How long has Milwaukee gone without snow?

Posted on December 20, 2012 by Weather Guys Editor

By Sunday, Dec. 9, Milwaukee had gone 280 consecutive days without measurable snowfall (defined as 0.1 inches or more of snow). That set the all-time record long streak for no snow in Milwaukee’s weather history. By the time you read this article, the streak will have continued into its 288th day — an amazing way to approach the end of a truly unusual, and in many ways, unsettling year of weather in our state.

The last time Milwaukee had measurable snow was on March 4, 2012, when nine-tenths of an inch fell. That same storm was our only snowstorm of the year in Madison last year that dropped more than 3 inches The latest date for the first measurable snow in a winter season in Milwaukee’s history is Dec. 26, 1888 when one-tenth of an inch of snow fell. The latest first 1-inch or greater snowfall was on Jan. 20, 1889 (the same winter) when 3.5 inches of snow finally fell.

Madison’s all-time longest snowless streak, surprisingly longer than Milwaukee’s, is 295 days and stretched from Feb. 6 to Nov. 28, 1902. This year we only got to 246 days as one-tenth of an inch of snow fell on Nov. 6.

The latest date for the first measurable snow in a winter season in Madison’s history is Dec. 15, 1999 when one-tenth of an inch of snow fell. The latest first 1-inch or greater snowfall was on Dec. 23, 2001. This year, we aren’t challenging any of those records.

Category: Climate
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How did we set an all-time high temperature record under cloudy skies?

Posted on December 10, 2012 by Weather Guys Editor

On Dec. 3 the high temperature of 65 degrees F was the all-time highest December temperature ever recorded in Madison. Among the interesting aspects of this record high was the fact that the entire day was cloudy so local sunshine had no role in achieving this record. This prompts an interesting question — what processes can contribute to changing the temperature at a location?

The answer is that there are basically two. Everyone knows that on a sunny, windless day, the fact that the sun is out always contributes to warming the air temperature. At night, in the absence of sunshine, the air cools. These changes are a result of radiative transfer, one of the two mechanisms.

The other mechanism is called advection and it involves the importation of air from remote locations by the action of the horizontal wind. Last Monday, the winds in Madison were blowing strongly from the southwest all day. It was much warmer, as is usually the case, at locations to our southwest. Therefore, the southwesterly winds were dragging that warmer air toward us all day and we reached our daily high temperature at 5:25 p.m., more than an hour after sunset.

The interaction of these mechanisms becomes a high-profile topic as we approach winter. The long nights of arctic winter provide a perfect environment for air to cool nearly continuously, by radiation, building huge masses of really frigid air to our north. Weather systems can tap that cold air and send it southward on northerly winds during periods of strong cold air advection that can drive the temperatures down even on sunny winter days.

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Is severe weather common in Italy?

Posted on December 3, 2012 by Weather Guys Editor

Since we live in a country with a famous Tornado Alley right in its center, it is easy to forget that severe weather can occur, though with substantially less frequency, in other parts of the world.

A recent example of this is the flooding in Venice, Italy in early November and the strong tornado that roared through Teranto, Italy on Nov. 28.

In both cases, strong thunderstorms were involved. Just as in our Tornado Alley, the strongest thunderstorms result from instability in the atmosphere combined with upward vertical motion of the air. The particular form of instability that leads to severe thunderstorms is known as convective instability and it results from dry air sitting atop moist air.

In Tornado Alley the dry air comes off of the elevated Mexican Plateau and the moist air from the Gulf of Mexico. Along the Adriatic Coast of Italy, the dry air comes from mid-levels over the Sahara Desert and the moist air comes from over the southern Mediterranean Sea. When these ingredients are assembled by a strong cyclone in the central Mediterranean, it can produce extreme rains in northeastern Italy and even tornadic activity.

Because these circumstances are most likely to get organized in the late fall, the limited tornado season that does occur in Italy occurs in October and November. It would be interesting to know how many merchant vessels in the long history of Venice have gone down in such autumn storms.

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How are clouds named?

Posted on November 27, 2012 by Weather Guys Editor

In 1803, British pharmacist and chemist Luke Howard devised a classification system for clouds. It has proved so successful that meteorologists have used Howard’s system ever since, with minor modifications. According to his system, clouds are given Latin names corresponding to their appearance — layered or convective — and their altitude. Clouds are also categorized based on whether or not they are precipitating.

Layered clouds are much wider than they are tall. They generally have flat bases and tops and can extend from horizon to horizon. The Latin word “stratus” describes the layered cloud category.

Convective clouds are as tall, or taller, than they are wide. These clouds look lumpy and piled up, like a cauliflower. Convective cloud types are indicated by the root word “cumulo,” which means “heap” in Latin. Convective clouds may become very tall and are rounded on top.

Clouds are also classified by their altitude and their ability to create precipitation. The root word “cirro” (meaning “curl”) describes a high cloud that is usually composed of wispy ice crystals. The Latin word “alto” (“high”) indicates a cloud in the middle of the troposphere that is below the high cirro-type clouds. The prefix or suffix “nimbus” (“rain”) denotes a cloud that is causing precipitation.

Using the combination of appearance, altitude, and ability to make precipitation, a wide range of cloud types can be identified. The 10 basic cloud types are cirrus, cirrostratus, cirrocumulus, altostratus, altocumulus, cumulus, stratus, stratocumulus, nimbostratus, and cumulonimbus.

Category: Meteorology
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What was the ring around the moon last month?

Posted on November 20, 2012 by Weather Guys Editor

As the remnants of Superstorm Sandy approached us on Oct. 29, people in Wisconsin observed a halo on two consecutive nights. These halos resulted from the ice clouds generated from the storm.

A halo is a whitish ring that encircles but does not touch the sun or moon. It is an optical phenomenon that owes its existence to the bending of light by ice crystals, much like the “rainbow crystals” you may hang in your windows.

The most commonly observed halo is the 22 degree halo. This halo encircles the moon or sun at about a hand’s width from the center of the moon, if your arm is fully extended. Small column-like ice crystals form the halo. Light rays enter a crystal, bend or refract, and then refract again as they exit the crystal. Because the crystals are randomly oriented in space, there are many different directions from which light rays can enter the crystals. More light rays are refracted at this 22-degree angle than at any other, producing the concentration of light known as the halo.

If you were lucky, you may have seen shiny, colored regions at either side of the moon. These are called moondogs, and are another optical effect caused by refraction. Moondogs appear because hexagonal ice crystals in the high clouds tend to drift downward with their flat bases parallel to the ground. The sunlight passing through the crystal refracts sideways.

Category: Phenomena
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