Thursday, October 20, 2011

Another La Nina Update

Thursday, October 20, 2011
12:38 P.M.

Normally, I would not update the La Nina situation, but I saw something startling today. I was looking over this "Pacific Northwest Weather" group on facebook (btw, you should join it!) and somebody posted this graphic. I looked into it and discovered that the model above is the latest CFS model from NOAA. It is forecastin a La Nina of epic proportions. Last year's La Nina peaked at a -2 Celsius SST anomaly in the region Nino 3.4, but this one is forecasting a -3 degree anomaly! Absolutely incredible. Right now, it is an outlier, but this is still very surprising to see because the CFS is usually one of the most accurate models for forecasting El Nino/La Nina events.

For your courtesy, a graphic of the specific El Nino/La Nina regions is given below.

I don't know if there ever has been a -3 degree anomaly in Nino 3.4, so that would be absolutely incredible. I seriously doubt that will happen. But one thing is for sure... this La Nina is trending to be more intense than previously forecast. Most models are trending slightly cooler, and as you have seen, the CFS is off the charts.

Here is an animation of the SST over the tropical Pacific over the last 2 1/2 months. You can see a weak-moderate La Nina thus far, and the CFS believes it will rapidly strengthen soon.

This is an awesome animation, and you can see the animation with additional material and data at the "Tropical Pacific SST" link on the right side of my blog.

As far as immediate weather goes, we will be cloudy today before seeing a series of weather systems over the weekend. None of these systems will be particularly strong, but they will some blustery conditions and varying amounts of rain, with more in the mountains and less around central Puget Sound due to rain-shadowing.

This picture shows one coming in at 11 A.M Friday.

Valid 11:00 am PDT Fri, 21 Oct 2011 - 30hr Fcst - UW 4km 12z WRF-GFS 3-hour precip

Then, we'll have a weak wave brush through our area around noon on Saturday.

Valid 11:00 am PDT Sat, 22 Oct 2011 - 54hr Fcst - UW 4km 12z WRF-GFS 3-hour precip

Finally, we'll see a weak cold front come through Saturday night/Sunday morning.

 Valid 02:00 am PDT Sun, 23 Oct 2011 - 69hr Fcst - UW 4km 12z WRF-GFS 3-hour precip

This next diagram shows the 48 hour precipitation for our area ending 5 A.M. PDT Sunday. Take a look at the large amounts of precipitation in the mountains and the lighter amounts by Seattle. The precipitation is being enhanced in the mountains from rising air, but as the air flows off of the Olympics, Seattle and places on the north Kitsap Peninsula will be shadowed. Of course, south-central Washington will be shadowed as well.

Valid 05:00 am PDT Sun, 23 Oct 2011 - 72hr Fcst - UW 4km 12z WRF-GFS 48-hour precip

The mountains, particularly the Olympics and North Cascades, are getting clobbered with rain, but you can see some pretty defined rain shadowing extending northwest from southern Lake Washington.

I have noticed that tv weather stations don't get into specifics about rain shadowing much, so don't be surprised if you turn out to have only a little bir of rain while some places in the Cascades pick up 5 inches from this storm. Ahh... the beauty of Pacific Northwest weather forecasting.

Have a good one you guys! Thank you for reading.
Charlie Phillips

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