The Weather Guys

What is the summer solstice?

Posted on June 21, 2021 by WeatherGuys Editor

The summer solstice marks the longest day of the year.

The summer solstice occurs at the moment the earth’s tilt toward the sun is at a maximum. Therefore, on the day of the summer solstice, the sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice. In fact, the word solstice comes from Latin *solstitium* or *sol* (the sun) + –*stit-, -stes* (standing). (Image credit: weather.gov)

It is an astronomical event caused by Earth’s tilt on its axis and its orbit around the sun.

Monuments such as Stonehenge on Salisbury Plain in Wiltshire, England, demonstrate that ancient cultures knew the path the sun traveled through our sky changed in a routine way throughout the year. They undoubtedly observed that how high the sun appears in the sky varied throughout the year and that the higher the sun gets in the sky, the longer the length of daylight.

Our summer solstice occurs when the sun is directly overhead at noon at 23.5 degrees north of the equator, the latitude called the Tropic of Cancer. This is the farthest north the sun ever gets. This year, the sun reached the Tropic of Cancer at 10:32 p.m. Sunday.

At the summer solstice, the sun reaches its highest point in the sky and daylight is longest. The sun rises and sets farthest north at the June solstice. However, our earliest sunrise occurred on June 14, while our latest sunset occurs about a week later than the summer solstice. So, while the summer solstice has the longest daylight hours, that day does not correspond to the earliest sunrise or the latest sunset.

The time when the sun reaches its highest point in the sky is called solar noon. Solar noon rarely occurs exactly at clock noon — it’s sometimes before and sometimes after noon on our clocks. In June, the day, as measured by successive solar noon, is nearly 1/4-minute longer than 24 hours. Hence, the midday sun, when the sun reaches its highest point in the sky, comes later by the clock on the June solstice than it does one week before. Therefore, the sunrise and sunset times also come later by our clock.

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, Seasons

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Is hot first part of June a sign of things to come?

Posted on June 14, 2021 by WeatherGuys Editor

A barely colder than normal May has been followed by an extremely warm and dry first two weeks of June.

Through Friday June 11th, Madison had five days with high temperatures above 90 degrees, and the month has thus far averaged more than 11 degrees above normal.

Simultaneously, the dry spring has continued into the early summer with the month of June already 1.69 inches of rain below normal, and that’s after April and May came in at a combined 4.24 inches below normal.

Coincidentally, this week the National Oceanic and Atmospheric Administration (NOAA) reported that the monthly average carbon dioxide (CO2) fraction in the atmosphere, as measured at the top of Mauna Loa in Hawaii, set a new record of 418.92 ppm (parts per million) in May.

This graph depicts the upward trajectory of carbon dioxide in the atmosphere as measured at the Mauna Loa Observatory in Hawaii.
Credit: NOAA Global Monitoring Laboratory

This represents a larger than 50% increase in atmospheric CO2 concentration since the pre-industrial age (1750-1800), when the value was about 280 ppm as measured by analysis of air bubbles in ice cores taken from ice sheets in Antarctica and Greenland. The current value has not been observed on Earth in the last 4.1 million to 4.5 million years, when sea levels were 78 feet higher than they are today and the global average temperature was 7 degrees warmer than at present.

Not even the COVID-19 pandemic was able to put a dent in the rate of increase in CO2, which suggests that, unless we change the nature of our energy use, we are continuing to forge a path toward a very different, and likely extremely adverse, climate future.

Since solar and wind energies are already cheaper than fossil fuels and they work at the scales necessary to power the world, there is no reasonable excuse for not moving aggressively to a more sustainable energy future.

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.

Category: Climate, Meteorology, Seasons

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How dangerous is hot weather?

Posted on June 7, 2021 by WeatherGuys Editor

Hot weather can be dangerous, particularly if the humidity is high as well.

Much of the Upper Midwest had temperatures near or above 90 degrees over the weekend, except along the shorelines of the Great Lakes. Several locations set record high daily temperatures — in Madison, Saturday’s high of 92 degrees tied the record for the day set in 1934.

So it’s a good time to consider the dangers of hot weather, as extreme heat kills more people in the U.S. than any other type of weather event. According to the National Weather Service, an average of 130 people die in the U.S. from heat exposure each year.

Mid-June Temperature Outlook from NOAA’s Climate Predication Center

Perspiring is how a body cools down. Sweating, by itself, does not cool the body. It is the evaporation of sweat that cools the body.

At the same pressure and temperature, water evaporates more slowly in air that has a high relative humidity and more quickly in air that has a low relative humidity. This means that in high humidity, your body will cool at a slower rate, possibly creating a dangerous situation.

When the weather turns warm, it’s great to be active outside. But when it gets really hot and humid, be careful. As our muscles contract during exercise, our body produces heat; the harder you exercise, the greater the amount of heat your body needs to dissipate.

Exercising in high temperatures can cause heat cramps, heat exhaustion and potentially heat stroke. So, on hot days be sure to drink enough water or juices before, during and after exercise. Fluids help your body to perspire, which cools the skin via evaporation and keeps your body temperatures at a safe level.

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 and featured weekly in the Wisconsin State Journal.

Category: Meteorology, Seasons, Severe Weather

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What is the prediction for the 2021 hurricane season?

Posted on June 1, 2021 by WeatherGuys Editor

Tropical cyclones are large, whirling storms that obtain their energy from warm ocean waters. Hurricanes are tropical cyclones that originate in the Atlantic Ocean, Caribbean Sea, Gulf of Mexico or the eastern North Pacific Ocean. Tropical storms have wind speeds between 39 and 73 mph, while hurricanes have wind speeds of greater than 74 mph. These storms form over warm waters. A general rule of thumb is that hurricanes will not form unless the water temperature is at least 80 degrees.

An average hurricane season produces 12 named storms, of which six become hurricanes, including three major hurricanes, with wind speeds greater than 111 mph.

An above-normal Atlantic hurricane season is expected this year. The National Oceanic and Atmospheric Administration prediction for 2021 is a likelihood of 13-20 named storms with sustained winds of at least 39 mph. Six to 10 of those are likely to become hurricanes, with winds of 74 mph or higher, including three to five major hurricanes.

Official 2021 Atlantic Hurricane Season Outlook from NOAA

The Atlantic hurricane season officially starts June 1 and lasts until Nov. 30. That is the time of year when most hurricanes occur — about 97% of them. But hurricanes can occur any month of the year. The calendar isn’t the important thing; the ocean temperatures and the lack of vertical wind shear are.

We already had our first named storm of the 2021 season. Tropical storm Ana formed on May 22, 10 days before the official start of the 2021 Atlantic hurricane season. This is the seventh consecutive year in which a tropical or subtropical cyclone formed before the official start of the season on June 1.

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

Category: Meteorology, Seasons, Tropical

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Where does water exist?

Posted on May 24, 2021 by WeatherGuys Editor

GOES East satellite image showing global water vapor. Values measured are temperature but colors also indicate moisture in the atmosphere where greens and blues reveal high water vapor content and yellows and orange indicates dry air.

Evidence of the presence of water in our atmosphere is ubiquitous.

Water occurs in the Earth’s atmosphere in all three of its phases — solid (snow and ice), liquid (rain and dew) and gas (invisible water vapor). As we begin to emerge from the recent cool spell and really enter spring/summer, we may begin to see more dew on the ground and on the windshields of cars in the morning.

The air nearly always holds some amount of water vapor. Dew is liquid water that condenses overnight onto objects when the air that contains the water vapor cools to a sufficiently low temperature.

One of the important and microscopic characteristics of the condensation process is that water vapor will not condense into liquid water very easily unless it condenses onto a foreign object such as the tiny hairlike structures on grasses or dust and pollen particles on windshields. In fact, on particularly dewy mornings, if you wait for the dew to evaporate you may find yellow stains on your windshield that are left as the liquid water evaporates, leaving the pollen particles on which it originally condensed.

The formation of raindrops requires a similar collection of foreign objects upon which water vapor can condense. Such objects are known as cloud condensation nuclei, and a great number of naturally occurring substances can serve this role, including dust particles, smoke particles, salt particles, pollen grains, particulate matter from smokestacks, and naturally occurring aerosol particles.

Without these cloud condensation nuclei, the formation of cloud liquid water droplets, and eventually precipitation-sized particles (which are 1 million times more voluminous), would be considerably more difficult in our atmosphere.

In that case, rain and snow would be rare occurrences and life on the planet would be put at risk.