Fundamentals of Spotting Part 2 – The Clear Slot

Professor Paul Sirvatka College of DuPage Meteorology What you REALLY need to know! Gilbert’s Marital Status

• Rumors are that he is checking out reception possibilities. Here he has found something that seems to make him happy. • Is it you? Over-emphasis on Wall Clouds

You reported what?!?! Wall Clouds

• Tell you the location of the updraft • Not easily identified sometimes • Over-identified by less- experienced spotters • Offer useless information to the NWS warn/no warn decision tree • What else does it matter? Characteristics of a Tornadic Wall Cloud

• Surface-based inflow • Rapid vertical motion (scud- sucking) • Persistent • Persistent rotation • The key, however, is the development of a clear slot Clear Slot and Tornado

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather First Clue

• No wall cloud • No apparent rotation • Only visible clue was a Horseshoe Updraft rain free base Clear Slot • Small scud tags started showing upward motion • Clear slot and horseshoe updraft clearly visible

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather A Storm’s Updraft Horseshoe Updraft The Clear Slot – Look for This!

Horseshoe updraft

Clear slot Preferred site for tornadogenesis

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Springfield, IL 1995

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Less then 10 Minutes of Time

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Clear Slot is Visible

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather RFD – Rear Flank Downdraft

RFD air is brought back into the tornado updraft!

Courtesy Paul Markowski

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Let’s Take a Look at a Storm

Courtesy Erik Rasmussen

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Let’s Take a Look at a Storm

Horseshoe Updraft

Precipitation Curtain – Hook Echo

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Two Areas of Rotation

Mesocyclone

Mesoanticyclone

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather Clear Slot “Cuts into” Updraft

Preferred site for tornadogenesis

Clear Slot

Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather What kind of tornadoes do not have a clear slot? • Landspouts and water spouts • QLCS Tornadoes? • Cyclical tornadoes? • Other weak tornadoes or “spin-ups.” This should result in an automatic tornado warning if it comes from a reputable spotter

• This assumes forecasters in the NWS office know what to do with this information. • Training is needed for more than just spotters. • Hence the reason wall clouds are still taught too often with too much emphasis. We are ALL getting better!

• Come chase with us and see how much we all can learn.

• Visit us at http://weather.cod.edu /chasing