Do hurricanes affect Wisconsin?

Posted on September 18, 2023 by WeatherGuys Editor
Map showing the previous tracks of tropical systems that have traveled close to Wisconsin. Blue line segments indicate where the systems where tropical depressions and grey line segments indicate where they weakened to extratropical cyclones. (Image credit: NOAA/NWS Sullivan, WI)

A tropical cyclone is a rotating low-pressure system that has organized thunderstorms but no fronts. When a tropical cyclone’s maximum sustained winds reach 74 mph, it is called a hurricane. Hurricanes have never directly impacted the Upper Midwest region of the U.S.; however, the remnants of a hurricane or tropical storm have impacted the weather in the Midwest, including Wisconsin.

If a hurricane is particularly strong at landfall, it can move far enough northward to cause a significant rain event for areas in the Midwest. For the most part, such storms originally make landfall in Texas, Louisiana or Mississippi. These storms can be tracked by satellites or surface weather observations because they maintain an identifiable circulation pattern along their entire path.

A University of Iowa study analyzed discharge measurements of the U.S. Geological Survey (USGS) stream gauge stations from 1981 to 2011. Their study analyzed the stream gauge water discharges with the passage of the storms over the Midwest and eastern states and constructed maps of the relationship between inland flooding and tropical cyclones. The analysis demonstrated that these tropical storms can impact large areas of the United States, including Illinois, Wisconsin and Michigan. The natural hazards associated with these weather events are similar to flooding, which can impact 10 to 15 states hundreds of miles from the coast.

The amount of financial damage caused by such storms in the Midwest and the eastern United States will be a subject of future study.

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, Meteorology, Severe Weather, Tropical

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Can we measure air pollution from satellites?

Posted on September 11, 2023 by WeatherGuys Editor
The TEMPO instrument is a UV-visible spectrometer, and will be the first ever space-based instrument to monitor air pollutants hourly across the North American continent during daytime. It will collect high-resolution measurements of ozone, nitrogen dioxide and other pollutants, data which will revolutionize air quality forecasts. (Image credit: NASA and Smithsonian Astrophysical Observatory)

The National Oceanic and Atmospheric Administration (NOAA) operates weather satellites with instruments capable of locating fires and determining fire characteristics such as size and intensity. These satellites also are critical to observing and monitoring smoke from those fires.

NASA recently launched a new satellite instrument to monitor air pollution. The Tropospheric Emissions: Monitoring of Pollution, or TEMPO, was launched into geostationary orbit on April 6, 2023. TEMPO measurements join an international satellite constellation of observations that will track pollution around the globe. The instrument measures sunlight reflected off Earth’s surface and solar energy scattered by clouds and the atmosphere. Gases in the atmosphere absorb sunlight at particular wavelengths, and the measured color spectra is used to determine the concentrations of several gases in the air, including nitrogen dioxide.

TEMPO is the first space-based instrument to monitor major air pollutants hourly and at high spatial resolution of 4 square miles. Observations of nitrogen dioxide concentration at this temporal and spatial detail will enable scientists to study rush hour pollution and the movement of pollution from forest fires. It can also help measure nitrogen dioxide released when the application of fertilizer on farms is followed by rainfall.

TEMPO data will help scientists evaluate the health impacts of pollutants and aid in the creation of air pollution maps at the neighborhood scale, improving understanding of disparities in air quality within a community. NASA will share the data with other agencies that monitor and forecast air quality, such as the Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA).

Scientists at the University of Wisconsin’s Space Science and Engineering Center are members of NASA’s TEMPO science team and will monitor the presence of air pollutants over North America to help improve air quality forecasts.

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, Weather Dangers

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Are daily weather forecasts affected by climate change?

Posted on September 5, 2023 by WeatherGuys Editor

This is a very interesting question whose answer helps to further elucidate the difference between climate and weather.

As it turns out, predictions of the coming weather are nearly exclusively dependent on the observed conditions of the atmosphere in the day prior to the forecast period. These conditions are known formally as initial conditions. Those initial conditions are only partially sampled by the many observational platforms (routine surface observations, upper air observations and various satellite platforms, for instance) that have been devised over the years.

These initial conditions are fed into sophisticated computer programs known as numerical weather prediction models, and the ensuing calculations give meteorologists guidance in creating their forecasts.

Even though the climate is changing in the background, accurate measurements of these initial conditions is not substantially affected by that change, and so the forecast models are unaffected. Consequently, it is not likely that climate change has any discernible effect on the quality of weather forecasts.

The NWS routinely provides 7-day weather forecasts via weather.gov

The behavior of the climate system, on the other hand, is governed by a different set of conditions, known as boundary conditions. These include fundamental measures such as the length of the day, the amount of energy coming from the sun and the chemical composition of the atmosphere. Though these conditions do change, they only do so on very long time scales — scales not important to day-to-day weather forecasts.

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, Meteorology, Uncategorized

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How is a heat index determined?

Posted on August 28, 2023 by WeatherGuys Editor

The heat index (HI) indicates how hot it feels.

This map shows air temperatures modeled at 6.5 feet (2 meters) above the ground the afternoon of August 23, 2023 generated by combining satellite observations with temperatures predicted by the GEOS model. The darkest reds indicate temperatures above 104°F (40°C). Heat indices were even HOTTER. (Image credit: NASA Earth Observatory)

The HI is calculated using an equation that is a function of air temperature and the relative humidity. The HI is sometimes referred to as the “feels-like” temperature.

When our bodies get hot, we cool down by sweating. The sweating does not directly cool our bodies; it is the evaporation of the sweat that cools us down. If the air has a high humidity, then the rate of evaporation is reduced. This hampers the body’s ability to maintain a nearly constant internal body temperature.

The HI helps the National Weather Service (NWS) to determine if they should issue a weather advisory. A weather advisory is issued to bring to the public’s attention a situation that may cause some inconvenience or difficulty for travelers or people who have to be outdoors. A heat advisory is one type of weather advisory.

The NWS will issue a heat advisory when the heat index is predicted to be 100 degrees. You are then advised to limit vigorous outdoor activity and drink plenty of fluids. The NWS will initiate alert procedures when the heat index is expected to exceed 105 to 110 degrees (depending on local climate) for at least two consecutive days.

NWS Heat Index Chart

The HI is calculated assuming you are standing in the shade and there are light winds. The NWS uses the Wet Bulb Globe Temperature (WBGT) to determine the heat stress in direct sunlight, which considers temperature, humidity, sun angle, cloud cover and wind speed in its calculation.

Exposed to direct sunlight, the WBGT can be up to 15 degrees hotter than the HI. When the WBGT is high, and you have to be outside, wear a hat and lightweight, light-fitting, light-colored clothes. Drink plenty of water and take breaks in shady areas.

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, Weather Dangers

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Are computers used in weather forecasting?

Posted on August 21, 2023 by WeatherGuys Editor
Twin supercomputers Dogwood (pictured here) and Cactus are the newest additions to NOAA’s weather and climate operational supercomputing system. Located in Manassas, Virginia, and Phoenix, Arizona, respectively, each supercomputer operates at a speed of 12.1 petaflops — three times faster than NOAA’s former system. (Image credit: General Dynamics Information Technology (GDIT))

Weather forecasting is a challenging and fascinating aspect of meteorology. An accurate forecast requires a thorough knowledge of all the variables of the atmosphere. There are also conservation principles of momentum, mass, energy and moisture, combined with the ideal gas law from chemistry that forecasters must consider.

The physical principles are represented as equations, and with current weather conditions, are used to solve for variables meteorologists care about — wind, temperature and precipitation. Computers are used in numerical weather prediction to solve these mathematical models to predict the weather based on current weather conditions.

A numerical forecast is only as accurate as the observations that go into the forecast at the beginning of its model run, referred to as “initial conditions.” Weather moves from one place to another rapidly; tomorrow’s weather is influenced by today’s weather far upstream. For this reason, forecasters must have lots of data worldwide. Large data storage enables better model initiation.

The National Weather Service uses supercomputers to produce weather forecasts, watches, warnings and a whole host of data for the public. These computers run sophisticated computer programs, called numerical models, to create forecasts used by the private sector and the public.

The U.S. Department of Commerce and the National Oceanic and Atmospheric Administration, or NOAA, have recently expanded the capacity of their Weather and Climate Operational Supercomputing System by 20%. The increased computing power and data storage helps improve weather prediction.

The supercomputing capacity supporting NOAA’s new operational prediction and research enables about 42 quadrillion operations per second. This faster computing allows NOAA to run more complex forecast models, while increased storage space enables more data to be used and assimilated into the system. The increased computing power and storage will help to improve weather forecasts for years to come and enable weather prediction advances.

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, Meteorology

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