Frontal Weather

Ripples or kinks are formed in the front due to varying speeds of movement of air at different places in the front.
Warm air moves over cool air at higher speed in these kinks. Coriolis force further rotates the air anticlockwise in the Northern Hemisphere.
Low pressure in the warm sector between the warm and cold front causes a rotational flow.
Pressure falls further due to warm and less dense air at higher levels, causing a chain reaction.
Low pressure further induces rotation of air and pushes more air over cool air, resulting in a secondary cold front. Pressure falls further, increasing the intensity of the low pressure.

Uplift of air in both cold and warm fronts causes vertical and layered clouds.
The lowest pressure or depression can be found in the warm sector.
Convergence near fronts increases uplift of air, resulting in vertically growing clouds like Cumulus and Cumulonimbus clouds.

Warm air rises over the cold air in the warm front with a slope of 1:150.
Forms stratiform type clouds, reducing in height from high-level clouds like Cirrus to lower-level clouds like Stratus.
Cloud sequence: CI – CS – AS – NS – SC – ST
Winds back (change in an anticlockwise direction) by about 30° and increase in speed.
After passage of the front, winds veer (change clockwise) by about 30° and reduce in speed.
Visibility is good outside precipitation.
Snow or rime ice can be expected in a warm front.
Jet streams flow parallel to the front at right angles (imagine them coming out of the screen).

Low pressure is found in the warm sector that lies between the cold and warm fronts.
The warm sector is a stable air mass found after the passage of the warm front.
Low-level Stratus and Stratocumulus clouds can be expected.
Advection fog may reduce visibility due to warm air flowing over cold air.
Wind speeds are generally steady and not gusty in this sector.

Cold air undercuts the warm air mass with a steep slope of 1:50.
Violent weather can be expected from 50–100 NM behind the cold front.
Clouds change from low-level Stratus to Cirrocumulus.
Cloud sequence: ST – SC – AS – AC – CT – CC
The 0°C isotherm is found at lower levels, resulting in lower freezing levels.
Severe icing can be expected in a cold front.
Jet stream is at right angles and appears to go into the screen along the front.

The lifespan of a frontal depression varies between 4 and 10 days.
It moves in the direction of the isobars at a speed calculated using the geostrophic wind scale.
The isobaric scale on pressure charts provides the geostrophic wind scale.
The speed of frontal movement is approximately two-thirds of the geostrophic wind speed.
Speed of Frontal Movement = (Geostrophic Wind Speed × 2) / 3

An occluded front is created when a cold front follows a warm front.
The cold front generally moves at about twice the speed of the warm front and eventually catches up.
As the cold front catches the warm front, an occluded front forms progressively.
The meeting point of the warm and cold fronts marks the beginning of the occluded front.
Severe weather can be expected in an occluded front while the warm sector reduces progressively.

Cold Occlusion: Occurs when the air in the cold front is colder than the cool air behind the warm front, causing it to undercut the air behind the warm front.
Weather sequence in a cold occlusion: warm front weather followed by cold front weather.
Warm Occlusion: Occurs when the air in the cold front is warmer than the cool air behind the warm front.
The cold front overrides the warm front ahead, producing warm front weather.
Back-bent occlusion may cause thundery and snowy weather.

Stationary Front: Remains stationary with contrasting air masses on either side, resulting in winds flowing parallel to the frontal boundary.
Polar Front: Found around 60° latitude between polar easterlies and mid-latitude westerlies.
Polar fronts are not continuous and remain active only in certain segments.
Arctic Front: Found between Arctic and Polar air masses, north of the Polar Front.
During winter, the Arctic Front may descend into the temperate latitudes.
Mediterranean Front: Found over the Mediterranean region between Polar Continental air from Europe and Tropical Continental air from North Africa.