Atmospheric Pressure.

Since we are settling into a dry period, let's delve into some atmospheric science.

High/low pressure.

Atmospheric pressure is the force exerted on a surface by the weight of air above.  Atmospheric pressure is closely approximated by the hydrostatic pressure caused by the mass of air above the measurement point. Low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lbf) (A column one square inch in cross-section would have a weight of about 14.7 lbs, or about 65.4 N). This is approximately the same as having a small car press down on you.

Today's 850mb MM5 model.  Large High Pressure dominating most of the North Central Pacific.  Notice the cold air driving air in from the north – hence our single digit low temps.    

This is the same model but for this coming Tuesday. The center of the high is forecasted to drift east /northeast.  This will push the cold air into the interior US and bring warm air over the PNW.  This could produce spring like “January Thaw” with little to no precipitation.