Chapter 18 Pt 2 Flashcards
Where do frontal squall lines typically form?
South of a low pressure center. The frontal squall line is the comma tail part of an extratropical cyclone
How do the winds change from the surface to aloft ahead of a frontal squall line - On East Side?
- SURFACE - SE to S (weak)
- ALOFT - SW (Stronger)
How do the winds change from the surface to aloft ahead of a frontal squall line - On West Side?
- Surface - NW to W
- Aloft - W to SW (Stronger)
What is the appearance of a frontal squall line on a radar reflectivity image?
Long line of thunderstorms (high reflectivity) with stratiform precipitation (low reflectivity) on either side (mostly behind it)
From a satellite perspective, what part of a mid-latitude cyclone comma cloud does a frontal squall line form?
The Tail
What is the lifetime of a frontal squall line?
Hours to days since the advancing front continually forces warm air to rise over it.
What mechanism is responsible for lifting the conditionally unstable air to its level of free convection (LFC) in a frontal squall line?
Either a Cold front, an upper level front, or a dryline
What causes the anvil of a squall line to form?
Since the tropopause acts as a lid on the t-storms, the cloud is forced to spread horizontally
What can Supercell Thunderstorms cause?
- Tornadoes
- Strong Straight Line Winds
- Large Hail (Up to grapefruit size)
How strong is the updraft in a supercell thunderstorm?
45 mph to greater that 100mph
What 4 conditions are required for supercell thunderstorm to form?
- Conditionally unstable atmosphere
- Very humid low level air
- Moderate to strong vertical wind shear in conditionally unstable layer
- A trigger mechanism
How can conditional instability develop in the atmosphere?
Either surface heating or by cold air advection aloft (Either increases environmental lapse rate)
What does CAPE tell us about the updraft in a thunderstorm?
The maximum upward speed of the updraft
What are the 8 features of a supercell thunderstorm?
- Tilted, rotating updraft (mesocyclone)
- Overshooting Top
- Anvil (Pushed to NE)
- Rear flanking line
- Bounded weak echo region
- Wall cloud
- Mammatus
- Virga
Can tornadoes form from a mesocyclone?
Yes, often
Is Mesocyclone just a fancy word for tornado?
No
Overshooting Tops
The the clouds pop over the tropopause into the stratosphere
Wall cloud
A lowered cloud base in the vicinity of the updraft that is often observed to be rotating. The wall cloud rotates as a result of the mesocyclone
Virga
Rain/Snow/Ice that evaporates/Sublimates before reaching ground.
Why is there a rain free base just below the updraft?
Small cloud droplets are first forming there in the updraft (, they flow up into tropospheric winds.
Why will the largest hail (if present) will fall on perimeter of rain-free base?
This is because large hail cant make it far from updraft before quickly falling out of storm
