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Category Archives: Seasons
Is there any trace of winter left in the Northern Hemisphere?
We have made reference a few times in this column to the areal extent of cold air over the Northern Hemisphere as a measure of wintertime severity, that is, the geographic reach of air of a certain temperature.
Specifically, we have reported on the 23-degree air at 1 mile above the ground (where the atmospheric pressure is just 85 percent of its near-surface value). By mid-July it is impossible to find air that cold at that elevation in the Northern Hemisphere. Continue reading
Category: Meteorology, Seasons
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When is the summer solstice?
The summer solstice in the Northern Hemisphere is the day when the sun is farthest north. In 2014, this occurs on June 21 at 5:51 a.m.
As Earth orbits the sun, its axis of rotation is tilted at an angle of 23.5 degrees from its orbital plane. Because Earth’s axis of spin always points in the same direction — toward the North Star — the orientation of Earth’s axis to the sun is always changing as Earth orbits around the sun. Continue reading
When is the last frost?
The growing season is often defined as the number of days between the last time the temperature was 32 degrees in spring and the first time the temperature falls to 32 in fall.
The latest frost in spring is important to gardeners as they seek to plant after a long winter, and for most plants it is wise to do so when the temperatures are likely to remain warmer than 32 degrees.
Continue reading
Are the jet stream and tornadoes related?
Wintertime weather is driven largely by the parade of upper-level weather systems carried rapidly eastward by the high level winds known as the jet stream.
The jet stream is a ribbon of high-speed wind (located at nearly 6 miles above the surface) that is related to the strength, and location, of the pole-to-equator temperature contrast. Continue reading
How long were Madison lakes frozen this year?
Lakes Mendota, Monona and Wingra opened during the second week of April.
Lake Mendota officially froze Dec. 16 and opened April 12, for an ice season of 117 days, which is 12 days longer than the median duration. Continue reading
