Thunderstorms

Question 1

Convective localised (stationary) type

Answer 1

• When surface temperatures increase the ELR will steepen, air will become unstable and a TS will form (provided other requirements are met) .
• It originates over land usually in the afternoon during spring/summer.
• There may be no precipitation if surface heating is high enough

Question 2

Convective travelling type

Answer 2

A convective TS can move location due to TS regeneration

Question 3

Orographic TS

Answer 3

• Occurs in a moist unstable airstream when a mountain/rising ground gives sufficient lift to trigger instability
• Can last up to days on end if unstable moist air is continuously transported onto mountains
• Precipitation can be heavy and hail can occur due to the high moisture content of orographic cloud

Question 4

Nocturnal tropical TS

Answer 4

• Occurs over oceanic areas within 10° latitude of the equator, the sea temperature at those latitudes can be around 30°C
• The air above the sea surface remains warm but due to radiation losses of air at high levels a steepening of the ELR follows as air and clouds aloft cool
• Most active towards dawn when the ELR is the steepest and the TS will cease to exist around mid-morning

Question 5

Convergence TS

Answer 5

Develop in the low-pressure areas associated with widespread ascent caused by convergence or on a local scale caused by a sea breeze

Question 6

Frontal TS

Answer 6

Occur along a line between 2 air masses, they are severe because the cells are more numerous/organized with lower bases. Squall lines when associated with the frontal TS represent the TS in its severest form. Commonly found with cold fronts but also associated with warm fronts

Question 7

Warm front embedded TS

Answer 7

Same as frontal, can occur in a warm occlusion as an embedded TS

Question 8

Surface and upper trough TS

Answer 8

The main feature in the upper layers is the jet stream. Jets are large scale features whose configuration is critical to the type of weather we see down at the surface. The jets sometimes produce large scale waves (Rossby waves) that move around the globe. The front side of a Rossby wave trough is a hotspot for severe TS. The strong winds aloft create a sheared environment (change in wind speed/direction with height). TS that develop in a ‘sheared’ environment are more likely to be severe/tornadic. Low-pressure circulations and frontal boundaries also tend to develop underneath strong upper jets further enhancing the low-level shear environment