A Winter Pattern An Exceptional Pattern A Summer Pattern

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Understanding weather patterns

Wind direction is the direction from which the wind is coming from.

For example, a South Westerly wind blows from the South West to the North East.

Wind direction is reported in degrees from true North.

The Indian Ocean and Atlantic Ocean high pressure systems are situated more southward of the country. A trough of low pressure is positioned over the central and eastern parts of the country with moisture being advected from the tropical Indian Ocean anticyclone which results in greater rainfall towards the eastern parts of the country and less towards the west.

The Indian Ocean and Atlantic Ocean high pressure systems shift northwards and merge over the country during winter, which largely creates the dry conditions over much of the continent. However, cold fronts, moving mostly over the southern half of South Africa together with the ridging of the Atlantic Ocean high pressure system behind the cold front cause rain, strong winds and gusts during winter over the south western and southern parts of the country.

Clear skies

1/8 of cloud

2/8 of cloud

3/8 of cloud

4/8 of cloud

5/8 of cloud

7/8 of cloud

Haze

Dust/sand storm

6/8 of cloud

8/8 of cloud

Smoke

Fog

Drizzle

Mist

Rain

Showers

Cumulus

Altostratus

Cirrostratus

Snow

Thunderstorm

Stratus

Cirrus

Hail

Stratocumulus

Altocumulus

Cumulonimbus

Nimbostratus

Cirrocumulus

SYMBOLS FOUND ON A SYNOPTIC CHART

WIND DIRECTION

WORLD METEOROLOGICAL DAY 2018

This is the most intense class of thunderstorm characterized by a deep rotating updraft with a lifespan of a few hours. It is associated with severe weather, such as large hail, tornadoes, strong winds and/or urban flooding in at least

90% of cases.

A flash flood is a sudden local flood, typically due to heavy or excessive rainfall in a short period of time, generally less

than 6 hours.

Gale force winds are winds with a speed of 34 to 40 knots (63 to 74 kilometers per

hour).

A tornado can develop during a severe thunderstorm and is an actual funnel cloud that is visible from the ground. Maximum wind speed in the tornado is usually between 120 and 360 km per hour. It makes a characteristic, loud, distinctive noise, described as the sound of “a

thousand trains”.

DID YOU KNOW?

On the 9th October 2017, a line of thunderstorms developed east of a cut-off low pressure system which was situated over the western parts of the country. These storms developed through the central parts of the central parts of the North West and northern Free State, and then started moving eastwards. Due to prevailing favourable conditions (including abundant low-level moisture and strongly sheared airflow in the lower portion of the storms), some of these storms developed into supercell thunderstorms.

SUPERCELL STORM TORNADOGALE FORCE WINDS FLASH FLOOD

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