The Iowa Environmental Mesonet (IEM) collects environmental data from cooperating members with observing networks. The data are stored and made available on this website.

IEM Daily Feature

Plenty of CAPE

Posted: 11 Aug 2026 05:30 AM, Views: 49
Tags:   cape  
Atmospheric soundings are an important observational dataset useful for the forecasting the weather. The often twice-daily balloon launches by the National Weather Service capture vertical profiles of temperature, humidity, pressure, and wind. These profiles can be used to compute many useful indices to access the state of the troposphere. Once such index is Convective Available Potential Energy (CAPE), which is useful for understanding how much potential energy is available for near surface air if it were to be lifted vertically and become buoyant. The CAPE index is not necessarily easy to compute and subject to many interpretations and assumptions. The featured chart presents the CAPE index for surface based "parcels" based on soundings from NWS Davenport. The balloon launch Monday evening (00 UTC 11 August 2026) captured a very unstable environment with a CAPE index around 7,700 J/kg. Based on unofficial archives, this was the largest CAPE value for August and one of the largest on record for the site. Large CAPE values are often associated with a "cap" of warm air aloft that prevents storm development, so these environments do not automatically produce severe storms. Generally speaking, CAPE is not a lifting mechanism but an energy reservoir available to support explosive development should air be lifted to levels were it can "freely convect".
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