AOS 100: Weather and Climate Instructor: Nick Bassill Class TA: Courtney Obergfell

Miscellaneous Homework due by the end of weather discussion Extra Credit Offer: - If you’re interested in an extra credit project, e-mail me with a topic you’re considering, and we’ll figure it out from there

Review of November 12th: Thunderstorms Continued Air-mass thunderstorms (which are non-severe thunderstorms) have updrafts which are eventually cut off by the thunderstorm’s own downdrafts Severe thunderstorms have strong wind shear, which tilts the updrafts and downdrafts so that this problem doesn’t occur This allows severe thunderstorms to last longer, and become more intense

Review Continued For our purposes, we can consider two types of severe weather: A squall line is mostly linear continuous line of thunderstorms associated with speed wind shear, and they often produce strong straight line winds Supercells are smaller storms associated with directional wind shear, and often cause tornados and large hail

Review Continued: Doppler RADAR Doppler RADAR makes use of the “Doppler Effect” to determine whether objects are traveling towards or away from the radar site Doppler RADAR measures the change in wavelength of the incoming signal (compared with the signal that was sent out) This allows meteorologists to locate areas where air is moving towards the radar with adjacent air moving away from the radar This usually indicates a tornado might be present or forming

A Supercell

A Supercell Reflectivity: Velocity: We call this feature a “velocity couplet”, and it often signifies a tornado From: http://kkd.ou.edu/METR%202603/supercell%20velocity.jpg

Classic Supercell

Classic Supercell

Classic Supercell – using doppler radar

Tornadoes Tornadoes are caused by the creation of a rotating updraft

A Supercell (with tornado)

A Supercell (with tornado) Figure 14.46 A classic tornadic supercell thunderstorm showing updrafts and downdrafts, along with surface air flowing counterclockwise and in toward the tornado. The flanking line is a line of cumulus clouds that form as surface air is lifted into the storm along the gust front. Fig. 14-46, p. 402

} Tornado Wall Cloud Figure 14.18 A supercell thunderstorm with a tornado sweeps over Texas. Tornado Wall Cloud

Tornado Damage Figure 14.43 Total destruction caused by an EF5 tornado that devastated parts of Oklahoma on May 3, 1999.

Supercell Setup Supercells form at near the surface cold front As you move upward in the atmosphere, the winds “veer” Oftentimes, very fast winds occur at upper levels These two factors help to increase the wind shear

A Squall Line Dry air coming in behind the storm causes rain to evaporate, quickly cooling the air This makes the air very dense, causing it to sink rapidly to the surface, which leads to strong straight-line winds

Approaching Squall Line Cold Air

Incoming Dry Air Squall Line Motion

Cold Air

A Squall Line Dry air coming in behind the storm causes rain to evaporate, quickly cooling the air This makes the air very dense, causing it to sink rapidly to the surface, which leads to strong straight-line winds