August 20, 2013

Extreme Temperatures in Oregon: The Seneca Oddity

Seneca, Oregon, located in the high plateau of eastern Oregon, has some amazing temperature extremes.

Consider July 21 of this year.   The low that morning was 30F--below freezing.  The high that day:  96F!  Talking about concrete-cracking extremes!

Seneca has some other holding the all-time record cold temperature record for any day, anywhere in the Pacific Northwest:  -54F in 1933.  

So what is going on in Seneca?  A major hint comes from terrain maps.

Let's start with a large scale terrain map for those of you unfamiliar with the region.

A local map around Seneca shows something important:  Seneca is in a topographic bowl within the high terrain.   Seneca is quite a bit about sea level: 4700 ft.
You can appreciate the fact that Seneca is in a bowl by looking at a picture at the observing site and on a nearby road:

So why so cold?  You start with a high elevation station in a bowl.   Cold, dense air tends to drain off the terrain and settle into lower elevations in the bowl.   Seneca is in dry eastern Oregon, where there is plenty of clear skies year round.  Clear skies allow radiational cooling to space--which enhances surface cooling.  But during the summer the place can really warms up with all that sun.  Seneca is isolated from the moderating influences of the Pacific by the high Cascade mountains.

Seneca has experienced multi-day periods of temperatures below -40F when an arctic air mass spread over the region, something that happened in 1989.  So why go to Fairbanks for cold fun, when Seneca offers you a similar chill?  There are unofficial reports of temperatures below -54F in the years before the official Seneca temperature site was established (in 1931).   For example, there are claims of -60F during the cold snap of 1927.

The chilly hamlet of Seneca, Oregon

1 comment:

  1. Eastern Oregon, including the area around Seneca, is dotted with Forest Service guard stations and lookout towers for rent. You can experience first-hand the dramatic weather rolling over the Cascades, the Blue Mountains and the many minor ranges.


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