Admiral Sir Francis Beaufort was one of the first weather forecasters of the modern era. In 1805, the Brit developed a low-tech way for sailors to determine without the use of any instruments whatsoever. And, according to the National Weather Service, it still holds up today in a pinch. Intensity, measured by a scale of zero to 12, can be estimated on land or sea through the use of visual cues. Here’s a quick rundown of the environmental factors to observe on terra firma.

SMOKE SIGNALS On land, rising smoke is a tell. If it rises vertically, you’re at a scale of zero. If smoke drifts but a weather vane doesn’t move, you’ve notched up to a factor of one, which is still only a wind speed of 1-3 mph.
face it Leaves rustling along the trail (minus the presence of a wild animal, mind you) coupled with the feeling of wind on your face is your clue intensity has reached a two on the scale (4-7 mph). Should twigs, dust, loose paper, or small branches be picked up into the air, you’re at a four (9-12 mph).

WAYWARD WINDS By the time wind intensity gets to a factor of six, it becomes the occurrence local news photographers like to shoot. Imagine the contorted faces of pedestrians struggling to open umbrellas, wind whistling through wires, and hulking branches doing the sort of swaying dance you might find at a rock concert. This strong breeze clocks in at 25-31 mph.
HEADS UP Once the regular pace of one’s stride slows, you’ve reached the “near gale” force of seven (32-38 mph). When twigs break from trees, you’re at eight (39-46 mph) and at nine, we’re talking severe gale forces of 47-54 mph, with projectiles flying about.

BLOW OUT  Ever walk down a trail and see a few uprooted trees? That’s probably a sign of winds reaching speeds between 55-63 mph (a factor of 10), which is when structural damage is likely. When you see an entire swath of leveled land, it could well be the remnants of a violent storm (11 on the scale). Lastly, hurricane-force winds reaching 73 mph are something few are unlucky enough to experience.