What was that stuff that fell on Wednesday and Thursday?

Posted on April 11, 2022 by WeatherGuys Editor
Graupel from Madison (Image credit: SSEC)

Last Wednesday and Thursday many locations in southern Wisconsin experienced snow squalls in which the falling precipitation was momentarily quite intense.

This event was an example of shallow convection — as opposed to the deep convection of summertime thunderstorms.

This shallow convection was spawned by a conspiracy of circumstances occurring at different levels in the atmosphere. Near the surface, the early morning sunshine led to an increase in the near-surface air temperature, while at about 3 miles above the ground the air was cooling rapidly as colder air at that level moved southward over the region.

Warming the surface and cooling the air at upper levels reduces the stability and encourages vigorous upward vertical motion and cloud production. What fell out of the sky was varied depending on your location, but many places saw snow grains, snow pellets or graupel.

These particles are frozen hydrometeors that maintain their original crystalline structure. When a preexisting piece of non-crystalline ice falls below the level at which the temperature is at or below 32 degrees, the freezing level, that particle accretes liquid water. When that particle is subsequently forced above the freezing level, that liquid coating freezes. A hailstone is produced when this process occurs several times before the particle is massive enough to fall to the ground.

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, Severe Weather

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How common is April snow in Madison?

Posted on April 4, 2022 by WeatherGuys Editor

The recent late March and early April snow in Madison may have stirred memories of, or raised questions about, past such late winter/early spring snows.

A large snow sculpture graces State Street Mall the day after Madison saw 7.2 inches of snow on April 18, 2018, more than doubling that date’s previous record from 1912. (Credit: State Journal archives)

Perhaps unsurprisingly to Madisonians, April snow is by no means unusual here in town. Thirty Madison Aprils — out of 84 — since 1939 have had at least one 1-inch snowfall event.

The greatest April snowfall ever in Madison is the 12.9 inches that fell on April 9, 1973 – the most substantial event in a month that tallied 17.4 inches for the entire month. More recently, we have had two Aprils in which more than 10 inches of total snow fell — April 1982 (10.3 inches) and April 2018 (13.5 inches, with 7.2 inches of that coming on April 18 of that year). Coming up just short of the 10-inch monthly total was April 1994, in which 9.7 inches fell, with a remarkable 7.8 inches falling on April 30.

This winter we have struggled to accumulate much snow in Madison with a seasonal total as of Sunday of 29.9 inches, the first winter since 1980-81 to total less than 30 inches. This meager total is a result of 0.6 inches in November, 6.5 inches in December, 9.1 inches in January, 5.4 inches in February, a perfectly average 7 inches in March and 1.3 inches in April.

In 1972-73, the snowiest month of the entire cold season was April. As boring as this cold season has been with regard to snowfall, there is still an outside chance that we could become only the second winter in the past 50 years to have its snowiest month be April.

We had some measurable snow on Saturday and in the coming week we have a chance to see more. Only three Aprils in the past 40 years have had as much as 9.2 inches of snow in the month — so it is not an easy task — but if we can somehow manage to do it in Madison this April, we will join that elite list of winter seasons.

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: History, Seasons

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Where in the U.S. are the most weather warnings issued?

Posted on March 28, 2022 by WeatherGuys Editor
The 10 National Weather Service offices that issued the most weather warnings from 2012 through 2021. (Image credit: Jonathan Erdman, Weather Underground)

Certain meteorological conditions may pose threats to life and property. Under these conditions, the National Weather Service (NWS) issues advisories, weather watches and weather warnings.

A weather watch informs us that current atmospheric conditions are favorable for hazardous weather. When the hazardous weather will soon occur in an area, a warning is issued. Weather watches and warnings are issued for a wide variety of hazardous weather, including tornadoes, hurricanes, severe thunderstorms, winter storms, high wind speeds and flooding.

The NWS issues weather watches and warnings under specific weather conditions. The term “watch” implies that you should be aware that a weather hazard may develop in your area. The term “warning” means the hazard is developing in your area. You should take immediate action in the event of a warning.

Pinpointing the location of hazardous weather in advance is extremely difficult. For this reason, watches are usually issued for large geographic areas. There are 122 NWS forecast offices responsible for issuing forecasts and warnings for their area. Wisconsin has three NWS offices.

Jonathan Erdman of the Weather Channel recently compiled over 300,000 NWS warnings issued in the U.S. over the latest 10-year period from 2012 through 2021. His data show that the Norman, Oklahoma, office issued the most with 9,103 warnings. Of those, 6,926 severe thunderstorm warnings were issued and 667 were for tornados. Jackson, Mississippi, ranked second with 7,639 warnings, including 816 tornado warnings and 1,240 flash flood warnings.

In Wisconsin, the La Crosse office ranked 65th nationally, having issued 2,193 warnings during this 10-year period. Most were severe thunderstorm warnings (1,160), followed by flooding (563). There were 67 winter storm warnings and 9 blizzard warnings. The Milwaukee office ranked 79th, issuing 1,631 warnings. Of those, 904 were for severe thunderstorms and 85 for tornados. Milwaukee issued 485 flood warnings. The Green Bay office ranked 86th with 1,271 warnings.

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

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Is it Spring Time?

Posted on March 21, 2022 by WeatherGuys Editor

Spring marks the transition from winter to summer. In astronomical terms, the date that marks the spring in the Northern Hemisphere is the vernal equinox.

The straight line of the terminator as seen from space conveys equal day and equal night worldwide.

This year the spring equinox occurred on at 10:33 a.m. Sunday. This is the first day in 2022 that the sun is above the horizon for all locations on Earth for 12 hours. The second time will be at the fall equinox.

The sun rises due east and sets due west at the equinox, no matter where you live. The length of time it takes for the sun to sink below the horizon is shortest during the equinoxes. Looking at Earth from space at an equinox, you’ll see the Earth’s terminator – the dividing line between day and night – is vertical and connects the north and south poles.

The tilt of the Earth’s axis is responsible for the seasonal variation in the amount of solar energy distributed at the top of the atmosphere. The Earth’s axis is tilted at an angle of 23.5 degrees from its orbital plane. Because the Earth’s axis always points toward the North Star, the orientation of the Earth’s axis to the sun is always changing as the Earth orbits around the sun.

As this orientation changes throughout the year, so does the distribution of sunlight on the Earth’s surface at any given latitude and this is the cause of the seasons. On the equinoxes the axis is not pointed at or away from the sun, which results in all areas experiencing a little more than 12 hours of daylight.

Besides astronomy, there are other ways to mark spring. Meteorologists refer to March, April and May as the three months of spring. Phenological signs of spring can include the blooming of cherry trees or the return of specific migrating birds. Some commuters mark spring by the increase in the number of potholes.

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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Is mathematical pi used in meteorology?

Posted on March 14, 2022 by WeatherGuys Editor
Pi is fundamental to determining satellites’ orbit around Earth. Credit: NOAA

The ratio of a circle’s circumference to its diameter is a constant value. The size of the circle does not matter; this ratio is always the same value and is called pi.

The existence of this constant was known by the Babylonians and the Egyptians dating back to at least 2000 B.C. The numerical value is represented by the Greek letter for p, or π.

The first three digits of pi are 3.14, so today — March 14 — is often celebrated as pi day with pie. The value of π turns out to be an irrational number: Its decimal form neither ends nor becomes repetitive. The exact value is unknowable. About a decade ago, a researcher calculated the value to 2.7 trillion digits.

You might have first encountered pi in early classes on geometry or trigonometry. You learned that pi, along with the radius, is used to calculate the circumference of a circle, the area of a circle or the volume of a sphere. Since cloud droplets are near spherical, pi is used to calculation how much water is in a cloud knowing the number and size of the drops.

Because of pi’s relationship to the circle and to spherical coordinate systems, it appears in many formulas in many areas of mathematics and physics. Meteorology is a physical science, steeped in math, so we inevitably encounter pi.

Pi appears in the field of electromagnetics, which is used to describe how light travels through the atmosphere. It is used in equations that describe why the sky is blue.

Pi appears in equations describing processes that are periodic, and therefore is intimately associated with waves. Atmospheric patterns and the movement of the winds can be described as waves. So, pi appears in mathematical equations that describe the movement of weather systems. The waviness pattern of the jet stream can be described by its “meandering ratio,” which includes the value of pi.

A world without pi, and pie, would be very different.

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: History, Meteorology

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