Discussing convective available potential energy (CAPE) as a forecasting variable


ALEXANDRIA, La. (KALB) - Throughout this web article, I’ll be discussing the weather forecasting variable, convective available potential energy, or "CAPE". This is one of those variables that we look at when putting together a weather forecast, especially in the case of severe weather.

This variable is the measure of the amount of energy available for possible convection to occur. Higher values of CAPE indicate the greater potential for possible severe weather.

Values can range quite a bit when it comes to CAPE when looking at weather forecasting websites like COD Meteorology or Weatherbell, anywhere from 1,000 to over 5,000 Joules per kilogram. Just like with other forecasting variables, there are no thresholds above which possible severe weather could occur.

This weather forecasting variable is determined by the positive area on a sounding that is proportional to the overall amount of CAPE. The higher the positive area, the higher the overall CAPE that is present. This overall positive area is where the parcel sounding is to the right (or warmer) than that environmental sounding. The units of CAPE are expressed as Joules per kilogram (the energy per unit mass).

There are three different levels of CAPE to discuss here throughout this article. 1,000 to 1,500 Joules per kilogram is considered Positive, 1,500 to 2,500 Joules per kilogram is considered Large, and then finally, anything of 2,500 or higher to be Extreme. Higher levels of CAPE lead to storms building vertically very quickly. Also, higher levels of CAPE lead to the hail potential increasing as well. Along with the storm height and hail potential increasing with higher levels of CAPE present, there is also abundant lightning possible too.

CAPE is one of several weather forecasting variables that the KALB First Alert Storm Team looks at when putting your Central Louisiana forecast together especially when it comes to severe weather.

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