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Thunderstorm Cumulonimbus Clouds

How do we get thunderstorm cumulonimbus clouds?

Thunder storm pictures

On a graph like this one, meteorologists plot daily soundings and assign Convection Parameters.  See them listed below.  The graph presented is called a Skew T - Log P.  Using the Skew-T Log-P diagram, meteorologists can identify the potential for thunderstorm formation and predict their severity.

Skew-T Log-P diagrams are commonly used in meteorology to analyze the thermodynamic state of the atmosphere and identify thunderstorm potential.  The diagrams have a vertical axis for pressure (in log scale) and a horizontal axis for temperature (in skew scale).  

The data on the diagram comes from weather balloons or airplanes measuring temperature, pressure, and humidity.  Meteorologists usually look for a few key features on the Skew-T Log-P diagram to identify thunderstorm potential:  

-Convective Available Potential Energy (CAPE): This is the amount of energy in the atmosphere that can cause convection.  This is the area between the environmental and parcel temperatures.  Thunderstorms are more likely to develop when CAPE is high.

-LCL: Lifted condensation level is where a parcel of air would get saturated if lifted to that level.  It's possible to tell how deep thunderstorm clouds will be by the height of the LCL.  See below.

-Convective Inhibition (CIN) measures the amount of energy needed to overcome atmospheric stability and start convection.  CIN values below zero indicate a thunderstorm is brewing.

Thunderstorm Cumulonimbus Clouds

The elements in the drawing:

T - Surface temperature, usually around 1000 mb pressure.  Also identifies the right hand curve on a skew T log P chart.

Td -  Surface mixing ratio, absolute humidity.  On the chart, it also identifies the left side curve.

LCL - Lifting condensation level, lower left corner of the negative area, where dry adiabat and mixing ratio pass through surface temperature and dewpoint.  Cumulonimbus clouds at the bottom of a thunderstorm.

LFC - Level of free convection, lower corner of positive area.  To keep moving upward on its own, the surface parcel must be lifted.

CCL - When enough heat is accumulated below, the descending LFC meets the rising LCL at the convective condensation level.

Tc - Convective temperature, the surface temperature on the dry adiabat at which LCL and LFC meet to form CCL and free convection.

Positive Area - A positive area is where a lifted parcel gets warmer than ambient air.  

Negative Area - stable region where the lifted parcel is colder than the surrounding air.

EL - At the top of the positive area, where the parcel ascent curve intersects the environmental curve above the LFC, is the equilibrium level.  This is a typical cloud top.

EBL - Energy balance level:  The EBL is not shown, but somewhere in the upper negative area, just high enough so that the area below the EBL within the upper negative area is equal to the area below the EBL.  Normally, this is the top of the storm clouds.

Tc is often unrealistic and hard to reach.  That's the end of surface-based convection.

Elevated Convection leads to Thunderstorm Cumulonimbus Clouds

Time Lapse of thunder storm

Convection forms thunderstorm cumulonimbus clouds.  How?  Warm air rises, and cool air sinks during convection.  

In the atmosphere, convection is usually caused by the sun heating the Earth's surface below.  Water vapor condenses into clouds as warm air rises leaving behind latent heat which destabilizes the air above. 

When there's a lot of moisture in the air and the air turns very unstable, convection can become more vigorous and lead to thunderstorm cumulonimbus clouds.  Tall, towering clouds, with tops reaching as high as 12 miles (20 kilometers) above Earth's surface, are characterized by their tall, towering appearance.  

Thunderstorm cumulonimbus clouds often bring heavy rain, lightning, strong winds, and hail.  Some of them can produce tornadoes.

Layers slip past each other, so convection starts at some upper level.  It either happens or it doesn't.  There are two possibilities to consider.

The warm air slips under the colder air or the colder air flows over the warm air.  

Warm air moving in - differential thermal advection they call it. Moisture is also needed in warm air.

Once it contacts the colder air above, up it goes.  Then we can figure out the LCL and cloud base using the same graphical techniques.

Observers might see alto cumulus castellanus (ACC) or cumulonimbus clouds (CB), which are different types of clouds.

Go back from this Thunderstorm Cumulonimbus Clouds to the Chasing Storms web page.

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