Extreme Offshore Storm Could Produce Damaging Winds over the Western Cascade Foothills

 The latest model forecasts are consistent:  an unusually powerful storm with extreme low pressure will develop rapidly offshore on Monday and Tuesday.

But there is something else not yet discussed:   this extreme offshore feature may cause a downslope windstorm on the western slopes of the Cascades.

One that could easily cause extensive power failures.

The latest sea level pressure forecast for Tuesday is scary, with an intense 952 hPa low center west of the Washington coast.    The strongest storm ever to hit the Northwest during the past century, the Columbus Day Storm of 1962, had a low-pressure center of 950 hPa.

The lines show the pressure analysis. Huge pressure gradients (pressure change over distance) and intense pressure changes over the Cascades.  Remember this, it will be important.

The sustained wind speeds at the same time are shown below. 70 kts and more around the storm.  Hurricane strength.  The BC, WA, and Oregon coastal zones will get a taste of it.  Expect some coastal power outages.

 

As in any late-night commercial, there's MORE.  Much more.

The low pressure offshore will create a large pressure difference down the Strait of Juan de Fuca.  As a result, winds will accelerate westward down the Strait, producing huge winds near Tatoosh Island.  They don't call the western exit of the Strait the "Graveyard of the Pacific" for no reason.  Rocks and wind and cloud.

The lowlands of western Washington will get a piece of the windy action as well.

Here in Seattle, it appears that winds will accelerate to 30-40 mph on Tuesday evening, which will blow down some leaves but do little damage (see wind forecast from the City Light WindWatch website, which my group runs).  I will have to rake the leaves....again.

But the real wind action for the western lowlands will be on the western slopes of the Cascades, due to easterly winds driven by a huge pressure difference across the Cascades.   

Below is the latest high-resolution model prediction of wind gusts on Tuesday evening.  Easterly winds gusting to 50-60 kt (57-69 mph).

Enumclaw, Black Diamond, North Bend, and other communities near the western Cascade slopes will get bruised by strong winds.  Get your candles ready.

You want to see an ultra-high resolution forecast of the winds at 10 PM Tuesday evening.  Here it is!   Strong enough for some power outages for sure.

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