How are fall colors impacted by our weather?

Posted on October 13, 2025 by WeatherGuys Editor

The most vibrant fall color will occur on years with ample moisture in the summer and dry, clear weather in the fall. Extreme heat and moderate-to-severe drought may negatively affect the fall foliage season. 

Sunlight coming through the fall leaves. (Photo credit: Steve Ackerman)

In summer and spring, leaves are green because they contain chlorophyll, which reflects green light more than other colors. Other colors are absorbed by chlorophyll for photosynthesis.

As temperatures begin to drop in late September, trees gradually slow down the production of chlorophyll. As the green chlorophyll disappears from the leaves, we begin to see yellow- and orange-colored leaves. These colors have been in the leaves all along; we can’t see them in the summer because of the chlorophyll. Orange colors come from carotene and the yellows from xanthophyll in the leaves. The bright red and purple colors come from anthocyanin pigments, which are made from leftover glucose trapped within the leaves of some trees (e.g. maples).

Brilliant fall colors with bright red and purple colors require conditions in which leaves can make a lot of anthocyanin pigments. The best weather conditions for this are an autumn with bright sunny days and cool, but not frosty, nights. A drab autumn has lots of cloudy days and warm nights. An early frost speeds up the fall of the leaves and brings a quick end to the fall color. Of course, too much strong winds or heavy precipitation would bring the leaves down.

Global warming is making the fall season much warmer on average. This warming trend allows chlorophyll production to continue and can delay the onset of fall colors.

If you are interested in taking a tour of the fall colors in Wisconsin, the Travel Wisconsin website provides a daily report of the fall colors (https://www.travelwisconsin.com/fall-color-report).

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, Seasons

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How has weather forecasting improved, assuming it has improved?

Posted on October 9, 2025 by WeatherGuys Editor

Weather forecasting is a science that has drastically improved over the last 50 years.  Modern weather forecasting goes back to the mid-20th century, when meteorologists began using numerical weather prediction (NWP) computer models to simulate atmospheric processes. These models rely on physics and mathematical equations to represent the behavior of the atmosphere.

Graph showing the improvement of weather forecasts since 1981. (Image credit: ECMWF)

Studies have shown that a five-day weather forecast today is as accurate as a one-day forecast was in 1980. Today, three-day predictions of a hurricane path are more accurate than the 24-hour forecasts of the 1970s and 1980s. In addition, today’s forecast is easily accessible on your smart phone.

Weather forecasting begins by observing the current state of the atmosphere. Today’s weather observing network is extensive. The network of Automated Surface Observing Systems routinely measures current weather at airports. A national network of Doppler radars monitor precipitation and weather balloons are launched twice daily across the country to measure the vertical structure of our atmosphere. Some commercial airlines equip their aircraft with sensors to take observations during takeoff, in flight, and through landing. Weather satellites, both geostationary and polar-orbiting systems, routinely observe our planet in real-time.

These weather observations are collected several times every day and around the globe and then converted into a current weather state that initiate a forecast. The two main weather prediction models operated by the National Weather Service have undergone recent improvements. The Global Forecast System (GFS) model has been upgraded with greater resolution that extends further out in time. The High-Resolution Rapid Refresh (HRRR) model is a real-time 3-km resolution, hourly updated, cloud-resolving, convection-allowing atmospheric model.

Recent budget reductions to NOAA are reducing the observations needed to support these accurate weather prediction models. This budget impact results in fewer observations of the atmosphere and elimination of future satellite systems.

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: Uncategorized

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Why is fog more common in the early morning?

Posted on September 30, 2025 by WeatherGuys Editor

Fog can occur any time of day throughout the year. In southern Wisconsin, fog is most frequent in the morning, between about 6 and 8 a.m.

Fog at the mouth of the Yahara as it enters Lake Mendota. (Photo credit: Steve Ackerman)

Fog formation is the result of two primary processes. First, the air is cooled to the dew point, and the relative humidity reaches 100%. When the air temperature is the same as the dew point temperature, condensation of the atmospheric water vapor occurs forming fog droplets. Another method of fog formation requires water to evaporate from the surface into the air, increasing the relative humidity until condensation occurs.

During this time of year, as the nights are getting longer, we can have clear skies and calm winds at night. These conditions help the ground, and the air near the ground, to rapidly cool. As the temperature of the air drops, the relative humidity increases as the dew point approaches the temperature, leading to fog formation.  Light winds can help with fog formation as they gently mix moist air near the ground upward. Strong winds mix the air near the ground with the drier, warmer air above, keeping the air near the surface from saturating.

If you take a long, hot shower, you may “fog up” the bathroom. Some of the warm water droplets from the shower evaporate into the cooler bathroom air, moistening it to saturation and forming a fog. Evaporation fogs also form over lakes when colder air moves over warmer water. Evaporation of the warm water into the air causes the relative humidity to increase and a fog may form.

Fogs often dissipate with the morning daylight. This is sometimes referred to as the fog ‘burning off’, but that analogy is not correct. When the sun rises, the air and ground warm up, which increases the air’s capacity to hold water vapor.  Since fog is a cloud of liquid water droplets the warming encourages the fog droplets to evaporate.

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, Seasons

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When will we stop seeing 80F this year?

Posted on September 22, 2025 by WeatherGuys Editor

At the time of this writing, Madison is in its 6th straight day of temperatures at or above 80F and it is likely we will have one more to reach seven in a row. 

Daily temperatures for Madison, Wisconsin, from 1869 to the present day, using combined data from the stations at the Madison city weather bureau office (January 1869–December 1946) and Dane County Regional Airport (January 1947–present). This chart shows the observed high and low temperatures compared with the normal highs and lows. The bumpy lines are the observed temperatures; the smooth lines are the normal temperatures. (Image credit: Wisconsin State Climatology Office)

As recently as 2022, we have had 13 of the first 21 days of September reach 80F or higher.  In fact, it was just last year that we set the all-time record for longest consecutive streak – initiated within September – of 80F or warmer days at 12 straight, running from September 10 – 21!  This also happens to be the longest consecutive streak of such days in September ever in Madison (1978 and 1981 both had 11 straight 80F September days).   It may have occurred to you that this mid-September heat is a bit unusual – though it is far from unprecedented. 

Interestingly, the earliest day on which Madison has ever recorded its last 80F day of the year was September 2, 1977 (and 2020).  The all-time latest 80F day in Madison’s history was, again, last year on October 29. 

The average last such day (since 1939) is September 29.  Within the 85 seasons (not including this one) since 1939 there have been 61 times when the last 80F day occurred after September 21 (the average date of the autumnal equinox).  Thus, summer-like warmth is a common feature of early fall in southern Wisconsin. 

So, we hope you have enjoyed the brilliant sunshine, light winds and dry conditions that have set in over us these last few days – we all know it won’t last – though, as the foregoing attests, there may still be time for another visit from summer before it is officially a thing of the past.

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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What does the CDC have to do with the National Weather Service?

Posted on September 15, 2025 by WeatherGuys Editor

As the flu season ramps up and brings along with it an increased threat of COVID-19 infections, it has been distressing for many to witness the assault on the leadership of the Centers for Disease Control and Prevention, known as the CDC. 

Under the leadership of Health and Human Services Secretary, Robert F. Kennedy Jr., an infamous vaccine skeptic, the leadership of the organization has been decimated and confidence in its ability to meet the challenges we regularly face from infectious disease has dramatically decreased.  These troubling developments come just weeks after the Department of Energy released a report on the impact of greenhouse gases on the climate of the United States written by five well-known skeptics of the broad scientific consensus on this urgent issue. 

At every turn the current administration appears determined to undermine expertise, rather than employ it, too often substituting hard won understanding of how the natural world works with the untested and sometimes flatly erroneous assertions of unqualified, overconfident activists who demonstrate little respect for the extraordinary effort and patience required to develop scientific understanding.

Imagine if our weather forecasts, the importance and ubiquity of which are manifest in some of the most popular apps on our smartphones, were left to be made by crazy uncles or chemtrail conspiracy theorists.  Would you have any confidence that such forecasts would be accurate?  Wouldn’t that matter on snow days, thunderstorm days, heavy rain and wind days?  Wouldn’t it matter to farmers and builders (among others) who often need time-specific forecasts to plan their many tasks? 

There is no better organization to turn to for such vital information than our exceptional National Weather Service (NWS) precisely because it is staffed by experienced, scientifically trained meteorologists.  The NWS is a clear example of the benefit accrued to societies wise enough to trust in, and invest in, expertise. 

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, Weather Dangers

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