The Evolution Index Calculator is used in meteorology to assess atmospheric instability and the likelihood of convective weather events such as thunderstorms. By analyzing temperatures at key pressure levels and comparing them with dew point readings, this calculator offers insight into how likely the air is to rise and form clouds or storms.
Forecasters use the evolution index (EI) as one of several tools for predicting severe weather, especially when determining whether a given atmospheric column supports strong vertical motion. High EI values suggest an unstable environment that could enhance storm development, especially when combined with other indicators like CAPE (Convective Available Potential Energy) or lifted index values.
This calculator simplifies the complex thermodynamic relationships within the atmosphere, making it easier for professionals and students alike to quickly evaluate vertical temperature profiles for instability.
formula of Evolution Index Calculator
EI = (T₈₅₀ − T₅₀₀) − (Td₈₅₀ − T₈₅₀)
Where:
- T₈₅₀ = Temperature at the 850 hPa pressure level (in °C)
- T₅₀₀ = Temperature at the 500 hPa pressure level (in °C)
- Td₈₅₀ = Dew point temperature at the 850 hPa pressure level (in °C)
This formula combines vertical temperature difference (a sign of instability) and dew point depression (an indicator of moisture content).
Interpretation:
- Higher EI values (>20): Strong vertical instability; more favorable for severe thunderstorms
- Moderate EI (10–20): Possible convective development
- Lower EI (<10): Stable air; low storm potential
This index is widely applied in convective outlooks, balloon soundings, and upper-air model diagnostics.
Helpful Reference Table
Here’s a simple reference to interpret EI values based on atmospheric inputs:
| T₈₅₀ (°C) | Td₈₅₀ (°C) | T₅₀₀ (°C) | EI Value | Stability Assessment |
|---|---|---|---|---|
| 20 | 15 | -10 | 25 | Strong instability |
| 15 | 10 | -5 | 20 | Moderately unstable |
| 12 | 8 | -3 | 15 | Neutral to slightly unstable |
| 10 | 8 | 0 | 12 | Weak instability |
| 8 | 7 | 2 | 9 | Stable conditions |
This table helps meteorology students and field professionals quickly interpret observations.
Example of Evolution Index Calculator
Suppose we have the following observed values:
- T₈₅₀ = 18°C
- Td₈₅₀ = 13°C
- T₅₀₀ = -8°C
Now calculate:
Step 1: (T₈₅₀ − T₅₀₀) = 18 − (−8) = 26
Step 2: (Td₈₅₀ − T₈₅₀) = 13 − 18 = −5
EI = 26 − (−5) = 31
Interpretation: An EI of 31 indicates very strong instability, suggesting a high chance of thunderstorm or severe weather development.
Most Common FAQs
No. It is usually used in combination with CAPE, lifted index, and vertical wind shear to get a full picture of atmospheric instability and storm potential.
A negative EI suggests a very stable environment, where warm air sits above cooler air, suppressing vertical motion and cloud development.
In dynamic weather environments, calculating EI at different times throughout the day helps monitor the evolution of instability. It’s especially useful before and during convective forecasting.