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By Tamia Nelson July 24, 2001
Unless they spawn tornadoes, knock out a power
station, or blow down a few thousand acres of trees, thunderstorms don't often
make the local news, let alone get the sort of national coverage given to
hurricanes. That's fair enough, I suppose. Hurricanes can be identified days or
weeks before they make landfall, and they frequently threaten hundreds of miles
of coastline. Thunderstorms are mostly local affairs. They boil up, rage across
the summer landscape, and then die out, all in less than an hour. End of story.
No sound-bites. No film at eleven. Just another summer storm.
The view's a little different from the seat of a canoe or kayak, however. If
you're out on the water in a small boat, it's hard to ignore the threat
implicit in a darkening horizon to windward, or the rumble of distant thunder.
And few natural spectacles can equal the awful majesty of a towering,
anvil-shaped cumulonimbus cloud—the classic "thunderhead."
Thunder or thunderhead, though, the message is the same: this isn't the
nightly news. This is Real Life. And it isn't happening to somebody else.
You're not sitting on the couch, watching a stranger get hammered. The storm
that's boiling up in the distance could be headed your way. You're
on-camera now, and the tape is rolling.
It happens to all of us, sooner or later. Some folks get pretty blasé.
"It's just a thunderstorm," they say. "Big deal!" And they shrug their
shoulders and keep paddling. A few folks even welcome the excitement. After
all, a summer storm can turn Golden Pond into something not too far removed
from the North Atlantic in winter. Sixty-mile-an-hour gusts. Big, breaking
waves. The flash and bang of nearby lightning strikes.
Does that sound like fun to you? It can be, I admit. To a climber on an
exposed ridge, or a kayaker in the middle of a big lake, a storm can be the
ultimate adrenaline high. But the fun comes at a price, and that, too, can be
high. The stats compiled by the National Weather Service suggest that lightning
strikes claim just about as many lives every year as hunting accidents. Many
more folks—several hundred a year, in fact—are struck and survive.
It's a safe bet that not very many of them want to repeat the experience. A few
will even suffer life-long disability.
Nor is lightning the only hazard. Wind gusts and breaking waves can dump
even expert paddlers in the drink and make rescue almost impossible. And you
don't have to be five miles offshore to have a bad time. Farwell once watched a
party of very competent sea kayakers get into trouble on little Middle Saranac
Lake, as fifty-mile-per-hour gusts knocked them down again and again. They
rolled back up every time, but they were worn out before they made the shore.
If they hadn't been very fit, or if they didn't all have bomb-proof rolls,
they'd have been in a world of hurt.
And wind gusts don't just knock down paddlers. A friend's niece went
canoe-camping on Lake George with some of her buddies from school. They had a
beautiful site on a forested island in the Narrows. Then a squall line rolled
through after dark, snapping eighty-foot-tall white pines like toothpicks. Two
of the campers were in a tent right under one of the falling pines. I'll leave
the rest to your imagination.
Enough Sturm und Drang. It's a no-brainer, really. Thunderstorms can
brew-up almost anywhere, and—in temperate latitudes, at least—they're
commonest during the late spring and summer months, just when folks are most
likely to be paddling and camping. The moral of the story? If you've spent much
time around small airfields, you've probably heard someone say, "There are old
pilots, and there are bold pilots, but there aren't many old, bold pilots."
What's true of pilots is equally true of paddlers. Courage is a good and
necessary thing, but the line between bravery and folly is often a narrow one,
and it pays to know when it's time to quit. Thunderstorms are powerful.
Thunderstorms can kill. Even if you can't out-muscle one, though, you ought to
be able to out-think it. Most storm-related deaths are avoidable. But you need
to know a little bit about the "enemy" first.
When Push Comes to Shove
Let's look at what causes thunderstorms. Two elements are necessary. The
first is warm, moist, unstable air. The second is some sort of upward push. The
push can be generated by the sun's heat alone. Or it can come from a mountain
range, standing in the path of an advancing air mass and forcing it up and
over. Or by a cold front, shoving its way through a pool of warm, humid air.
Mountain-generated storms are limited to windward slopes and the areas
immediately downwind. Local knowledge is usually your best guide to these. Most
typical summer thunderstorms, on the other hand, are caused by the sun's heat
alone. As the day warms up, the sun warms the ground, and some places get
hotter than others. Driveways get hotter than lawns, for example, and meadows
get hotter than adjacent woodlands. This is known as differential heating. When
the earth heats up, it warms the air above it. Then the heated air starts to
rise. The result? Isolated cumulus clouds soon start to form. If conditions are
right—lots of warm, moist unstable air—these clouds will grow and
grow, and the puffy cotton-ball cumulus will morph into dark, ominous
thunderheads.
Obviously, not every cumulus cloud becomes a thunderhead. So how do you tell
if conditions are right? Well, unless you bring a lot more gear along with you
than I do, you probably can't send up weather balloons to determine the
environmental lapse rate in the air above you. You can listen to NOAA weather
radio, of course—in the United States, at any rate. Good as the National
Weather Service is, though, it can't monitor every square inch of the country's
surface. You're the expert on the weather where you are, after all.
OK. You're the expert, but you still need data. So pay attention to what you
can see and feel. Is the air oppressively hot and humid? Are you breaking out
in a sweat just breathing? Most importantly, do the little cotton-ball summer
cumulus clouds seem to be growing upward? Then the day's what country folk used
to call a "weather breeder." Keep your eyes on the horizon to windward, and
watch those building cumulus clouds. If the horizon darkens, if one or more of
the building clouds keeps growing and starts to develop a broad, spreading top,
or if you hear the rumble of distant thunder, chances are pretty good that
you're in for some fireworks.
Does the thunder sound too far away to be a threat? Don't be fooled. If you
can hear thunder, you're already within range of a lightning strike. The
thunder can also tell you something about the path of a storm. Look for a
lightning flash. When you see one, start counting seconds: "One
one-thousand, two one-thousand, three one-thousand,…." Stop
counting when you hear the thunder-clap. Now divide the number of seconds by
five. That's how many miles away the lightning strike was.
Keep doing this as long as you can hear thunder. If the distance gets less
and less, the storm is headed your way, and it's time to think about getting
off the water. Each towering cumulus cloud is a huge Van de Graaf
generator, developing enormous electrostatic potentials. Sooner or later, the
accumulating charge is going to start looking for a quick route to the earth's
surface. If you're out in the middle of a lake when that happens, you're likely
to be the tallest thing around—and therefore the shortest path on offer.
Even aboard an eighty-foot schooner, a bolt of lightning striking a
properly-grounded mast is a sight to remember. But there's no safe place from
which to watch the show aboard a sixteen-foot sea kayak. Worse yet, you're the
"mast." It's not a reassuring thought.
Once a thunderhead forms, rain can't be far behind. Cold downdrafts develop
and spread out from the base. If you're in the path of the storm, you'll likely
see a line of rapidly advancing low clouds ("scud") coming toward you, driven
by gusty winds. Forty miles an hour is commonplace. Eighty miles an
hour—that's hurricane force—isn't unknown. As the storm gets closer,
the temperature will fall dramatically, sometimes by more that 20°
Fahrenheit. Periodically, the rapidly darkening sky will be illuminated by a
flash of lightning. Soon the rain will be sheeting down, often mixed with hail.
The heaviest rain usually doesn't last very long—no more than half an hour
or so—but one to two inches can fall in those few minutes. You'll be glad
to be under a securely-guyed tarp!
That's the story of typical summer thunderstorms. Since they develop in
response to differential heating, they're most often encountered in afternoon
or early evening. But there's another type of storm that's both less
predictable and more dangerous: the squall line.
Götterdämmerung
Fronts can also produce lift, and when a strong cold front plows into a mass
of stagnant, humid air, the result can be spectacular. Summer thunderstorms are
usually local, more-or-less isolated affairs. When a vigorous cold front blows
down from the north in late spring and early summer, however, and when
upper-atmospheric conditions are right, multiple thunderstorms can form in a
narrow band well in advance of the front. Sometimes these lines stretch out for
several hundred miles. The passage of a squall line is a very bad time to be
out on the water. One-hundred-mile-an-hour winds are possible, as are tornadoes
and waterspouts.
This isn't your idea of a good time? It's not mine, either. But what can you
do to anticipate a squall line? First, if you're planning a weekend trip, pay
close attention to the official forecast. If the weatherman starts talking
about a "vigorous frontal passage" with accompanying thunderstorms, listen very
carefully. You may decide it's a good weekend to do some chores around the
house.
If you're back of beyond, however, and half-way through a month-long trip,
you're on your own. Don't put too much reliance on the calendar or clock. While
the conditions that give birth to squall lines are most often seen in in the
early months of the paddling season, at least in the northern United States,
they can arise at almost any time of year. And unlike typical summer
thunderstorms, they're not limited to afternoon and evening hours. So it's up
to you. On a long trip, you're the weatherman. Check your barometer
every four hours and log the readings. Note the wind speed and direction, and
look at the sky around you. The combination of a falling barometer and
thickening mid-level and lower cumulus should get your attention, particularly
when accompanied by increasing winds, and especially if the air is hot and
humid. If this describes what's happening when you're on the move, keep your
eyes and ears open, and start looking around for a good heavy-weather campsite.
Long before the gods start banging on their anvils in earnest, you want to be
someplace safe.
What's that? You're not sure what a "good heavy-weather campsite" is? No
problem. We'll talk about that next week.
To be continued….
Copyright © 2001 by Verloren Hoop Productions. All rights
reserved.
The Restless Air
Thunderstorms—Anvils of the Gods
tamia@paddling.net
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