How does a lake freeze? Enlarge Photo: NOAA Ice forming around the shore of Lake Michigan Lakes freeze from the top down. Ice is less dense than water, which is why ice floats. The density of liquid water is determined… More
How does a lake freeze?
Category Archives: January
How does frost form?
How does frost form? Heavy frost on Burr Oak tree in Wisconsin Frost on objects is just water vapor in the air that has condensed as ice onto a surface. Frost forms on objects close to the ground, such as… More
Why does El Nino often lead to a warmer winter in Madison?
Why does El Niño often lead to a warmer winter in Madison? Image: NASA Forecasts of a relatively mild winter are being tied to a phenomenon called “El Niño” in the tropical Pacific Ocean. El Niño is so often invoked… More
Is global warming real?
Is global warming real? Image: NASA Over the past two decades, the global average surface temperature has increased noticeably. This observed warming trend indicates a significant global change and is consistent with other observed changes on our planet: There is… More
How long have satellites been used to study Earth’s weather?
How long have satellites been used to study Earth’s weather? NASA image of Explorer VII satellite, 1964 The first successful meteorological experiment conducted from a satellite was launched on Explorer VII on October 13, 1959, just over 50 years ago.… More
What is the jet stream?
What is the jet stream? Photo: NOAA The jet stream is a narrow current of strong wind that blows through the upper regions of the troposphere, about seven miles above ground. The jet stream generally moves from west to east,… More
Numerical Weather Forecasting is younger than rock ‘n roll!!
Numerical Weather Forecasting is younger than rock ‘n roll!! From NOAA Before 1960, the idea that a reasonably accurate two-day weather forecast could be made routinely was a pipe dream – now it’s a routine reality. In fact, it was… More
How accurate are weather forecasts?
How accurate are weather forecasts? Image: NOAA In general, weather forecasts are getting better, due to improvements in computer models, observations and our understanding of atmospheric. Accuracy depends on the purpose of the forecast and how far out it extends.… More
Is there a relationship between sun spots and climate?
Is there a relationship between sun spots and climate? Since the invention of the telescope in the 1600s, observers have recorded variations in the numbers of dark spots – “sunspots” – on the Sun’s surface. These variations normally follow a… More
What are heating degree-days?
What do heating degree-days tell us? Each degree that the mean temperature is below 65 degrees F is one heating degree-day. So if today’s average temperature is 55 degrees F, the day accounts for 10 heating degree-days. Engineers determined that… More
What is space weather?
What is space weather? Space weather describes the conditions in space that affect Earth and its technological systems. Space weather storms originate from the sun and occur in space near Earth or in the atmosphere. Space weather, like weather here… More
What is the dewpoint temperature?
What is the dewpoint temperature? Dew on evergreens, by Michael Theberge at NOAA Think of a morning when you walked on a grass lawn or through a field. Did your shoes get wet? If yes, that is because the grass… More
How does weather radar work?
Crane moves radome into position during installation of radar antennae at NOAA’s National Severe Storms Laboratory in Norman, Oklahoma Photo from NOAA How does weather radar work? Radar, an acronym for RAdio Detection And Ranging, was invented during World War… More
Why are clouds white?
Why are clouds white? Photograph of Cumulus clouds in fair weather taken by Michael Jastremsk Clouds are made of water and clean water is clear. So why are clouds white? Because clouds are made of billions of small water droplets… More
What does a 60 percent chance of precipitation mean?
What does a 60 percent chance of precipitation mean? The probability of precipitation (fondly known as PoP) has been part of weather forecasts since the late 1960s, and is the only forecast element that includes a probability. Unfortunately, there is… More