Capping Inversion?

Question

Please explain to me how it works. Seems to be my major weakness, and I have read several text books and still don't get it.

Kills my forecasts almost every time.

Answer 1

The above are correct, I just wanted to add a little from the severe weather side of things.  This inversion usually occurs around 800-700mb between the moist boundary layer and the elevated mixed layer, or the very dry air in the upper part of the classic "loaded gun" sounding.  It happens when warm, dry air from the high elevations of Mexico advects over the warm, moist air from the Gulf.  Usually the Mexican air is a touch warmer, resulting in the inversion.

Since the inversion "caps" the air, keeping it from rising, it suppresses convection.  That said, this can be a good thing.  The capping inversion can keep storms from developing early on in the day, allowing the surface to warm and become more unstable, and in some cases allow more moisture to advect in.  It can also keep the amount of convection down, resulting in more isolated storms.  On the other hand, it can cap the atmosphere until nighttime, or completely suppress storms altogether.  The key to the forecast is when, if ever, the cap with "break" and parcels of air can rise, and if it will isolate convection or it is weak and convection will be numerous.

Answer 2

If you are speaking of a temperature inversion, that is where is the warmer air resides above cooler air.  Fog will form below this layer when winds are calm or very light.  A positive lapse rate indicates temperatures are rising as they lift but a negative lapse rate means the temperatures warm as you go aloft.   This situation resolves itself when heating from the sun raises the surface temperatures and convective activity breaks the inversion.  Fog will dissipate and clouds can form as the fog begins to lift.

You can plot your temperatures on a diurnal curve.  Take the temperature at let's say 7am and follow the curve til the temperature at the surface exceeds the temperature at the top of the inversion.

Answer 3

A capping inversion is usually a situation where a layer of relatively warm air exists over a cooler lower air layer.  Recall that an inversion is a layer of warm air above a cooler layer.  It is sometimes referred to as a capping inversion because as the lower layer air begins to rise, it encounters the inversion layer and stops rising.  In other word, the inversion is "capping" the lower layer air from continuing to rise.

Does that help?