Weather results from many interacting facets of the planet: the shape and cover of the land; the amount of water in the air and soil; the chemical composition of the atmosphere; the Earth's rotation and orbit.
Each of these factors exerts its own influence. As a result, the overriding impulse of our out-of-balance planet is to seek balance. This is what creates changes in our weather.
Air pressure – the weight of air -- is an important part of this. Warm air is lighter than cold air (think of the warmth near the ceiling of a room compared to the chill near the floor). Also, wet air is lighter than dry air.
Thus warm, moist air rises while cool, dry air sinks.
When relatively cool, dry air moves into a region, it is called a high pressure system. As this cool, dry air sinks from its own weight, it pushes the air that's in its way outward. As result, winds are moving to the outside of the system and the interior is still. High pressure systems are known for quiet weather.
In the winter, the dryness of a high pressure system allows temperatures to plummet at night, after the warming effect of the sun is gone. (Water droplets in moist air harbor warmth.)
So why is this relevant now?
Temperatures plummeted across the region on Tuesday as an intense high pressure system settled over the region with its core above the Omaha metro.
According to the National Weather Service, the Omaha metro area recorded its seventh coldest Nov. 12 on record Tuesday, when the overnight low dropped to 11 degrees. Had there been snow on the ground, temperatures would have dropped even more.
In Verdel, Neb., the coldest spot in the state, temperatures dropped to 4 degrees, according to Natalie Umphlett, regional climatologist at the High Plains Regional Climate Center.
In Iowa, the lowest overnight low was 1 degree below zero in Spencer, according to Harry Hillaker, state climatologist. One reason Spencer got colder was that it had snow on the ground, he said.
Those low temperatures coincided with the Omaha metro recording its highest pressure reading since Janaury 2009, according to Cathy Zapotocny, meteorologist with the National Weather Service.
The pressure reading on Tuesday peaked at 30.90” (inches of mercury) at 8:52 a.m., about two hours after temperatures bottomed out.
Source, National Weather Service; AccuWeather Inc. expert senior meteorologist Jack Boston; National Oceanic and Atmospheric Administration; Iowa Bureau of Climatology; High Plains Regional Climate Center.