What is a gale wind?

Posted on November 13, 2023 by WeatherGuys Editor

A gale is a strong, sustained wind with wind speeds between 39 mph and 54 mph. The word is typically used as a descriptor for maritime weather.

The National Weather Service issues gale warnings when winds of this strength are expected for maritime settings. Gale warnings allow mariners to take precautionary actions to ensure their safety or to seek safe shelter. A gale warning flag is solid red and in the shape of an isosceles triangle. The equivalent warning for land is a wind advisory. The next level of warning for maritime winds that NWS issues is a storm warning for winds of 55-72 mph at sea.

Gale winds are common in November on the Great Lakes. Last week saw the anniversaries of some strong November gales in the Great Lakes region. The most famous of these include the White Hurricane (Nov. 7-10, 1913), the Armistice Day Blizzard (Nov. 11, 1940), the Edmund Fitzgerald storm (Nov. 9-10, 1975), and the Nov. 10-11, 1998, storm.

The 1913 storm sank 19 ships and killed more than 250 people. Most of the damage occurred in Lake Huron.

The Armistice Day Blizzard dropped 16.7 inches of snow in Minneapolis/St. Paul. The cyclone intensified rapidly and was accompanied by a very intense surface cold front that quickly dropped the temperatures as much as 50 degrees in parts of the Midwest. This rapid drop in temperature caught many people by surprise, and more than 150 people perished.

The Edmund Fitzgerald storm achieved grisly fame through its association with the sinking of the ore freighter and the loss of its 29 crew members.

Gale winds that sunk the SS Edmund Fitzgerald.
Credit: NOAA

That storm also was accompanied by extremely strong winds and rapid intensification over the mid-continent.

That event was memorialized by Gordon Lightfoot’s ballad “The Wreck of the Edmund Fitzgerald.”

The November 10-11 storm from 1998 saw a six-hour period during which its minimum sea-level pressure dropped 15 millibars.

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. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Severe Weather

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Are hurricanes intensifying more quickly?

Posted on October 31, 2023 by WeatherGuys Editor

Hurricane intensities are classified using the Saffir–Simpson scale, which rates hurricanes on a scale of 1 to 5 based on the damage their winds would cause upon landfall. Major hurricanes are those classified as Category 3 and higher on this scale.

Category 3 hurricanes have one minute of sustained winds between 111 mph and 130 mph. The one-minute sustained winds in a Category 5 hurricane are greater than 155 mph.

Forecasting hurricane intensity is a difficult task, and forecasting how rapidly they might intensify is particularly difficult. Rapid intensification is when a tropical cyclone strengthens dramatically in a short period of time. The National Hurricane Center (NHC) defines rapid intensification as an increase in the maximum sustained winds of a tropical cyclone by at least 35 mph in a 24-hour period.

Intensification of a hurricane requires the right environmental conditions. One is water temperature. If water in the ocean beneath the hurricane is warm enough, it releases large amounts of energy as it evaporates, creating a dip in air pressure that generates powerful winds.

Otis, a storm that struck the southern coast of Mexico, was initially forecast to be a weak tropical storm (one-minute maximum sustained winds between 39 and 73 mph) at peak intensity. Instead, Otis underwent rapid intensification, reaching peak winds of 165 mph when it made landfall near Acapulco, Mexico, at 1:25 a.m. Wednesday. Otis strengthened from a tropical storm to a Category 5 hurricane in only 12 hours. This rapid intensification occurred over a patch of ocean with sea surface temperatures approaching 88 degrees. It came ashore as the strongest storm on record to hit Mexico’s Pacific coast.

Hurricane Otis prior to landfall. Click for an animation. Credit: CIMSS

While forecasts of intensification have improved, challenges remain. A recent paper in Nature found that rapidly intensifying storms that are within 240 miles of coastlines are now significantly more common than they were 40 years ago.

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. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Phenomena, Tropical

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What is the status of sea ice this year?

Posted on October 23, 2023 by WeatherGuys Editor

The surface waters of our polar oceans freeze seasonally, forming a layer of sea ice that varies in thickness from centimeters to meters. The era of polar orbiting satellites has enabled the monitoring of sea ice distribution for more than four decades.

Seasons are reversed between the Northern and Southern hemispheres, so the sea ice maximum and minimum occur at different times of the year. Generally speaking, around mid-September the extent of the sea ice at the south pole is reaching a maximum, while in the Arctic it is approaching a minimum in September as our Northern Hemisphere summer comes to an end.

Arctic sea ice extent for September 19 2023, was 4.23 million square kilometers (1.63 million square miles). The orange line shows the 1981 to 2010 average extent for that day.  (Image Credit: National Snow and Ice Data Center)

This year, the sea ice amount around Antarctica has fallen to a record low. Satellite observations indicate the sea ice extent around Antarctica peaked on Sept. 10. At that time, sea ice covered 6.55 million square miles, which is the lowest winter maximum since satellite records began in 1979. That’s about 386,000 square miles less ice than the previous winter low, set in 1986. The extent of the summer’s Antarctic sea ice also hit a record low in February, breaking the previous mark, set in 2022.

Arctic sea ice reached its minimum extent for this year on Sept. 19, covering 1.63 million square miles. This 2023 minimum extent is the sixth-lowest in the nearly 45-year satellite record. For reference, the combined surface area of the Great Lakes is 94,250 square miles.

The satellite data show a trend in sea ice extent over the Arctic that is decreasing annually at a rate of 4%, plus or minus 1%, per decade. The reduction of Arctic sea ice is rapid, as the northern polar region is warming four times faster than the global average. Over the Southern Hemisphere, satellite data shows no significant trend in sea ice extent. The climate change associated with global warming contributes to melt glaciers in Antarctica, which impacts sea ice extent around the continent.

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. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: History, Seasons

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Atmospheric and Oceanic Sciences turns 75

Posted on October 9, 2023 by WeatherGuys Editor
The rooftop of the UW–Madison Atmospheric, Oceanic and Space Sciences building. (Photo credit; UW-Madison)

On Friday, the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison celebrated its 75th anniversary.

When the department was founded in June 1948, the modern science of meteorology was arguably just a few years old, and even basic understanding of the nature of the mid-latitude cyclones that batter us from October to May was truly in its infant stages.

The scholarship within our department over this three-quarters of a century has made enormous contributions to our science and, in turn, to the protection of lives and property through improved forecasts of both tropical and mid-latitude cyclones.

Some of the highlights include the launching of the first weather satellites in the late 1950s and early 1960s. These tools now contribute a huge amount of data to global weather forecasting models, and the UW-Madison remains at the very forefront of the research efforts dedicated to remotely sensing the atmosphere and oceans of Earth.

Developments in the computer models that make such forecasts also has a strong Wisconsin pedigree. The recently retired director of the National Weather Service got all three of his degrees from UW-Madison. The Space Science and Engineering Center, or SSEC, originally developed as an outgrowth of the department, has been at the heart of improved forecasts of tropical weather systems, fire detection and severe storms research for decades.

Clearer understanding of both tropical and extra-tropical weather systems, the global oceans and their interactions with sea ice, the complex climate system and many other important, fundamental issues in the atmospheric and oceanic sciences are being generated every day in our dynamic and diverse department. We are grateful to the citizens of the state of Wisconsin for their support of our endeavors, and those of all of our colleagues at our great University of Wisconsin-Madison.

On, Wisconsin!

Steve Ackerman and Jonathan Martin, professors in the UWMadison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec. wisc.edu or jemarti1@wisc.edu.

Category: History, Meteorology

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Higher overnight lows led to warm September

Posted on October 2, 2023 by WeatherGuys Editor

As we enter the month of October and the traditional end of the warm season, it’s interesting to note that the average temperature last month, through Sept. 28, was 4.0 degrees above normal in Madison.

Monthly climate observations for September 2023 showing deviation from normal. (Image credit: NOAA/NWS Sullivan office)

That is by far the biggest deviation among traditional warm-season months — June, July, August and September. All were warmer than average this year: June was 0.8 degrees, July just 0.5 degree and August only 1.2 degree above the respective norm.

If we break down the September temperature departure into contributions made by increased daytime highs and those made by higher overnight lows, the story gets even more interesting — and more telling. Through Sept. 28, the daily maximum temperatures have averaged 2.7 degrees Fahrenheit above normal, while the overnight lows have been 5.5 degrees warmer than average. Thus, warmer overnight lows last month have contributed about two-thirds of the total temperature anomaly.

Underlying the spike in overnight lows is the fact that the air is systematically a bit more humid as the global temperature increases, and water vapor is a very efficient greenhouse gas. Consequently, if there is more water vapor in the air, it is harder for the surface of the planet to lose energy to space overnight.

Change in overnight lows (°F)
Credit: WICCI

Our lowest daily temperatures have been a bit higher as a result.

This physics is not limited to the warm season — it applies generally.

The bias toward overnight temperature increases as the emblem of climate change is yet another way that the current slow warming of the planet nurtures a level of public skepticism that is out of proportion to the urgency of the threat.

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. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, History, Seasons

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