Today's synoptic chart, updates 6,12,18 & 24:00hrs

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Today's synoptic chart, updates 6,12,18 & 24:00hrs

Synpotic means,

1. Of or constituting a synopsis; presenting a summary of the principal parts or a general view of the whole.

2a. Taking the same point of view.

2b. often Synoptic Relating to or being the first three gospels of the New Testament, which share content, style, and order of events and which differ largely from John.

3. Meteorology Of or relating to data obtained nearly simultaneously over a large area of the atmosphere.

High pressure or anticyclones (Picture Below)

Anticyclones are areas of high pressure, whose centres are often less well defined than depressions, and are associated with quiet, settled weather. Winds blow in a clockwise direction around anticyclones in the northern hemisphere, this is reversed in the southern hemisphere.

Low pressure or depressions (Picture Below)

Depressions are areas of low pressure, usually with a well-defined centre, and are associated with unsettled weather. Winds blow in an anticlockwise direction around depressions in the northern hemisphere, this is reversed in the southern hemisphere.

Fronts

Early weather charts consisted simply of station plots and isobars, with the weather being written as comments, like 'Rain, heavy at times'. During the 1920s, a group of Scandinavian meteorologists, known collectively as the Bergen School, developed the concept of representing the atmosphere in terms of air masses. Since the air masses could be considered as being in conflict with each other, the term 'front' was used to describe the boundary between them. Three types of front were identified which depend on the relative movement of the air masses.

Cold Front

A cold front marks the leading edge of an advancing cold air mass. On a synoptic chart a cold front appear as a blue line with triangles. The direction in which the triangles point is the direction in which the front is moving.

Warm Front

A warm front marks the leading edge of an advancing warm air mass. On a synoptic chart a warm front appears as a red line with semi-circles. The direction in which the semi-circles point is the direction in which the front is moving.

Occlusion (or occluded front)

Occlusions form when the cold front of a depression catches up with the warm front, lifting the warm air between the fronts into a narrow wedge above the surface. On a synoptic chart an occluded front appears as a purple line with a combination of triangles and semi-circles. The direction in which the symbols point is the direction in which the front is moving.

Troughs

Fronts describe thermal characteristics. They also happen to be where there is significant precipitation. However, precipitation is not confined to fronts. Drizzle in warm sectors or showers in cold air occur fairly randomly, but occasionally, lines of more organised precipitation can develop. These are called troughs.

Isobars

Isobars are lines joining places with equal mean sea-level pressures (MSLP).

Relationship between isobars and wind

Wind is a significant feature of the weather (see picture below). A fine, sunny day with light winds can be very pleasant.

Stronger winds can become inconvenient and, in extreme cases, winds can be powerful enough to cause widespread destruction. The wind can easily be assessed when looking at a weather map by remembering that:

* closer isobars mean stronger winds;

* the wind blows almost parallel to the isobars;

* in the northern hemisphere, the wind blows round a depression in an anticlockwise direction and around an anticyclone in a clockwise direction. In the southern hemisphere, the opposite is true;

* winds around anticyclones can sometimes be even stronger than indicated by the isobars;

* in warm air, the wind is relatively steady and tends to blow at about two-thirds the speed that the chart would suggest, though there are exceptions to this ;

* in cold air, the wind is usually as strong as indicated by the isobars and can be very gusty.

Will update with more information as time passes.

SW