Weather

TexasUniv_NewLogoQ:  You hear a lot about El Niño and La Niña. What’s the difference?

A: The main difference between the two involves water temperature, explains Brent McRoberts at Texas A&M University.  El Niño and La Niña – Spanish for “the child” – both occur in the central Pacific Ocean.  “During an El Niño event, which can last almost a year, the waters in that region are warmer than usual,” he says. “The opposite occurs during a La Niña – the waters tend to be cooler than usual.  But the important thing is that both events can affect weather patterns in the United States and around the world.”

Q: How do they change our weather?

A:  In years when a La Niña occurs, there tends to be warmer and drier conditions in many areas, including Texas, McRoberts says.  “In general terms, a La Niña period means drier weather patterns for Texas. There are been numerous studies done on how El Niño and La Niña affect weather patterns, and specifically, hurricanes and their intensity. Some research indicates that the sorts of hurricanes that affect Texas are more common during La Niña periods than during a neutral or El Niño year.”

TexasUniv_NewLogoQ: You sometimes hear the term “Alberta Clipper.” What is it?

A: An Alberta Clipper is a winter storm that forms over regions of Canada near the province of Alberta and sweeps in a southeastern direction over the northern United States, says Brent McRoberts of Texas A&M University. “It is believed the name comes from the big sailing ships of the 1800s, the ones with the huge sails that could travel quite quickly for vessels of that time period and were among the fastest ships on the seas. An Alberta Clipper storm moves quickly once it forms and brings cold temperatures, strong winds, and snowfall to the northern Great Plains and Great Lakes regions,” McRoberts explains.

Q: Are the storms considered blizzards?

A: No, says McRoberts. “An Alberta Clipper usually has very cold temperatures and gusty winds, but because of its quick movement, tends to produce small snow totals,” McRoberts explains. “If snow does occur, it’s usually just a light dusting to a few inches. However, if a Clipper moves over the Great Lakes region, it can produce lake-effect snowfall in those areas that are on the downwind of a lake. But generally, an Alberta Clipper produces gusty winds and very cold air over the areas in moves into and very rarely is categorized as a blizzard.”

TexasUniv_NewLogoQ: Can the weather affect how you feel?

A: For certain people, the answer is definitely yes, says Brent McRoberts of Texas A&M University. “Many people have said they can tell a change in the weather is about to happen because their joints or muscles start to ache,” says McRoberts. “This is likely due to a change in the barometric pressure, which often happens before a thunderstorm or in advance of a cold front. Damp weather is often associated with a low pressure system. A decrease in the air pressure decreases the tension in some large blood vessels, meaning they tend to expand. When this happens, it tends to lead to increased discomfort in joints and muscles. Also, we know that very rapid changes in temperature and humidity can make some people say they feel ‘stiff and achy.’ Many people who have arthritis say their joints are definitely affected by weather changes.”

Q:  So can any weather change be a health problem?

A:  Probably so, he adds. Some people like rainy days, which can bring muscle misery to others and even breathing trouble, and some people may enjoy cool, dry days, which can also bring aches and pains for some people, including increased sniffing. Since it appears almost certain that weather has an affect how we feel, there has been a dramatic increase in interest in the field of biometeorology – the study of how weather affects our bodies. One German study shows that as much as 25 percent of the human population is ‘weather sensitive,’ meaning weather changes tend to worsen some pre-existing health conditions. Even headaches are being investigated – some researchers say migraine headaches are linked to sudden weather changes.”

TexasUniv_NewLogoQ: How strong does a snowstorm have to be before it’s called a blizzard?

A:  There are some specifics regarding blizzards, says Brent McRoberts of Texas A&M University. “In meteorological terms, a blizzard is a severe storm that has below-freezing temperatures, winds of at least 35 miles per hour and heavy snowfall, with visibility reduced to just 1/4 of a mile, and all of these conditions have to last at least three hours,” he explains. “So just a heavy snowfall is not always a blizzard. Blizzard conditions occur most often in the Great Plains, North Central United States and parts of the Northeast.”

Q: What are some of the country’s worst blizzards?

A:  The blizzard that hit the Northeast in recent days may well wind up in the record books, he notes, as it shut down Washington, D.C., Baltimore and other cities, and final snow totals are still being recorded.  In previous years, Buffalo had a blizzard that paralyzed the city for days in 1999, Colorado had a similar situation in 1997 and Boston suffered terrible blizzard conditions in 1978, McRoberts says. “Chicago had devastating blizzards in 1979 and one in 1967,” he adds. “The ’67 blizzard totaled 23 inches of snow with drifts up to 9 feet and the city was virtually shut down for days, with the Department of Streets and Sanitation estimating that about 75 million tons of snow fell. At least 60 people died, many of them from heart attacks while shoveling snow. Although records tend to be sketchy, perhaps the country’s worst blizzard occurred in 1888. In parts of the Midwest, the temperature fell from 74 degrees to minus 28 within hours, and the Colorado River froze solid throughout much of Texas. That blizzard claimed 235 lives.”

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TexasUniv_NewLogoQ: What causes frost to form?

A: Frost forms when the temperature at the ground reaches freezing, says Brent McRoberts of Texas A&M University. “Very often on calm, clear nights, the temperature near the ground can be several degrees cooler than temperatures above the ground,” he explains. “The thermometer might read 34 degrees on top of a roof, but at the ground, it might read 32 degrees. This is because the ground loses heat quickly. So water vapor in the air, because it is so cool, condenses as supercooled dew and then turns to frost and maybe ice. Frost tends to form on glass, such as car windshields or windows, metal or rock surfaces first because these tend to lose more heat quicker. So usually, a car windshield will frost over before vegetation does.”

Q: Does frost form quicker in some areas than others?

A: Yes, McRoberts says. “Cold air is dense and it tends to sink,” he explains. “On a calm night, cold air will tend to sink into low spots. That’s why valleys can be much cooler than the surrounding area because the cold air from the hills sinks into the lower areas. So when the cold air starts sinking, frost will form quicker in the low spots than the high ones. It’s not uncommon for some valleys to be cooler by 10 degrees or more, thus more frost tends to form in these low areas. Also, some soil types, such as sand, retain less heat than others, and frost tends to form quicker on these.”