What created season’s first snowstorm?

Even if you are not a particular fan of winter weather, it is hard to deny that there is something about the first snow of the season.

In fact, British author J.B. Priestley expressed its transcendent nature beautifully when he wrote: “The first fall of snow is not only an event, it is a magical event. You go to bed in one kind of world and wake up in another quite different, and if this is not enchantment then where is it to be found?”

A snow covered park along Madison’s Lake Monona
on Saturday December 12th.

On Friday night and Saturday, Dane County experienced its first substantial snow with 6.4 inches recorded at the airport. This magical event is the result of very specific physical circumstances. The sun has been down at the North Pole since Sept. 21, and the Arctic night has subsequently crept slowly southward each day since helping to produce larger and larger amounts of cold wintertime air to the north.

Several days before the first flakes fell, the atmosphere was stirring many thousands of miles away throughout the full 6-mile depth of the troposphere. Almost imperceptible at first, a weak counterclockwise spinning air mass began to develop at the tropopause — the top of the troposphere. As this feature gradually matured it was empowered to create a similar vortex near the surface of the Earth — a surface low-pressure center. As that circulation intensified, it forced the production of clouds and precipitation over a wide area, with some of the precipitation falling as rain and some as snow.

The precise track of that low-pressure center determined who got rain and who got snow. At this time of the year, if the track of a surface low is to our southeast, say on a line from St. Louis to Chicago, we here in Dane County remain on the cold air side of the storm during its lifecycle.

So the next time you enjoy a quiet walk in the snow, consider that a long list of circumstances had to have played out in precise sequence in order to deliver you the magic. It is nothing less than a miracle.

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, Seasons

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Q: Who was Verner Suomi?

Verner Suomi was born on Dec. 6, 1915, and became a professor at UW-Madison. He is known as the “Father of Satellite Meteorology” because of his historic role in defining that field of study.

In the late 1950s, he and Robert Parent, a UW professor of electrical engineering, developed an instrument to measure the Earth’s heat balance from a satellite. It was the first successful satellite mission to make measurements of Earth.

In 1963, he designed the Spin-Scan Cloud Camera, a milestone in satellite instrumentation that flew throughout the 1960s, providing high-quality images of the Earth’s surface and atmosphere. These instruments laid the foundation for how to image weather for the world’s operational weather satellites. He proposed the instrument to measure the atmosphere’s temperature and water vapor distribution from a geostationary satellite; these were measurements that became available in the 1980s.

Professor Suomi also directed the development of McIDAS, a computer software system designed to analyze and interpret the big data sets generated from satellite observations. This software, first developed in the early 1970s and maintained for over 40 years, remains a primary tool for analysis of satellite weather observations in forecasting centers and universities across the globe.

Earth wasn’t his only interest. Professor Suomi was a member of the Venus/Mercury 1973 Imaging Science Team, NASA’s Mariner/Jupiter/Saturn Imaging Science Team, and the Pioneer Venus Science Steering Group.

Professor Suomi received many honors during his scientific career. Recently, NASA named a satellite after him — the Suomi National Polar-orbiting Partnership Satellite.

Suomi-NPP Satellite Schematic

Professor Suomi’s scientific accomplishments defined the young field of satellite meteorology. His leadership in the development of satellite weather observations and analysis led to weather forecasting improvements that benefited Wisconsin, the nation and the world — the Wisconsin Idea in action.

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: History, Meteorology, Uncategorized

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How was the 2020 hurricane season?

Preliminary tropical storm tracks for the 2020 Atlantic hurricane season. (Image credit: NOAA’s National Hurricane Center)

The 2020 Atlantic hurricane season ends today and will go down as the most active hurricane season on record.

A total of 30 named storms, 13 hurricanes, and six major hurricanes have formed throughout the season. Twelve of the named storms made landfall in the contiguous United States, breaking the record of nine set in 1916.

This season also has featured a record 10 tropical cyclones that have undergone rapid intensification, tying it with 1995. This was only the second season — the other was in 2005 — to use the Greek alphabet to name storms.

The Atlantic hurricane season officially starts June 1 and ends Nov. 30, but tropical storms can appear at any time. The 2020 season began with subtropical storm Arthur, which formed on May 16, followed by Bertha on May 27.

The 2020 season was the sixth consecutive year in which the hurricane season began before the official start of June 1. Hanna was the season’s first hurricane, which reached hurricane intensity on July 25 and made landfall in southern Texas. The 2020 season included the most active September on record with 10 named storms.

The 2020 season featured one Category 5 hurricane, which is a storm with sustained winds over 156 mph. Named Iota, this was the only the second time in recorded history that a Category 5 hurricane occurred in November, and it is the latest-forming Category 5 hurricane on record. The National Oceanic and Atmospheric Administration did predict an abnormally active hurricane season this year, but not the record-breaking one we experienced. All told, this season caused more than $41 billion in damage and resulted in more than 436 deaths.

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, Severe Weather, Tropical

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What causes a mid-latitude cyclone to develop?

GOES East water vapor view of a mid-latitude cyclone from spring 2019

Our recent weekend storm on Nov. 14-15 was the first strong storm of the autumn/winter season.

As you found yourself caught in the strong winds, you may well have wondered how do storms like this one come to be?

That has been the central motivating question in meteorological science for most of the past 100 years. During that time, meteorologists have learned a great deal about how such storms are formed.

In most instances, two or more days before the storm is noticed at the surface of the Earth, processes are at work in the upper troposphere. Specifically, at the height of the jet stream (about 6 miles above the surface), weak downward vertical motions begin to drag the tropopause downward into the middle troposphere. This process eventually results in the creation of a mid-level vortex, a region of counterclockwise rotating winds, at about 3 miles above the ground.

Once generated, this vortex is then moved around by the atmospheric winds in its vicinity. At the forward side of this moving vortex, the air is forced to rise. Such upward vertical motion evacuates air from the lower troposphere, lowering the pressure at the surface. Simultaneously, the upward vertical motion produces clouds and precipitation.

So long as the mid-level vortex continues to intensify and move, so too does the surface cyclone. In many cases, the mid-level vortex eventually becomes quasi-stationary and positioned directly above the surface cyclone. This usually marks the end of the intensification for the storm though it can still deliver high-impact weather at this stage.

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, Seasons, Severe Weather

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How is Wisconsin winter weather affected by La Niña?

La Niña is likely to continue through the Northern Hemisphere winter 2020-21 (~95% chance during January-March) and into spring 2021 (~65% chance during March-May). (Image credit: NOAA/NWS/NCEP/Climate Prediction Center)

Both La Niña and El Niño refer to big changes in the sea-surface temperature across much of the eastern tropical Pacific Ocean.

The water temperatures off the west coast of South America are typically 60 to 70 degrees. During a La Niña, these waters get as much as 7 degrees colder. These La Niña conditions recur every few years and last nine to 12 months, though some events have lingered for as many as two years. This cooling results from a strengthening of the winds over the tropical Pacific and its interaction with the underlying ocean waters.

This year, a La Niña event developed in the tropical Pacific from August to September. The latest forecasts indicate a high likelihood — 90% — of tropical Pacific sea surface temperatures remaining at La Niña levels until the end of the year. Most models indicate the 2020-21 La Niña is likely to be a moderate to strong event.

Wisconsin winters tend to have more precipitation and near-average temperatures during a typical La Niña. Above-average precipitation is expected over the Great Lakes from December through February.

The strength of a La Niña varies from year to year. A strong La Niña occurred in 2007-08, when Madison had more than 100 inches of snow, shattering the all-time seasonal snowfall record for the city.

Elsewhere in the United States, La Niña conditions in winter mean warmer and drier than normal weather in the Southeast and Southwest and colder than normal weather in the Northwest. With a well-established La Niña, the Pacific Northwest is wetter than normal in the late fall and early winter.

Category: Phenomena, Seasons

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