Weather Forecasting in UK Waters, Using Barometer Readings and Local Observations

A Short-range forecast of changes in the weather can often be made by intelligent observation of wind, cloud and sky and of the movements and readings of the barometer. Local weather lore is also of assistance, though it must be remembered that not even the best-known and most reliable saying about the weather is infallible; no saying based upon the phrases of the moon has any meteorological significance whatsoever. It must also be remembered that local weather lore applies to the locality of origin, and cannot be applied indisciminately elsewhere.The following indications, when taken in conjunction with such other evidence as may be available, should help an isolated observer to forecast the weather for the next few hours in the eastern North Atlantic.


Barometer

The Average barometer reading in the south of England is about 1014 millibars, and in the north of Scotland it varies from about 1013 millibars in summer to 1008 millibars in Winter; the following table shows the probable weather to be expected for different departures from these normals.


Barometer 5 mb. or more below normal, and steady or falling.

Unsettled.

Barometer 5 mb. or more above normal, and steady or rising.

Settled for at least a day, with light or moderate winds.

Barometer below 1000 mb. or falling rapidly at 1 mb. or more in an hour.

Strong winds and rain.

Barometer rising rapidly.

Fair or fine, usually followed in a day or so by another fall and more unsettled weather.

'Long foretold, long last;

Short notice, soon past'.

Indicating that a steady fall over a long period foretells a long spell of bad weather, but a rapid falls indicates a short but severe spell.

'First rise after low Foretells a stronger blow'.

Indicating that the full force of a gale is often felt after the centre of a depression has passed. Gales with a rising barometer are always squally.


Wind

In the absence of a weather map the relationship between wind direction and weather in Home waters and the north-eastern Atlantic is not well defined, but it is possible very broadly to distinguish the following four main types.

South-westerly winds.

These come from the warmer waters of the Atlantic further southward and are cooled at the surface by the progressively decreasing sea temperatures as they travel towards us. Weather is mild and damp, with poor visibility, and skies are nearly or quite overcast with a pall of low cloud.Drizzle is common on windward coasts, and weather is generally unsettled, with the probability of rain. In late spring and early summer sea fog may occur.

North-westerly winds.

These bring cold air from higher latitudes, which is warmed at the surface during its passage over progressively warmer water.Weather is cool or cold, with good visibility, and clouds of the cumulus type are formed from which showers fall. In winter the showers may be of snow.

North-easterly winds.

These have usually come from Scandinavia or north Russia.Weather is cool in summer and cold in winter. Skies are most often cloudy or overcast, and snow is common in the winter.

South-easterly winds.

These have usually come from central Europe, and are cold and dry in winter and warm and dry in summer. Cloud amounts are generally small.

The following sayings originated in the days of sail, long before weather forecasting became a science, but they are well worth remembering; they apply, of course, only to UK waters and the north-eastern part of the Atlantic.



A veering wind fair weather:

A backing wind foul weather.

A wind backing towards a southerly point is often an early sign of an approaching depression; a veering wind indicates that the low is passing away eastward and that improving weather will be expected.

'If the wind is north-east three days without rain,

Eight days will pass before south wind again'.

One of the most striking features about weather in these latitudes is the tendency for a given type - good or bad to persist once it has become established. This tendency is recognised in these sayings.

'When the rain's before the wind,

Topsail halliards you must mind;

When the wind's before the rain,

Hoist your topsails up again'.

With an approaching depression, if there is little wind when the rain starts it will probably blow hard before long; whereas if the gale comes first it will probably have done its worst by the time the rain comes.

Sky


A low sunset fair weather; a high sunset rain and/or wind.

A sunset is low when the sun sets on a clear horizon; a sunset is high when it sets behind a bank of cloud well above the horizon. Bad weather usually approaches from westward and is preceded by a bank of cloud which hides the sunset.

Bright yellow sunset

Wind

Pale yellow sunset

Rain

Red sunset

Fair Weather

Clouds

Soft-looking, delicate, low clouds

Fine weather, with light or moderate breezes.

Hard-edged, oily-looking clouds

Wind

Small, inky-looking clouds

Rain

After fine, clear weather the first signs in the sky of a coming change are usually light streaks, curls, or wisps of distant white cloud, which increase until the sky takes on a milky appearance and the sun and moon become surrounded by haloes. The cloud thickens until the sun and moon are seen only indistinctly through a watery sky, which foretells rain within a few hours. These are infallible signs of an approaching depression, but often they cannot be seen because the sky is covered with lower clouds.


Misty clouds forming or hanging on heights.

If they remain, there will be wind and rain;

if they rise or disperse, the weather will improve or become fine.

General Sayings:


When sea birds fly out early and far to Seaward.

Fair weather and light or moderate winds.

When sea birds remain over land or fly inland.

Stormy weather.

Dew and fog forming inland at night.

Fine weather; neither dew nor fog form under an overcast sky, or when there is much wind.


This material has been adapted from old Admitalty Manuals of Seamanship, written between the 30's the 50's, and is probably of more relevance to the small craft mariner than modern material.



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