Table 1

This table contains lots of common severe weather parameters, including different lifting methods for side by side comparison.

Interactive Features

parcel lifting method - If you click on the PARCEL text in the upper left column (e.g. ML PARCEL), the Skew-T will display the selected parcel lifting method. The LCL-EL(Cloud Layer) parameter will also update with the selected parcel lifting method.

More complete discussion of the parameters and how they are calculated will come in future releases. For now, here is a listing of the parameter names for reference.

You do not need to review the details of this page unless you have a particular question about a parameter.

The parameters include:

• SB Parcel (surface based parcel)
• Fcst Parcel (forecast parcel)
• MU Parcel (most unstable parcel)
• ML Parcel (mixed layer parcel)
  • lowest 100mb
• User Parcel (user defined parcel)
• Eff Parcel (effective parcel)
  • computes layer of > 100 J/kg CAPE and > -250 J/kg CIN
  • used in many other parameters (e.g. ESRH)
• PW (precipitable water)
  • total amount of condensed water within the lowest 400mb
• K (K index)
• MidRH (mid-level relative humidity)
  • average RH at 150mb and 350mb above the ground
• LowRH (low-level relative humidity)
  • average RH at surface and 150mb above the ground
• 3CAPE (0-3km CAPE)
  • MLCAPE in the lowest 3km AGL
• DCAPE (downdraft CAPE)
  • Follow moist adiabat down to the ground from the minimum theta-E in the lowest 400mb of the sounding, and then calculate positive and negative area. DCAPE values greater than 1000 J/kg have been associated with increasing potential for strong downdrafts and damaging outflow winds.
• DownT (downrush temperature)
  • temperature at the ground for the downdraft DCAPE parcel (esimate of surface temperature within core of a saturated downdraft)
• MeanW (mean mixing ratio)
  • mean mixing ratio in lowest 100mb AGL
• WBZ (web bulb zero)
  • melting level in feet AGL
  • values less than roughly 10,000 ft AGL favor small hail reaching the ground, while values larger than roughly 13,000 ft AGL suggest substantial melting of small hail
• FZL (freezing level)
  • height of the 0C isotherm in ft AGL
• ConvT (convective temperature)
  • lowest surface temperature with < 5 J/kg convective inhibition, using the 100mb mean parcel mixing ratio to account for afternoon mixing
• MaxT (maximum temperature)
  • 100mb AGL parcel brought down dry adiabatically to the ground and adding 2C (superadiabatic contact layer proxy) to approximate max afternoon temperature
• WNDG (wind damage parameter)
  • A non-dimensional composite parameter that identifies area where large CAPE, steep low-level lapse rates, enhanced flow in the low-mid levels, and minimal convective inhibition are co-located.
  • The parameter is formulated as follows:
    
    WNDG = (MLCAPE / 2000 J kg-1) * (0-3 km lapse rate / 9 C km-1) * (1000-3500 m AGL mean wind / 15 m s-1) * ((50 + MLCIN) / 40 J kg-1)
    
    where 0-3 km lapse rate < 7 is set to zero, and MLCIN < -50 J kg-1 is set to -50.
    
  • WNDG values > 1 favor an enhanced risk for scattered damaging outflow gusts with multicell thunderstorm clusters, primarily during the afternoon in the summer.
• ESP (enhanced stretching potential)
  • This composite parameter identifies areas where low-level buoyancy and steep low-level lapse rates are co-located, which may favor low-level vortex stretching and tornado potential.
  • ESP is formulated as follows:
    
    ESP = (0-3 km MLCAPE / 50 J kg-1) * ((0-3 km lapse rate - 7.0) / 1.0 C km-1)
    
    where ESP is set to zero when the 0-3 km lapse rate is < 7 C km-1, or when the total MLCAPE < 250 J kg-1.
• MMP (MCS Maintenance Probability)
  • probability that a mature MCS will maintain peak intensity for the next hour.
• NCAPE
  • Normalized CAPE
• sfc-3km Agl lapse rate
• 3-6km Agl lapse rate
• 850-500mb lapse rate - temperature difference and temperature change per km
• 700-500mb lapse rate - temperature difference and temperature change per km
• Supercell (Supercell Composite Parameter)
  • A multiple component index that is meant to highlight the co-existence of ingredients favoring supercell thunderstorms.
  • The SCP is formulated as follows:
    
    SCP = (muCAPE / 1000 J/kg) * (ESRH / 50 m2/s2) * (EBWD / 10 m/s)
    
    where ESRH = storm-relative helicity for the effective inflow layer using an assumed supercell motion, and the EBWD = effective bulk wind difference over the lower half of the storm depth (effective inflow base to EL height).
  • The EBWD term is capped at a value of 1.5 (e.g., EBWD > 30 m/s is set to 30 m/s), and this same term is set to zero when EBWD < 10 m/s.
    
    
  • The normalization values for each term are based on the work of Thompson et al. (2003) and Thompson et al. (2007).
    
    
  • SCP > 1 favor right-moving (cyclonic in northern hemisphere) supercells, while values of SCP < -1 favor left-moving (anticyclonic) supercells.
• STP(CIN) - Significant Tornado Parameter using CIN
  • A multiple component index that is meant to highlight the co-existence of ingredients favoring right-moving supercells capable of producing F2-F5 tornadoes.
  • The STP is formulated as follows:
    
    Sig Tor (CIN) = (mlCAPE / 1500 J/kg) * (ESRH / 150 m2/s2) * (EBWD / 12 m/s) * ((2000 - mlLCL) / 1000) * ((mlCINH + 200) / 150)
    
    where "ml" denotes the lowest 100 mb mean parcel, ESRH = the effective storm-relative helicity, EBWD = the effective bulk wind difference over the lower half of the storm depth (effective inflow base to EL height).
  • The EBWD term is capped at a value of 1.5 as in the Supercell Composite Parameter, though the minumum value is raised to 12 m/s.
  • The mlLCL term is set to 1 for mlLCL heights < 1000 m AGL, and the mlCINH is set to 1 for mlCINH values > -50 J/kg.
    
    
• STP(fixed) -Significant Tornado Parameter using fixed inflow layer
  • The "Sig Tor (fixed)" is similar to the "sig Tor (CIN)", except that mlCAPE is replace with sbCAPE (surface parcel), ESRH is replaced with 0-1 km SRH, the EBWD is replaced with 0-6 km bulk wind difference, and the CINH term is dropped.
• SHIP - Significant Hail Parameter
  • 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.
    
    SHIP = [(MUCAPE j/kg) * (Mixing Ratio of MU PARCEL g/kg) * (700-500mb LAPSE RATE c/km) * (-500mb TEMP C) * (0-6km Shear m/s) ] / 44,000,000
    
    
  • It is important to note that SHIP is NOT a forecast hail size.
    
    
  • Developed in the same vein as the STP and SCP parameters, values of SHIP greater than 1.00 indicate a favorable environment for SIG hail.
  • Values greater than 4 are considered very high.
  • In practice, maximum contour values of 1.5-2.0 or higher will typically be present when SIG hail is going to be reported.