Pattern Change

7:05 P.M.

Hey everybody! I hope everybody had a nice Veteran’s Day weekend. I didn’t do much… besides sleeping of course. Funny story actually… I was going to bed last night (at my house) and our dog was already asleep on my bed. I tried to move him… but that guy is essentially a warm lump of organic matter when he is asleep. So I shoved him to the end of my bed and he tried to sleep there. Eventually he got off my bed… he was probably irked that I took his spot.

Anyway, I had two posts on WeatherOn today. One was a long range outlook, and you can find it here! The other was for the climate blog I run there, and it was just a copy of an old post I wrote on this blog. The title of the blog post is “A Response to the Deniers of Anthropogenic Global Warming.” I’m the long range and climate blogger over at WeatherOn. You can find that blog post here under “Recent Posts” on the right side of the blog, or you can check it out on WeatherOn here.

As I’ve stressed before, my blogging at WeatherOn does not mean I cease blogging here. I’ll post links to my WeatherOn posts though. The more blogging, the better, right?

Alrighty then, let’s take at what’s in store for us over the next several days.

The short answer is that the weather will be pretty mundane, particularly for mid-late November, which is, on average, our stormiest period of the year. Take a look at the current 500mb setup over us.

Valid 04:00 am PST Tue, 13 Nov 2012 – UW 36km 12z WRF-GFS 500mb absolute vorticity, heights

This chart shows the heights of the atmosphere at the 500mb level and the vorticity of the air parcels. The vorticity is defined as the tendency for an air parcel to spin and is generally low over areas of high pressure and higher over areas of low pressure (look at the storm in the Alaskan panhandle for an example), but don’t worry about that. 

The main thing we are looking for here is the gradient of the 500mb height lines. If the lines are close together, that means the upper level winds in that particular area are strong because there is a strong pressure gradient. It does not necessarily mean that the winds at the surface are strong (although the two are related). 

Over us, the lines are fairly far apart. This means that the 500mb winds are weak. Many of you have heard the colloquial term “jet stream” used before. You can trace the approximate location and strength of the jet stream from looking for the area with the steepest gradient lines. As you can see, the jet stream is extremely weak over the Pacific Northwest, as the lines are very far apart. 

Take a look at the 300mb isotach chart below. It shows the height lines at 300mb and the estimated wind speed, and is also useful for tracing the jet stream.

Valid 04:00 am PST Tue, 13 Nov 2012 – UW 36km 12z WRF-GFS 300mb isotachs, heights

You can never get exciting weather with this type of setup. Mid-latitude storms thrive off of horizontal temperature gradients in, well, the mid-latitudes. A strong jet stream implies strong temperature gradients, and areas of low pressure are formed by divergence aloft ahead of the direction the storm is travelling, and convergence behind the direction of the storm. The stronger the jet stream, the more air is brought up from the surface to the top, where it diverges, and the storm at the surface becomes lower in pressure and strengthens. Strong jet streams lead to strong storms. Our Hanukkah Eve Storm rode into our area on a 190 knot jet stream. The jet stream above our area in the above picture is a mind-boggling 60 knots. 

But, there is hope.

Over the next week, the jet stream pretty much departs from our area completely. But after 7 days, both the ECMWF and GFS place a fairly strong jet over our area. Here’s the 500 mb chart, and below that is the 300mb chart.

Valid 04:00 am PST Tue, 20 Nov 2012 – 168hr Fcst – UW 36km 12z WRF-GFS 500mb absolute vorticity, heights

Valid 04:00 am PST Tue, 20 Nov 2012 – 168hr Fcst – UW 36km 12z WRF-GFS 300mb isotachs, heights

By day seven, there is a 140 knot jet stream centered right over our area. It’s not historic by any means, and there aren’t any big storms coming over our area within the end of this run (hour 180). However, if this pattern continues, we could see some nice systems swinging over our area.

Until next time,

Charlie