When will Spring arrive?

Posted on March 27, 2013 by Weather Guys Editor

By two measures, spring has arrived. Astronomically, spring, or the vernal equinox, occurs around March 20 each year. It is defined as when the tilt of Earth’s axis is inclined neither toward nor away from the Sun. The moment that marks the beginning of spring is when the sun is directly overhead at the equator. This year that occurred on March 20, when the maximum temperature in Madison was only 21 degrees.

Meteorologically, we can define the first day of spring as when, based on at least 30 years of observations, the probability is greater than 50 percent that should some sort of precipitation fall, it will be rain rather than snow. That date has also passed. For southern Wisconsin, that calendar day is around March 16.

Some people define spring as the first day they see a robin. We’ve seen flocks of robins in Madison this month, so that day also has passed.

While various definitions of spring indicate it has arrived, it sure seems wintry. From a climate perspective, it is not common to have this much snow on the ground after the vernal equinox. The outlook for the coming week includes below-normal temperatures.

Springtime is generally considered to be the three months of March, April and May. The official National Oceanic and Atmospheric Administration, or NOAA, outlook for spring is for warmer-than-normal weather across most of the U.S. There will have to be some warm months ahead to have that happen in Madison.

On a related note: NOAA cautions that the melting of late-season snow may cause minor to moderate flooding in the upper Mississippi River basin, including southern Wisconsin.

Category: Seasons
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Just how snowy has it been these past six weeks?

Posted on March 18, 2013 by Weather Guys Editor

It sure has been a snowy last few weeks.  As of Jan. 1, 2013, Madison had officially received only 32.4 inches of snow — nearly half of which (15.2 inches) was delivered in our Dec. 19-20 snowstorm.  However, since Feb. 1 we have accumulated 30.8 additional inches of snow (as of March 14).

In those 42 days, Madison has had 30 days on which at least some snow has fallen.  This is a truly remarkable period for frequency of snowfall.  Aside from the regularity of snowfall in February and March, our seasonal total of 63.2 inches (as of March 14) ranks 14th all-time in Madison for seasonal snowfall.  In fact, we only need an additional 7.5 inches to break into the top 10 snowiest winters of all time as the 70.7 inches that fell in 1897-98 currently holds the No. 10 spot in the record books.

Our guess is that this is rather unlikely — but not impossible — as the longer-range forecasts are not suggesting any really dramatic warm-up through late March, well after the Spring equinox that falls on March 20 this year.

This has been a nearly exact opposite of last March when, by the 14th, we were experiencing temperatures in the high 70s (it was 78 on March 14 last year!).  March 15, 2012 was our first in a string of five days (over a single week) with temperatures over 80F.  What a difference a year makes.

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How can it feel humid during a drought?

Posted on March 5, 2013 by Weather Guys Editor

The drought that began in the spring of 2012 is actually an extension of the 2010 drought. The recent February storms have lessened the current drought, which covered 80 percent of the lower 48 states of the United States with at least abnormally dry conditions. The economic impact on the Midwest has been estimated to be more than $35 billion.

The field corn and soybeans crops of the Midwest have been particularly hard hit. Water systems throughout the country have been affected by the lack of moisture. Low water levels in parts of the Mississippi have a negative effect on trade and commerce. Even with this dry weather, some have noted the uncomfortable humidity. To address how this can be, we need to first define a drought.

There are several definitions of drought, but in general there are three types. A meteorological drought is any substantial and prolonged lack of rainfall over a period of time in a given region. A hydrological drought is a deficiency in surface or subsurface water supplies. An agriculture drought exists when there is not enough soil moisture to meet the needs of a crop at a particular time.

There can be many water vapor molecules in the air, which increases the humidity of the air, but if those water molecules in the gas phase do not condense to form clouds that eventually grow to raindrop-sized particles, it will not rain. The humid air near the ground must rise, which will cause clouds to form and possibly precipitate. Without that air rising, there can be a lot of uncomfortable humidity while in a drought condition.

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How do citrus farmers battle the cold?

Posted on February 25, 2013 by Weather Guys Editor

Last week was one of the coldest of the season in the southeast United States. Though not as bad as prior cold air outbreaks in late January or early February, such events have been known to present a substantial threat to the citrus industry in Florida. The problem is that when the temperature gets below freezing, the fruit itself can freeze rendering it substantially less valuable to the market.

One of the most ingenious tricks citrus farmers can use to combat this takes advantage of the fact that phase changes of water involve substantial amounts of energy known as latent heats. Everyone knows that ice only melts into liquid water after some energy has been supplied to the ice — the latent heat of melting. In the process, the environment that surrounds the original ice becomes colder since it has been forced to spend some energy to do the melting.

A classic, kitchen-ready example involves placing ice cubes in a glass of water. Two things happen — the ice melts and the original liquid water cools. The water cools because it has spent some of its energy in accomplishing the phase change. The interesting thing is that if liquid water is converted to solid ice, the same amount of energy is released to the environment — this time it is called the latent heat of fusion.

So, when a freeze is forecast for a citrus farm, the farmers often spray the trees with water. When the temperature drops, this water freezes and releases heat to its environment, some of which is the still-ripening fruit. This heat is enough to preserve the fruit inside from freezing. So, paradoxically, causing ice to form on the fruit saves it from freezing.

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How are climates classified?

Posted on February 21, 2013 by Weather Guys Editor

There are a few ways to classify climates. The plant hardiness zones often published with seed packages are one way to group climates. That approach is based on minimum wintertime temperatures but is limited in its usefulness because a good climate map should include reference to more than one weather variable.

Between 1918 and 1936 Vladimir Köppen (pronounced KEPP-in) devised the climate classification scheme that is most widely used today. He used vegetation and temperature as natural indications of the climate of a region. Climate scientists have made improvements to the original Köppen scheme, most recently in 2007; it is now called the Köppen-Geiger map.

The current Köppen-Geiger classification scheme has five main groups, each designated with a letter: Tropical Moist (A), Dry (B), Moist with Mild Winters (C), Moist with Severe Winters (D) and Polar (E).

Some groups are described by two- and three-letter designations. The second letter usually refers to whether and when a dry season occurs, and the third letter denotes differences in temperatures. The dominant climate classification over land is arid B (about 30 percent) followed by cold D (about 25 percent) and tropical A (19 percent). The moist and mild C climate only occupies about 13 percent, about the same as polar E zones. Following this major classification, denoted by a capital letter, is a second letter that is not capitalized that usually refers to whether and when a dry season occurs.

Wisconsin is a “Df” climate type. The “D” part of this classification means the climate includes variable weather patterns with a large variation in seasonal temperatures. The average temperature of the coldest month is less than 32 degrees F, and the warmest month has an average temperature exceeding 50 degrees. These climate types usually have snow on the ground for extended periods. The “f” designation indicates that there is no dry season.

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