Severe weather

  • CAPE

    Convective Available Potential Energy:Convective Available Potential Energy, a characterization parameter of convection potential and the greater value is more conducive to the convective weather. CAPE is a measure of instability through the depth of the atmosphere, and is related to updraft strength in thunderstorms. Generally, forecasters refer to "weak instability" (CAPE less than 1000 Jkg-1), "moderate instability" (CAPE from 1000-2500 Jkg-1), "strong instability" (CAPE from 2500-4000 Jkg-1), and "extreme instability" (CAPE greater than 4000 Jkg-1).Where  is the height of the level of free convection and  is the height of the equilibrium level(neutral buoyancy), where  is the virtual temperature of the specific parcel, where  is the virtual temperature of the environment, and where is the acceleration due to gravity. 

  • Wind shear

    0-6km vertical shear:The surface to 6 km above ground level change in wind. Thunderstorms tend to become more organized and persistent as vertical shear increases, while supercells are commonly associated with vertical shear values of 20-35 m/s and greater through this depth.Calculation formula:Where    is the wind of 6 km above ground level and  is the surface wind.

  • PWAT

    Total Precipitable Water: a water vapor related parameter indicating hourly rainfall intensities. The numbers represent inches of water as mentioned above for a geographical location. Generally, the greater the value of pwat, the stronger for rainfall intensities.


    Downdraft CAPE:DCAPE can be used to estimate the potential strength of rain-cooled downdrafts with thunderstorms convection, and is similar to CAPE. Larger DCAPE values are associated with stronger downdrafts. Generally, forecasters refer to " not conducive to strong wind" (DCAPE less than -500 Jkg-1), " conducive to strong wind" (DCAPE from -500-(-2000)Jkg-1), " very conducive to strong wind" (DCAPE greater than2000 Jkg-1). Certainly, it is effective only in the area where strong convective happens.