They can be caused by a combination of unstable air, solar heating, orographic lifting and an atmospheric trigger that lifts moist air parcels into areas of instability, amplifying buoyancy and propelling a building cumulus cloud to ever greater heights.
Absent orographic lifting as the mass of air moves upslope, air mass thunderstorms are driven by solar heating, so the driving mechanism shuts off at the end of each day.
Orographic lifting had the potential to cause heavy rainfall as this flow reached the Coast Ranges.
Large water drops can also be chucked into the atmosphere by the energy of a thunderstorm or
orographic lifting.
The maximum reduction in rainfall amount is registered over the mountains and foothills and is associated with the reduction in
orographic lifting and the associated vertical water vapor flux.
Orographic lifting produces regions of LWC accumulation on the windward slope.
In the world of meteorology, that is called
orographic lifting.
As winds force air up a mountain, in a process known as
orographic lifting, water vapor in the air condenses to form clouds, and further lifting "squeezes out" the rain.
Although
orographic lifting was a key process contributing to heavy rainfall, the southeast-to-northwest swath of heaviest rainfall (see Fig.
Although the layers had that breaking-up-after-a-storm look, it was cold enough and there was enough
orographic lifting to make what appeared to be benign clouds unflyable in an unprotected airplane.
Orographic lifting has been widely proposed as the causative mechanism (e.g., Rotunno and Ferretti 2001; Bousquet and Smull 2006).
What's more likely is the flight encountered an area of turbulence--probably the result of localized
orographic lifting. But--and especially since Cherokees are tough little airplanes--why the pilot either lost control or the turbulence broke the airplane before he could react are mysteries.