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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Does lightning travel from the sky downward or ground upward?

Posted on November 3, 2025 by WeatherGuys Editor

Lightning is a huge electrical discharge that results from vigorous motions that occur in thunderstorms.

The average number of cloud-to-ground lightning flashes per square kilometer across the lower 48 United States. (Image credit: Ackerman and Knox, Meteorology: Understanding the Atmosphere, Fourth edition)

Lightning can travel from cloud to cloud, within the same cloud, or between the cloud and ground. In-cloud lightning discharges are more common than cloud-to-ground discharges and are not as hazardous. Cloud-to-ground is the best known type of lightning and it poses the greatest risk.

A typical cloud-to-ground flash begins as negative charges travel towards the ground in a sequence of spurts. This makes the ground positively charged. As the negative charge approaches the ground, there is an upward stream of positive charges. When the two streams meet, an initial flash occurs and a channel forms so that electricity can flow back forth between the cloud and ground. This occurs so quickly that it looks like a single brilliant flash, but high speed photography shows several bolts.  Cloud-to-ground lightning starts from the sky and heads downward, but what we see can travel from the ground upward.

Lightning also has different appearances. Staccato lightning is a cloud-to-ground lightning strike which is a short-duration stroke that often, but not always, appears as a single very bright flash and often has considerable branching.  Forked lightning is a name, not in formal usage, for cloud-to-ground lightning that exhibits branching of its path. Ribbon lightning occurs in thunderstorms with high cross winds and multiple strokes. The wind will blow each successive stroke slightly to one side of the previous stroke, causing a ribbon appearance. Bead lightning is a type of cloud-to-ground lightning which appears to break up into a string of short, bright sections.

Heat lightning is a common name for a lightning flash that appears to produce no discernible thunder because it occurs too far away for the thunder to be heard.

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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Are the Arctic and Antarctic warming at the same rate?

Posted on October 27, 2025 by WeatherGuys Editor

Global warming is occurring. We know this through scientific observations and our understanding of atmospheric physics and chemistry. We understand that human activities associated with burning fossil fuels is a primary forcing function. While global warming is occurring, observations indicate that rate of warming varies by region.

Comparison of Arctic vs global surface air temperature anomalies. (Image credit: NOAA Climate, archived)

The Arctic and Antarctic are geographic opposites, and not just because they sit on opposite ends of the globe. The land-sea arrangements are different. Antarctica is a continent surrounded by water; the Arctic is basically a water body surrounded by land.

Observations show that the Arctic is warming faster than Antarctica. The Antarctica continent is very high (about 7,500 feet) and thus much colder to begin with so the snow and ice on the land are not melting as fast as the snow and sea ice in the Arctic.

The ice thickness on Antarctica averages about 1.4 miles. The brightness of this ice sheet reflects solar energy out to space, which limits regional warming in summer.  The Antarctic peninsula, which juts further north into the Southern Ocean, warmed faster than any other terrestrial environment in the Southern Hemisphere during the latter half of the 20th century.

Observations indicate that the Arctic is the fastest warming region on the globe, a phenomenon called Arctic amplification. Summer sea ice in the Arctic has been shrinking more than 10 percent per decade over the past 40 years. As sea ice melts, solar energy is not reflected to space and helps warm the region. The accelerated Arctic warming influences the weather around the Northern Hemisphere by changing the temperature contrast between middle and high latitudes. Such influences are being studied intensively at 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: Climate, History

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Does the federal shutdown impact weather forecasting?

Posted on October 20, 2025 by WeatherGuys Editor

Weather forecasts provided by the government will continue during the shutdown. The National Weather Service (NWS) and other National Oceanic and Atmospheric Administration (NOAA) agencies provide essential services; therefore, most NWS federal forecasters are considered emergency employees and are required to work without pay during the shutdown.

The National Digital Forecast Database (NDFD) is a suite of products generated by the National Weather Service (NWS) using data from regional NWS Weather Forecast Offices (WFOs) and the National Centers for Environmental Prediction (NCEP).

While NWS will continue their life-saving essential work, some weather and climate data feeds and public-facing services will have limited or no access to researchers and the public. According to a NWS webpage announcement, “Due to the government shutdown, all public National Weather Service activities, including tours and other outreach activities, have been canceled or postponed until further notice. We apologize for any inconvenience. The NWS will continue to provide critical forecast, watch, and warning information to protect life and property throughout the shutdown.”

The National Hurricane Center (NHC) will also continue to provide hurricane updates and forecasts. There are a few “non-essential” fields in NOAA that are not operating during the shutdown, including some active research.

Thousands of government forecasters monitor the weather 24 hours a day, 7 days a week. They issue forecasts, watches, and warnings that are critical to the protection of life and property. As essential workers they are expected to report as usual during a shutdown, working without pay for the duration of the shutdown.

As of this writing, Republicans and Democrats appear no closer to an agreement to reopen the government. Federal workers will miss their paychecks during the government shutdown. There also are contractors who perform work for the federal government and it is not certain they will be eligible for back pay after the shutdown.

Accurate weather forecasting requires equipment like weather radars, satellites, and observation stations. These will continue operating during the shutdown, although repairs and upgrades may be delayed until a federal budget is restored.

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, Weather Dangers

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