Is winter winding down?

Posted on January 30, 2018 by WeatherGuys Editor

Ice accumulations formed by winds and sub-freezing temperatures hold to tree branches along the Lakeshore Path on the campus of UW-Madison in November. After mid-Feburary, it is rather unlikely we will experience another cold air event. (Photo credit:: John Hart, State Journal Archives)

Despite a prolonged deep freeze that straddled the end of December and the first week of January, during which we had below-zero morning low temperatures on 12 of 13 consecutive days, the month of January is likely to end at just about normal for Madison.

We are not, however, out of the woods just yet. Climatologically, the last week of January/first week of February is the coldest time of the year as a result of several physical factors.

First, the number of daylight hours at high latitudes in the Northern Hemisphere is very small – reaching its annual minimum on Dec. 21. For nearly a month, the increase in sunlight is very meager.

This means that very little input of solar energy is available in high latitude locations and nearly continual nighttime cooling prevails. Consequently, the generation of cold air masses is at its peak during this first four to six weeks of winter.

In line with these factors, Madison’s all-time lowest temperature, minus-37, was recorded on Jan. 30, 1951.

After the first week of February, however, the daily increase in daylight accelerates everywhere – this is even noticeable in Madison as the time of sunset is appreciably later by then.

As a result, it becomes more difficult to manufacture truly frigid air at high latitudes and this, in turn, greatly reduces our chances of an additional prolonged blast of arctic air.

So, even though the medium-range forecast suggests we will have another cold air event in the coming 10 days, take solace in the fact that it is rather unlikely that an additional such event will follow after mid-February. The cosmological and climatological decks are stacked against it.

Category: Meteorology, Seasons

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What was 2017 weather summary?

Posted on January 23, 2018 by WeatherGuys Editor

People move through flooded streets in Havana after the passage of Hurricane Irma in September. The 2017 season had the highest number of major hurricanes since 2005. (Photo credit: Ramon Espinosa, Associated Press)

The National Oceanic and Atmospheric Administration has completed its scientific analysis and the globally averaged surface temperature for 2017 was the third-highest since record keeping began in 1880.

The warmest year is 2016, and 2015 is the second warmest. Since 1977 global temperatures have been at least nominally above the 20th century average. The six warmest years on record have occurred since 2010.

Everyone has his or her own personal stories of top 2017 weather events. Chances are many will remember the cold weather at the end of December.

Temperatures were mostly above normal in the first two-thirds of December, particularly the week before Christmas. Then Arctic air pushed south across the region and extended all the way to the Gulf of Mexico in the last week of the year, bringing cold temperatures to southern Wisconsin. The cold outbreak was enough to make average December temperature in southern Wisconsin below normal by 2 to 3 degrees. A lake-effect snowfall dumped 66 inches in Erie, Pennsylvania, at the end of December.

At the end of the year, southern Wisconsin was 20 inches below normal in total snowfall. Yet the average annual Northern Hemisphere snow cover extent during 2017 was above the 1981-2010 average, the largest since 1985 and the eighth-largest in the 1968-2017 record.

Recent trends in the decline of Arctic sea ice extent continued in 2017. The average annual sea ice extent in the Arctic was approximately 4.01 million square miles, the second-smallest annual average in the 1979-2017 record.

The 2017 hurricane season was one of only six seasons on record to feature multiple Category 5 hurricanes. This was the second season on record (after 2007) to feature two hurricanes making landfall at Category 5, Irma’s landfalls on multiple Caribbean islands and Maria’s landfall on Dominica. This season had the highest number of major hurricanes since 2005.

On a warmer note, the summer average temperature for Wisconsin was about average, with summer precipitation above average.

Category: Climate, Meteorology

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What is a ‘bomb cyclone’?

Posted on January 8, 2018 by WeatherGuys Editor

Vehicles move along a snow and ice covered Interstate 26, near Savannah, Ga., Wednesday, Jan. 3, 2018. A brutal winter storm dumped snow in Tallahassee, Fla., on Wednesday for the first time in nearly three decades before slogging up the Atlantic coast and smacking Southern cities such as Savannah and Charleston, South Carolina, with a rare blast of snow and ice. (Photo credit: Robert Ray, Associated Press)

The term “bomb cyclone” refers to the formation and rapid development of a mid-latitude cyclone. A mid-latitude cyclone is a large-scale, low-pressure system, characteristic of the middle latitudes, that has counter-clockwise flow around its center (in the Northern Hemisphere).

A primary measure of development in these storms is a drop in the atmospheric pressure at the center of the storm. Air near the ground is forced to move inward to the center of the circulation — this is known as convergence.

In the upper levels of the atmosphere above the center of a developing mid-latitude cyclone there is divergence, the opposite of convergence. If the divergence of air above is stronger than the convergence of air near the surface, the surface pressure will fall and the mid-latitude cyclone will intensify.

If the barometric pressure of a mid-latitude cyclone falls by at least 1 millibar per hour for 24 hours, the storm is referred to as a “bomb.” A millibar is a unit of pressure that measures the weight of the atmosphere above you. The average sea-level pressure is about 1,010 millibars, so in a bomb cyclone about 2.3 percent of the atmosphere above is removed and moved someplace else.

Meteorologists have used the term ‘bomb cyclone’ for at least 50 years.

They are not rare events, as on average there are about 40 events each year in the Northern Hemisphere. As with any weather event, the number of bomb cyclones varies from year to year.

The recent storm on the East Coast was a bomb cyclone. It is also referred to as a nor’easter – a mid-latitude cyclone that affects the northeastern United States and extreme eastern Canada.

Category: Phenomena, Seasons, Severe Weather

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Did climate change kill the dinosaurs?

Posted on December 18, 2017 by WeatherGuys Editor

Landsat image of the Sudbury Basin in Ontario,
the remnants of an asteroid impact that
occurred ~1.8 billion years ago.  Credit: USGS.

Sixty-six million years ago, the age of the dinosaurs ended abruptly, coinciding with the extinction of about 75 percent of the total number of living species.

Evidence and climate modeling indicate that global wildfires resulted from a collision with a massive asteroid that could have lofted large amounts of soot into the atmosphere. The smoke would have plunged Earth into darkness for nearly two years, which would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinctions as evidenced in the fossil record.

It is now an accepted scientific fact that objects from outer space can and do collide with planets. The collision of the Shoemaker-Levy comet with Jupiter in 1994 provided spectacular evidence that extraterrestrial objects can affect a planet’s atmosphere.

Depending on its exact location, a major asteroid impact on Earth and the debris ejected by the impact can cause extended darkness due to global fires, acid rain, ozone loss and even mile-high tsunamis.

In 1990, evidence was discovered of an impact with an asteroid that occurred about 66 million years ago near the Yucatán Peninsula. Named for a local village, the Chicxulub crater is a 112-mile-wide impact crater visible in gravity and magnetic field data. The crater size is consistent with a 6- to 12-mile-wide asteroid.

Remnants of the asteroid have been found in sediments worldwide, confirming its global influence. The Chicxulub impact was probably not a once-in-history event. There are indications in the fossil record of other extinction events that occur every 26 million years or so.

Scientists are coming to the realization that on very long time scales the history of Earth, including its climate, may be periodically upset by asteroid and comet impacts.

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: Climate, Phenomena

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How are the National Weather Service and Wisconsin connected?

Posted on November 27, 2017 by WeatherGuys Editor

The roots of our National Weather Service have a distinctive Wisconsin flavor. Professor Increase A. Lapham, a University of Wisconsin professor at the time of the founding of the university, was the first official Smithsonian Institution weather observer in Milwaukee and long argued for the establishment of a national weather observation network.

With the election of President Ulysses S. Grant in November 1868, Lapham and Rep. Halbert Paine, the U.S. congressman from Milwaukee, thought the time was right to pursue this goal. Grant had developed a keen sense of the influence of weather on military operations through his experiences in the Civil War.

On Feb. 2, 1870, Paine introduced a Joint Congressional Resolution that tasked the Secretary of War “… to provide for taking meteorological observations at the military stations in the interior of the continent and at other points in the States and Territories … and for giving notice on the northern [Great] lakes … of the approach and force of storms.”

Congress passed the resolution with little hesitation and a week later, on Feb. 9, 1870, President Grant signed it into law – effectively establishing the first iteration of the National Weather Service (then called the U.S. Army Signal Service). Operation of the Signal Service began Nov. 1, 1870, and one week later, Lapham issued the first high wind warning for the Great Lakes from Chicago. The forecast was accurate and was credited with saving considerable property and protecting lives.

The Wisconsin connection to the National Weather Service continues to this day, as the current director of the NWS is a UW-Madison graduate, Dr. Louis Uccellini.

NWS Director Louis Uccellini awards ‘Storm-Ready’ plaque to UW-Madison Chancellor Becky Blank in 2015. Photo credit: Bill Bellon

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

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