What is our Halloween weather usually like?

Posted on October 31, 2016 by WeatherGuys Editor

As the end of October arrives, the weather in Madison becomes increasingly subject to large variations, especially when measured from one year to the next.

The city’s record high temperature on Oct. 31 is 77 degrees, recorded in 1950, while the lowest temperature for the day is 16, recorded in 1925.

In 1960, we had 1.21” of rain on Halloween, surely dampening the spirits of lots of small children. In 1926, we received 3.2” of snow as a Halloween treat. As recently as 2014, we received snow on Halloween, just 0.2”, but it stands as the only snowy Halloween in the last 30 years.

On average, the high temperature is 52 on Oct. 31 while the low is 34, usually recorded in the early morning of the day. Nearly 2/3 of the past 30 Halloweens have been completely dry and only 3 of 30 have recorded more than 0.25” of rain.

Thus, our guess is that the usual conditions for setting out on trick or treat in Madison consist of no rain and a temperature between 46 and 50. All in all, not bad.

It certainly appears that this evening’s conditions will be well above the average, with a temperature likely to be as much as 10 degrees warmer than usual and no rain. It may, in fact, be our warmest Halloween since 2008, when the high temperature was 70 in the middle of an unusual and extremely late October-early November warm spell that lasted through Election Day that year.

Category: Meteorology, Seasons

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Are fall colors related to the weather?

Posted on October 24, 2016 by WeatherGuys Editor
Am early frost speeds up the fall of the leaves and brings a quick end to the fall color. Too much wind or heavy precipitation also brings the leaves down. (Photo credit: La Crosse Tribune Archives)

Am early frost speeds up the fall of the leaves and brings a quick end to the fall color. Too much wind or heavy precipitation also brings the leaves down. (Photo credit: La Crosse Tribune Archives)

The season of autumn color is beginning with tints of yellow and orange in southern Wisconsin.

Sunny days and cool nights are the key weather ingredient for brilliant fall colors. The best weather conditions are bright sunny days and cool, but not frosty, nights. A drab autumn has lots of cloudy days and warm nights.

Southern Wisconsin has had above-average nighttime temperatures. Since Sept. 22, the average minimum temperature for southern Wisconsin has been in the upper 40s.

An early frost speeds up the fall of the leaves and brings a quick end to the fall color. Many southern Wisconsin regions have not experienced frost. Of course, a lot of wind or heavy precipitation would bring the leaves down.

Leaves contain chlorophyll and are green because chlorophyll reflects green light more than other colors. Other colors are absorbed by chlorophyll for photosynthesis. During autumn, the green chlorophyll disappears, and we begin to see yellow and orange.

These colors have been in the leaves all along; we can’t see them in the summer because of the chlorophyll. The color orange comes from carotene, and the yellows from xanthophyll. The bright red and purple colors come from anthocyanin pigments, which are made from leftover glucose trapped within the leaves of some trees, such as maples. Brilliant fall colors with bright red and purple colors require conditions in which leaves can make a lot of anthocyanin pigments. These discussions are a function of the weather.

While there may have been more brilliant colors during previous falls, it is still inspiring to walk the woods of Wisconsin.

Category: Meteorology, Seasons

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When will the first snow arrive?

Posted on October 19, 2016 by WeatherGuys Editor
Sakari the polar bear frolics in his first snowfall in the Arctic Passsage exhibit at the Vilas Zoo on Nov. 21, 2015. We have now entered the season in which snow is possible, but it isn't until Nov. 15 that the chances that precipitation will be snow is equal to the chances it will be rain. (Photo credit: Amber Arnold, State Journal)

Sakari the polar bear frolics in his first snowfall in the Arctic Passsage exhibit at the Vilas Zoo on Nov. 21, 2015. We have now entered the season in which snow is possible, but it isn’t until Nov. 15 that the chances that precipitation will be snow is equal to the chances it will be rain. (Photo credit: Amber Arnold, State Journal)

The first cold mornings of the season visited southern Wisconsin last week with the morning low temperatures dipping to 34 and 33 degrees on Thursday and Friday mornings, respectively.

The first chill of the year has the tendency to turn our attention to the prospects of snow and when it might first arrive in Madison.

Over the last 36 years, the earliest measurable snow has fallen between Oct. 11 and 20, according to the Midwestern Regional Climate Center in Champaign, Illinois. Clearly that means we have now entered the season in which snow is possible.

However, as we have mentioned in a prior column, it is not until Nov. 15 that the chances that precipitation will be snow is finally equal to the chances that it will be rain. Consequently, the snow threat becomes substantial only after the middle of November.

In the same 36-year period, Madison has had to sometimes wait until the week of Christmas to receive its first measurable snow. So, a common but difficult-to-answer question arises — what can we expect this year?

Seasonal snowfall is highly variable in Madison, ranging from 4 inches in 1900-01 to 102 inches in 2007-08. Over the last 36 years, the average seasonal total is about 50 inches.

The current 90-day outlook from the Climate Prediction Center points to Wisconsin being slightly warmer than normal but with about normal precipitation through the end of December.

These outlooks are based largely on statistical analyses and are thus not comparable in methodology, or in accuracy, to the short-term weather forecasts provided by the National Weather Service. Right now there is no physical reason to suspect a snowier or less snowy winter than average.

It can be said, however, that since last year’s total of 33 inches and 2014-15’s total of 32 inches were quite below normal, even if this year is only normal it will the snowiest in three years.

Category: Climate, Meteorology, Seasons

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What role did weather play in the Peshtigo Fire?

Posted on October 10, 2016 by WeatherGuys Editor
An artist's rendering of the Peshtigo Fire, October 8, 1871. As wind-fed fire raged through town, people fled to the river. (Photo credit: The Capital Times Archives)

An artist’s rendering of the Peshtigo Fire, October 8, 1871. As wind-fed fire raged through town, people fled to the river. (Photo credit: The Capital Times Archives)

 The Peshtigo Fire was the largest wildfire in U.S. history and occurred on Oct. 8, 1871.

The fire swept through the eastern and western shores of Green Bay, burning more than 1.28 million acres.

The town of Peshtigo — where an estimated 1,200 people died in the blaze — was hit particularly hard, resulting in the blaze being called the Peshtigo Fire.

The fire also destroyed Williamsonville, one of the shingle mill sites of Door County. Tornado Memorial Park is near this former town and commemorates victims who lost their lives fighting a “tornado of fire.”

A fire tornado is a swirl of fire that extends upward from a ground fire.

These vortices can occur over a range of fire sizes but the largest are associated with wildfires. Fire tornadoes are usually 30-200 feet tall and about 10 feet wide. Generally, they last for only a few minutes.

Fires require fuel to burn, air to supply oxygen and a heat source to get the fuel to its ignition temperature. The logging and land clearing practices of the time period, along with the sawmills of the area, provided debris that served as fuel for the Peshtigo Fire.

There were many small fires in the summer of 1871. While instrument weather stations were not available, diaries and other records indicated below-average rainfall over most of the area from June through September 1871. This was likely an important factor in the devastating October fire.

Once a fire starts, weather can influence how it will spread and if it will grow. The important weather factors are temperature, wind and humidity.

Warmer temperatures allow fuels to ignite quickly and low humidity keeps fuel dry and easy to burn. Wind brings oxygen to a fire and can also help it spread. A large fire can generate a wind pattern of its own that can help spread the fire, too.

The fame of the Peshtigo Fire is limited by the better-known Great Chicago Fire, which occurred on the same day, burning up 3.3 square miles of land and killing 300.

Category: Phenomena, Severe Weather, Weather Dangers

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How are hurricane intensities measured?

Posted on October 3, 2016 by WeatherGuys Editor
A GOES East satellite image provided by the National Oceanic and Atmospheric Administration (NOAA) on Thursday shows Hurrican Matthew -- the first Category 5 hurricane in the Atlantic basin since Hurricane Felix in 2007 -- in the Caribbean Sea about 190 miles northeast of Curacao. The category of a hurricane is determined by reconnaissance aircraft flights into the storm along with analysis of satellite images. The satellite approach is led by scientists at the UW-Madison as part of the Cooperative Institute for Meteorological Satellite Studies, or CIMSS (Photo credit: NOAA)

A GOES East satellite image provided by the National Oceanic and Atmospheric Administration (NOAA) on Thursday shows Hurrican Matthew — the first Category 5 hurricane in the Atlantic basin since Hurricane Felix in 2007 — in the Caribbean Sea about 190 miles northeast of Curacao. The category of a hurricane is determined by reconnaissance aircraft flights into the storm along with analysis of satellite images. The satellite approach is led by scientists at the UW-Madison as part of the Cooperative Institute for Meteorological Satellite Studies, or CIMSS (Photo credit: NOAA)

An obvious hurricane threat is its powerful wind, which can blow in a single spot for many hours.

Wind damage is such a hallmark of hurricanes that hurricane intensities are classified by meteorologists using the Saffir–Simpson scale, which rates hurricanes on a scale of 1 to 5 based on the damage their winds would cause upon landfall.

Major hurricanes are those classified as Category 3 and higher on this scale. Category 3 hurricanes have a one-minute sustained wind between 111 mph and 130 mph.

The one-minute sustained winds in a Category 5 hurricane are greater than 155 mph.

The category of a hurricane is determined by reconnaissance aircraft flights into the storm along with analysis of satellite images.

The satellite approach is led by scientists at UW-Madison as part of the Cooperative Institute for Meteorological Satellite Studies, or CIMSS.

This collaboration between the university and the National Oceanic and Atmospheric Administration (NOAA) supports research on weather satellites.

Hurricane Matthew intensified in the Atlantic Ocean this past weekend and will threaten the U.S. mainland this week.

A reconnaissance plane recently measured wind speeds in this storm and those measurements along with the CIMSS analysis led NOAA to list Matthew as a Category 5 storm.

This is the first Category 5 hurricane in the Atlantic basin since Hurricane Felix in 2007.

Fortunately, most hurricanes do not produce the extreme winds linked with the highest category on the Saffir–Simpson scale, but any category storm can do major damage when it hits land.

Flooding from hurricanes causes major damage to shorelines and buildings. The winds in a hurricane push ocean water in front of them. The stronger the wind, the more water is “piled up.”

As the hurricane nears shore, the wind pushes this water inland. This process of wind-induced seawater flooding is called storm surge.

Historically, the storm surge has caused as much as 90 percent of all hurricane-related deaths.

Flooding from rain can also be dangerous.

Hurricane Floyd made landfall in 1999 as a Category 2 storm. Flooding that ensued along the U.S. East Coast accounted for most of the death toll of 57.

Category: Meteorology, Severe Weather, Tropical

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