Sihara wrote:Thank you for the explanations. So divergence at the upper levels involves thunderstorms that will affect Fay - this is one of the most fascinating storms to watch, seems to want to defy all forecasts and logic.
Our area sat right in the center of the cone all weekend, to be completely missed when Fay decided she had a mind of her own. Can't help but wonder what she'll do next.
Btw - I liked the photos, too - thanks for posting.
Divergence aloft simply means that air in the upper levels is moving outward from a point. You can think of it as leaving something of a partial vacuum. If air is moving away from a region aloft, the pressure will fall at the surface because there is less air above that point. This leads to convergence of air in the low levels to replace the "lost' air. There is a lot of divergence aloft over Fay, which helping drop the pressure in the center and intensify the low-level winds blowing in toward the center.
Note, it has nothing to do per se with instability or even thunderstorms, but the process above can help create a favorable environment for thunderstorms.
