How did Madison get a foot of snow on Saturday?

The 12.1 inches of snow that fell over Madison in the first nine hours of Saturday morning was surely a surprise to many residents while setting the all-time monthly record.

Forecasts made through the late afternoon on Friday, consistent with those made on Wednesday and Thursday, were suggesting that the heaviest band of snow would run southwestward from Racine/Kenosha back to northwestern Illinois and leave Madison with an inch or two.

GOES East Visible satellite imagery from March 25th paired with Day Cloud Phase distinction RGB imagery showing where the heaviest snow fell and a sharp cutoff where no snow occurred.

The forecast was in error not because the heavy snow band was not foreseen, but rather because the band ended up occurring farther northwestward than the computer forecast models had predicted.

This error underscores how hard it is to pinpoint the location of heavy precipitation bands in winter storms, especially rather weak winter storms like the one that hit on Saturday morning.

Even such weak storms have circulations that impact millions of square kilometers, while the precipitation bands impact only a small fraction of that area. In this case, the important structures and dynamics that conspired to produce the snow were well represented in the computer forecasts, but their location was different than the forecasted location for reasons that can be determined only in an after-the-fact investigation of the event.

Though much of the stunning progress in forecasting that has occurred in the past half century has been a result of relentless advances in theory, observational capabilities and the expanding power of computers, an often overlooked ingredient is the grueling detective work that ensues in the aftermath of such forecast errors. Meteorologists undertake “case studies” of such incidents to determine what physical factors were responsible for the weather as it actually occurred and also to better understand how and why the computer models went astray.

This difficult but necessary work informs the future development of these forecast models with the hope of minimizing future forecast errors. Thus, though such incidents as our Saturday snow might inspire the cynical view that weather forecasting is not a scientific endeavor, the exact opposite is actually true.

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

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What is the spring equinox?

The spring equinox marks the beginning of the spring season in the Northern Hemisphere. Also called the vernal equinox, it is the time of year when the sun rises due east and sets due west, no matter where you live. Earth’s axis of spin is tilted at an angle of 23.5 degrees from its orbital plane and always points to the North Star. The orientation of Earth’s axis with respect to the sun changes throughout the year and is the fundamental cause of our seasons.

On the equinoxes, the axis is not pointed at or away from the sun. This results in all areas on Earth experiencing 12 hours of direct sunlight. On the equinox and at the equator, the sun appears directly overhead at noon.

Satellite view of Earth on March 20th 2023, Spring Equinox in the Northern Hemisphere.

The equinoxes occur when the sun’s rays strike the equator at noon at an angle of 90 degrees. During the spring and fall equinoxes, the sun is above the horizon for all locations on Earth for 12 hours. During the vernal equinox, the sun is moving from south to north as it crosses above the equator.

For a long time, people have marked the changing of seasons and the sun’s track across our skies. Stonehenge was constructed in a way that marks its relation to the Sun’s position in the sky and in different seasons. At Machu Picchu, stones mark the four cardinal directions so that exactly at noon on the equinox, no shadow is cast. In Chaco Canyon, the ancestral Puebloan people carved spiral designs into rock that track the seasons.

The sun crosses the equator today at 4:24 p.m. Central Daylight Time, a good time to go outside and celebrate the event.

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, Seasons

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How are storm warnings defined?

Weather watches and warnings are issued by the National Weather Service under specific weather conditions.

A watch means that you should be aware that a weather hazard may develop in your area. A warning message is when the hazard is developing in your area.

When a warning occurs, you should take immediate action as suggested by the NWS. Warnings are based on observations of hazardous weather and are thus often issued for smaller areas. An advisory is a less urgent statement issued to raise awareness of a coming weather event that may cause some inconvenience.

As for winter storms, the NWS defines the following:

  • Winter storm watch: A watch means that severe winter conditions, such as heavy snow or ice, may affect your area, but where, when and how much snow are still uncertain. A watch is intended to provide enough lead time for you to prepare and thus is issued 12 to 36 hours before the predicted event.
  • Winter storm warning: The NWS issues a warning when there is a forecast of a significant winter weather event including snow, ice, sleet, or blowing snow, or a combination of these hazards that exceed locally defined criteria.
  • Winter weather advisories inform you that winter weather conditions are expected to cause significant inconveniences that may be hazardous. If caution is exercised, advisory situations should not become life-threatening.
  • Blizzard warnings: These let you know that snow and strong winds will combine to produce a blinding snow (near zero visibility), deep drifts and life-threatening wind chill.
Weather Guy Steve Ackerman (3rd from right) attended the UW-Madison StormReady ceremony in 2015. UW Chancellor Becky Blank is holding the StormReady sign with NWS Director Louis Uccellini. The designation of the University was a collaborative effort by UW Emergency Management, Campus Police, CIMSS, SSEC, AOS, and the NWS.

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: Severe Weather, Weather Dangers

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How did this year’s winter rank?

Meteorological winter in the Northern Hemisphere is often defined as the three months of December, January and February. The just-ended winter of 2022-23 was notable in a number of ways.

First, here in Madison we started with a chilly month of December during which we averaged 0.8 degrees below normal. This was also the only month of the season in which we had a day with a high temperature below zero — minus 3 on Dec. 23.

January was 7.6 degrees above normal and was followed by a February that was 4.4 degrees above normal. Thus, overall, December, January and February were 3.71 degrees above normal in Madison this winter.

Winter climate statistics for Madison, Wisconsin. Credit: NWS

On the hemispheric scale, we can measure the areal extent of air colder than minus 5 degrees Celsius — 23 degrees Fahrenheit — at about 1 mile above sea-level (formally, at a level where the atmospheric pressure is 850 millibars) with records back to 1948-49. This year turned out to have the 16th smallest average areal extent over December, January and February — thus, by this measure, it was the 16th warmest winter in the last 75 years.

In fact, of the top 20 warmest winters measured this way, 17 have come since 2000-01. This is not a weird coincidence but instead is part of a longer trend that unequivocally reveals a slow but systematic warming of the planet. It is well past time that we as a society stop arguing about what is now settled fact — that global warming is real and ongoing — and start spending our collective intellectual energy on deciding how best to confront this reality.

Trends in average surface temperature from 1993-2022. Overall, land areas warmed faster than oceans. The most extreme warming (darkest red) was in the northern hemisphere. Data from NOAA NCEI.

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

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How much energy goes into making snow?

Since Dec. 1, Madison and Dane County have received approximately 40 inches of snow — 3 inches above normal for that span.

Snow is a form of solid water, and water is the only substance that occurs naturally in all three phases — solid, liquid and invisible gas — in the Earth’s atmosphere.

Snowflake (Photo credit: Wilson Bentley Snowflake Collection)

Of course, that means that the 40 inches of snow began as the equivalent amount of water in the invisible vapor, or gas, phase before being transformed into solid water.

Everyone knows that melting ice into liquid water requires energy. Not surprisingly, energy is also required to transform liquid water into water vapor, the familiar process of evaporation.

The particular amounts of energy needed to accomplish these changes of phase are known as latent heats — the latent heat of melting for the first one and the latent heat of evaporation for the second.

When a cloud of invisible water vapor condenses into a puddle of liquid water, the latent heat of condensation (equal to the latent heat of evaporation) is released to the environment. Also, when that puddle freezes into ice, the latent heat of fusion (equal to the latent heat of melting) is similarly released, incoherently, to the environment.

Since we know the depth of liquid equivalent precipitation involved in delivering us 40 inches of snow since Dec. 1, the area of Dane County, and the latent heats of condensation and fusion, we can calculate how much energy has been released to the atmosphere in the production of that much snow. Without providing the details of the calculation, we can report that the amount of energy involved could power the entire Madison metro area for approximately 8.8 years. Clearly, there are huge amounts of energy involved.

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, Seasons

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