The week ahead – Santa Ana winds in Snoqualmie Valley?

[Article by Ryan Porter of Snoqualmie Weather]

The week begins with a familiar theme of late, sunny and pleasant for early September. But the literal ‘winds of change’ are coming.

A rare late summer pressure gradient is expected to set up Monday evening into Tuesday as an unseasonably strong upper-level trough dives down from Canada towards the Rockies. This air will try to balance out with lower pressure out over the Pacific, generating our all too familiar Cascadia (gap) wind setup. The National Weather Service believes the type of incoming pattern at this time of year probably only occurs about every 30 years.

I believe uncertainty is a bit higher than advertised with this one. Looking at current model runs, expect North Bend and Snoqualmie to be windy (25-35 mph), but not likely getting the brunt. Areas like Enumclaw on south to the Columbia Gorge could see howling easterly winds pushing 50 mph. A small shift in the forecasted pattern could bring Snoqualmie Valley up towards the higher wind gust figures, or on the flipside of scenarios – less gusty and more just breezy than anything. Be prepared for all of the above.

Given the plummeting humidity associated with downslope winds, fire danger will be much higher than usual for Western Washington.

Though the windy experience here won’t quite be like a hairdryer hitting you, the common feeling in southern California when the Santa Ana’s hit, our local situation could feel a bit like a somewhat cooler version.

As for the smoke forecast, much will depend on the local wildfire situation. Any flareups in eastern WA will likely have an impact on our air quality, given the east-to-west offshore flow.

A layer of smoke could be seen capping Mt. Si from Snoqualmie Falls Golf Course – Friday morning (9/4)

For the rest of the week, we’ll see a thermal trough setup into Wednesday and Thursday, very likely pushing the mercury up into the 90°’s. We should moderate into the weekend as a ridge moves inland and brings a return to onshore flow, but still no rain in sight!