Just how warm has this winter been?

Posted on February 13, 2012 by Weather Guys Editor

This winter began much warmer than normal, but where does this year’s mildness rank all-time? You might be surprised to learn that although we are in the top 10 warmest starts to winter, we are not really close to the top. In fact, we are experiencing only the sixth warmest Dec. 1-Feb. 8 in Madison history with an average temperature of 28.3 degrees Fahrenheit during that stretch.

Only one other year within the last 10 makes the same top 10 list, and that was 2001-2002, which came in at No. 3 with an average Dec. 1- Feb. 8 temperature of 28.9 F.

The all-time warmest such period occurred in 1877-1878, when the average temperature was 31.9 F — incredibly warm. That winter went on to be the warmest (December, January, February) ever in Madison with a daily average temperature of 32 F. In fact, of the 12 winters that made the top 10 list for Dec. 1 — Feb. 8 (there were three tied at 10th place), nine of them also made the top 10 list for warmest winter in Madison.

Very warm Februarys in 1931, 1954, and 1998 (when Lake Mendota was ice free on Feb. 28, the only February end to the ice season on record) put those winters in the top 10 for warmest winter even though they did not get off to as warm a start as this year has.

So, it seems likely that our winter will end up being one of the warmest but not even close to the warmest.

Category: Seasons
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What is the concept of heating degree-days?

Posted on February 6, 2012 by Weather Guys Editor

Each degree that the mean temperature is below 65 degrees is one heating degree-day. So, if today’s average temperature is 55 degrees, that is 10 heating degree-days.

Engineers determined that when the mean outdoor temperature drops below 65 degrees, most buildings require heating to maintain an indoor temperature of 70 degrees. In an effort to make weather data easy to use in planning, they developed this definition to estimate fuel consumption needs. Fuel distributors often use this index to schedule home deliveries. Since energy consumption in homes derives primarily from natural gas and electricity, these utilities predict power demands by adding up this index over time.

The amount of heat required to maintain a building’s temperature is proportional to the accumulated heating degree-days. So, heating degree-day totals are usually reported each day, as well as a total for the season. This allows us to quickly judge whether the season is above, below or near normal.

Over a year, northern Wisconsin has about 9,000 heating degree-days, while southern Wisconsin has about 7,000 heating degree-days. Over a year the indoor heating requirements for southern Wisconsin are about 7/9ths that of northern Wisconsin.

This past January most of southern Wisconsin had temperatures that were 4 degrees above normal while December’s temperatures were more than 5 degrees above the mean. With those warm temperatures, Madison’s cumulative heating degree-days this winter is a few hundred below normal.

Category: Climate
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What is Groundhog Day and do the forecasts work?

Posted on January 30, 2012 by Weather Guys Editor

Long before computers, the Weather Channel and the Internet, humans needed weather forecasts. Farmers and sailors particularly needed to know if storms were approaching. Over time, various folklore forecasts, often in the form of short rhymes, were devised and passed down through the generations. Although memorable, the folklore forecasts are of uneven quality — some good, others bad.

Groundhog Day is an example of predicting the weather based on folklore. If the groundhog comes out of its hole and sees its shadow, we are in store for 40 more days of winter. Of course, after Feb. 2, there are only 47 days left of astronomical winter — which ends on or about March 21.

The roots of Groundhog Day go back to the sixth century. Feb. 2 is 40 days after Christmas and is known as Candlemas. On this day, candles that are used for the rest of the year are blessed. This is also about the mid-point in winter, in meteorological not astronomical terms. The forecast rhyme goes:

If Candlemas Day is bright and clear

There’ll be two winters in that year;

But if Candlemas Day is mild or brings rain,

Winter is gone and will not come again.

If the day is bright and clear, the groundhog “sees” his shadow and we have more winter. Of course, the weather conditions on Feb. 2 at a single location — like Punxsutawney, Pa., or Sun Prairie — tell us very little about the weather for the rest of the winter season.

As for accuracy, the predictions are correct about 40 percent of the time — vastly inferior to what is delivered by modern science.

Right or wrong, they are fun community celebrations.

Category: Meteorology
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How do you measure snow accumulation in high winds?

Posted on January 23, 2012 by Weather Guys Editor

Accurate and precise measurement of snow accumulation is a difficult task. The measurement tools are simple: a ruler or yardstick that measures in inches and tenths of an inch.

The trick in measuring snow consistently is simply finding a good place to measure and a firm surface for your ruler to set on. It is recommended to use a snow board, which is a square piece of wood 16 inches on a side and painted white. Other surface options are wooden decks, picnic tables and cars.

Your measurement location should be 20 to 30 feet away from the house with an unobstructed view of the sky. Sidewalks are not recommended as good sites as they tend to accelerate melting of the snow. Neither is grass a good site as snow tends to sit up on top of the blades of grass, while the ruler goes down to the ground. With this setup, measuring new snow accumulation is straightforward, if there’s no wind. When the wind blows and the snow drifts, measuring snow is a challenge.

To deal with drifting snow, make measurements at a various places in your yard and then average them to get what is considered a representative measurement.

Snow is also measured with the standard rain gauge — an 8-inch diameter cylinder that collects precipitation. In winter the gauge can be equipped with a known amount of antifreeze so that the snow melts when it enters. This measurement yields the liquid water equivalent of the snowfall.

Category: Meteorology
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Do the tropics influence the weather in Madison?

Posted on January 17, 2012 by Weather Guys Editor

It may seem implausible at first glance, but current research in the Department of Atmospheric and Oceanic Sciences at UW-Madison is exploring connections between tropical cyclones (hurricanes) near the Philippines and extreme weather events in southern Wisconsin.

The connection appears to derive from unusual jet stream structures forced by the outflow from the hurricane at high levels in the atmosphere.

Hurricanes are well-organized collections of tropical thunderstorms that take warm, moist air from the lowest levels of the tropical atmosphere and very quickly thrust it nine miles or more above the surface. This rapid upward motion substantially distorts the shape of the tropopause which, in turn, intensifies the normal jet stream located on the northern periphery of the vast hurricane outflow.

The intensified jet, often a very long-lived structure, can become a major weather event produced in the central United States several days later. Currently, we think this type of connection is most likely to occur in spring and fall.

Our incredible windstorm in October 2010 was a clear example of this tropical connection to Wisconsin weather. We are just beginning to explore these ideas in detail and will keep you informed of our results.

Category: Tropical
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