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Atmospheric Caps
My question is, what makes up an atmospheric "cap" and what do you look for in defining one?
--Mike
I thought I would address Mike's capping question this afternoon. Two blog entries in one day... WOW!! :)
When you hear the phrase, "The atmosphere is capped"... it really means just that. Picture it like a bottle of soda. If you shake that soda bottle really hard... and remove the cap... it will explode!! The same thing can happen if developing thunderstorms penetrate the atmospheric cap.
The cap is a region of stable air in the troposphere that keeps a lid on convective lifting (developing thunderstorms). What causes the cap?? A region of warm air aloft. (remember, when we have warm air over cold air... it is a sable situation).
The cap can be the difference between quiet weather and a severe weather situation. If the cap HOLDS... it will be a quiet weather day. However, if the cap weakens or BREAKS, daytime convection could explode to produce damaging storms. This would be the situation if the cap breaks at a time we are seeing a lot of instability...(Our peak instability is usually in the afternoon hours).
The cap is measured in degrees Celsius... a cap of 1 is weak, while a cap of 4 is strong. We sometimes look at a SKEW-T chart to get a feel for the cap. A SKEW T chart is below, it is basically a VERTICAL profile of the atmosphere:
Click to enlarge
On this sounding, the cap is 2.8... so a moderate cap is in place.
Jamie
Posted by at May 13, 2005 11:20 AM
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Thank you for the answer, and so quickly. Now, my question concerns this afternoon. It looks as though the sun was able to break through for a portion of the day today (I'm in an office completely devoid of windows so I'm at the mercy of my computer and hearsay). Have we had enough warming to produce strong to severe thunderstorms in the area, or are we looking at more of a rain/general thunderstorm event? Thanks again for the quick and thorough answer to my previous question.
MIKE:
We are just too cool to get any severe weather this evening. Even though we've seen some sun... temperatures are still in the 60s. We may see a few passing showers/thunderstorms, but that is about it. Have a great weekend!
Jamie
Posted by: Mike at May 13, 2005 3:28 PM
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