Blog: Inbound short wave so Gorge goes from MILD to WILD

windfind · Joined: 18 Mar 1997 Posts: 1901

Hi Gang,

The current heat producing upper ridge departs fast Wednesday night as a potent shortwave upper trough comes over us at ≈ 18,000 ft. And most signs suggest wild winds by Thursday.

But what the hell is a shortwave? And how can it make the current smoky listless winds begin to rage by Thursday.

This blog gives some answers in video animations.

http://blog.weatherflow.com/west-coast-wind-blog-dissection-of-how-the-gorge-wind-goes-from-mild-to-wild/

Mike Godsey
iwindsurf.com

AlexM · Joined: 03 Jun 2005 Posts: 49 Location: Mosier, Oregon

windfind · Joined: 18 Mar 1997 Posts: 1901

Hi Alex.

Trying to explain some of these concepts in words and with my rudimentary graphic skills is very difficult since upper troughs etc are 3D events and constantly change both in time and space. So let me try again with more words and pictures .

The distinction between a LONG wave upper trough and a short wave upper trough is somewhat arbitrary. Typically there are about 3-7 LONG wave upper troughs winding around the earth in the N. hemisphere moving from west to east at ≈ 18,000 ft.. Mixed in with LONG wave upper troughs are especially sharp kinks in the upper level winds called short waves.

In the first image below you can see a short wave moving towards the west coast of the USA. You can also see an upper ridge and a long wave upper trough. Notice that the short wave is just a much sharper kink in the upper level winds compared to a long wave. These short waves move faster than long waves.

The atmosphere in the area within the loop of the upper ridge is relatively thicker in the vertical dimension so it exerts more pressure on the surface. You can see this with any barometer today in the Gorge. This air below the leading edge of the upper ridge is descending and it compresses as it reaches the surface resulting in compressional heating so the temps go up.

The atmosphere in the area within the loop of the upper upper trough is relatively thinner in the vertical dimension so it exerts less pressure on the surface. The air in the leading edge of the upper trough air is ascending which will deepen surface low pressure. If you live out in the Columbia Basin you will notice this happening Thursday if you have a barometer.

The second diagram below shows this process greatly simplified.

For more detail go to: http://www.atmo.arizona.edu/students/courselinks/fall12/atmo170a1s1/coming_up/week_3/lect9_upper_level_charts.html

Mike Godsey
iwindsurf.com