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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Why is Fog Usually Seen in the Morning?

Posted on September 26, 2011 by Weather Guys Editor

A fog is just a cloud at the ground. Fog formation can occur in two ways. First, the air is cooled to the dew point which leads to the formation of fog droplets. When the air temperature is the same as the dew point temperature, condensation occurs on tiny particles floating in the air. The second method of fog formation requires water to evaporate from the surface into the air, raising the dew point until condensation occurs.

Fog often dissipates with daylight. This is sometimes referred to as the fog “burning off” but that analogy is not correct. When the sun rises, the air and ground warm up. This leads to the air temperature being warmer than the dew point temperature, which causes the fog droplets to evaporate.

As the nights are getting longer in autumn, we often have clear and cloudless skies at night. The conditions help the ground, and the air near the ground, to rapidly cool during evening are clear and cloudless skies and long nights. These are the type of conditions we often have in autumn. As the air cools during the longer night the relative humidity increases, which can result in to fog formation. Windy mornings are fog free as strong winds mix the air near the ground with the drier, warmer air above.

As autumn progresses, we will see a fog during the day forming over the unfrozen lakes. This fog, called evaporation fog, forms when colder air moves over warmer water. Evaporation fog over a lake gives the appearance of steam rising out of the water and is sometimes referred to as a steam fog.

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How is Smoke from a Wildfire in Minnesota Affecting Wisconsin Weather?

Posted on September 19, 2011 by Weather Guys Editor

On Tuesday a large part of our state either saw or smelled smoke from a raging wildfire in the Boundary Waters Canoe Area in northern Minnesota. The smoke was particularly easy to detect in the northern parts of Wisconsin, but it spread southward during the day and eventually led to the Milwaukee Brewers deciding to close the Miller Park roof on an otherwise delightful early fall evening just to keep the smoke out.

This was a good decision, as prolonged exposure to smoke plume from wildfires is a health hazard. In fact, officials were recommending that people in the northern parts of the state limit their outdoor activities in the face the invading smoke.

The fire responsible for this pall of smoke was actually initiated by a lightning strike in the Boundary Waters on August 18 and has burned, slowly and over a relatively small portion of that unpopulated area, for nearly a month before a vigorous cyclone passed just to its north over the weekend. The strong winds associated with that storm fanned the flames, resulting in the fire racing 16 miles east between Monday and Tuesday, quadrupling in size. The same storm accounted for our abrupt and welcome change to fall-like conditions early this week.

The weather is a major factor in the growth of wildfires as dryness preconditions the fuels at the ground and winds quickly spread the fire. Though not an everyday occurrence, long-range transport of smoke from remote fires is far from unusual. The proximity of this fire to our state accounts for the pungent nature of this remote smoke event.

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How Much Condensed Liquid Water is in a Cubic Mile of Fog?

Posted on September 12, 2011 by Weather Guys Editor

Fog is composed of tiny water drops, each one with a diameter of about one-one thousandth (0.001) of an inch. They are small and fairly uniform in size. You also would find about one of these drops in each cubic inch of fog.

If you do the math, that is about 56,000 gallons of water in one cubic mile of fog.

Given that each gallon of water weighs a bit over 8 pounds, that’s about 450,000 pounds of liquid water. That is a lot of water. How does that compare to other clouds?

A large cumulus cloud that you might find on a nice summer day is made up of about 1 million pounds of water drops.

A thunderstorm cloud contains enough water drops to fill up approximately 275 million gallon jars. That’s about 2.3 billion pounds, or 1.1 million tons of water. To see that much water fall over Niagara Falls, you’d have to watch the falls for six minutes.

If that thunderstorm produced one inch of rain over one square mile, that would be 17.4 million gallons of water weighing 143 million pounds (about 72,000 tons).

A hurricane has about 250 million tons of water swirling in the storm. How does that much water stay up in the atmosphere?

The key is to remember that the water is in the form of tiny drops, not gallon jugs. The rising motion in the cloud is able to keep these drops suspended in the atmosphere.

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Was the Forecast of Irene a Success?

Posted on September 4, 2011 by Weather Guys Editor

The emergency response and warnings prompted by the approach of Hurricane Irene along the East Coast last week has, sadly but predictably, become a subject of much controversy.

Much of the furor surrounds whether or not the decisions made by the mayors of New York City or Ocean City, Mary., were too extreme. New York’s Mayor, Michael Bloomberg, ordered the evacuation of lower Manhattan in the face of a threatened storm surge of eight feet that would have inundated the area.

Meanwhile, the mayor of Ocean City, a popular tourist destination on the eastern shore of Maryland, ordered businesses to shut down as the storm approached. Given the forecasts that were issued by the National Hurricane Center, staffed by the most knowledgeable hurricane scientists in the world, there was every reason to believe that a substantial hit from Irene was going to be delivered in these locations. In fact, the region was hit hard by the storm, though it was weaker than expected. Thus, these moves were wholly appropriate.

Luckily, Irene weakened enough before making landfall in the Northeast thus saving New York and Ocean City from the worst case scenario. The insistence that public officials overreacted to the threat posed by Irene represents a particularly dangerous type of Monday morning quarterbacking, perhaps engendering passivity in the face of future threats. Such an attitude would also suggest a distrust of science as a means to the end of protecting the lives and property of our fellow citizens.

It would be a shame if, given the outstanding progress that has been made in hurricane prediction in the last 25 years, the combination of media hype and a slightly errant forecast such as occurred with Irene might encourage such distrust and contribute to the willful disregard of future warnings.

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