From the Freezer into the Fire: Extreme Daily Temperature Temperature Change on Thursday

 Can you imagine waking up with a sub-freezing temperature of 14F, with ice and frozen soil, needing a heavy jacket and something to warm your head?

A few hours later, the temperature jumped to 83F, and you dreamed of AC, shorts, and some icy drink?

A daily (diurnal) temperature change of 69F!   

You might think you were mad or dreaming.

It happened, in Seneca, Oregon yesterday.  But why?

The station in question was the Seneca BLM Agrimet site located at 4600 ft in a high mountain basin in eastern Oregon (location shown by red marker on maps).

Being in such a basin turns out to be very important.  

To show this, here are the minimum temperatures that morning (again the morning of August 29).  The coldest temperatures are in the Seneca depression, with the 14F observation at the lowest portion of the basin.  A few miles away in the surrounding hills, temperatures only fell into the 40s!

So what is going on?

Our nights are getting longer, so there is more time for cooling at night.   The skies were clear yesterday morning and afternoon, allowing good solar heating during the day and effective infrared cooling at night (see satellite image Thursday morning).   Clouds both reflect solar radiation (reducing the daily maximum) and act as blankets at night, reducing the ability of the surface to cool by emitting infrared radiation.

The air was dry over eastern Oregon, with relative humidity yesterday morning well below 100% (see map)

 Dry air allows better cooling at night and reduces the chance of warming fog.  

So Seneca had great cooling at night and full sun during the day.  The cool temperatures on Thursday were aided by a slug of cold air that had moved in the previous day (see map of the difference 5000 ft temperatures from normal on Wednesday).  Blue is colder than normal.

Cold air is denser and heavier than warm air and tends to settle into basins and valleys ---just like the one around Seneca.  There was undoubtedly warmer air a few hundred feet above the ground

The cold air in the valley was not very deep and during the day solar heating of the surface caused the cold air to be mixed out, resulting in a surge of temperatures into the 80s.

Here is a view from the surface near the Seneca weather station.  You can see the surrounding hills in the background.

The high mountain valleys of eastern Oregon are well known for amazing cooling at night and a large temperature range during the summer months.  Here is a map of the typical daily (or diurnal) range across the US during July.  Eastern Oregon is probably the "best" place in the nation to freeze at night and fry during the day.  Not sure if that would attract tourists.

 Seattle's diurnal variation for the same day was only 65 to 79F, just 14 F.  

Embarrassing.