The Weather Guys

How does Hurricane Hermine measure up?

Posted on September 6, 2016 by WeatherGuys Editor

Water from Roanoke Sound pounds the Virginia Dare Trail in Manteo, NC, Saturday, as Tropical Storm Hermine passes the Outer Banks. Hermine lost hurricane strength over land but intensified along the Atlantic Coast. (Photo credit: Tom Copeland, Associated Press)

On Friday Hurricane Hermine made landfall in Florida, making it the first to make landfall in the state in more than a decade.

Hermine, which weakened to a tropical storm shortly after landfall as is commonly the case with weak hurricanes, was poised to redevelop and pose a threat to the Mid-Atlantic states and possibly southern New England into the middle of the week.

Eighty-one years ago, nearly to the day, the famous Labor Day Hurricane of 1935 struck Florida with greater intensity than any other landfalling hurricane in the country’s history.

While Hermine had sustained winds of about 75 mph and dropped nearly 17 inches of rain in the Tampa/St. Petersburg area, the Labor Day Hurricane made landfall with sustained winds near 185 mph.

Both storms developed within days of Sept. 12, the date of the average peak frequency for such storms in the Atlantic Basin. Though the number of tropical cyclones in an average year numbers in the low teens, these storms are deserving of attention because they can wreak enormous damage to life and property.

They also play a substantial role in ventilating the tropical ocean and mixing heat from the tropics, where an annual surplus accumulates, to the high latitudes where an annual deficit stands in need of remedy.

It may seem surprising given our location in the middle of the North American continent, but hurricane research, employing both satellite observations and theoretical advances, at UW-Madison has led the way toward improved understanding and forecasting of these powerful storms.

Category: Meteorology, Severe Weather, Tropical

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Is this a rainy summer?

Posted on August 29, 2016 by WeatherGuys Editor

Chavez Elementary School students Josh Gonzales, left, and Dorgee Tsering enjoy a rain shower during a trip to the UW-Madison campus in May. Spring showers gave way to a rainy summer for southern Wisconsin. (Photo credit: John Hart, State Journal archives)

For southern Wisconsin, this has been a rainy summer.

This August, the precipitation that fell over southern Wisconsin is about 200 percent of normal.

Total precipitation was also above normal for June and July. With the summer coming to a close, we are about 6 inches above normal.

On Aug. 19, 2.74 inches fell on Madison, setting a daily record, beating the old mark of 2.13 inches set in 2007. In particular, August has been exceptionally rainy compared to the prior five Augusts, as the only above-normal August in that stretch occurred in 2014 (plus-1.14 inches).

In Madison, the official measurement is made at the Dane County Airport. Even given the convective nature of the storm systems, all of Wisconsin was above normal in terms of the average precipitation for the month of June.

Because of the good rain, there is no area in Wisconsin that currently is classified as experiencing a drought condition. The soil moisture content for most of southern Wisconsin is above normal. The water levels in Lake Mendota and Lake Monona are above their average maximum summer levels.

The convective nature of summertime precipitation makes the amounts vary widely across the county and even across the city. So it is important to make as many observations of rainfall as possible. If you are interested in contributing observations, you can join the Community Collaborative Rain, Hail and Snow networks, or CoCoRaHS. This community includes over 15,000 volunteers who help measure and report precipitation type and amounts every day.

Observations of precipitation by a large group of volunteers are critical to understanding storms as precipitation varies widely from place to place even in a single storm. Such observations are useful for assessing flooding hazards. You can join CoCoRaHS at www.cocorahs.org.

Category: Meteorology, Seasons

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Is another transition around the corner?

Posted on August 15, 2016 by WeatherGuys Editor

Convective clouds such as these from a storm over Hudson Bay in Canada last week can drop large amounts of rain very quickly. (Photo credit: Steve Ackerman, UW-Madison)

This classic comma shaped cloud, also called a mid-latitude cyclone, deepened over Hudson Bay Canada during mid-August 2016.
(credit: Steve Ackerman, CIMSS)

As we head into the second half of August a subtle transition in our weather begins to occur — one that is probably hard to detect at first but that eventually becomes very obvious and then lasts for approximately eight months.

We are not talking about the gradual reduction in daytime high temperatures or the increasingly cooler to cold nights, though these are also beginning to invade.

Instead, we are talking about the nature of the storms that deliver our precipitation.

Throughout the summer, most of our precipitation comes in the form of thunderstorms, wherein large amounts of precipitation fall in a short amount of time from what we call convective clouds.

Most often these storms have life cycles of only a few hours and drop precipitation over a relatively small area.

These characteristics also make the exact timing and location of summertime precipitation difficult to forecast.

As we transition to late summer/early autumn, the thunderstorm frequency abruptly decreases and precipitation tends to occur in persistent, light to moderate rain events that will sometimes last an entire day.

This mode of precipitation is associated with the passage of what are known as mid-latitude cyclones — storms that live for over a week, during which time they can cover an area the size of 10 states and characteristically take on a comma-shaped appearance in satellite imagery.

As they progress across the country, these mid-latitude cyclones can drop precipitation (rain or snow) over enormous portions of the country.

Though not entirely missing from summertime precipitation, such events are definitely the exception rather than the rule in the summer.

This past week, the first really well developed such storm of the season paraded across Hudson’s Bay in Canada and another one like it is poised to do the same late this week.

Category: Climate, Meteorology, Seasons

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Has global warming stopped?

Posted on August 9, 2016 by WeatherGuys Editor

In a recent interview on the Glenn Klein Show on WRJN radio, U.S. Sen. Ron Johnson, R-Oshkosh, asserted that “the climate hasn’t warmed in quite a few years … that is proven scientifically.”

This statement is entirely untrue but echoes a line of argument that many climate change and global warming skeptics have introduced into the discussion for a number of years. The so-called “global warming hiatus” argument suggests that since the beginning of the present century there has been a slower rate of increase in the global average surface temperature than climate models suggested would be the case.

This is very different from saying that the warming has stopped.

In fact, a recent analysis of 67 years of continuous temperature data by UW scientists has demonstrated that the areal extent of the cold air at 1 mile above the ground during Northern Hemisphere winter has systematically decreased in that time period and that two of the last three winters have had the smallest such areal extent in the entire record.

There is no question that the air temperature just above the surface is continuing to warm at an alarming rate — even in wintertime.

The U.S. National Centers for Environmental Information issued a new State of the Climate report confirming that 2015 surpassed 2014 as the warmest year since at least the mid- to late 19th century. This scientifically accepted report is based on contributions from scientists from around the world and reflects tens of thousands of rigorous measurements. The globally averaged sea surface temperature was also the highest on record, breaking the previous mark set in 2014.

In a clear example of what President Abraham Lincoln intended when he established the National Academy of Sciences, the scientific community has contributed to our nation’s response to this threat by endeavoring to better understand the many dimensions of this complicated problem. It behoves those who proudly invoke the memory of Lincoln to accede to his original intent.

Category: Climate, Meteorology

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What is a heat wave?

Posted on July 25, 2016 by WeatherGuys Editor

A heat wave is a period of abnormally and uncomfortably hot and usually humid weather. The World Meteorological Organization is specific in its definition by stating that a heat wave is when the daily maximum temperature for more than five consecutive days exceeds the average maximum temperature by 9 degrees.

Heat waves are caused by very hot, stagnant air masses. Regions that suffer under intense hot spells are usually dominated by a surface high-pressure system with a mid-tropospheric ridge aloft. Dew points are also high, and to compound matters, wind speeds are often low.

Clear or partly cloudy skies allow intense solar energy to further heat the ground and the air mass. High humidity and stagnant air reduce the body’s ability to cool down through sweating. Lives are endangered when these conditions persist day and night for several days.

Each summer in the United States, about 175 to 200 deaths are attributed to heat waves. Most of these deaths occur in cities, particularly northern cities. Heat waves also have a strong economic impact.

A prolonged heat wave can cause the widespread use of air conditioning, leading to increased demands for power that stress gas and electric utilities. Transportation can be stymied when highway surfaces and railways buckle and warp in the heat. All types of outdoor work, such as landscaping and construction, experience reduced productivity. Agriculture is especially vulnerable as heat waves stunt crops and kill livestock.

The National Weather Service issues excessive heat warnings within 12 hours of the onset of extremely dangerous heat conditions. This warning is generally issued when the maximum heat index temperature is expected to be 105 degrees or higher for at least two days and nighttime air temperatures will not drop below 75.

These criteria for issuing a warning vary across the country, especially for northern regions that are not used to hot, humid conditions.

Category: Meteorology, Seasons, Weather Dangers

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