Why are viruses more common in Winter?

Posted on January 26, 2026 by WeatherGuys Editor

Colds and the flu are caused by viruses, not by cold wintery conditions. Viruses such as rhinoviruses, which cause the common cold, and influenza viruses spread from person to person through respiratory droplets or physical contact, regardless of the temperature outside.

However, weather and climate do play a role in why colds and the flu are more common in winter though. The colder temperatures associated with winter affect how viruses behave in the environment. Winter’s colder temperatures and lower humidity help viruses survive longer and spread more easily. Research studies show that many respiratory viruses survive longer and remain infectious for extended periods of time in cold, dry environmental conditions.

This 2009 photograph captured a sneeze in progress, revealing the plume of salivary droplets as they are expelled in a large cone-shaped array from this man’s open mouth… (Photo credit: Wikipedia)

Dry air also causes tiny droplets released when people breathe, talk, cough, or sneeze to evaporate quickly. These droplets evaporate quickly, creating smaller particles that stay suspended in the air longer and travel farther, increasing the chance that others will inhale them.

Winter’s low humidity can dry the lining of one’s nose and throat. This reduces the effectiveness of mucus, which normally traps viruses and helps move them out of the airways.

In cold weather, social events tend to be indoors, bringing us in close contact with others.  This increases the chance of the spread of a virus. Preventive measures such as vaccinations, good hygiene practices, and wearing masks in crowds help to reduce the risk of viral infections. Improving indoor ventilation and maintaining adequate humidity during winter can also reduce transmission risk. Cold weather can be challenging for people with existing respiratory conditions such as asthma.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon 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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Why is Wisconsin winter weather so cloudy and grey?

Posted on January 20, 2026 by WeatherGuys Editor

Climatologically, the winter months are the cloudiest time of the year in Wisconsin. Wisconsin’s average monthly cloud cover for December, January, and February for the years 2006 to 2024 was 65.3%, 61.1% and 50.5% respectively. There are a few factors that contribute to this climate observation.

Thanks to Amanda Latham and Ed Hopkins of the WI State Climate Office for providing the analysis. (Image credit: Iowa Environmental Mesonet)

Wisconsin sits in a latitude band where synoptic scale storm systems often pass nearby. This scale is associated with large weather patterns like mid-latitude cyclones and anticyclones. During the winter, the mid-latitude storm tracks tend to be along the polar front and the upper tropospheric jet stream. These winter storms have large stratiform cloud shields that move across the Midwest, producing more persistent cloudy conditions. Even when storm centers miss the state, these cloud shields can linger for days afterward.

As winter arrives, we experience fewer hours of sunlight and the sun is lower on the horizon. This reduces solar heating at the ground and adds a factor that leads to increased cloudiness. The absence of solar warmth causes a cooling effect on Earth’s surface and affects the lower atmosphere.

However, with the low angle of the sun, the surface doesn’t warm as much. This can lead to cold air staying at the surface, with a warmer layer of air developing above; this is called a temperature inversion. In the layer between the warm and cold air, moisture gets stuck and clouds persist there. If the sun were able to warm the air at the surface, it would dry out easier, thus allowing air to rise and skies to clear.

Much winter cloud cover in Wisconsin is low-level stratus. These clouds form in cold, stable air and can exist for days without producing much snow or rain, just gray skies.

But when clear days do happen in Wisconsin’s winter, they’re often very crisp and bright.

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

Category: Climate, Meteorology, Seasons

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Is global warming happening?

Posted on January 12, 2026 by WeatherGuys Editor

Scientific research has awakened us to the realization that our planet is warming at an unprecedented rate, and human activities are the principal cause. Claims that the observed global warming is not occurring or not related to human activities are false. There is no scientific research that supports that misconception.

Yearly surface temperature compared to the 20th-century average from 1880–2022. Blue bars indicate cooler-than-average years; red bars show warmer-than-average years. Image credit: National Centers for Environmental Information, NOAA)

Confidence in our answer comes from decades of scientific research — a systematic investigation that acquires new knowledge, validates existing knowledge, or addresses specific questions through rigorous methodologies.

Scientific research requires diligent inquiry and systematic observation of phenomena. The conditions under which specific observations are made must be carefully controlled, and records must be meticulously maintained. This ensures that observations and results can be reproduced. Scientific research is the backbone of atmospheric sciences that enables advancements in our understanding of how the atmosphere works, leading to improvements in weather forecasting as well as understanding of climate change.

For decades society has asked questions about climate change and what role human activities may play in influencing any observed changes. These questions can only be reliable answered via scientific research. This scientific research has awakened us to the realization that human activities are changing our climate.

While Earth’s climate has changed throughout its history, the current warming trend is clearly the result of human activities since the mid-1800s. The current warming is proceeding at a rate not seen over the past 100,000 years.

We have the scientific understanding of the heat-trapping nature of carbon dioxide and other gases, and these greenhouse gases have increased in concentration. There is no scientific doubt that the observed increases in greenhouse gas levels warm Earth in response.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, History

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Was 2025 an interesting weather year for Wisconsin?

Posted on January 5, 2026 by WeatherGuys Editor

Wisconsin has interesting weather in EVERY year. 2025 started with extreme cold warnings issued for all Wisconsin counties from Jan. 19 to Jan. 21. Wind chill indices were as low as minus 45. The year also ended with cold temperatures and low wind chills at the end of December.

Severe thunderstorms struck southern Wisconsin during the early morning of April 18, with baseball-size hail falling from New Glarus to Edgerton.

One-minute GOES-19 Infrared images with plots of GLM Flash Points (white), Flood Watches (gray hatched area) / Flash Flood Warnings (red polygons) / Flood Statements (dark green polygons) / Flood Warnings (light green polygons) and 1-hour Precipitation amounts (cyan), from 0000-1300 UTC on 10 August. Interstate highways are plotted in violet. (Image credit: CIMSS Satellite Blog)

Wisconsin recorded 39 tornadoes, 15 of which occurred on May 15. Three were ranked at EF2 strength. Softball-size hail fell in Eau Claire County on May 15.

Heavy rain caused widespread flooding in southeast Wisconsin on the evening of Aug. 9 through the morning of Aug. 10. The northwest side of Milwaukee reported a 24-hour rain total of 14.55 inches on Aug. 9-10, setting a 24-hour precipitation record in the state — breaking the old record by nearly 3 inches!

Oct. 3 through 5 were exceptionally hot, with at least 18 temperature records broken or tied across the state. Green Bay’s high temperature reached 88 degrees, its hottest October temperature. This was eerily reminiscent of the extreme heat that preceded the disastrous Peshtigo fire of Oct. 8, 1871.

Both Milwaukee and Madison set their all-time record high temperatures for Nov. 15, at 69 and 68 degrees, respectively. Madison recorded its snowiest November day ever with 9.3 inches of snow on Nov. 29. Milwaukee’s 6.1 inches on the same day also set a new daily record for the city. December ended up being 4 degrees colder than normal, largely a function of the first eight days of the month, during which the average daily temperature was 13.9 degrees below normal. December, our climatologically snowiest month, was this past year nearly 3 inches below normal for total snowfall. Thus, it was a year punctuated with extremes — the kind that ends up as memorable.

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

Category: History, Phenomena, Severe Weather

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Will shifts in the polar vortex cause extreme day-to-day temperature fluctuations to become more common?

Posted on December 29, 2025 by WeatherGuys Editor

The polar vortex is a large area of low pressure in the lower stratosphere that is bordered on its southern edge by the polar night jet — so-called because it develops as the sun sets at high latitudes after the autumnal equinox, creating large and deep pools of cold air. The characteristics of this stratospheric polar vortex have a substantial influence on wintertime temperatures in the lowest part of the underlying troposphere, which is where we all live.

The science behind the polar vortex. (Image credit: NOAA)

The nature of the polar vortex changes throughout the winter. When the vortex circulation is largely west-to-east around the pole, it tends to contain the most extreme cold air masses at high latitudes. When it is characterized by high amplitude waves, often associated with a weaker vortex, it can initiate rapid transport of warm air poleward in some locations and frigid air equatorward in others. Such waves, or lobes, of the polar vortex can pinwheel over the Northern Hemisphere, sending cold air southward in association with weather systems tied to the underlying tropospheric jet stream.

Our global climate is warming because of human activity. Near-surface Arctic temperatures are rising more than twice as fast as those at lower latitudes because of the retreat of snow and ice, which reduces the amount of reflected solar radiation at high latitudes. This is known as “Arctic amplification,” and it reduces the mid-tropospheric temperature contrasts that support a strong, circular polar vortex.

Some research suggests a weaker temperature gradient allows the jet stream to meander more easily, promoting the kind of wave amplification that disrupts the polar vortex. If so, this would indirectly increase the likelihood of a midwinter polar vortex sending cold air south.

So, while global warming is reducing average cold temperatures overall, disturbances in the high-latitude circulation can still create sharp, temporary cold air outbreaks.

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

Category: Meteorology, Phenomena, Seasons

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