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What is the status of the ozone hole?
The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic. Each year for the past few decades during the Southern Hemisphere spring (August-October), chemical reactions involving chlorine and bromine cause ozone to be rapidly destroyed. This depleted region is known as the “ozone hole.”
Chlorofluorocarbons, or CFCs, are ozone-depleting chemicals that do not occur naturally. They were invented by chemists in 1928 and used as propellants in spray cans, in Styrofoam puffing agents and as coolants for refrigerators and air conditioners. In 1974, these human-made gases were first linked to ozone destruction. The United States banned the use of CFCs in 1978. Continue reading
How unusual was our recent snow and what might it portend?
With the exception of a freaky 12.1 inches of slushy snow that fell on Madison on March 25, 2023, the most recent 10-inch snowfall in the city was Dec. 20, 2012 — nearly 13 years ago!
So, it’s been a very long time since we have been visited by the kind of snowfall we saw on Nov. 29-30 — the total over the two days was 11.7 inches. More than that, the 9.3-inch accumulation officially registered at Dane County Regional Airport on Nov. 29 was the largest single-day November snowfall total ever, eclipsing the former record of 8.5 inches that fell on Nov. 30, 1940. So, not only did we finally see a hefty snowfall event after more than a decade of waiting, but we also set an early-season record as well. Continue reading
What is the largest snowflake?
An ice crystal can grow if the air around it has a relative humidity near 100%. The ice particle grows by water vapor deposition. Growth by deposition is generally slow. If you find nicely shaped snowflakes, they likely were produced by vapor deposition. A snowflake can be an individual ice crystal or an aggregate of ice crystals.
There are four basic shapes of ice crystals: the hexagonal plate, the needle, the column and the dendrite. The dendrites are hexagonal with elongated branches, or fingers, of ice; they most closely resemble what we think of as snowflakes. The temperature at which the crystal grows determines the shape. Continue reading
Despite record warmth, winter is coming
It is a fair bet that we would get near universal agreement that the weekend of November 15-16 was incredibly nice, even the slightly cooler Sunday that followed a truly remarkable Saturday. Both Milwaukee and Madison set all-time record high temperatures for November 15 at 69 and 68 degrees Fahrenheit, respectively.
Apart from the fact that each city recorded highs that were at least 20 degrees lower the very next day (46 for Milwaukee and 48 for Madison), the weekend was also noteworthy for another meteorological reason: At least for Madison, November 15 is the date on which the probability of precipitation falling as snow first reaches 50%. This means that, from here on out, if precipitation is in the forecast, there is at least an even chance that it will fall as snow. Only 10 days later comes the average date of our first 1-inch snowfall. Continue reading
What is lake effect snow?
Lake effect snow forms when cold air passes over the warmer water of a lake. As cold air moves over water, the lower layers are warmed and moistened by the lake below. This makes the air mass unstable. Evaporation increases the moisture content of the air mass, which is then precipitated in the form of snow on the land downwind.
Maximum heat and moisture exchanges occur when the air is cold and the temperature difference between the air and the water is large. This condition tends to occur during early winter; this is when the most lake effect snow is produced. A long path across warm water by the air mass results in heavy precipitation over the land. Continue reading
