The Revenge of the Ridge: Arid first half of February

The last few weeks in the Northwest have been much drier than usual….and the reason is clear. A very persistent ridge located along the West Coast or just offshore.

The image below shows the difference (over the past month) from normal in the altitude of a pressure surface of 500 hPa – you can think of this as the difference in pressure at 18,000 ft above normal in the past 30 days. Dark red indicates a much higher than normal pressure off our coast. According to the vernacular of the weather, there is a large mountain range offshore.

To the east of the ridges are generally air-submerged and dry conditions. That’s where we were.

Last week? Essentially the same pattern (see below). One thing you will notice right away is the wave-like nature of the atmosphere. There is a high pressure peak offshore, but a trench in the central US, and a peak on the West Coast. This is called the amplified waveform.

What about the future? Let’s take a look at the best of the best! Central Europe composite projections (multiple forecasts averaged). All pictures are from, a really great service you can subscribe to. They show the altitude of the upper atmosphere (solid line) and the difference from normal (red to pink are more about normal)

A weak trough moves through on Monday, but by Tuesday night, a large ridge will develop offshore. And yes, a strong bottom in the Midwest.

By 4 p.m. Friday, the ridge weakened slightly and moved toward our shores.

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And believe it or not, next Tuesday (February 15) the ridge will be strong again and move away a little bit. Ides of February. And the Ides will dry.

What about the predicted rainfall? This is the predicted difference from normal over the next ten days, where red indicates below normal.
Yes…you guessed it….much drier than normal conditions would be expected. Sorry skiers. But there should be more sun than usual. Good for people with SAD.

But it would be cruel to me to let you all lose hope.Some long-range forecasts have suggested the possibility of a regime change, with a cold trough developing over the Northwest. This is the predicted upper flow for Sunday, February 20. Blue indicates lower-than-normal pressure/altitude.

A Great Trench on the West Coast!!
Skiers – what do you want this to do. But the uncertainty in the distance is great, so don’t get too excited.

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