Monthly Archives: November 2021
Ski resorts often use snow machines to make snow and lay down a good base for the coming season.
To make snow for ski trails requires temperatures near or below freezing. The humidity also plays a role in snow-making; a lower humidity is better. A low temperature and a low humidity is the best atmospheric condition for snow-makers, as it yields the driest snow.
Our recent cold snap has brought the November average to just 0.5 degrees above normal through the first 17 days of November after a relatively warm October in Madison, where the average temperature was 5.9 degrees above normal. It is … Continue reading
On Nov. 7, numerous “holes” appeared to be punched out of a cloud deck across the Upper Midwest.
Punch holes can occur after a plane flies through the cloud if the cloud droplets are supercooled, with their temperatures below freezing. Continue reading
La Niña refers to a departure from normal in the sea-surface temperature across much of the eastern tropical Pacific Ocean.
The water temperatures off the west coast of South America are typically 60 to 70 degrees. During a La Niña these waters get as much as 7 degrees colder than normal. La Niña conditions recur every few years and last nine to 12 months, though some events have lingered for as many as two years. This cooling results from a strengthening of the winds over the tropical Pacific and its interaction with the underlying ocean waters. Continue reading
Frost on objects is just water vapor in the air that has deposited itself as ice onto a surface. Frost forms on objects close to the ground, such as blades of grass.
At night, a blade of grass loses energy by emitting radiation (a non-lethal kind) while it gains energy by absorbing the energy emitted from surrounding objects. Under clear nighttime skies, objects near the ground emit more radiation than they receive from the sky, and so a blade of grass cools as its energy losses are greater than its energy gains. If the temperature of a grass blade gets cold enough and there is sufficient water vapor in the environment, frost will form on the grass. Continue reading