How unusual was our recent snow and what might it portend?

Posted on December 8, 2025 by WeatherGuys Editor

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!

Snowfall 11/29/2025 on Madison’s west side. (Photo credit: M Vasys, CIMSS)

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.

Of course, none of this really bears on the complexion of the rest of the winter season. In fact, the month of December 2000 was both unusually cold and snowy, with an average temperature that was 14.1 degrees below normal accompanied by 35 inches of snowfall that was 23 inches above normal for the month. It appeared we were off to a great start for a cold, snowy winter. However, January and February followed with 12.1 inches and 5 inches below normal snowfall, respectively, and a middling 2 degrees above and 3.3 degrees below average in temperature.

So, only time will tell if this early wintry start will translate into a prolonged, robust winter season.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

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What is the largest snowflake?

Posted on December 1, 2025 by WeatherGuys Editor

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.

Temperature dependance on formation of ice crystals. (Image credit: Ackerman and Knox, “Meteorology – Understanding the Atmosphere”)

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.

Aggregation is the process by which ice crystals collide, get entangled or stick together and form a single larger ice particle. The probability that two crystals will stick together depends on the shape of the crystals. If two dendrites collide, it is likely that their branches will become entangled and the two crystals will stick together. When two plates collide there is a good chance that they will simply bounce off one another. Temperature also plays a role in aggregation. If the temperature of one crystal is slightly above freezing, it may be encased in a thin film of liquid water. If this particle collides with another crystal, the thin film of water may freeze at the point of contact and bond the two particles into one.

The record size for an aggregate snowflake occurred in January 1887 in Fort Keough, Montana, when some flakes were measured at 15 inches in diameter. That is about the size of a family sized pizza pie!

The world’s largest solitary ice crystal measured 10 millimeters, or 0.394 inches, from tip to tip. This dendritic-shaped crystal was photographed by Kenneth G Libbrecht on Dec. 30, 2003, during a gentle snowfall in Cochrane, Ontario.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Phenomena, Severe Weather

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Despite record warmth, winter is coming

Posted on November 24, 2025 by WeatherGuys Editor

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.

This chart shows the daily and total snowfall amounts at the Dane County Airport compared with the normal total snowfall. The vertical lines and left axis represent the daily snowfall; the horizontal lines and right axis represent the snow depth, yearly total, and normal total snowfall. (Image credit: Wisconsin State Climatology Office)

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.

So if the thought occurred to you as you enjoyed an almost summery day on November 15 that we were way over our meteorological skis, you were exactly right.

Currently the tropical Pacific Ocean is undergoing a weak La Nina event, which means the ocean temperatures in the central tropical Pacific are slightly cooler than normal. Such an anomaly does not have a very consistent impact on the winter weather over our region, unlike its opposite, the El Nino.

In fact, the latest outlook for this winter (December, January and February), released by the Climate Diagnostics Center on October 16, suggests that we have “equal chances” of being warmer or colder than normal in southern Wisconsin. The same forecast suggests “leaning above” for our precipitation outlook for the winter.

Of course, neither of these outlooks precludes us being visited by either a big snow or a frigid cold air outbreak during our coming winter. However, it may be that the winter will feature only limited appearances by such events.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Meteorology, Seasons

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What is lake effect snow?

Posted on November 17, 2025 by WeatherGuys Editor

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.

The figure above shows the average annual snowfall for the Great Lakes region. In general,snow depth increases northward. This is expected because temperature usually decreases poleward. The other distinct feature is the difference in the amount of snow along the shoreline. (Image credit: Meteorology; Understanding the Atmosphere by Ackerman and Knox)

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.

The longer the path, or “fetch,” the more the evaporation will increase along with greater potential for large snowfall amounts over the land on the downwind side of the lake. Hills can amplify the snowfall amounts by providing additional lifting. The location of a snowbelt along a particular lake is a function of the temperature difference between the air mass and the water, the fetch, and the terrain on the leeward side of the lake.

Lake effect snows are good for the economy of a region, particularly ski resorts. They also provide water for reservoirs and rivers. Too much lake effect snow can be hazardous, however; on October 12 to 13, 2006, Buffalo, New York was blitzed with 22.6 inches of snow in less than 1 day. Because trees had not yet shed their autumn leaves, the snow weighed down and broke tree branches. Nearly 1 million residents lost electrical power at the height of the storm because of falling trees and power lines.

Lake effect snow can bombard a location as long as all the ingredients—cold winds, warm water, and a long fetch—are present.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Seasons, Severe Weather

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What is a November gale?

Posted on November 10, 2025 by WeatherGuys Editor

A gale is a sustained wind between 39 mph and 54 mph. Gales are usually caused by large differences in the air pressure between a low pressure system and a strong high pressure system. Gale winds are common in November on the Great Lakes.

Recently recovered, digitized and navigated from the first geostationary weather satellite imagery on Nov 10, 1975, as featured on the CIMSS Satellite Blog. (Image credit; SSEC’s Satellite Data Services team)

This week marks anniversaries of some strong November gales in the Great Lakes region. The most famous of these include the White Hurricane (Nov. 7-10, 1913), the Armistice Day Blizzard (Nov. 11, 1940), the Edmund Fitzgerald Storm (Nov. 9-10, 1975) and the storm Nov. 10-11, 1998.

The White Hurricane, also referred to as the Big Blow and the Freshwater Fury, resulted in more than 250 people dying. Nineteen ships were destroyed and 19 others were stranded.

The Armistice Day Blizzard dropped 16.7 inches of snow in Minneapolis/St. Paul. The cyclone intensified rapidly and was accompanied by a very intense surface cold front that quickly dropped the temperatures as much as 50 degrees Fahrenheit in parts of the Midwest. This rapid drop in temperature caught many people by surprise, and more than 150 people perished as the storm moved across the Great Lakes region. The apple growing industry in Iowa was destroyed. Additionally, 1.5 million turkeys intended for Thanksgiving dinner across Minnesota and Wisconsin perished from exposure to the cold conditions.

The Edmund Fitzgerald Storm achieved grisly fame through its association with the sinking of the mammoth ore freighter and the loss of its 29 crew members. That storm also was accompanied by extremely strong winds and rapid intensification over the midcontinent. It was memorialized by Gordon Lightfoot’s ballad “The Wreck of the Edmund Fitzgerald.”

The Nov. 10-11, 1998, storm underwent a six-hour period in which its minimum sea-level pressure dropped 15 mb, and 10 deaths were attributed to the windstorm.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at noon the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: History, Seasons, Severe Weather

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