Breaking the 20/20 Rule

I have a simple rule that helps me remember when we are getting to the extremes of temperature in northern Utah.  I call it the 20/20 rule.  Usually, generally, and most of the time the 700-mb (crest-level) temperature lies between +20ºC and -20ºC.  On a very hot day in the summer, the 700-mb temperature is usually about +20ºC.  On a very cold day during the winter, the 700-mb temperature is usually about -20ºC.  If you go beyond those extremes, you are getting into rarified air.

Well, we're going to break the 20/20 rule today and tomorrow.  This morning's sounding shows we're sitting at a 700-mb temperature of -20ºC.

That is, as the English say, bloody cold, but it's going to get colder.  How about -22ºC by tomorrow morning.

And the models keep us at or below -20ºC into Monday.  At the resorts, this is pretty much as cold as it gets.  Expect sub zero temperatures through Monday in the upper elevations.

As the storm is tapering down and we look to the future, I am increasingly worried that we could experience the Mother of All Inversions next week.  We have a deep snowpack in place, very cold air entrenched in the valleys, and the forecast models call for a warm ridge to move over us.  We'll take a closer look at this perhaps tomorrow.