We are in a very strong El Nino and typically its influence on Northern Hemisphere weather circulation increases during December, with the most profound impacts after January 1.
We will get a potent taste of a typical El Nino pattern next week.
Let me show you.
As I noted in a previous blog, the sea surface temperature of the tropical Pacific has become far warmer than normal (see below). In fact, the critical El Nino index (region 3.4 sea surface temperatures anomaly from normal) is now about 2°C above normal, resulting in a strong El Nino.
The difference in temperature from normal.
El Ninos tend to produce a certain atmospheric pattern over the eastern Pacific (see below), with a portion of the Pacific Jet Stream heading into California, bringing wetter-than-normal conditions over central and southern California. In addition, low pressure develops offshore of the West Coast, and warmer than normal temperatures are observed over the western U.S., particularly across the upper plains.
And a very similar pattern is predicted next week.
The predicted upper-level map (300 hPa pressure level, about 30000 ft) for Wednesday shows heights (solid lines) and winds (shading), indicating a jet stream (strong winds in knots, reds and orange colors strongest) entering southern California and a low offshore.
Classic El Nino.
Also classic is the very warm conditions prediction for the western U.S., particularly the upper plains.
So those heading south for the holiday season are well advised to take their raincoats and umbrellas. Northwest weather will move to the Southwest for a while.
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This month's weather continues to be marked by remarkably high relative humidity. I have never seen such consistently saturated/nearly saturated air. The average relative humidity for the month at my location in Bellingham is 96%. The lowest relative humidity that has occurred is 71% on the morning of 12/9. Only 12/2 and 12/3 had daily mean relative humidity <90% while all other days had mean relative humidity of at least 95% including 12/6, 12/7, 12/10 and 12/14 which had daily mean relative humidity of 100%. 12/10 takes the cake, though, with a daily minimum relative humidity of 100%. Potential evapotranspiration has been accordingly exceptionally low. It just seems that everything outside is basically wet all the time. My soil moisture sensors indicate 95% saturation. I think that the abundant precipitation during this month combined with generally cool, humid conditions over the past month brought on by persistent, anomalous high pressure. At my location the mean barometric pressure anomaly is +6.5mb which is equivalent to a thickness of 200'. Without some influx of dry air, which looks rather unlikely given the current weather forecast, it's likely that the very damp air will continue to persist. On the upside, it's a great time to be moss...
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