When an upper-level disturbance approaches the front and removes mass from the column of air, such as upper-level divergence, this causes pressures to fall at the surface.
And when this happens, the upper-level disturbances intensify and can produce stronger forces.
The storms and suspected tornadoes, which forecasters say were caused by an upper-level disturbance
from Mexico, hit an already-sodden swath of Texas that was still drying out from the remnants of Hurricane Patricia.
And just when you think you're getting a break in the clouds, you might find that you were the source of the upper-level disturbance
On December 14th, an upper-level disturbance moving across southern portions of California and Nevada spread moisture into a chilly air mass that was in place across the Mojave Desert.
On December 23rd, an upper-level disturbance produced a brief snow shower.
A strong upper-level disturbance
and an area of low pressure over the Four Corners region is currently bringing heavy snow, local downpours, scattered thunderstorms and gusty winds to Arizona and New Mexico.
Clouds come primarily from eastward-moving upper-level disturbances or weakening cold fronts blown in from the Great Australian Bight in the south.
Furthermore, the low altitude of the eclipsed Sun magnifies the effect of even a small amount of cloudiness, especially the deep cloud cover that comes with upper-level disturbances.
But on certain days, upper-level disturbances
will approach the area and break down the cap, causing the storms to spread up and down the stronger boundaries and possibly even develop along weak boundaries.