We, and I speak for all skippers, have been lectured ad infinitum about how to prepare and what to do when the electronics go zap. We’re told repeatedly to learn basic navigation and how to communicate when the gremlins are playing with the systems that we take for granted.
But the one thing that seems to be overlooked is weather. When the black boxes literally go black, so does our connection with weather prediction. We’re used to the Twinkies on TV who deliver our weather, the VHF has the WX channels, and many of our yachts have sophisticated fax or computer programs to monitor weather. Until everything stops.
At that point, you need to fall back on the skills that helped Columbus cross the Atlantic and Cook reach Australia. They didn’t get emails telling them to dress warmly or carry an umbrella tomorrow, they had to figure it out themselves, and so can you.
The starting point is to open your eyes. You don’t need a forecast to tell you that black wall of cloud is bringing you a squall. You’ve been on the water, so start using what you already know.
It’s never bad to err on the conservative side. I knew something felt wrong when we left Morro Bay, California to power north around the legendary graveyard of Point Conception, but I went anyway and had my head handed to me in buckets of wind and breaking seas. The forecast was clear, and it caught the local fishing fleet flatfooted, too. We all shoulda’ known better. The 1979 Fastnet Race ended as the worst yacht racing disaster with 18 dead, but the forecasts at the start were for, you guessed it, fine weather. So go with your instincts.
To do your own forecasting, you need at least one piece of equipment that’s been around since the 1600s: a barometer. This instrument senses the atmospheric pressure and is as essential to the yachtsman as a thermometer to a doctor.
Usually in a fancy housing on a bulkhead as décor, you should immediately start noting the readings every hour to begin your predictions. Even better than a barometer is the more expensive barograph, which records the readings continuously on a roll of paper so you don’t have to keep such a careful watch.
Entire articles have been written about using the barometer, but here’s the essence. Tap the barometer (gently!) to settle the needle. Falling pressure indicates bad weather, and the speed of the decrease over several hours tells you the severity. Gently falling pressure, which is almost a straight line on a barograph (or on graph paper you use to plot the readings) means a mild low is nearby. If the pressure drops suddenly, batten down the hatches. It works the other way, too: increasing pressure suggests a high and good weather.
A second piece of useful equipment is an anemometer to give you wind speed and direction. This, combined with “checking the glass” (barometer), can give you an idea of where the storm is located, and thus suggest which way to run if you want to duck it.
You can get a good bearing on the center of a storm by facing directly into the wind. Because the winds in the northern hemisphere move counterclockwise around a low, the center of the storm will be slightly behind your right shoulder or at about 120 degrees from the wind.
Knowing the wind speed and direction is another clue to the track of a storm. If the glass is falling and the wind starts to build from a constant direction, the storm is heading directly toward you.
Time to open your eyes again. A landlubber looks at clouds and says, “Pretty!” A seaman looks at clouds and says, “Aha!”
But first, you need to know what those white fluffies mean. A good starting point is the Skywatcher Cloud Chart from NOAA (posted at www.passagemaker.com as a web extra) that gives you an excellent visual reference for cloud spotting.
Once you’ve got a handle on which are which, you can start to draw conclusions from what you see. Again in the northern hemisphere, the usual pattern of an approaching cyclonic storm (as opposed to an afternoon squall) is to first see the high thready cirrus, which are borne on the jet stream at a great altitude. If they stay thready and wispy, they may predict continued good weather, but if they spread to cover the entire sky or thicken into a layer, plan on some weather arriving within a day.
Next to arrive are clouds in the middle, or “alto” level. There are several types of alto clouds, but what you’ll notice is a lowering cloud base, and you may even get dark and torn clouds (scud) moving fast below the alto level.
A warm front brings low stratus or nimbostratus thick enough to hide the sun, with a light drizzle. As this is taking place, the barometer continues to fall but will stop with the end of the rain. This is just a prelude, in many cases in this hemisphere, to a following cold front with heavy rain and stratocumulus clouds. As this rain and wind ends, the barometer will start up fast and the sky will settle with layers of cumulus.
These are all generalities, of course, but the more you know about clouds and what conditions they indicate, the better your abilities will be to predict the weather.
Fog is common from Downeast Maine to San Francisco Bay and, to predict it, skippers need two more devices. The first is a good thermometer and the second is a device for measuring humidity called a psychrometer or, more commonly, a hygrometer. You can pick up a thermometer at an outdoor shop, and hygrometers are under 25 bucks at Wal-Mart. Or you can opt for a battery-powered instrument that includes both.
To understand fog, you have to understand “dew point,” which is the temperature of an air mass at which the air can no longer suspend water vapor. In short, the air is saturated and dew point is when condensation begins to take place.
You’ll need a chart to figure out if dew point is likely to occur (print one off the Internet). Take the current air temperature from the thermometer and the relative humidity from the hygrometer. At the intersection of these two numbers on the chart is dew point. It takes a 1-degree drop in temperature below dew point to cause fog. For example, if the temperature is 70 degrees and the humidity is 70 percent, the dew point will be 60 degrees. If the temperature drops to 59 degrees, you’ll be in fog.
Knowing how close you are to dew point tells you the likelihood of a sudden fog, and you can plan accordingly.
Of course, keep in mind that highly trained meteorologists with doctorate degrees often don’t know it’s raining until they step outside. So use all the tools available to you, make your best estimate, and don’t be surprised if Mother Nature tricks you.
After all, you can always fall back on the old maxim, “Red sky at night, sailor’s delight. Red sky at morning, sailor take warning.” Don’t ask me to explain it, it just works!
To download a PDF of NOAA's Introduction to Clouds, click here.