Actual Pattern Change!

December 20, 2011
4:55 P.M.

A week and a half ago, I posted a big blog about how things were gonna change. We were gonna get out of this inversion, get some rain in the lowlands, and start building some serious snowpack in the mountains.

Like Obama, very little ended up changing. I don’t hate Obama, and he’s sure doing a lot better than Bush, but that isn’t saying much.

But I’m convinced now that we will see some actual change in the weather. First, take a look at the 500mb thickness and vorticity charts from the UW WRF-GFS model run this morning.

Valid 04:00 am PST Tue, 20 Dec 2011 – UW WRF-GFS 12z 36km 1000-500mb thickness, SLP
Valid 04:00 am PST Tue, 20 Dec 2011 – UW WRF-GFS 12z 36km 500mb vorticity, heights
When the chart was initialized, we were under a weak ridge of high pressure. Initially, we won’t see much change. In fact, the high may grow stronger tomorrow. A weak system will come through on Thursday, but it won’t do much other than bring some clouds to the region, and Seattle will probably remain dry. On the chart, you can see some lower thicknesses over the Pacific Northwest though, signaling that lower pressure is in fact upon us.
Valid 01:00 am PST Fri, 23 Dec 2011 – 69hr Fcst – UW WRF-GFS 12z 36km 1000-500mb thickness, SLP

After this, that pesky little ridge builds again through Saturday. But on Saturday, everything is going to change. A relatively strong low pressure system will head up around Vancouver Island, giving us breezy conditions and a shot of rain.

    Valid 01:00 am PST Sun, 25 Dec 2011 – 117hr Fcst – UW WRF-GFS 12z 36km 3-hour precip, SLP

The significant thing about this storm is that it will finally break down the ridge, opening up the door for Pacific storms to roll into our region. One last picture… take a look at another 500mb chart that shows height lines and overall vorticity in the atmosphere. Don’t worry about the vorticity part… but take a look at how close together the height lines are over our region, and compare this to the picture I showed earlier. The flow is much more zonal over our region, meaning that the upper-level winds are flowing directly from east to west instead of having wave-like undulations in them caused by ridges of high pressure. 
Valid 10:00 am PST Sun, 25 Dec 2011 – 126hr Fcst – UW 12z 36km 500mb vorticity, heights

That is a very encouraging sign to see! We will finally get some weather that will be more active. The 18z GFS model actually showed some pretty heavy rain over our area on Christmas Day, but I’m not going to show it because it is a global model and offers very little resolution for our specific area. That’s why I love the UW models; they take the big GFS model and give it a lot more detail for our specific area.

Let’s make Barack Obama proud!
Charlie Phillips
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2 thoughts on “Actual Pattern Change!

  1. I have looked at the Euro, the models are in pretty good agreement. I just love the UW GFS… even if the GFS is a worse overall model, it seems to have a good handle on this pattern, and I love the detail the WRF gives

    Like

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