Thursday, July 7, 2011

High Winds Hit the Eastern Cascade Slopes

Today a weak front moved across the Cascades resulting in very strong winds along the eastern slopes.  Here is a nice MODIS satellite picture this afternoon..the front was associated with the north-south cloud band--and you can see convergence zone clouds forming behind it.  Ironically there is enhanced clearing to the north and south of the convergence zone band. 

With pressure rising behind the front as cool, dense air deepened west of the Cascades and as pressure fell east of the Cascades due to persistent warm temperatures and pressure falls associated with the front, a very large pressure difference developed across the mountains...as much as 11 millibars during the mid-afternoon (that is a lot!).

During such conditions, Ellensburg and the Kittitas Valley get hammered as air accelerated across the Cascades, particularly in low areas through the mountains...and today the winds approached 50 mph.  Here are the wind gusts at Ellensburg today (peak winds in knots):
A peak wind of 43 knots is 49 mph.    There are a lot of wind turbines in the Ellensburg area and there is a good chance that some of the them had to feather their blades today from TOO MUCH wind--most do so around 45-50 mph.

    Here are the observations at 4 PM over Kittitas County and vicinity (KELN is Ellensburg).   Temperatures were in the mid-90s at some eastern Washington locations--while western Washington was 30F cooler.  The winds were from the northwest along the eastern slopes--with many locations with sustained winds of 20-30 knots.



Below is a high-resolution 11-hour forecast of the sustained surface winds (actually 10 meters above the surface) at 4 PM from the UW WRF predictionsystem.  The model predicted strong winds along the eastern slopes, with sustained winds  reaching 30 kts--not a bad forecast.  The Weather Service had a high-wind advisory and I suspect there was some blowing dust. 



You will also note strong winds in the Strait of Juan de Fuca, where winds have increased to 30-40 mph at times.  Here are the winds at Smith Island, located in the eastern side of the Strait.  Yesterday winds gusted to 40 knots there (roughly 46 mph).  You will notice a large diurnal (daily) variation in winds there--produced by the diurnal heating over land versus water.


2 comments:

joanne said...

the winds have been fierce here in port townsend for two days, it seems they are FINALLY easing at 11:56pm.

Tyree Callahan said...

I just have to say again: this blog is AWESOME. Thanks, Cliff. So great to get such specialized knowledge about fourth corner weather patterns distilled into a friendly format. I sincerely appreciate it!

Tyree