NewsChannel 8 Weather

Here’s a thought for all you optimists: meteorological spring begins March 1. While we’ll have to wait until March 20 for the Spring Equinox, when the vertical rays of the sun are over the Equator, it’s clear that the sun is setting later, rising earlier, and beginning to take a more vertical angle over the region. If that weren’t enough, Sun Prairie Jimmy, our local groundhog, didn’t see his shadow on February 2 — a clear indication that more spring-like conditions are right around the corner.

With about three weeks left in meteorological winter, it looks like we’re on track for a pretty normal winter. While we’ve had some Arctic blasts this winter, temperatures, overall, have been only slightly below normal. The average monthly temperature at the La Crosse Airport was 20.1 degrees Fahrenheit in December (1.7 degrees Fahrenheit below normal) and 14.8 degrees Fahrenheit in January (1.1 degrees Fahrenheit below normal). As of February 11, the average monthly temperature is 20.5 degrees Fahrenheit (0.9 degrees Fahrenheit above normal).

The coldest temperature we’ve seen so far this meteorological winter is -16 degrees Fahrenheit on January 3. It’s interesting to note that high temperatures have climbed above 0 degrees Fahrenheit every day (so far) from December 1. On the other hand, we’re in the middle of what is now the sixth longest stretch of weather (as of February 11) when high temperatures have not reached 40 degrees Fahrenheit. It’s likely we’ll keep below normal high temperatures through the next eight days, which means we’re on track for one of the top three longest stretches of maximum temperatures below 40 degrees Fahrenheit.

As for snow, we’re on track for a pretty normal snow season. We normally see about 44″ of snow during a July 1 - June 30 snow season. So far, we’ve received 37.5″ of snow at the La Crosse Airport since July 1, 2009. As of February 11, this is 7.0″ above normal for the season, with the bulk of this snow coming during the early-December blizzard.

Average temperatures begin to increase rapidly with the start of meteorological spring on March 1. In fact, average daily temperatures (found by taking the average of the normal high and low temperature for a single day) climb from 28 degrees Fahrenheit on March 1 to 41 degrees Fahrenheit by March 31. According to the National Weather Service in La Crosse, spring-like weather generally begins the end of March and lasts into early-June.

Spring, truly, is just around the corner!

The first decade of the 21st Century was the warmest decade ever recorded since modern records have been kept, according to new data released by the Goddard Institute for Space Studies (GISS), a branch of the National Aeronautics and Space Administration (NASA). In addition, 2009 tied for the second warmest year across the globe in the modern record.

The warmest year on record is still 2005, and 2009 is tied with 1998, 2002, 2003, 2006 and 2007 in the cluster of warmest years ever recorded.

Since modern analysis of global climate began in 1880, Earth’s surface temperatures have steadily increased. The only leveling off in the temperature record occurred between the 1940s and 1970s.

According to data kept by the GISS, average global temperatures have increased about 0.2 degrees Centigrade (0.36 degrees Fahrenheit) over the past three decades. Since 1880, average global temperatures have increased by about 0.8 degrees Centigrade, or 1.4 degrees Fahrenheit.

Scientists point to a numer of factors that they believe are contributing to these global temperature increases.

Along with the increase of carbon dioxide and other greenhouse gasses that prevent heat from escaping back into space, changes in solar radiation, fluctuations in sea surface temperatures and changes in aerosol levels also contribute to slight increases in global temperature. However, scientists note that these factors alone are not enough to account for the increase in temperatures since 1880.

El Nino and La Nina conditions, which are the names given to abnormally warm (El Nino) and cool (La Nina) sea surface temperatures in the Pacific Ocean, also are thought to have a significant impact on average global temperatures.

In general, global temperatures tend to decrease during and just after La Nina conditions. These conditions are characterized by an upwelling of cold water off the coast of Peru that spreads west across the Pacific and leads to cooler sea surface temperatures. La Nina conditions came to an end in early 2009 and were replaced by El Nino conditions, which are expected to continue this year.

Some of the warmest global average temperatures have occurred when El Nino conditions (warmer than normal sea surface temperatures) occur in the Pacific Ocean. A very strong El Nino is blamed for unusually high average global temperatures in 1998, and scientists estimate that 2010 could be on track to be one of the warmest years on record if El Nino conditions persist through the year.

As Dr. James Hansen, director of NASA’s Goddard Institute for Space Studies, notes, “When we average temperature over five or 10 years to minimize [changes in ocean heating and cooling cycles], we find global warming is continuing unabated.”

One of the more important forecasts I make during the year is on February 2. It’s actually an easy forecast to produce, and I don’t even have to rely on an analysis of mathematical models, expensive equipment, or even years of meteorology classes. All I have to do is wait for a small rodent to wake up.

The legend of Groundhog Day is simple: On February 2, the local groundhog emerges from his (or her) burrow. If he sees his shadow, he heads back inside and we’re in for another six weeks of wintery weather. If, however, he doesn’t see his shadow, he’ll stay outside and spring is just around the corner. That’s a lot of responsibility for a marmot!

When I was younger, Groundhog Day was a much bigger event than it is today. In my elementary school in Atlanta, GA, we sang songs, watched film strips about groundhogs, and, once, even had a visit from Atlanta’s local groundhog at the Atlanta Zoo. It seems like the groundhog has fallen on hard times!

The groundhog, or woodchuck (we’ll get to how much wood he can chuck in a bit), is a rodent belonging to the large group of ground squirrels called marmots. Groundhogs are widely distributed across North America, but are especially prevalent in the northeastern and central United States. Your average groundhog is about a foot-and-a-half to two-feet long, and generally weighs between five and 10 pounds.

Groundhogs are mostly herbivorous, and generally feed on grasses, vegetation and agricultural crops (like alfalfa). They will eat small insects and, in some instances, small animals.

After a long summer and fall, groundhogs retreat to their burrow for a true hibernation. This usually begins in October and lasts until March or April. This hibernation period may be much shorter in warmer, more temperate areas.

Since goundhogs and woodchucks are the same animal, this brings us to woodchucks and the wood they could chuck. I did some extensive research after our 6pm broadcast and found that not much as been published in the standard peer-reviewed journals about this topic. Bsically, there are several criteria that need to be considered:

1) Amount and, more importantly, type of wood to be chucked (oak vs. pine, for example);

2) Mass of the individual wood pieces to be chucked (which is heavily dependent on wood species, humidity, and other factors);

3) Amount of torque an average woodchuck could apply to a “standard” piece of wood;

4) Why would a woodchuck chuck wood? This falls more in the realm of behavior, though, which is outside the scope of my search.

In the end, there’s little climatological data to back up the prognostications made by groundhogs and woodchucks on February 2. Average temperatures generally climb through the month of February after hitting their low point in January, and longer periods of daylight are a welcome relief after the darker months of December and January.

As the groundhog awakes after a winter slumber, it is, in the end, a sure sign that warmer days shortly will arrive.

Area drivers got to deal with icy roads over the past few days thanks to light, but persistent freezing rain. So how does freezing rain form? Well, you’ve come to the right place!

Unlike summer, when all of our precipitation will fall in the form of liquid, the winter months can bring several types of precipitation. We can see snow, sleet, freezing rain, and rain.

When the air at the surface and aloft are below freezing, the precipitation type will usually be in the form of snow. Now, snow can actually be classified into six basic patterns. They are needles, columns, plates, columns capped with plates, dendrites, and stars. Each type is the result of different atmospheric and temperature conditions within the cloud. I won’t go into much more detail about that as it may cause your eyes to glaze over. However… you now have a fun fact to share at parties.

Sometimes, a wedge of warmer air moves into the middle layers of the atmosphere. When this happens, we call it an inversion. If you took a cross section of it, it would look a bit like an oreo cookie. Imagine the top of our cookie as an area of below freezing temperatures where the cloud layer has formed. The yummy middle layer of our oreo would represent that wedge of warm air in the middle levels of the atmosphere, while the bottom of the cookie would represent a layer of below freezing air at the surface. 

Here’s how it works… precipitation would start out as snow in that upper cloud layer (the top part of our oreo cookie. But, as it encounters that wedge of above freezing temperatures (the middle of the oreo cookie) the snow melts. If that wedge of above freezing air is shallow, the snow flake will melt into a drop, but re-freeze into a pellet when it falls into the layer of below freezing air at the surface (the bottom of our oreo cookie). If that wedge of above freezing air is deep enough, the melted snow flake will stay liquid until it hits the surface which is below freezing. It then freezes on contact. Of course, we all know the result, a skating rink courtesy of mother nature.

There are other variables that can influence precipitation type, but the above explanation is a great and simple way to illustrate the process.

So, the next time you hear freezing rain in the forecast, grab an oreo and explain the process to a friend. i guarantee they will never look at an oreo the same way. Of course… they may not look at you  the same way, either! 

Talk to you soon!

Mother Nature has been very busy lately creating some gorgeous winter scenes across the region. Weather conditions have been perfect the last 4 nights and early mornings for widespread and dense fog to form. We’ve had mostly clear nights, light winds and lots of low-level moisture from a slowly melting snow-pack. We’ve also had a strong temperature inversion lately, meaning the air near the ground is colder than the air aloft. Cold air is heavier and sinks, which in turn traps moisture, smoke and pollutants near the surface and creates stagnant air that aids in the development of low clouds, haze and fog.

Now dense fog is no stranger to this area, but when the air is damp enough and temperatures are below freezing… then the development of hoarfrost is possible. Usually we think of frost in the winter time as more of a nuisance thing. It means we have to leave a few minutes early for work because we have to allow some time to scrape the frost off of our car windshields if we parked outside. But when conditions are right for hoarfrost to develop, then we’re treated to a beautiful scene the next morning with everything coated in a fluffy and feathery layer of white. In fact, you don’t even have to scrape hoarfrost, a swipe or two of the wiper blades usually does the trick. It almost looks like we had a light dusting of snow.

So what exactly is hoarfrost and how does it develop? Hoarfrost is a deposit of interlocking ice crystals on objects exposed to the free air (usually those of small diameter), such as grass blades, tree branches, plant stems and leaf edges, wires, poles, etc. The temperature of these objects must be below freezing. It is formed by direct condensation of water vapor (fog) to ice at temperatures below freezing and occurs when air is brought to its frost point by cooling. In other words, the air temperature and dew point temperature are the same or very close. Hoarfrost is formed by a process similar to how dew forms in warmer months, except of course in the case of dew, the saturation point of the air mass is above freezing. However, a temperature below freezing is not a guarantee that hoarfrost will develop. Additionally, the air must be initially damp enough so that when cooled it reaches saturation, and any additional cooling will cause condensation to occur. Hoarfrost is also sometimes called “white frost” (which should make perfect sense to you if you’ve seen the landscape the past several mornings) and is also similar to “rime ice“.

Hopefully I didn’t just bore you to sleep with that explanation. Many of you have posted wonderful pictures of the “white-frosted” wintry scene created by the hoarfrost on our website. Check them out by clicking on this link: http://slideshows.embtv.com/gallery/?site=wkbt&gallery=309.

The National Weather Service in La Crosse has also posted a brief explanation of hoarfrost and a couple of pictures on their website: http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=arx&storyid=46685&source=0.

Dense fog and hoarfrost can make for slower travel due to reduced visibilities and slick spots created by the frost/ice crystals… but it sure makes for a pretty drive as well.

Until next time, see you in the morning!