What sensors indicate the weather: part 1

Temperature, barometric pressure, humidity, wind speed and direction, and possible rainfall (or snowfall) in specific areas are common indicators of current and future weather conditions. However, other sensor inputs, such as pressure drop, air quality, particulate matter (including dust), and more (storm surge), are frequently required to identify and react to extreme weather conditions. The recent hurricanes (Helena and Milton) in the 2024 hurricane season provide dramatic examples of not only the unique requirements of hurricanes but also the tide/surge levels and tornadoes that can occur as well.

What’s today’s forecast?

Normally, the day-to-day weather forecast provides sufficient information for people to know what to wear (such as a warmer coat) when they leave their home and if they need to have additional items, such as an umbrella, gloves, and/or boots to cope with the current and near-term weather conditions. For these purposes, a rough indication of temperature, barometric pressure, humidity, wind speed, and possible rainfall or snowfall are sufficient. Consequently, it is not unusual for local forecasts to vary considerably for these predictions (even though the Federal Government provides detailed measurements and analysis). However, even in these normal forecasts, when a large variation occurs that could produce hazardous conditions such as wind gusts, microbursts, flash, and other local flooding, the variations from normal or average become much more important.

Unusual weather

Some unusual weather situations have occurred within the last 50 or so years that have prompted other measurements, such as acid rain.

Acid rain, including snow, fog, hail or even dust, has acidic components, such as sulfuric acid or nitric acid that fall to the ground from the atmosphere. They can occur in either wet or dry forms. Measured using a pH scale, where 7.0 is neutral, normal rain has a pH of about 5.6. This is due to carbon dioxide (CO₂) dissolving into it forming weak carbonic acid. In contrast, acid rain usually has a pH between 4.2 and 4.4.

The impact of acid rain is most clearly observed in streams, lakes, and marshes, where it can harm fish and other wildlife. However, dead or dying trees are common in areas affected by acid rain. Also, when it lands on statues, buildings, and other man-made structures, acid rain can corrode metal and cause paint and stone to deteriorate more rapidly.

Acid rain was a major concern in the 1970s and ’80s. Because of strong air pollution regulations, nitrogen dioxide in the air has decreased by 57% and sulfur dioxide by 89% since 1990, according to U.S. Environmental Protection Agency (EPA) data. However, some countries in Asia, like China, continue to experience widespread effects of acid precipitation. In 2020, approximately 34% of cities monitored in China experienced acid rain.

In contrast to acid rain, an extreme weather phenomenon that seems to have increased recently is the occurrence of microbursts. A microburst is a localized column of sinking air (or downdraft) within a thunderstorm, typically less than 2.5 miles in diameter. In microbursts, wind speeds can reach up to 100 mph or even higher and cause severe damage.

Forecasters use several atmospheric parameters to help determine the potential for a microburst during a storm. These include atmospheric instability, high precipitable water (PW), dry air in the mid-levels, and strong winds in the dry layer.

Part 2 of this blog will explore where and how measurements are made to predict extreme weather.