Mackerel Skies and Mares Tails…
While sitting in the warm sun aboard a client’s boat yesterday the question was asked – “how can you possibly know what the wind will do? Do those clouds tell us anything?” The sky was clear, there was little to no wind and only a few whispy cirrocumulus clouds in the sky. While today’s sailors are hopeless inured to devices, immediate buoy data and forecasting tools; the sky still has an awful lot to tell us about what to expect next.
There are plenty of old weather rhymes to help make your next forecast accurate and easy. Using yesterday as an example, one of my favorite rhymes came to mind.
Mackerel skies and mares’ tails, soon will be time to shorten sails.
There are four basic cloud classifications. Their names are a little confusing to remember, but understanding what the different types of clouds portend is a necessary part of good seamanship.
The highest altitude clouds, cirrus, are your long-range weather forecasters. These clouds come in various shapes and sizes, including the “mare’s tail” variety, but they are always thin because they are formed by a thin layer of ice crystals. Getting familiar with cirrus formations is important in forecasting weather. Once you begin to notice and classify clouds, you’ll notice that high-altitude cirrus is responsible for a blue sky gradually turning into a milky haze and thickening, or “lowering” weather.
Cirro-cumulus clouds are the “mackerel skies” which develop from cirrus clouds beginning to lower and clump together. Due to their relatively high altitude, they have a dappled look, and a silvery sheen.
Cumulus clouds, or “fair-weather clouds,” are the middle range of cloud which are characteristically white, fluffy, and lend themselves to imaginary shape-shifting. These are the happy-go-lucky clouds of the trade winds and high-pressure systems. If uncomplicated by further development, a parade of these simple cumulus against a true blue sky, absent any cirrus or cirro-cumulus background, is a good indicator of decent or calm weather ahead.
Cumulo-nimbus clouds result when cumulus build up into the shape of a blacksmith’s anvil. The heat of a summer day often causes morning’s innocent cumulus fluff-balls to develop into towering anvils with very white tops and very dark lower edges (squall lines) by late afternoon. The good news is that cumulo-nimbus developments (if uncomplicated) tend to be very localized, though potentially extremely powerful in their vicinity – they are squalls. Because of their tremendous height from top to bottom, you can spot them a long way off on the water.
The barometer is also a great forecaster of wind and weather yet to come.
- “When the wind sets in form points between south and southeast and the barometer falls steadily, a storm is approaching from the west or northwest, and its center will pass near or north of the observer within 12 to 24 hours, with wind shifting to the northwest by way of south and southwest.
- “When the wind sets in from points between east and northeast and the barometer falls steadily, a storm is approaching from the south or southwest, and its center will pass near or to the south of the observer within 12 to 24 hours, with winds shifting to northwest by way of north. The rapidity of the storm’s approach and its intensity will be indicated by the rate and amount of the fall in the barometer.
- “As a rule, winds from the east quadrants and falling barometric pressure indicate foul weather, and winds shifting to the west quadrants indicate clearing and fair weather, but again there are exceptions and in some parts of the country these rules do not apply.”
The following table generally summarizes wind and barometer indications in the United States. The amateur forecaster should modify the table in accordance with his or her own observations. The following show the wind direction, the barometer reduced to sea level and the character of the weather indicated:
- SW to NW, 30.10 to 30.20 and steady – Fair with slight temperature change for 1 to 2 days.
- SW to NW, 30.10 to 30.20 and rising rapidly – Fair, followed within 2 days by rain.
- SW to NW, 30.20 and above and stationary – Continued fair, with no decided temperature change.
- SW to NW, 30.20 and above and falling slowly – Slowly rising temperature and fair for 2 days.
- S to SE, 30.10 to 30.20 and falling slowly – Rain within 24 hours.
- S to SE, 30.10 to 30.20 and falling rapidly – Wind increasing in force, with rain within 12 to 24 hours.
- SE to NE, 30.10 to 30.20 and falling slowly – Rain in 12 to 18 hours.
- SE to NE, 30.10 to 30.20 and falling rapidly – Increasing wind, and rain within 12 hours.
- E to NE, 30.10 and above and falling slowly – In summer, with light winds, rain may not fall for several days. In winter, rain within 24 hours.
- E to NE, 30.10 and above and falling rapidly – In summer, rain probably within 12 to 24 hours. In winter, rain or snow, with increasing winds, will often set in when the barometer begins to fall and the wind sets in from the NE.
- SE to NE, 30.00 or below and falling slowly – Rain will continue 1 to 2 days. SE to NE, 30.00 or below and falling rapidly – Rain, with high wind, followed, within 36 hours by clearing, and in winter by colder.
- S to SW, 30.00 or below and rising slowly – Clearing within a few hours, and fair for several days.
- S to E, 29.80 or below and falling rapidly – Severe storm imminent, followed within 24 hours, by clearing, and in winter by colder.
- E to N, 29.80 or below and falling rapidly – Severe northeast gale and heavy precipitation; in winter, heavy snow, followed by a cold wave.
- Going to W, 29.80 or below and rising rapidly – Clearing and colder.