A Very Dry Week Ahead

For December, we are going to have an unusually dry and sunny week: perfectly timed to lessen the incidence of SAD (Seasonal Affective Disorder) and to allow some outdoor exercise during the COVID restriction period. 

 Take a look at the forecast cumulative precipitation through Saturday at 4 PM.  Plenty of precipitation offshore, but virtually nothing over WA, OR, or CA.

The cloud forecast?  Mostly clear, as shown by the model cloud prediction for Wednesday afternoon. 

The downside of the clear skies will be frosty mornings, as the earth is able to radiate infrared energy to space effectively without the clouds.

The reason for this sunny bounty?    A very persistent upper level ridge that will remain parked over the West Coast.  

To illustrate, Below is the upper level (500 hPa--about 18,000 ft) for this afternoon at 4 PM.

Impressive.  And with troughs on both sides, we have something called an Omega pattern, which is very stable and hard to move out.

Friday at 4 PM?  The ridge is still there, with a small trough over California.  The Northwest will be in the clear.

One final issue.  The surface reflection of this upper level ridge puts high pressure to the east of the Cascade crest, producing a large pressure difference across the Cascades (see sea level pressure map a 1 PM today).  As a result, there will be strong easterly (from the east) winds in the passes and in the Columbia Gorge. Expect wind gusts of 40-50 mph at the Vista House overlooking the Gorge!

Enjoy the sun.