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 weatherbell.com, 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.
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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.
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.
