Thunderstorms

Air mass thunderstorms

form within single mT air mass – not fronts; convectional lifting in nature (self-limiting; last the shortest amount of time due to descending cold air shutting off the moisture supply)

Frontal thunderstorms

forced uplift; density differences (sever thunderstorms)

Orographic thunderstorms

forced uplift; topography

Severe thunderstorms

(overshoots tropopause) hail and surface gusts of 58 mph

Supercell thunderstorms

last for hours; grapefruit sized hail – conditions give rise to long lasting tornadoes

Squall line thunderstorm

can form along front and up to 180 miles ahead of frontal boundary; several hundred miles long; intense storms

Squall line

line of intense thunderstorm activity; may develop along the frontal boundary

Why do tilted clouds

more severe storms? Strong vertical wind shear tilts clouds: precipitation falls into down-drafts and intensifies them; the updraft is fed by the gust front

What is a gust front?

Downdraft hits the ground and flows outward

Microburst

winds extend < 4 km (2.5 miles) at the surface

o   Damage pattern: Trees blown down in multiple directions from a central point outward

Macroburst

winds extend > 4 km at surface

Wall cloud

descends from larger cumulonimbus system; sever storm and some wind rotation

Mammatus clouds

instability in atmosphere and pockets of cold air sinking, while there is moisture rising into the system

Shelf clouds

pronounced boundary along the frontal slope; moisture pushes up intensely

Roll clouds

develop above the gust front; elongates, cylindrically-shaped clouds that are separate from cloud base and roll horizontally (not as severe weather – due to non-vertical tilt)

What is a derecho?

Widespread, long-lived wind storm – bands or rapidly moving t-storms (straight lined winds)

derecho (Radar and damage pattern?)

similar to tornadoes BUT the damage is in the same direction that the winds are blowing- On a radar we look for large area coverage and a long duration (up toward 2 miles of damage)

derecho (Wind speeds)

At least 58mph and can reach gusts exceeding 100 mph 

When do derechos occur? 

Most common in the warm season  

What impact does the jet stream have?

Enhances sever weather because of how fast it moves; it catches the air moving up leading to major growth along boundaries and causes rapid cloud upgrowth and vertical tilt  

What are the conditions present that lead to severe thunderstorms? Why do they lead to storm intensification?

Strong vertical wind shear titls cloud helping it to become severe, and rain falls into downdrafts and intensifies them, uplift is fed by the gust front creating a continuing cycle