Ice Storm, Heavy Rain, Cold Wave, Warm Wave, and Now A Powerful Storm Approaches

First, we had unusual cold, then a freezing-rain ice storm, then heavy rain, and then unusual warmth.

But the weather gods are not through with us.

A powerful storm may develop off our coast on Tuesday.  


In such circumstances during ancient days, folks would ask themselves why the gods were angry and ask their priests to intercede with an appropriate prayer or sacrifice.   Today, our modern weather priests often blame such storminess on sins of carbon emission and predict doom without the proper response.    

Human nature hasn't changed.  But in this blog, let's stick to the science.

A Profound Change in Atmospheric Circulation

Let me show you the upper level (500 hPa, about 18,000 ft) weather maps from three days ago (Wednesday at 10 AM) and yesterday at the same time.  

A profound change.  On Wednesday, a deep trough of low pressure was inland while a ridge of low pressure was offshore, resulting in a strong, cold airstream from the northwest.

But the weather gods are not through with us Ice Storm, Heavy Rain, Cold Wave, Warm Wave, and Now A Powerful Storm Approaches
Wednesday

By yesterday, the ridge of high pressure had shifted inland and south, while low pressure has amplified over the Gulf of Alaska.    The result is a strong, warm, moist flow from the southwest.

We will be in this pattern for quite a long time.

But the weather gods are not through with us Ice Storm, Heavy Rain, Cold Wave, Warm Wave, and Now A Powerful Storm Approaches
Saturday

The resulting temperature change in western Washington has been remarkable (see temperatures at SEATAC below, purple is the normal high, cyan the normal low).  We were generally cooler than normal through 21 December and then the bottom fell out.  And then yesterday we warmed to well above normal.

But the weather gods are not through with us Ice Storm, Heavy Rain, Cold Wave, Warm Wave, and Now A Powerful Storm Approaches

This warming was accompanied by very heavy rain that led to local street flooding. The precipitation over the past 36h has been remarkable (see below), with some locations getting over 5 inches.  Over an inch over the Puget Sound lowlands.

The poor ice had no chance.  At least the airports can operate normally again.  And many of our rivers have filled to bankful.


The Approaching Storm

Both American and European models suggest a major low-pressure system will develop off our coast Tuesday morning, with very low pressure.

Here is the UW model's prediction of the sea level pressure at 10 AM Tuesday.  A deep 971 hPa low is off the WA coast, with an intense pressure change (gradient) along the Oregon Coast.    That means strong winds.

But the weather gods are not through with us Ice Storm, Heavy Rain, Cold Wave, Warm Wave, and Now A Powerful Storm Approaches

The European Center model at the same time has a 970 hPa low in a slightly different position.  There is going to be a major low off our coast.  The question is where it will go.


I am confident now that the Oregon coast will get a good blow.

The storm will then move east and north, but there is still substantial uncertainty regarding its impact on the interior of western Washington.   But 20-40 knots around Puget Sound is not unreasonable.   

I will leave that analysis for another blog tomorrow, so stay tuned.  But you might consider making an offering in your holiday fireplace.








 

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