The Thursday clouds will clear out leaving us with a sunny weekend and a slow warmup. Winds will be light and the air will be dry under a high pressure ridge that still shows no real signs of leaving the region. There is a slight chance of some showers moving into the area starting early to mid-next week         , but it is unlikely that they will amount to very much, as they would be the result of a light southerly flow and not a standard winter-type of storm.

 Time series of shifts in sign of the Pacific Decadal Oscillation (PDO), 1925 to present. Values are averaged over the months of May through September. Red bars indicate positive (warm) years; blue bars negative (cool) years. Note that 2008 and 2012 were the most negative values recorded since 1956.   (Courtesy NOAA Fisheries.)

Time series of shifts in sign of the Pacific Decadal Oscillation (PDO), 1925 to present. Values are averaged over the months of May through September. Red bars indicate positive (warm) years; blue bars negative (cool) years. Note that 2008 and 2012 were the most negative values recorded since 1956. (Courtesy NOAA Fisheries.)

I’ve been talking about how the Pacific Decadal Oscillation (PDO) will generally move the polar jet stream northward (away from us) when it is in its negative phase, like it has been for most of the last decade. But it’s not that simple. Earlier last year, the PDO shifted into a positive (warm) phase, so why hasn’t the strong polar jet stream returned? There are probably several reasons for that. There is often a time lag between ocean phases changing and its reflection on weather patterns. And there is always the complicated world of teleconnections. I’ll tell you about those tomorrow.

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