How remarkable was the recent winter storm?

Posted on January 2, 2023 by WeatherGuys Editor

The recent winter storm that affected large portions of the United States just days before the Christmas holiday was remarkable in a number of dimensions.

It was an example of a “bomb cyclone” which simply means that the rate at which its central pressure dropped — about 2.5% in a single day — was extremely unusual. Even though a 2.5% change in central pressure does not sound like very much, it was responsible for revving up the extreme winds that brought wind chills into the minus 30s and ground blizzard conditions to a large portion of the Great Lakes states on Dec. 23.

In addition, this particular storm was the agent for delivery of an extremely cold Arctic airmass in its wake — dropping the temperature in Madison to minus 12 on the morning of Dec. 23. Since it subsequently only rose to minus 3 for that day’s high, the daily average temperature of minus 7.5 that day ranks as the seventh-coldest December day in Madison since 1939.


GOES East view of the powerful winter storm wrapping arctic air into it’s core (milky orange) while ushering bitter cold conditions south and east across the U.S. (Credit:NOAA)

Another aspect of the storm that was noteworthy was the remarkable degree of accuracy surrounding its prediction. Though there was some change in the days leading to the event, the forecasts for ground blizzard conditions, quite light snow amounts (Madison received 3.7 inches total), and desperate cold were fairly well locked in by Monday afternoon — three-plus days prior — at the latest.

This is a triumph of modern science that often goes unheralded. The combination of unceasing progress in theoretical understanding of the atmosphere, computer science, observing technologies (especially satellite observations), and data science over the past 50 years have led to stunning advances in predictive skill.

Though it is still true that forecasts are not 100% accurate, it is beyond doubt — even in the heart of the most ardent skeptic — that accurately painting the complexion of a future meteorological event days in advance has become the rule rather than the exception.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Phenomena, Seasons, Severe Weather

Comments Off on How remarkable was the recent winter storm?

What is a mesonet?

Posted on December 26, 2022 by WeatherGuys Editor

In meteorology and climatology, a mesoscale network, or mesonet, is a network of automated environmental monitoring stations designed to observe meteorological phenomena on the mesoscale. In meteorology, “mesoscale” refers to weather events that range in size from about 1 mile to about 150 miles.

Mesoscale events last from several minutes to several hours. Thunderstorms, snow squalls and wind gusts are examples of mesoscale events. Due to the space and time scales associated with mesoscale phenomena, weather stations comprising a mesonet are spaced closer together and report more frequently than the larger synoptic scale observing networks run by the National Weather Service.

The Institute for Rural Partnerships is a great example of the Wisconsin Idea.

Just recently, UW-Madison received funding from the Wisconsin Alumni Research Foundation (WARF) and the United States Department of Agriculture (USDA) to purchase and install a mesonet across Wisconsin. A Wisconsin Environmental Mesonet and the data provided will support a wide range of research interests, including applications that involve many collaborators across the state.

A majority of Midwest states already have some type of mesonet guiding everyday use and decision-making. Wisconsin will now join that infrastructure.

Mesonets provide real-time weather and soil data for anyone to use. This helps support farmers, crop consultants and extension agents, support fire weather prediction, reduce economic losses in agricultural production, assist in weather warning issuance and forecasting, assist in emergency planning and preparedness, improve public safety, and support K-12 education.

Mesonets also provide data to a wide variety of researchers, scientists and teachers. Data from existing mesonets support a variety of weather and agriculture models. Observations from a mesonet can help support and improve the development of local temperature forecasts, as well as predictions for water demand by crops.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Severe Weather

Comments Off on What is a mesonet?

Can a snowstorm have lightning?

Posted on December 19, 2022 by WeatherGuys Editor

Yes, and if you were awake late Wednesday night you might have observed lightning and heard thunder with the snowstorm.

This video compilation from AOSS rooftop cameras captured thundersnow on the UW-Madsion campus on Wednesday December 14th around 11:30 PM. (Video courtesy of Pete Pokrandt, UW-Madison Dept of Atmospheric and Oceanic Sciences)

It is not a common occurrence, but when lightning and thunder occur during a snowstorm, the event is reported as “thundersnow.”

Thundersnow is a thunderstorm with snow falling as the primary precipitation instead of rain. It is a rare phenomenon in comparison with summertime thunderstorms, but the underlying mechanisms are the same. The storm has sustained strong vertical mixing which allows for favorable conditions for lightning and thunder to occur.

Lightning is a huge electrical discharge. Static charges form in a storm composed of ice crystals and liquid water drops. Turbulent winds inside the storm cause particles to rub against one another, causing electrons to be stripped off, making the particles either negatively or positively charged.

The charges get grouped in the cloud, often with negatively charged particles near the bottom of the cloud and positively charged particles up high. This is an electric field and, because air is a good insulator, the electrical fields become incredibly strong. Eventually, lightning occurs to neutralize the electric field.

The type of lightning in a thundersnow storm is the cloud-to-cloud variety, as opposed to lightning bolts that travel to the ground. At night, the lightning in a thundersnow may appear bright, as the light reflects off the snowflakes in the storm.

Thunder always accompanies lightning, but in thundersnow storms the sound is muffled by the snowfall. While the thunder from a summertime thunderstorm might be heard many miles away, the thunder during a thundersnow event will be heard only within 2 to 3 miles of the lightning. The thunder is more of a rumble than the booming sounds often heard in summertime storms.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Phenomena, Severe Weather

Comments Off on Can a snowstorm have lightning?

Was our recent snowfall typical for a Madison winter?

Posted on December 12, 2022 by WeatherGuys Editor

Our first substantial snowfall of the season visited Madison on Friday morning as a period of moderate to heavy snow fell from around 7 to 9:45 a.m.

Scenes from the Yahara River in Madison Wisconsin during the December 9th snowfall.
Photo credit: M. Mooney

In the end, we accumulated 4.4 inches of heavy wet snow timed perfectly to snarl the morning commute.

Friday’s event was just the fourth snowfall of 4 inches or more since the COVID-19 pandemic started in 2020. We wondered how often a cold season is visited by a storm with that much snow.

Using records from Dane County Airport as well as the prior site of the Madison airport, it turns out that 209 such snowfalls have occurred since 1939 — 75 of them since 2000. Interestingly, 20 of the last 83 winters have had only one 4-inch or greater snowfall, and seven others have passed without a single event of that magnitude.

That means that just shy of one-third of the time, a winter season in Madison comes along in which, at most, only one snowfall of 4 inches or more occurs.

That may seem hard to believe given that our seasonal snowfall averages 50 inches each year. However, the majority of a seasonal snow total in Madison is often made up of a series of quite small amounts.

Though the average number of days on which at least 1 inch of snow accumulation occurs in Madison varies enormously from year to year, the long-term average over the same interval has increased from roughly 12 days each winter to about 15. The record is 27 such days in 2007-08 — when we set the all-time seasonal snowfall record of 101.4 inches — while the record minimum number is just 2 in 1967-68.

Thus, it is hard to tell whether what we experienced on Friday morning will be a common occurrence this winter.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Meteorology, Seasons

Comments Off on Was our recent snowfall typical for a Madison winter?

What does a warm fall portend about winter?

Posted on December 5, 2022 by WeatherGuys Editor

Most of the weather experts we know have rated this fall’s weather as reasonably benign in our region. The past month’s average temperature here in Madison was 1.9 degrees above normal, which rounded out a fall season (September through November) that was 1.13 degrees above normal overall – a measurement that supports this widely held opinion.

NWS climate statistics for Madison and Milwaukee Wisconsin for Autumn 2022

At about 1 mile above sea-level, the areal extent of cold air (minus 5 centigrade, or 23 degrees Fahrenheit) over the entire Northern Hemisphere was the eighth smallest in the last 75 years over the September-November period.

This reflects the fact that the most locations in the Northern Hemisphere were on the warm side of their averages this fall.

When one lists all September-November periods since 1948 from “warmest” (number 1) to “coldest” (number 74) by this measure, one creates what is known as a rank list. The same can be done with the areal extent of the cold air during the winter months (December through February).

In the last 73 cold seasons through February 2022, 38 winters were ranked warmer than their corresponding falls, while 35 were colder.

It is not yet known what circumstances might conspire to change the nature of the cold season so abruptly some years, but it is an interesting question whose answer may bear on the ability to make more accurate seasonal forecasts in the future.

As it stands, it is not really possible to tell if the December-to-February stretch this winter will turn sharply colder after our remarkably warm fall.

Winter Temperature Outlook from NOAA

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, Seasons

Comments Off on What does a warm fall portend about winter?