Thunderstorms visible from afar

[CanisLupusArctos]

As I write this (Monday evening, 6 July) there is an anvil-shaped cloud visible to the southwest of Lake Winnipesaukee. An experienced boater, pilot, farmer, or outdoorsperson should know that's a thunderstorm with some decent energy inside it, a high-topped cumulonimbus. The weather at the lake has been sunny and benign all day long.

Satellite and radar imagery indicate the nearest tall cumulonimbus cloud to the southwest of Lake Winnipesaukee is in the Springfield, MA area. The "current alerts" map says the National Weather Service has a severe thunderstorm warning and a flash flood warning in effect there. It's no threat to the lake, but the massive cloud responsible for that mayhem (clips of insurance commercials come to mind) is tall enough to be clearly visible from Lake Winnipesaukee right now.

The eastern U.S. is well-known among storm chasers to have an obstructed view thanks to trees and buildings everywhere, and as a result most chasers won't come to this part of the country. Lakes like Winnipesaukee are large enough to provide a Great Plains-style view of significant weather that can extend 100 miles or more, depending on the altitude of that weather and the condition of the air.

Last night a severe-warned thunderstorm over I-89 hit Concord and moved into the seacoast region, and its lightning pulsed high over Lake Winnipesaukee the entire time. It made no thunder, because sound waves fade completely after a few miles, but the cloud-to-cloud pulses of electricity were vivid in the southern sky. It looked threatening, but the absence of thunder meant it was too far off to be a hazard at the Big Lake. One look at radar, satellite, and NWS alerts images confirmed that.

Sometimes, well after sunset, the lightning from tall thunderstorms over the Canadian border or the Gulf of Maine makes a nice (benign) light show in the unobstructed vantage points on and around Lake Winnipesaukee, just as it does for storm chasers and other observers on the wide-open Great Plains. Think of lightning in the same way as a camera flash: How far away is it noticeable in daylight? At dusk your cell phone's camera flash might get your next-door neighbor's attention, and at midnight it can put enough light through his bedroom window to wake him up.

Similarly, a flashing cloud that's 40,000 feet tall can light up the ground underneath for 100+ miles during the overnight hours. It can also light up the air around it for a much greater distance when there's a lot of humidity, because that consists of tiny water droplets suspended in the air and each one acts as a diffuser. Ask any professional photographer about that effect. Perhaps you've noticed that some cover the flash with wax paper and bounce the light off a white ceiling or umbrella.

Hence, we have the term "heat lightning." It's ordinary lightning from a thunderstorm -- heat doesn't cause lightning at all. Hot weather in the eastern U.S. usually comes with high humidity -- ideal conditions for seeing distant lightning flashes at night. Wherever that lightning is, it's an arc of electricity between one point and another, but raindrops and humidity in the air produce the same effect as a photographer's wax-paper flash cover.

If you're a boater, it's good to know about weather. In this age of handheld computers it's just as good to bookmark local radar, satellite, and alerts imagery for referencing when you see something on the horizon. It's popular advice that a good time on the water isn't worth risking your life, but if you know when you can safely remain on the water to enjoy a view of natural phenomena, those are the moments we tend to remember fondly years later.