Severe and Unusual Weather ESAS 1115 Spotter Training and Radar Meteorology Part 3 – Thunderstorm Varieties Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Thunderstorm Ingredients A source of lift – i.e. a front, sea-breeze, orography, outflows of previous thunderstorms, etc… Moisture – low-level moisture provides the fuel needed for thunderstorms (dew point temperatures are the easiest way to assess the threat of strong to severe thunderstorms) Instability – the ability of air to rise on its own (i.e. buoyancy) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Launching a Radiosonde Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Receiving Data Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Thunderstorm Development Cumulus Humilis Cumulus Congestus Towering Cumulus Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Cumulonimbus (Cb) Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Texture A “rock hard” texture implies that most of the cloud is still in liquid phase A growing updraft, or one that is strong, will exhibit this rock hard texture It is marked by a “cauliflower”-type look with strong shadows Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Rock Hard Growth with Anvil Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Texture When the updraft weakens or reaches high in the troposphere, the liquid freezes, giving the cloud a “glaciated” texture When the updraft exhibits mostly a glaciated texture, the updraft is considered fairly weak The glaciated texture refers to the updraft, not the outflow features of the storm nor falling rain Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Texture Soft and fuzzy; glaciated Rock hard updraft growth Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Glaciated Anvil Crisp vs. Fuzzy Crisp delineation between anvil and sky Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Vertical Shear Increases longevity and organization Ultimately, strong shear results in storm-scale rotation by tilting horizontal vorticity into vertical vorticity Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Supercell and Flanking Line Tower Main tower is vertically erect in a sheared environment due to its very strong updraft Flanking line tower to the main cell’s southwest is tilted due to the environmental shear Notice the rock-hard overshooting top, another clue to the vigorous nature of the updraft Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Extremely Sheared Updraft Surprisingly, this tower maintained itself for some time before dying out Strong localized point convergence helped maintain the inflow source of unstable air If CAPE is too weak and shear too strong, thunderstorms tend to be sheared apart, resulting in a short-lived thunderstorm with minimal threat Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Updraft vs. Downdraft Updraft strength is primarily a function of instability Downdraft strength is primarily a result of dry air The top diagram would be a fairly weak shower or thunderstorm The bottom diagram would result in primarily strong down drafts or microbursts Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Updraft vs. Downdraft High instability would increase the threat of severe hail (although most likely not very large hail) but would have a lesser threat for damaging winds When dry air and high instability are both present, the likelihood of severe weather increases Dry air increases the likelihood of large hail as well as strong winds Supercells are the result of strong vertical shear where buoyancy and shear are well-balanced Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Low Base The Lifting Condensation Level (LCL) helps indicate the relative humidity of the sub-cloud layer High LCL’s indicate lower RH and more chance for microbursts Low LCL’s indicate more moisture in the sub-cloud layer Lower LCL storms have a higher tornado potential Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Weak Storm Still Dangerous High base indicates threat for damaging winds Forest fires are also a great threat due to lightning, strong winds and dry conditions Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather High-based Storm Low LCL’s correlate well to tornado potential. High LCL’s like in the storm shown here will struggle to produce tornadoes Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Storm Evolution Movie Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Thunderstorm Types There are three basic types of thunderstorms: single cells, multicells and supercells. Theses are loosely defined, as no thunderstorm is completely a “single” cell Multicell storms can be either clusters or lines The most important distinction in thunderstorm types is the presence or absence of storm-scale rotation Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Buoyancy, Gust Fronts and Dynamics Single cell thunderstorms are dominated by buoyancy processes Multicell thunderstorms are dominated by gust front processes Supercell thunderstorms are dominated by dynamic processes Instability Vertical Wind Shear Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Single Cell Thunderstorms Sometimes called “air mass” t-storms, these storms are poorly organized and pose relatively little threat to the public (lightning and hail) Typical of afternoon thunderstorms Updrafts form in relatively random locations The dominant forcing feature is instability since they form in a low-shear environment Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Convective Initiation on Radar Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Convective Initiation on Radar Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Single Cell Thunderstorms Movie Buoyancy dominates single cell processes Without significant vertical wind shear, the cold pool will undercut the updrafts Lack of vertical shear means that new updrafts will not be able to be generated along the outflow boundaries Cells will go through their cycle in about 30-60 minutes The severe threat is minimal except in cases of strong instability and then even then the threat is relatively short-lived Any severe weather occurrence in difficult to predict and even then, lead time will be minimal Tornadoes are unlikely but can occur as landspouts Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Pulse Severe Storm A single cell storm may still produce large hail or damaging winds in which case the storm is called a “pulse” severe A pulse storm produces severe weather, usually in the form of large hail, although the severe event will be relatively short-lived Identification of a pulse severe storm is difficult and gives little lead time for warnings “Popcorn severe” Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Using VIL for Discriminating Between Ordinary and Pulse Storms Warn when the VIL exceeds the VIL of the day Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Land Spouts These are non-supercell tornadoes Spouts form on boundaries where pre-existing vertical vorticity is already high The updraft stretches the vertical vorticity into a vortex that results in tornado Conservation of Angular Momentum helps explain their existence Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

ESAS 1115 Severe and Unusual Weather Land Spouts Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather

Waterspouts Multiple Waterspouts over Lake Michigan Prof. Paul Sirvatka ESAS 1115 Severe and Unusual Weather