Is our rainy summer finally drying out a bit?

Posted on August 19, 2024 by WeatherGuys Editor

Readers may recall we reported on the unusually wet nature of our late spring/ early summer about a month ago. At that time, Madison had recorded the wettest May 1-July 15 period since at least 1939 while averaging more than 2.5 degrees Fahrenheit above normal for that same period.

Another month has ticked away in this summer, and it has been a bit different than the ones that came before it. Through Aug. 15, Madison has recorded 1.73 inches of precipitation, which is 0.35 below normal. Ten of the first 15 days of the month had no precipitation at all and, from Aug. 7 to Aug. 13 we had a streak of seven straight days with no rain at all. That is now the longest dry streak since May 1.

One last update for the current month is that we have averaged 0.8 degrees Fahrenheit below normal for the first 15 days.

So, both the coolness and the dryness have been very different thus far in the new month.

Despite this recent lack of precipitation recently, we will still have the wettest May 1 to Aug. 15 ever recorded in Madison. To top it off, if we were to receive more than 4.63 inches of rain between now and September 1, we would surpass the all time record for wettest May 1 through September 1, 29.09 inches, set in 2018. That would require an average of nearly 0.29 inches each day until then — not likely since this time of the year averages less than half that amount.

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: Uncategorized

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What is Tornado Alley?

Posted on August 12, 2024 by WeatherGuys Editor

A tornado is a powerful column of winds that rotate around a center of low pressure. The winds inside a tornado spiral inward and upward, often exceeding speeds of 300 mph. Tornadoes form in atmospheres that have extremely unstable moist air, large amounts of vertical wind shear and weather systems, such as fronts or thunderstorms, that force air upward.

The yellow areas, darker with increasing frequency, show large tornado outbreaks from the 1950s through 1980s. The blue striped areas show the corresponding frequency of outbreaks from 1989 through 2019. (Image credit: Daniel P. Huffman in Scientific American)
The yellow areas, darker with increasing frequency, show large tornado outbreaks from the 1950s through 1980s. The blue striped areas show the corresponding frequency of outbreaks from 1989 through 2019. (Image credit: Daniel P. Huffman in Scientific American)

The continental United States provides these three ingredients in abundance.

A plot of tornado tracks in the contiguous U.S. from 1990 through 2011 reveals a relatively high frequency in the central Great Plains. Texas to Kansas stands out as a region of high tornado occurrence. Tornado Alley traditionally refers to this region known for frequent tornadoes. It is a colloquial term, and there are no explicit boundaries to Tornado Alley.

A recent study found the corridor where many tornadoes in the U.S. occur has changed in recent decades. There appears to be an eastward shift of tornado activity, with a corridor that encompasses the states of Arkansas, Louisiana, Tennessee, Alabama and Georgia.

The published study analyzed tornado tracks that spanned two 35-year periods, one from 1951 to 1985 and the second from 1986 to 2010. In the first 35-year span tornado formations peaked in northern Texas, Oklahoma and Kansas — the area traditionally known as Tornado Alley. From 1986 to 2020 the most active tornado corridor shifted eastward, peaking in Mississippi, Louisiana and Alabama.

Within the United States, tornadoes can occur in nearly every state and in every month of the year. When considering tornado activity, meteorologists focus on the specific conditions conducive to their formation: warm, moist, unstable air, and changes in wind speed and direction with height, rather than a fixed geographical area.

The scientific study also demonstrated that there are more winter tornadoes than in past decades. Wisconsin had its first tornado in February this year.

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: Severe Weather, Weather Dangers

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Do thunderstorms cause milk to spoil?

Posted on August 5, 2024 by WeatherGuys Editor

No, but it was once widely thought that summertime thunderstorms could cause fresh milk to curdle.

This thinking was based on observations that raw milk would spoil during lightning and thunderstorms. But it was neither the thunderstorms nor lightning that caused the spoiling; rather it was the atmospheric conditions. The conditions that are optimum for thunderstorm development are the same as those that would cause milk to spoil.

Milk curdles because of bacteria, not because of thunderstorms. Microbes in milk consume the milk’s natural sugars and produce lactic acid as a waste product. This coagulates the milk’s proteins, resulting in lumps in the milk and making the milk taste sour. Bacteria thrive in warm, humid conditions, so hot and humid days were particularly troublesome to early dairy farmers. These same atmospheric conditions are also favorable for summertime thunderstorms.

Thunderstorms require warm moist air that rises, so the environmental conditions that support thunderstorm development are like those in which milk can spoil. This similarity led to the observed correlation of milk spoiling during thunderstorms. But the conclusion that the thunderstorm caused the milk to spoil was incorrect.

An article in the journal Science in 1891 by A.L. Treadwell may be the first to suggest that milk spoils because of bacteria. In 1927, E.H. Farrington published an article that summarized his experiments and noted that “sultry atmosphere usually precedes thunder showers and provides favorable conditions for the growth of milk-souring bacteria.” Part of his career included a professorship at the University of Wisconsin, where the paper was published. “Sultry” is typically used to describe summer stretches of warm days and nights with high dew points.

Pasteurization and refrigeration prevent the milk from spoiling, as they make environments that are too hot or cold for bacteria to thrive. We have not developed the technologies to prevent thunderstorms from developing.

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, Severe Weather

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Are thunderstorm rain amounts hard to predict?

Posted on July 29, 2024 by WeatherGuys Editor

Meteorologists would generally agree that summer is the most challenging time of year for making accurate rain forecasts.

Neither scattered nor isolated stroms give any indication of whether the storm is severe or when it’s happening. These two terms only refer to how much of an area it is expected to cover. (Image credit: Weather Station Advisor)

During summer, there generally is enough moisture and atmospheric instability to help fuel the development of rain showers. Scattered thunderstorms are one of the most difficult weather events to forecast.

Thunderstorm development also is difficult to pinpoint in the summer. Summer thunderstorms sometimes develop from subtle outflow boundaries from previous thunderstorms, sea-breeze fronts, higher terrain or localized solar heating.

Numerical weather prediction models help define areas where conditions will be right for the development of thunderstorms.

These models are designed to calculate atmospheric conditions over a large area but cannot pinpoint the locations of a particular thunderstorm development. Summer thunderstorm forecasts are often broad, using terms like “isolated” and “scattered.”

“Isolated” corresponds with a 10% chance of measurable precipitation (0.01 inches or greater). “Scattered” indicates that there will be 30% to 50% coverage of convective weather, such as thunderstorms, in the forecast zone. “Widely scattered” is used for a forecast of 20% coverage. If you are planning outdoor activities and the chances of rain are 10% to 20%, it is a good idea to have backup plans for moving indoors.

Along with numerical models, satellites and ground based radars contribute a significant amount of additional information for forecasters as the storms develop. It is wise to have a weather radar app on your smartphone to see whether any thunderstorms are nearby.

The National Weather Service issues a severe thunderstorm warning when a thunderstorm is producing wind gusts of at least 58 miles per hour or hail of at least 1 inch in diameter.

If a tornado is detected, a tornado warning will be issued either in replacement of or concurrently with the existing severe thunderstorm warning. Severe thunderstorm warnings should not be ignored, as severe thunderstorms are dangerous and occasionally deadly.

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, Severe Weather

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How does our late spring/early summer precipitation stack up historically?

Posted on July 22, 2024 by WeatherGuys Editor

If you think the first half of the summer has been unusually wet, it is not merely your impression — it is a measured fact.

Between May 1 and July 15, Madison received 21.85 inches of precipitation, punctuated by the 18th-wettest day in Madison history (3.3 inches on July 14) — which is 10.16 inches above normal.

In other words, since May 1 we have received nearly twice the normal rainfall in the wettest part of the year. In fact, this amount is the all-time record for May 1 to July 15 in Madison and one of only two such periods (the other was in 2000) during which 20 inches of rain or more has fallen. Perhaps unsurprisingly, in the 76 days of this interval, we have had only 30 completely dry days — well less than half. Consistent with this incredible total, only one time in this period have we had as many as five consecutive days during which not even a trace of precipitation fell — May 14-18.

Yet another interesting fact regarding this remarkable wet period is that over the same interval the daily average temperature has been 2.54 degrees Fahrenheit above normal. Historically, rainy late spring/early summers have been closer to average or even a bit cooler than normal as a result of the persistent cloud cover that usually accompanies such prolonged rainy periods. The four other rainiest May 1 through July 15 periods, for instance, averaged 0.55 degrees below average (2000), 0.44 degrees above average (2013), 1.76 degrees below average (2008) and 0.30 degrees below average (1993) — nothing at all like this year.

Since warmer air has a greater capacity for water vapor which is then available for conversion into precipitation, the combination of unusual precipitation amounts and higher than average temperatures is clearly suggestive of global warming.

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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