How often do the ‘gales of November’ come early?

Posted on November 7, 2011 by Weather Guys Editor

Some historic storms have occurred around Veterans Day (formally known as Armistice Day). Friday marks the centennial of a winter storm that blew across the Midwest on “11-11-11.”

The storm developed over southern Wyoming the morning of Nov. 10, 1911, and traveled east, reaching southwestern Iowa by the morning of the 11th. The storm’s center traveled northeast across Wisconsin, reaching central Wisconsin by noon and Michigan’s Upper Peninsula by evening.

An F-4 tornado on the five-category Fujita Scale traveled to the northeast across southwestern Rock County, leveling farms, killing nine people and injuring 50. Within an hour of the tornado, survivors were digging out in blizzard conditions and near-zero temperatures.

The rapid drop in temperature was impressive. At the U.S. Weather Bureau’s Madison office, the temperature at noon on the 11th reached 70 degrees, but by midnight, the temperature fell to 20 degrees. Morning and afternoon thunderstorms gave way to snow flurries.

Another memorable storm is the Armistice Day Storm that ravaged the Upper Great Lakes region Nov. 11 and 12, 1940. This storm took down the Tacoma Narrows Bridge that spanned Puget Sound before heading to the Midwest. By the time this storm ended, it killed more than 150 people, sank at least 3 ships, stranded hundreds of train passengers and isolated Midwestern towns with 20-foot snow drifts.

On Nov. 10, 1975, a storm developed that was a near repeat of the 1940 Armistice Day Storm. This storm sent the freighter SS Edmund Fitzgerald to the bottom of Lake Superior with all 29 hands. Lightfoot’s 1976 ballad helped make the incident famous disaster in Great Lakes shipping history.

All this history suggests we should get ready for a potentially exciting month of weather.

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What is typical Halloween weather?

Posted on October 31, 2011 by Weather Guys Editor

We tend to remember those Halloweens with bad weather. Slogging through rain or snow in costumes with trick-or-treat bags is tough. But according to Dr. Ed Hopkins of the Wisconsin State Climatology Office, in the last 30 years (1981-2010), Madison has had only 10 Halloween days when measurable precipitation (0.01 inches or greater) fell, which translates to a probability of 33 percent that rain falls on that date. Halloween 1985 was memorable in Madison for its 1.05 inches of rain. The most precipitation for Oct. 31 was 1.21 inches in 1960.

Of greater interest is the amount of rain that falls during the late afternoon and early evening when most trick-or-treaters are making their rounds. In 1979, 0.31 inches of rain fell from about 4 p.m. until 7 p.m., of which nearly a quarter of an inch fell during the hour between 4 p.m. and 5 p.m. Since 1996, little significant rain has fallen during the afternoon and evening.

Air temperatures have varied widely during the late afternoon and early evening hours, including one Halloween low of 28 degrees in 1996. Over the last decade, Madison trick-or-treaters have experienced only two holidays with the temperature near freezing. While trace amounts of snow fell in 1993 and 1995, no measurable snow (0.1 inches or more) has fallen on Halloween since records have been kept at the Dane County Regional Airport.

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Why was it so windy last week?

Posted on October 24, 2011 by Weather Guys Editor

The wind is air in motion. Moving anything requires a force. Violent destructive winds, as well as gentle summer breezes, result from a complex interplay of different forces. One of these forces results from a pressure gradient, or how fast pressure changes over distance. Strong winds almost always result from large pressure gradients. Recently, southern Wisconsin has been under the influence of a weather pattern that has strong pressure gradients, and thus strong winds.

Near the Earth’s surface, the friction plays a pivotal role in wind, acting to slow the wind. Over the open lakes the wind will be faster than through a stand of trees, where it will be slowed by friction. In the presence of buildings, the air can be funneled between buildings and pick up speed.

The air flows from high atmospheric pressures to low pressures. The Coriolis force pulls the wind to the right so that winds blow counterclockwise around lows and clockwise around highs in the Northern Hemisphere. Friction slows down the wind and weakens the Coriolis force. So, if you stand with your back to the wind, and then turn about 30 percent to your right, low pressure will be on your left-hand side

Thunderstorms also can cause strong winds. Thunderstorms have upward air motions, called updrafts. There are also downdrafts, or sinking air in a storm. Such downdrafts carry air from high elevations in the atmosphere rapidly to the ground. Since wind speed is nearly always much larger at high elevations, the downdrafts carry very high-velocity air to the surface creating the winds of more than 100 mph.

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What is the status of the ozone hole?

Posted on October 17, 2011 by Weather Guys Editor

The winter atmosphere above Antarctica is very cold. The cold temperatures result in a temperature gradient between the South Pole and the Southern Hemisphere middle latitudes.

These temperature gradients lead to a belt of strong westerly stratospheric winds that encircle the South Pole region. These strong winds prevent the transport of warm equatorial air to the polar latitudes.

The extremely cold temperatures confined inside the ring of strong winds help to form unique types of clouds called Polar Stratospheric Clouds, or PSC. In the southern hemisphere winter, chemical reactions on the particles composing PSCs remove the chlorine from atmospheric compounds such as man-made CFCs. When the sun returns to the Antarctic stratosphere in the spring, sunlight splits the chlorine molecules into highly reactive chlorine atoms and ozone is rapidly depleted. Destruction is so rapid over the South Pole region in the Southern Hemisphere springtime that it has been termed a “hole in the ozone layer,” and it is seen every October.

Ozone depletion now is widespread over Antarctica. The Antarctic ozone hole varies in size each year. Current measurements indicate the size of the ozone hole is about five times the size of California. This is anomalously large in comparison to recent years.

Representatives from 23 nations met in 1987 in Montreal to address concerns of ozone depletion by CFCs. The resulting Montreal Protocol, and subsequent international agreements have limited usage and production of CFCs. Although the use of these chemicals has declined, their concentrations in the atmosphere have not responded as quickly. This is because CFCs are very stable molecules and will stay in the atmosphere for nearly 100 years after their release before they decompose. Despite this waiting period, the Montreal Protocol successfully put a stop to the rapid ozone loss that was occurring and has set the stage for recovery of this important chemical.

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How common is beautiful, sunny October?

Posted on October 10, 2011 by Weather Guys Editor

After a fairly dreary end of September, October has dawned with some gorgeous fall weather in our area. In fact, it appears as though we will rack up 11 straight days of not even a trace of precipitation in Madison to begin October 2011. One might wonder how common such a long string of rain-free, sunny days is in a Madison October. A very limited look back into the recent past suggests it is not at all common.

The longest such streak in 2006 occurred from October 5-9 during which the average high temperature was 64.4 degrees – perfectly average for this time of year. A warmer five-day streak occurred in October 2007 (3rd – 7th) when the average high was 81 degrees – more than 16 degrees above normal.

Slightly less impressive was the four-day streak in October 2008 in which the average high was 74.8 degrees, just a bit more than 6 degrees above normal. We were well into the middle of October 2009 before we had even a three-day precipitation-free streak (17th – 19th). During this period the average high temperature was 56 degrees, almost 4 degrees below normal. It is worth noting that this short streak occurred after the first snowflakes had fallen in Madison.

October 2010 was legendary for the major windstorm that occurred on the 26th. It also makes the record books for logging the longest rain-free streak in this short record at 17 straight days (3rd – 19th). During that period the average high was 69.9 degrees, 3 degrees above normal. So, enjoy this incredible string of beautiful fall days; recent history suggests it is pretty unusual.

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