Is wildfire season getting longer?

Posted on July 27, 2026 by WeatherGuys Editor

Wildfires are an important part of many ecosystems and an essential part of forest and rangeland health.

Fires require fuel to burn, heat to ignite and oxygen to burn. Wildfire season is defined as the time of year when wildfires are most likely to ignite and spread. A combination of high temperatures, low humidity, lack of precipitation days and high winds make wildfires more likely to spread and lengthen fire seasons.

Weather and climate are important in making fuel available by determining the moisture content of the vegetation. Since the weather and climate of a region play key roles in these required ingredients, fire season varies in timing and duration based on geographic location.

Wildfire season’s duration is increasing, as demonstrated by several scientifically documented trends. Studies show that fire seasons are lasting longer and that more acres are burning annually than in previous decades.

An analysis of 35 years of meteorological data by the U.S. Forest Service found that fire seasons are starting earlier in the spring and extending later into autumn. The National Interagency Fire Center has recorded the size and number of wildfires in the United States since 1983. Over the past 20 years, the amount of land area burned each year has increased as wildfires have grown larger, while the number of fires each year has remained fairly constant.

Many weather satellites can detect active wildfires from the heat signatures of the fires. Various weather satellites include observations to detect active fires. Using NASA satellites over the 21-year data span from Jan. 1, 2003, to Nov. 30, 2023, researchers found that extreme wildfires have become more frequent, more intense, and larger.

The satellites can also track the smoke produced during daylight hours. Smoke plumes are not detected at night nor in some cloudy areas. Smoke observations from satellites are useful in estimating air quality.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on Wisconsin Public Radio at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Meteorology, Severe Weather

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What is the wet-bulb temperature?

Posted on July 20, 2026 by WeatherGuys Editor

 The wet-bulb temperature is the lowest temperature to which unsaturated air can be cooled by evaporating liquid water into it.

The dry-bulb temperature is an indicator of heat content and is shown along the bottom axis of the psychrometric chart. Constant dry bulb temperatures appear as vertical lines in the psychrometric chart. Wet Bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin, then exposed to the air flow. The Wet Bulb temperature is the temperature of adiabatic saturation. Lines of constant wet bulb temperatures run diagonally from the upper left to the lower right in the psychrometric chart. The adiabatic evaporation of water from the thermometer and the cooling effect is indicated by a “wet bulb temperature” lower than the “dry bulb temperature” in the air. Combining the dry bulb and wet bulb temperature in a psychrometric diagram or Mollier chart, gives the state of the humid air. (Image credit: weather.gov)

This may sound horribly obscure, but it serves as a very useful measure of human comfort. It combines atmospheric humidity and temperature in a way that helps determine our comfort level while in the shade, especially during hot and humid conditions.

Wet-bulb temperature is related to other humidity indicators such as dew point temperature. For example, at 100% relative humidity, the wet-bulb temperature is equal to air temperature. At lower humidity, the wet-bulb temperature is lower than air temperature due to evaporative cooling.

We determine wet-bulb temperature by using a thermometer that has a water-moistened cloth, or wet wick, wrapped around its bulb. The wet wick is connected to a water reservoir and then ventilated with ambient air. As air flows over the wet wick, water evaporates. Evaporation requires energy. As water evaporates from the wick, it absorbs heat from the surrounding air and the thermometer itself, lowering the temperature reading. After a few minutes, the temperature of the wet bulb stabilizes, and that temperature is the wetbulb temperature.

The world is getting hotter and there is a limit to how much heat our bodies can endure. Our body’s ability to cool itself relies on sweating and evaporative cooling. High wet-bulb temperatures indicate dangerous heat stress levels, as the body’s ability to cool itself becomes compromised when evaporation is limited. Exposure to a wet-bulb temperature of 95 degrees Fahrenheit (35 degrees Celsius) for longer than six hours is dangerous, as the human body cannot cool itself. Prolonged exposure to these conditions can become life-threatening.

The wet-bulb globe temperature is another heat stress index: It extends the wet bulb temperature by combining air temperature, humidity, radiant heat and wind to assess the risk of human heat exposure.

Steve Ackerman and Jonathan Martin, professors in the UWMadison department of atmospheric and oceanic sciences, are guests on Wisconsin Public radio at noon the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Seasons

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Does NOAA conduct fire weather forecasting?

Posted on July 13, 2026 by WeatherGuys Editor

Wildfire outbreaks require the alignment of several factors, including temperature, humidity, winds and the lack of moisture in fuels such as trees, shrubs and grasses. These factors have strong direct or indirect ties to current weather, climate variability and climate change. The National Oceanic and Atmospheric Administration supports weather forecasting throughout a wildfire’s lifecycle: before, during and after the wildfire.

1-minute GOES-19 Shortwave Infrared images, with plots of Surface Wind barbs and Peak Wind Gusts (yellow/red) and Surface Fronts, from 1701 UTC on 17 February to 0100 UTC on 18 February. (Image credit: CIMSS Satellite Blog)

Drought conditions can set the stage for wildfires.

NOAA’s Climate Prediction Center provides seasonal temperature and precipitation predictions important to assessing fire risk. The National Center for Environmental Prediction, or NCEP, uses a suite of numerical weather prediction models to provide fire managers with actionable information on how near-term environmental conditions will influence fire risk, fire behavior and smoke impacts. These models provide temperature, humidity, wind, lightning and precipitation forecasts to aid in planning at the scale of days to a week.

During wildfire events, NOAA’s National Weather Service provides weather forecasts and interpretation services to help emergency personnel and public safety officials make decisions. Specially trained incident meteorologists, or IMETs, can be deployed to wildfire command centers, where they generate real-time fire weather forecasts to support firefighting operations. GOES and POES satellites are used to monitor wildfires and track smoke. High-resolution weather models are used to simulate how smoke will move and to predict its effects on weather, air quality and visibility.

Once the fire is extinguished, there may still be weather-related hazards. For example, communities below a burn scar face increased flooding threat. NWS forecasters closely monitor burn scars, using high-resolution weather models, satellite observations, Doppler radar and their knowledge of local terrain to identify when even modest rainstorms could produce a flooding threat.

Research shows that changes in climate are creating warmer and drier conditions, leading to longer and more active fire seasons in the western United States.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on Wisconsin Public Radio at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Seasons, Severe Weather, Weather Dangers

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What is a “wake low”?

Posted on July 8, 2026 by WeatherGuys Editor

Wake lows are short-lived mesoscale phenomena. Mesoscale weather ranges from about 5 kilometers to 1,000 kilometers in size.

Small arrows indicate surface wind; large arrows relative flow into the wake. Stippling indicates extent of precipitation-cooled air. (After Fujita, T.T., 1955: Results of detailed synoptic studies of squall lines. Tellus, 7, 405-436.)

Wake lows are relatively uncommon. They produce strong winds after a storm moves out. The term “wake low” was defined by Ted Fujita, the same meteorologist who came up with the F-scale ranking of tornadoes. These areas of low-pressure form on the backside of heavy rain, causing winds to surge in at fast speeds.

A mesoscale convective system, or MCS, is a collection of thunderstorms that becomes organized on a scale larger than individual thunderstorms and typically lasts for several hours. MCSs may be accompanied by severe weather hazards: heavy rain, flooding, strong winds, tornadoes and hail.

As a MCS moves out of a region, dry air sinks along the back side of the storm. The sinking air often leads to clearing skies. This descending air warms up rapidly through compression, generating a localized area of low pressure in the storm’s wake. The pressure difference between the rain-cooled air of the MCS and the warm air descending in the storm’s wake, creates a strong pressure gradient that generates strong winds.

Winds speeds can rapidly reach 40 mph to greater than 60 mph. The winds often blow in the direction opposite of the direction the MCS originally traveled, since the wind is rushing toward the storm’s wake.

Wake lows are notoriously difficult to forecast because they rely on the complex decay dynamics of a storm, are of small scale and are not common. The modernization of the National Weather Service improved tracking capability of mesoscale phenomena with Doppler radar, surface observations, satellite observations and finer resolution models. The development of mesoscale weather station networks has improved the ability to locate wake lows.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on Wisconsin Public Radio at noon the last Monday of each month. Send them your questions at stevea@ ssec.wisc.edu or jemarti1@wisc. edu.

Category: Meteorology, Phenomena, Severe Weather

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Was this spring milder than normal?

Posted on June 29, 2026 by WeatherGuys Editor

With only a few exceptions, it seems as if this year’s run-up to summer, which arrived at 3:24 a.m. Sunday, June 21, was relatively mild. By that we mean very few really oppressively hot and humid days.

Naturally, we wondered if this were actually a true impression and also how this year’s spring stacked up against others that have visited Madison over the years. One way (but not the only way) to make such an assessment is to consider how many days in the interval from April 1 to June 21 have had a daily high temperature greater than or equal to 80 degrees Fahrenheit.

For 2026, that number is 15 or about once every 5.5 days. Using records all the way back to 1869, the average number of such days in that calendar interval is 13.7 (once every six days), so this year is just barely above that long term average. Interesting individual years according to this measure are 1878 when not a single day between April 1 and June 21 was 80 degrees in Madison. On the other extreme, in 1991 there were 36 such days in the same interval — almost every other day!

Because this measure is highly variable from year to year, looking at decade averages can lend more insight into trends that might exist in this data. The coldest decades were the 1900s and the 1870s with 8.4 and 8.9 such days on average each year. The warmest decades were the 1970s and 1950s with 19.5 and 18.9 such days per year on average. The 2010s, averaged 16.7 such days each year.

With 15 days at 80 degrees or warmer, this year is the 94th coldest spring of the last 158 springs, decidedly on the warm side of the distribution.

However, there appears to be no correlation between number of days at or above 80 degrees during spring and the severity of summer heat, so we will have to wait and see on that.

Steve Ackerman and Jonathan Martin, professors in the UWMadison department of atmospheric and oceanic sciences, are guests on Wisconsin Public radio at noon the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Seasons

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