Is Lyme disease connected to the weather?

Scientists at the National Center for Atmospheric Research and the U.S. Centers for Disease Control recently explored the relationship between the reports of Lyme disease and weather observations. They found that warmer temperatures, higher humidity and less rain are correlated with an earlier start and peak of the Lyme disease season.

The start of the Lyme disease season begins in late May on average and lasts for about 14 weeks. An above average amount of precipitation from the start of the year tends to result in a later beginning of the Lyme disease season. An earlier start to the season is associated with more days with temperatures above 50 degrees, except for the most northern regions of the U.S.

Deer ticks carry Lyme disease and can infect humans when they bite us. The disease is found predominately in Wisconsin, Minnesota and the northeastern United States.

The ticks that commonly spread the disease develop faster with warmer temperatures, and they are more active in feeding with warmer temperatures, higher humidity and a lack of heavy precipitation. Of course, these are times many people seek the outdoors.

Weather conditions not only affect the tick life cycle and our outdoor habits, but also the population of the ticks’ primary host — the white-footed mouse. A dry summer can result in less vegetation that is the food supply for the mice. This can result in a reduced population of mice, reducing the tick population and thus the cases of Lyme disease.

The correlation between weather and the start of Lyme disease season is strong enough that one can forecast the start of the season by analyzing the daily temperatures for the first 10 weeks of the year. Unfortunately, there are few correlations that support predicting the end of a particular Lyme disease season.

Category: Seasons

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Does meteorological science have an impact on public policy?

One key piece of the world’s evolution toward nuclear sanity during the height of the Cold War was motivated by growing understanding of a fundamental meteorological phenomenon: the development of what’s now known as upper-level frontal systems.

The first atomic bomb was tested on July 16, 1945, in New Mexico, ushering in the nuclear age. Over the next decade and a half, continuously bigger bombs were tested in our atmosphere and oceans. Most of these bombs were exploded in the Earth’s stratosphere under the assumption that the air never mixed downward into the troposphere, where we all live.

During this time, meteorologists at MIT began to find evidence poking holes in this assumption. Professor Richard Reed was discovering that upper-level fronts were a possible pathway by which stratospheric air could mix into the troposphere.

His ideas were initially met with derision. However, evidence for the ubiquity of these upper fronts and the efficiency of the stratospheric/tropospheric mixing that they encouraged grew in proportion to the strength of the bombs that were being tested.

Eventually, the evidence was accepted by the meteorological community at large and this new scientific insight was employed in the shaping of important public policy.

In a June 1963 address at American University, President John F. Kennedy announced a new round of high-level arms negotiations with the Russians. This speech was considered so important by Premier Nikita Khrushchev that the Soviet press allowed it to be printed in its entirety.

On July 25, 1963, after only 12 days of negotiations, the United States and the Soviet Union agreed to the Nuclear Test Ban Treaty ending atmospheric tests of nuclear devices; it was signed 11 days later.

Category: Meteorology

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Is there any trace of winter left in the Northern Hemisphere?

We have made reference a few times in this column to the areal extent of cold air over the Northern Hemisphere as a measure of wintertime severity, that is, the geographic reach of air of a certain temperature.

Specifically, we have reported on the 23-degree air at 1 mile above the ground (where the atmospheric pressure is just 85 percent of its near-surface value). By mid-July it is impossible to find air that cold at that elevation in the Northern Hemisphere.

In other words, the cold air that in mid-winter covers over 26.2 million square miles disappears entirely in midsummer.

This is vivid testimony to the power of the increased sun angle and the longer days that characterize our summer versus the winter.

As we move past the summer solstice toward the autumnal equinox, both the sun angle and the length of the day begin to decline, with the length of day shortening dramatically faster at high latitudes than it does here in Madison.

The shorter day means, of course, a longer night, which allows more time for the ground to radiate energy away to space. This energy loss eventually and inevitably leads to the production of cold air near the surface of the planet.

As we head further into the late summer and early fall, high-latitude cold air production continues to benefit from the short day and low sun angle. The cold air builds up to the point where it is exported regularly from high latitudes to lower latitudes and the areal coverage of the 23-degree air grows, on average, at a uniform rate from Sept. 1 to Dec. 1. It reaches its peak near late January and then shrinks uniformly from around April 1 to late June.

Our longest day of the year has already come and gone. In the next week or two we will begin to see the inevitable return of cold air to the Northern Hemisphere, a harbinger of winter.

Category: Meteorology, Seasons

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What is the difference between a ‘warning’ and a ‘watch’?

The difference is that a weather watch indicates that hazardous weather may occur, while a warning is issued when hazardous weather is occurring, is about to occur or has a very high probability of occurring.

A warning indicates that conditions pose a threat to life or property, and people in the area of the warning should take action to protect themselves. A watch is intended to provide people with enough time to set safety plans in motion for possible hazardous weather.

Watches and warnings outline areas where the weather may occur. Pinpointing the location of hazardous weather in advance is extremely difficult. For this reason, watches are usually issued for large regions, sometimes covering several states. Warnings are issued for much smaller areas, often only a county or two, because they are based on actual observations of hazardous weather.

The National Weather Service issues weather watches and warnings under specific weather conditions.

A severe thunderstorm watch means that conditions are favorable for the development of severe thunderstorms in and close to the watch area.

A warning means that a severe thunderstorm has been sighted visually or indicated by radar, and that the thunderstorm is producing hail at least 3/4 of an inch in diameter and/or has winds equal to or exceeding 58 mph.

Then there are weather advisories, which may be issued when actual or expected weather conditions are not hazardous but may cause inconvenience or concern.

Category: Severe Weather, Weather Dangers

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How do you stay safe from lightning?

There is no place outdoors that is completely safe during a thunderstorm, so the saying goes, “When thunder roars, go indoors!”

The safest thing to do is to get inside a safe building or vehicle. A safe building is one that is covered with a roof, walls and floor, and has plumbing or wiring. Stay away from metal and electrical equipment, including computer, plumbing and faucets. Keep away from windows and doors, and don’t hang out on a porch to watch the lightning storm.

Many lightning injuries and deaths occur on boats that do not have cabins.

So, listen to the weather when boating, and if thunderstorms are forecast, get off the water.

If you cannot get indoors, avoid elevated areas like mountain tops and open fields. Never lie on the ground or seek protection under an isolated tree. Stay away from metal objects like fences, golf carts and farm equipment.

A lightning bolt can travel many miles away from a thunderstorm before striking the ground. These are called “bolts from the blue” because they appear to strike out of the clear blue sky. New instruments to study lightning have measured lightning bolts that seem to come out of the cloud base, striking ground 50 miles from where they originate.

The National Weather Service keeps track of when, where and who gets hit by lightning.

Lightning strikes Wisconsin soil about 300,000 times a year, mostly during spring and summer. On a yearly average, lightning causes about one death in Wisconsin and 62 deaths nationally. Your chances of getting hit by lightning are about one in 1 million.

Category: Severe Weather, Weather Dangers

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