Stable atmosphere and thunderstorms?

Question

It is june 7th today (Western Virginia) the past few days and the next week are really hot and humid beyond belief the dew point was in the low 70's and the high's are in the mid 90's in some places. It is so humid that I can feel the moisture in my hands when I step outside.

However I remember a lot of days like this meant strong thunderstorms later on and sometimes that was a relief. However the last few days there was not a drop of rain and nothing showed up on the doppler. I was wondering why if all the elements to form thunderstorms (moisture, high dew point, heat) is there why aren't there any thunderstorms forming?

I saw a lot of cumulus clouds becoming really puffy and some were forming into cumulus congestus but thats it. Is the atmosphere too stable? What makes an atmosphere stable vs. unstable? What causes it? How do you measure it?

Answer 1

Thunderstorms normally form from air warmed in contact with the ground that rises up.  The way stability is measured is by considering what happens to a bubble of air (a "parcel") that rises up in the atmosphere.  If it is warmer than the surrounding air in that level it will keep rising, if it rises up high enough so that condensation form then that will add heat to the parcel and make it more buoyant. In the morning there is often a level at which the parcel is not warmer than its surroundings (the "cap"), and the parcel stops rising.  As the day heats up the parcels get warmer and warmer and the cap gets eroded away, once the cap is gone then thunderstorms can form very rapidly.  Some days, particularly if there is warm air aloft, it the cap may be too strong and storms will not form.

There are a couple of numbers that meteorologists use to judge these things, one is Convective Available Potential Energy (CAPE) found by adding up how much warmer the parcel is at different levels.  The cap is measured by the Convective Inhibition (CINH), which is pretty much the opposite of CAPE--that is, how much energy must be added to a parcel to keep it rising.

I checked the balloon soundings in Virginia at http://weather.cod.edu/analysis/analysis...

and I see that while there is substantial CAPE (energy available to make thunderstorms) there is also substantial CINH, so nothing may happen.