Ventusky Indices

CAPE:

This is a surface based Convective Available Potential Energy (CAPE) measurement only. In the cool season, elevated instability may be much higher than surface based cape. On average, CAPE of 1000 J/Kg is usually sufficient for strong to severe storms. CAPE of 3,000 to 4,000 J/Kg or higher is usually a signal of a very volatile atmosphere that could produce severe storms if other environmental parameters are in place. Shear (0-6Km):p The 0-6 km shear vector. Values generally greater than 40 knots are supportive of supercells, although in high instability environments this can be as low as 30 knots. CIN: Convective INhibition (CIN) sometimes more commonly referred to as the strength of the cap. The value is capped off at 500 J/KG. In general, the Cap is said to be breakable when CIN is 30 J/Kg or less Lifted Index The lifted index (LI) is the temperature difference between an air parcel when it reaches the 500 hPa level and the actual temperature of the environmental air at 500 hPa. When the value is positive, the atmosphere is stable and when the value is negative, the atmosphere is unstable. Values below 0 indicating instability and an increasing chance of thunderstorms. Lifted Index is generally scaled as follows:

6 or greater: very stable conditions (without thunderstorms), between 1 and 6: stable conditions, (thunderstorms not likely), between 0 and -2: slightly unstable (thunderstorms possible), between -2 and -6 : unstable (thunderstorms likely), less than -6: very unstable (severe thunderstorms likely). SRH (Storm Relative Helicity):

SRH= 150:The approximate threshold for supercell development. SRH= 150 to 299: Weak tornadoes (F0 and F1) possible. SRH= 300 to 449:Strong tornadoes (F2 and F3) possible. SRH over 450: Violent tornadoes (F4 and F5) possible. BRN Shear Bulk Richardson's Number: A BRN below 10: Strong vertical wind shear and weak CAPE. The shear may be too strong given the weak buoyancy to develop sustained convective updrafts. However, given sufficient forcing, thunderstorms may still develop; if so, rotating supercells could evolve given the high shear.

BRN = 10 to 45: Associated with supercell development. BRN over 50: Relatively weak vertical wind shear and high CAPE which suggests multicellular thunderstorm development is most likely. MUCAPE:

MUCAPE represents potential energy in the atmosphere. The greater the value reached, the greater the likelihood of the formation of a storm. Values less than 300 are low, between 300 to 1000 are weak, 1000 to 2000 are moderate, and over 2000 are high, when the possibility of the occurrence of strong storms is highly likely. Total Totals Index

40-45 - Thunderstorms are possible; 45-50 - Severe thunderstorms possible; 55 or greater - Severe thunderstorms likely and possible tornado