1.   As a compact but potent jet stream disturbance emerges from the Rockies on Thursday morning, an area of surface low pressure will intensify over eastern South Dakota.

2.   A sudden adjustment in the jet stream can lead to rapid rises and drops in surface pressure.

3.   Compared with summer, surface pressure over the interior West is higher in winter.

4.   Cloudy, cool, rainy weather will extend across southeast Wisconsin and northwest Michigan as surface low pressure approaches the western Great Lakes.

5.   During seasons of lower than average surface pressure, Atlantic Basin tropical cyclone activity increases.

6.   Heating lowers the density of the air, which in turn, causes local surface barometric pressure to fall.

7.   In the West, air pressure tends to be lowest during the summer months, when warm air, being buoyant, rises, lowering the surface pressure.

8.   Rising surface pressure over the Northeast is associated with an expanding fair weather system moving southeast from Quebec.

9.   Showers and thunderstorms will develop over the upper Middle West across the upper Mississippi Valley and western Great Lakes as a surface low pressure draws moist air northward.

10.   Such a pile-up would have produced a weightiness that would have unfavorably increased surface pressures in the eye.