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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Do birds get struck by lightning?

Posted on August 14, 2023 by WeatherGuys Editor

Lightning over Madison Wisconsin in July 2016. Photographer: Chris Niendorf

Yes, birds do get struck by lightning, although it’s not very common. When birds are flying during a storm, they are exposed to lightning strikes and thus can get hit directly.

Birds will typically avoid flying in a thunderstorm. They prefer to find hiding spots, such as in bushes, trees and tall grasses. If a bird is waiting out a storm in a tree and the tree gets struck by lightning, the bird likely will die. If struck, an electric charge will be carried along the tree and electrocute any birds sitting in it.

Recently, there were photographs on social media showing several dead birds around the base of a tree after a recent thunderstorm in the Madison area. It is likely the birds were in the tree when it got struck by lightning.

Lightning poses an ongoing threat to all living beings, including humans. Lightning tends to strike the tallest object in an area, and in many cases that is a tree. The physical flash you see strikes a point, but the lightning is radiating out from that point as a current and can be deadly.

Standing under a tree in a lightning storm is extremely dangerous, especially under an isolated tree. When lightning strikes a tree, the charge doesn’t penetrate deep into the ground but spreads out along the ground surface in a ground current that can lead to injuries and death for those beneath the tree.

While standing under a tree in a lightning storm is extremely dangerous, according to National Oceanic and Atmospheric Administration records, most people who died from lightning strikes were hit while out in the open.

There is no completely safe place outside in a thunderstorm. The best thing to do is to get inside a safe building or vehicle.

“When thunder roars, go indoors!”

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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What are the trade winds?

Posted on August 7, 2023 by WeatherGuys Editor

On the morning of August 3, 1492, Christopher Columbus set sail on his first voyage to the Americas. He sailed south along the west coast of Africa, searching for the easterly “trade winds,” discovered earlier by the Portuguese, that would propel his fleet westward toward what he thought was India.

The trade winds are created by a cycle of warm, moist air rising near the equator. The air eventually cools and sinks a bit further north in the tropics. This phenomenon is called the Hadley cell. (Image credit: NASA/JPL-Caltech)

The trade winds are a component of a global-scale tropical circulation feature known as the Hadley cell. This cell is driven by the fact that the equator is heated more intensely than latitudes to its north and south, resulting in the production of collections of thunderstorms girdling the globe roughly along the equator.

The rising air that fuels these thunderstorms spreads out at the tropopause (about nine miles high) and heads both north and south. Cooling at the cloud tops of this poleward-directed air forces it to sink at about 25 degrees latitude on either side of the equator. The sinking air that reaches the surface in the Northern Hemisphere heads southward toward the equator in a huge vertical circulation cell. The rotation of the Earth, and the resulting Coriolis force, turns this southward moving air to its right, creating the near surface trade winds.

Though known by mariners for centuries, it was not until 1735 that George Hadley proposed this explanation for the trade winds. It was not until the 1950s, amazingly, that observational evidence provided by balloon soundings of the atmosphere finally confirmed the veracity of Hadley’s conjecture.

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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