Predicting thunderstorms is one of the most exciting and challenging aspects of weather forecasting. For weather enthusiasts and hobbyists, model soundings are an invaluable tool for understanding the potential for storm development. These vertical profiles of the atmosphere reveal temperature, moisture, and wind data from the surface up through the atmosphere, offering insight into instability and other storm-supporting ingredients.
In this post, we’ll explore what model soundings are, how to read them, and how they can help you predict thunderstorms more accurately.
What Are Model Soundings?
Let’s start with the basics. A model sounding is a vertical profile of the atmosphere produced by a numerical weather model such as the GFS, NAM, or HRRR. It shows temperature, dew point, wind speed, and wind direction at various levels of the atmosphere. You can learn more about how to use the GFS, NAM and other weather models here.
The most common way to view a model sounding is through a Skew-T log-P diagram, which plots temperature and dew point on a skewed temperature axis. You can access model soundings through reputable sources like:
Each of these platforms offers easy-to-read diagrams that allow you to visualize the structure of the atmosphere and identify conditions favorable for thunderstorms.
Key Parameters to Identify Thunderstorm Potential Using Model Soundings
When analyzing a model sounding, several parameters stand out as critical indicators of thunderstorm development:
1. CAPE (Convective Available Potential Energy)
CAPE measures the amount of energy available for convection, expressed in joules per kilogram (J/kg). Higher CAPE values suggest a greater potential for strong updrafts and thunderstorms.
- 0–500 J/kg: Minimal convection potential
- 500–1500 J/kg: Weak thunderstorms possible
- 1500–3000 J/kg: Moderate to strong storms
- 3000+ J/kg: Severe thunderstorms possible
You can think of CAPE as the “fuel” that powers thunderstorm growth.
2. CIN (Convective Inhibition)
CIN, or the “cap,” represents a layer of stable air that prevents warm air from rising. A small amount of CIN can delay storm development until enough heating occurs, often leading to explosive thunderstorm formation later in the day.
3. Lifted Index (LI)
The Lifted Index measures the temperature difference between an air parcel lifted from the surface and the surrounding environment at 500 mb.
- 0 to -2: Weak instability
- -3 to -6: Moderate instability
- Below -6: Strong instability and possible severe weather
4. Wind Shear
Wind shear refers to the change in wind speed and direction with height. Shear helps organize storms and can lead to the development of rotating supercells.
- Low shear (<20 knots): Isolated single-cell storms
- Moderate shear (20–40 knots): Multicell clusters or lines
- High shear (40+ knots): Supercells and tornado potential
5. LCL and LFC
- LCL (Lifted Condensation Level): The height where air becomes saturated and clouds begin to form.
- LFC (Level of Free Convection): The point where the air parcel becomes warmer than its environment and rises freely.
Low LCL heights can indicate higher humidity and a greater chance of tornadoes when strong shear is present.
How to Interpret a Skew-T Diagram
At first glance, a Skew-T diagram can seem intimidating. However, it becomes intuitive once you understand the basics.
- Red Line: Air temperature profile.
- Green Line: Dew point profile.
- Blue Wind Barbs: Indicate wind direction and speed at various levels.
When the red and green lines are close together, the air is moist. Large separations indicate dry air. Thunderstorms thrive when warm, moist air near the surface rises into cooler, drier air aloft.
Look for:
- A strong lapse rate (temperature decreasing rapidly with height)
- High CAPE values
- Adequate wind shear
- A weak but breakable cap (CIN)
These ingredients together suggest a favorable environment for thunderstorm development.
Using Model Soundings for Forecasting
To predict thunderstorms, begin by checking model soundings in regions where storms are expected to form. Compare different model outputs such as the HRRR and NAM to see how conditions evolve over time.
Steps to follow:
- Choose a forecast hour on a site like the SPC or College of DuPage.
- Select a location (often near forecast boundaries or surface lows).
- Review CAPE, CIN, shear, and Lifted Index values.
- Look at temperature and dew point alignment.
- Assess wind barbs for turning with height (indicating rotation).
Using multiple parameters together gives a clearer picture than relying on any one number alone.
Example: Identifying a Thunderstorm Setup
Let’s say you pull a sounding for eastern Kansas on a June afternoon. The data shows:
- CAPE: 2500 J/kg
- CIN: -50 J/kg
- Lifted Index: -7
- Shear: 45 knots
- LCL: 900 meters
This profile suggests a highly unstable atmosphere with sufficient shear for organized storms. If surface heating breaks the cap, severe thunderstorms, possibly supercells, could develop.
Common Mistakes to Avoid
- Relying on one parameter: CAPE alone doesn’t guarantee storms if CIN is too strong or moisture is lacking.
- Ignoring time trends: Conditions can evolve rapidly. Revisit model soundings throughout the day.
- Misreading skew-T orientation: Remember that the temperature lines are skewed, not vertical.
Practice and comparison with actual observations will sharpen your ability to interpret these diagrams accurately.
Further Learning Resources
To expand your knowledge of model soundings and thunderstorm forecasting, explore:
These resources offer free, detailed tutorials on atmospheric thermodynamics, convection, and severe weather forecasting.
Model soundings are one of the most powerful tools available to amateur weather forecasters. By learning how to interpret temperature, moisture, and wind data vertically through the atmosphere, you can predict when and where thunderstorms are most likely to form. With regular practice and attention to detail, model soundings can turn your storm predictions from guesswork into science-based forecasts.
