How did fall temperatures locally compare with the northern hemisphere?

As we have reported several times over the years, the evidence is clear that over the entire Northern Hemisphere winter temperatures have been systematically warming over the past 70 years.

We base that conclusion on measuring the extent of air with a temperature of 23 or colder at the 850 millibar level, which is located about 1 mile above sea level. Such a measure can equally be made in the autumn months.

In fact, September-November 2019 ranked as the 12th warmest such period in the 72 years records are available.

That may come as a shock to Madison residents who have endured a relatively cold September-November this year (2.7 degrees colder than normal) characterized by record amounts of snow. ×

It is also notable that the top 15 warmest September-Novembers have occurred since 2000, suggesting that something systematic is occurring in the autumn as well.

In fact, the seeming contradictions exemplify aspects of the conceptual difference between climate and weather.

The weather brings day-to-day variability in meteorological conditions to a given location while the climate sets the backdrop for the parade of weather systems that deliver such variability.

That’s why it is still possible to get periods of severe cold in Madison in an overall warming climate.

It is likely, however, that such episodes will become less frequent and less severe as the planet continues to warm.

Category: Climate, Seasons

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What is the most snow Madison has received in one day?

Passers-by push a car stuck in snow at the intersection of Main and Fairchild streets during a record-setting snowfall Dec. 3, 1990, in Madison. (Photo credit: Carolyn Pflasterer)

What a storm!

Tuesday is the 29th anniversary of the greatest 24-hour snowfall ever in Madison.

Like most storms, this one had humble origins, but, by a conspiracy of meteorological circumstances, quickly grew into a historic monster.

Early on Dec. 1, 1990, a region of low pressure that had originated in the lee of the Rocky Mountains, made its way into the Oklahoma/Texas panhandle. Such features are a regular occurrence during the cold season.

The storm subsequently developed rapidly as it moved northeastward into Missouri, influenced by its serendipitous association with a potent wave disturbance in the middle troposphere.

As it developed, it spread substantial snows to the north and west of the cyclone track. That type of development and propagation of surface cyclones is an enduring characteristic of storms that bring Madison big snows.

In fact, because of their origins and tracks, such storms are known colloquially as “panhandle hookers.”

As the calendar turned to Dec. 3, the storm continued to develop as it moved northeastward toward Chicago, ensuring that the southern counties of Wisconsin remained on the cold side of the track.

Snow began in Madison just after midnight on Dec. 3 and fell heavily all day, totaling 17.3 inches in town by the time the day was over.

Blizzard conditions prevailed throughout the day from Grant County through Madison to Green Bay.

Nearby Adams-Friendship received 22 inches from the storm. The heavy snow was also accompanied by strong winds, gusting to 60 mph, that drifted the snow up to 7 feet in Madison.

Unfortunately, nine people in Wisconsin died from heart attacks related to snow shoveling.

Category: Meteorology, Severe Weather

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How was the 2019 hurricane season?

Hurricane Dorian as a new Category 5 hurricane on September 1, 2019
(Image credit: Dave Stettner, CIMSS)

The 2019 Atlantic hurricane season, which ends on Nov. 30, will go down as the fourth-most active hurricane season on record.

There were 18 named storms and 20 tropical cyclones in total, although many were weak and short-lived, especially late in the season.

The season began with subtropical storm Andrea, which formed on May 20. Andrea made 2019 the fifth consecutive year in which the hurricane season began before the official start of June 1. Barry was the season’s first hurricane, which formed in mid-July in the northern Gulf of Mexico and struck Louisiana.

The 2019 season was one of seven seasons to feature multiple Category 5 hurricanes, which are storms with sustained winds over 156 mph.

Dorian, the first Category 5 hurricane of 2019, hit the Bahamas, devastating the Abaco Islands and Grand Bahama. Dorian continued on to the U.S. East Coast where it caused additional damage. The total damage caused by Dorian was more than $600 million. ×

Hurricane Lorenzo was also a Category 5 and set the record for the easternmost Category 5 Atlantic hurricane to date. There were more than 60 deaths associated with Lorenzo. The offshore tug Bourbon Rhode sank after sailing through Lorenzo.

Hurricane Humberto was a Category 3 storm, with sustained winds of 111–129 mph. In September, Humberto passed just north of Bermuda and brought hurricane-force winds to the island. Humberto caused more than $1 million in damage and resulted in one death.

Spring forecasts typically predicted slightly above average activity with 13–16 named storms.

There is no single forecast model that is consistently better than other forecast models so forecasters use a collection of models to determine a likely track and intensity of a hurricane.

Over the past decade, track forecasts have steadily improved while hurricane intensity forecasts have only slightly improved.

Category: Meteorology, Tropical

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Why does fog form over the lake?

Steam fog on a Wisconsin lake in October.
Photo credit: Tom Achtor

The recent cold weather was accompanied by interesting fog over the open water of our lakes.

Fog is essentially a ground-hugging cloud, composed of tiny liquid water droplets.

This particular fog, called a steam fog, forms when cold air drifts across relatively warm water. The lake water evaporates into the air above the lake surface. The lake must be unfrozen.

The air is cooled and moistened, causing the dew point to increase. As the dew point approaches the air temperature, condensation occurs, forming fog droplets.

The condensation further warms the air. The warmed air rises and mixes with the cold air above it, reaching saturation and causing more fog to form.

When there is a large difference in temperature between the air above the lake and the water at the surface of the lake, there will also be considerable turbulence in the air over the lake.

The combination of steam fog production, turbulence over the lake, and strong winds can create one of nature’s most awesome spectacles — steam devils.

The name was first used in 1971 after observations over Lake Michigan.

Steam devils are swirling columns of steam fog (analogous to dust devils) that look like a whirlwind of steam fog on a cold day. Steam devils can rise up to 1,500 feet above the lake.

One of the many features of living near large lakes is that they are often shrouded in a fog in the fall and early winter.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

Category: Meteorology, Phenomena

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What is a polar vortex

From, provided by the Climate Change Institute at the University of Maine.

The term “polar vortex” was popularized by media outlets in 2014, when the country experienced a brutal January cold snap.

The polar vortex is a band of strong winds, high up in the atmosphere that spins counter-clockwise around the North Pole.

During the summer months, the vortex is weak, and its southern edge sits at high latitude. As the sun sets on the North Pole in late September, the vortex gains strength and gradually edges southward.

At the southern edge of the vortex is the so-called polar jet stream, which separates warm air to its south from the ever expanding and increasingly colder air to its north.

The nature of the polar vortex changes throughout the winter — sometimes it is strongly west-to-east, and other times it is characterized by high amplitude waves, which can rapidly transport warm air toward the North Pole in some locations and frigid air southward in others.

For instance, last week during our cold spell over the central United States, it was balmy in Anchorage, Alaska, which enjoyed highs in the low 40s.

Our recent cold spell has not prompted media to use the term and, as it turns out, that is actually appropriate.

A characteristic aspect of the true wintertime polar vortex is the existence of strong polar night jet — a band of strong west-to-east winds in the lower stratosphere (between 10-15 miles high).

The polar night jet is just beginning to establish itself at this time of year. If pieces of that vortex break off later in the winter and head southward, it is appropriate to refer to the ensuing cold air outbreaks as being related to changes in the polar vortex. But that is not the case in early November.

Category: Climate, Seasons

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