Terminology question

[Jon Miller]

Pardon my ignorance but I see the term “ FORCING FOR ASCENT “ used frequently in SPC discussions and am not quite sure what that means meteorologically.

I’m assuming it pertains to causing air to lift and thus convection if the other components are there - am I correct or not on this ?

Thanks for any help or information on this

Jon Miller
KT8NDO

 

[Paul Knightley]

Forcing is usually just another name for some kind of lifting. This can come about in a number of ways, and at different levels of the atmosphere. Without seeing the term in more context it's hard to say what is meant in this case.

However, and for example: an outflow boundary could be considered to force ascent in the lower layers of the atmosphere if convergence is good along it...this could lead to a surface parcel being mechanically lifted enough to reach its level of free convection and continue to rise, perhaps developing into a thunderstorm.

Another method of 'lift' is when an upper trough approaches - air in the mid and upper levels rises as a trough approaches, as divergence aloft overspreads an area. If this air is non-saturated, the lifting can cause lapse rates to steepen somewhat - however, it also can cause cooling, as air which is forced to rise expands and cools. This cooling can then erode a capping inversion and allow storms to develop.