The Level of Free Convection (LFC) is the level at which a lifted parcel begins a free acceleration upward to the equilibrium level. Recent preliminary research suggests that tornadoes become more likely in supercells when LFC heights are less than 2000 m (6500 feet) above ground level. The EL (equilibrium level) is the level at which a lifted parcel becomes cooler than the environmental temperature and is no longer buoyant (i.e., "unstable" ). The EL is used primarily to estimate the height of a thunderstorm anvil. The height difference between this parameter and the LCL is important when determining convection initiation. The smaller the difference between the LFC and the LCL, the more likely deep convection becomes. The LFC-LCL difference is similar to CIN (convective inhibition).

The Lifting Condensation Level (LCL) is the level at which a parcel becomes saturated. It is a reasonable estimate of cloud base height when parcels experience forced ascent. The height difference between this parameter and the LFC is important when determining convection initiation. The smaller the difference between the LCL and the LFC, the more likely deep convection becomes. The LFC-LCL difference is similar to CIN (convective inhibition). LCL heights from approximately 500 m (1600 ft) to 800 m (2600 ft) above ground level are associated with F2 to F5 tornadoes. Low LCL heights and low surface dewpoint depressions (high low level RH) suggest a warm RFD which may play a role in tornado development.

The Convective Condensation Level (CCL) is the level at which condensation will occur if sufficient afternoon heating causes rising parcels of air to reach saturation. The CCL is greater than or equal in height (lower or equal pressure level) than the LCL. The CCL and the LCL are equal when the atmosphere is saturated. The CCL is found at the intersection of the saturation mixing ratio line (through the surface dewpoint) and the environmental temperature.

The Equilibrium Level (EL) is the level at which a lifted parcel becomes cooler than the environmental temperature and is no longer buoyant (i.e. unstable). The EL is used primarily to estimate the height of a thunderstorm anvil. You may notice that the "virtual" and "non-virtual" lifted parcels both end up with the same EL. This happens because the virtual temperature converges to the actual temperature when temperatures are very cold (less than -20C) and moisture effects become negligible.

A lapse rate is the rate of temperature change with height. The faster the temperature decreases with height, the "steeper" the lapse rate and the more "unstable" the atmosphere becomes. Lapse rates are typically displayed in ranges from 850-500-mb (4,500-18,000-ft above sea level) and 700-500-mb (10,000-18,000-ft above sea level).

Lapse rates are shown in terms of degrees Celsius change per kilometer in height. Values less than 5.5-6.0 degrees C/km ("moist" adiabatic) represent "stable" conditions, while values near 9.5 degrees C/km ("dry" adiabatic) are considered "absolutely unstable." In between these two values, lapse rates are considered "conditionally unstable." Conditional instability means that if enough moisture is present, lifted air parcels could have a negative LI (lifted index) or positive CAPE.

SBCAPE (

CIN (

SBLI (

MUCAPE (

The LPL (

MLCAPE (

CAPE in the lowest 3-km above ground level, and surface relative vorticity. Areas of large 0-3-km CAPE tend to favor strong low-level stretching, and can support tornado formation when co-located with significant vertical vorticity near the ground.

The NCAPE (

The DCAPE (

The Boundary Layer through 6-km above ground level shear vector denotes the change in wind throughout this height. Thunderstorms tend to become more organized and persistent as vertical shear increases. Supercells are commonly associated with vertical shear values of 35-40 knots and greater through this depth.

The maximum bulk shear from the most unstable parcel level upward to 40-60% of the equilibrium level height. This parameter is similar to the 0-6 km bulk shear, though it accounts for storm depth (LPL to EL) and is designed to identify both surface-based and "elevated" supercell environments. Supercells become more probable as the effective bulk shear increases through the range of 25-40 kt and greater.

The BRN (

SRH (

Effective SRH (

Surface-1-km Vertical Shear is the difference between the surface wind and the wind at 1-km above ground level. These data are plotted as vectors with shear magnitudes contoured. 0-1-km shear magnitudes greater than 15-20 knots tend to favor supercell tornadoes.

Low-Level SR (

Mid-Level SR (

The Anvil Level SR (

A multi-parameter index that includes effective SRH, muCAPE, and effective bulk shear. Each parameter is normalized to supercell "threshold" values. Effective SRH is divided by 50 m2/s2, muCAPE is divided by 1000 J/kg, and effective bulk shear is divided by 20 m/s in the shear range of 10-20 m/s. Effective bulk shear less than 10 m/s is set to zero, and effective bulk shear greater than 20 m/s is set to one.

A multi-parameter index that includes effective bulk shear, effective SRH, 100-mb mean parcel CAPE, 100-mb mean parcel CIN, and 100-mb mean parcel LCL height. When the mlLCL is less than 1000 m AGL, the mlLCL term is set to one, and when the mlCIN is greater than -50 J kg

The Sig. Hail Parameter (SHIP) was developed using a large database of surface-modified, observed severe hail proximity soundings. It is based on 5 parameters, and is meant to delineate between SIG (>=2" diameter) and NON-SIG (<2" diameter) hail environments. It is important to note that

The simple product of 100mb MLCAPE and 0-6km magnitude of the vector difference (m/s; often referred to as "deep layer shear") accounts for the compensation between instability and shear magnitude. Using a database of about 60,000 soundings, the majority of significant severe events (2+ inch hail, 65+ knot winds, F2+ tornadoes) occur when the product exceeds 20,000 m3/s3. For example, a 0-6-km shear of 40 knots and CAPE of 3000 J/kg results in a Craven SigSvr index of 60,000. Units are scaled to the nearest 1000 on the web plot.

The basic premise behind the EHI (

The VGP