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Category Archives: Seasons
Does the warmest autumn on record mean anything about the coming winter?
In the past several years we have occasionally mentioned our tracking of the areal extent of air colder than minus 5 degrees centigrade at about 1 mile above the surface of the Earth. This measurement has proven to be a very valuable addition to the collection of metrics of global warming. We have particularly commented on the wintertime (December, January and February) average of this extent measured over the entire Northern Hemisphere, noting that since 1948 the wintertime average extent has systematically decreased.
We have also been tracking this variable throughout the autumn over all these years and can report that this fall (Sept. through Nov. 30) recorded the smallest average areal extent of this cold air since at least 1948. That means we have just experienced the warmest Northern Hemisphere autumn in at least the past 77 years. Continue reading
How and when do Madison lakes freeze?
The surface of a lake exchanges energy with the air above. Cold air cools the lake surface through energy exchanges with the atmosphere, determined by the weather above. As cool surface water cools, it becomes denser than the warmer water below and so the cooled water sinks. Water from below then rises to the surface where it begins to cool.
What is unique about the H2O water molecule is that as liquid water cools, its density increases until about 39°F (4°C). At that point, the colder water becomes less dense, stays at the surface, and continues to cool. Once the surface water cools to approximately 32°F, the water molecules crystallize into interlocking lattice-like patterns and ice is formed. For a lake surface to freeze, the entire lake needs to be at a temperature of 39°F; only then as the surface cools will the temperature of the liquid water at the surface remain less dense than the water below and thus float and begin to form ice. Shallower lakes usually freeze before deeper lakes since shallower lakes contain less water that needs to be cooled.
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Do weather radars detect more than precipitation?
Yes. Radar, an acronym for RAdio Detection And Ranging, consists of a transmitter and a receiver. The transmitter emits radio wave pulses outward in a circular pattern. Objects scatter these radio waves, sending some energy back to the transmitting point where it is detected by the radar’s receiver. The intensity of this received signal indicates the size and density of the suspended objects, such as precipitation. The time it takes for the radio wave to leave the radar and return indicates the distance.
Radar is designed to detect precipitation intensity and type, but it can detect living things as well. Flying insects in huge numbers can reflect enough energy back to a radar site to be detected. As an example, mayflies emerge in summer in enormous numbers around the Mississippi River between Wisconsin and Minnesota and are often detected by the weather radar in La Crosse, WI. Continue reading
What is “The Old Farmer’s Almanac” forecast for winter?
“The Old Farmer’s Almanac” recently published its 2024-25 winter forecast. For the Upper Midwest region, it predicts winter will not be as cold as usual. The precipitation and snowfall forecast are for below average.
But don’t count on that forecast, as there is no proven skill. “The Old Farmer’s Almanac” does not share how it makes its forecast, so it cannot be judged scientifically. “The Old Farmer’s Almanac” also makes a weather forecast for specific time periods in a given season. Such detailed forecasts can be announced but are not trustworthy scientifically. Continue reading
Do oceans have heat waves?
As with the atmosphere, oceans can experience heat waves. The National Weather Service defines an atmospheric heat wave as a period of abnormally hot weather generally lasting more than two days. To be considered a heat wave, the temperatures must be outside the historical averages for a given area.
Marine heat waves are defined as any time the ocean temperatures are warmer than 90% of the previous observations for the region at a given time of year. Marine heat waves can last for weeks, months and even years. Continue reading
