The weather gods have been very kind to us this year, providing a generally dry period throughout wettest time of the year.
To illustrate, here’s the probability that the climate gets one hundredth of an inch or more in Seattle for the year. The climatic probability of rain per day is more than 60% from November 7 to mid-December. This is usually the wettest time of the year!
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Forecast for this week? Completely dry with plenty of sun. Take a look at the total rainfall forecast through Saturday at 4pm. No rain over the Northwest and California.
The reason for these dry conditions? The Great West Coast ridge returned, as shown on the upper-level map (500 hPa, about 18,000 ft) around 4 p.m. Tuesday. The solid lines are altitude, but you can think of them as pressure at about 18,000 ft.
For a better view of the upper-level situation, the following map is at the same level, with shaded areas showing climate anomalies (normal). Red indicates a 500-hPa elevation above normal, and blue/green the opposite.
You can see our ridge has “book compartment” low altitude/pressure tracks. This is a very stable pattern, called a omega block. We will be dry, but the eastern half of the United States will be cold and wet.
It looks like this pattern will break next Sunday, with a total of 72 hours of rain ending Wednesday the 23rd rather soggy (see forecast below).
