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Gfs CAPE and Lifted Index                                                                   source:http://www.wetterzentrale.de
Grey or White-lines: Lifted Index  solid grey lines > 0 (poor LI values),  dashed white lines<=0degC (moderate or 'good' LI values)
CAPE (Convective Available Potential Energy) See scale at right of diagram: blue/green - low values of CAPE , orange/red - high values of CAPE

First note the temperature and dewpoint that is 50 mb above the surface pressure. Draw a line parallel to the dry adiabatic lapse rate starting from the temperature that is 50 mb above the surface. Draw a line parallel to the mixing ratio lines starting from the dewpoint that is 50 mb above the surface. The intersection of these two lines is the LCL. From the LCL, parallel the wet adiabatic lapse rate with height until the 500 mb pressure level is reached. Compare this 500 mb parcel temperature to the actual (environmental) 500 mb temperature.

a. The LI only assesses instability in one level of the troposphere. Unlike LI, CAPE is better at assessing instability in the troposphere as a whole.

b. Only use the LI for warm season convection. LI is most relevant in the warm sector of a mid-latitude cyclone or in a barotropic troposphere. LI is worthless when a shallow polar air mass moves into the PBL and is usually worthless for forecasting winter precipitation.




Positive number Stable
0 to -4 Marginal instability
-4 to -7 Large instability
-8 or less Extreme instability