CAPE (Convective Available Potential Energy) change shows how much the CAPE has changed over a given time period. A common time frame is the change over a 3 hour period. CAPE (when it is present) will tend to increase during the morning and afternoon and decrease in the evening and at night. Other considerations though can cause an increase or decrease in CAPE at different portions of the day compared to what typically occurs. Below are factors that can cause the CAPE to increase or decrease. It is a good idea to be aware of the factors that are causing CAPE to increase since it can contribute to stronger storms. There are also many factors that can cause CAPE to decrease. Factors that can increase CAPE 1. Increasing boundary layer temperature from solar radiation 2. Increasing boundary layer dewpoint from moisture advection 3. Low level warm air advection (warmer air moving into area) 4. Cooling aloft such as at 700 mb and 500 mb from cold air advection 5. A combination of 2 or more of the above Factors that can decrease CAPE 1. Decreased boundary layer temperature from the decrease or loss of solar radiation 2. Decreasing boundary layer dewpoint 3. Low level cold air advection 4. Warming aloft such as at 700 mb and 500 mb 5. Cooling from thunderstorm outflow 6. Increased cloud cover, especially overcast conditions 7. A combination of 2 or more of the above The image below shows an example of a 3 hour change in CAPE. In the example the CAPE has decreased. The larger the number, then the more significant the decrease.  |