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What is a 100-year flood?
A flood occurs when water flows into a region faster than it can be stored in a lake or reservoir, absorbed into the soil, or removed by runoff into a drainage basin.
There are several conditions that can result in flooding: a long-lasting rainfall over a watershed, intense thunderstorms, or rainfall that causes rapid snow melt. Continue reading
Is hurricane forecasting improving?
There are two important components of hurricane forecasting: the hurricane track (or where it is going) and hurricane intensity (or how and if its winds are increasing). Track forecasts have improved over the last two decades; intensity forecasts have not improved.
In 1992, when Hurricane Andrew hit Florida, the average three-day forecast error in hurricane track was about 300 miles. Today, a six-day forecast of the typical hurricane track error is now less than 200 miles, more accurate than the three-day forecast was 23 years ago. Continue reading
What does El Nino mean for southern Wisconsin’s winter this year?
El Nino is an atmosphere/ocean phenomenon in which the waters of the eastern equatorial Pacific Ocean are warmer than normal for an extended period of time.
This unusual warmth forces changes in the distribution of deep convective thunderstorms over the tropical ocean which, in turn, affect the position and strength of the jet stream. Since the jet stream acts a conduit of winter storms and can regulate intrusions of cold arctic air, changes in jet stream characteristics can have a profound influence on our winter weather. Continue reading
Category: Meteorology, Phenomena, Seasons
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When is the autumnal equinox?
On Wednesday morning, we will officially enter fall as the autumnal equinox occurs at 3:20 a.m.
On Wednesday, in common with every location on Earth, we will enjoy exactly 12 hours of daylight and 12 hours of night.
Of course, 12 hours of daylight in Madison (latitude 43N) is substantially different from 12 hours of daylight at the North Pole (latitude 90N) where the sun will barely be visible above the horizon for the 12 hours of “daylight.” On the very next day, the sun will not appear above the horizon at the Pole and will not come back for six months. As the days march on, the same fate will gradually overtake other latitudes in the Northern Hemisphere until by Dec. 21, the sun will not rise even at 66.5N. Continue reading
When does the first freeze occur in fall?
The cooldown that we enjoyed over the weekend, after the prolonged warm and humid spell that began September, got us thinking about the inevitable first morning with a temperature below 32 degrees.
We are less than two weeks away from the autumnal equinox, the last day until late March on which the day is at least as long as the night. Continue reading
