there!
This [Calcutta, Ohio tornado] is the 14th confirmed tornado so far this year in our county warning area. On average, we see five tornadoes a year. This is the first November tornado since 2003 /14 years/ in New Philadelphia, Ohio. This is the 5th tornado in November for Columbiana county since 1950.
Experts say that climate change increases the frequency of severe weather. I'd say that 15 tornadoes in November look like a good example.