Thursday, October 11, 2012

I Am Actually Looking At Weather Models

Thursday, October 11, 2012
2:52 P.M.

I'm a weather fanatic, and most of you know that. But during the last 80 days, I've been out of touch with my meteorological side. Back in September, if you asked me what the weather was going to be a week from now, I would have no clue. All I knew is that it would probably be boring. I honestly didn't care about the weather, and I did not look at the weather models, because it would be depressing and pointless. Looking at the weather models this past summer would be like watching the UW - LSU football game this past season in the 4th quarter. There's nothing to see. You could be doing so many other productive things with your time, like calling a friend, taking a nap, or watching funny Youtube videos. Summer is great, but let me tell you, this past summer's weather is more boring than watching my roommate play ten hours of League of Legends each day (ok, I admit, it's actually pretty entertaining).

So, I heard through the grapevine that we could see some rain in the coming days, and I looked at the weather models. Since then, I've been looking at them constantly. I've also been reading the forecast discussions put out by the National Weather Service, the hydrology forecasts, and the direct model output for certain places using a program made by a weather/computer genius out of Portland named Brian Schmit that extracts the model output and gives various quantifiable information for certain locations about the forecast. Go to and click on "downloads" on the lower left hand corner, and then click the first download, which is the "16-Day GFS Extraction." He also has a bunch of other free downloads that are very cool and useful.

After a couple days of getting re-involved with the weather scene, I had a revelation; I was actually looking at weather models. Of course, this sounds obvious, but it really hit me to my core. I, Charlie Phillips, was, for the first time in months, actually looking at weather models. I dunno... it's kind of stupid... it kind of sounds like something a person would say while smoking weed. No weed here though... it was really that fascinating for me.

ANYWAY, let's get down to business. The weather models have been consistent in their main idea, but inconsistent in the details. The main idea is that we will end our incredibly long dry spell (0.03 inches of rain at SeaTac since July 23) on Friday, as a moderate front swings through our area. It won't be very strong... Seattle will probably not get more than 0.30 inches of rain from this storm, but seeing as 0.30 inches of rain is ten times the amount of rain we have seen in the last 80 days, it will probably feel like a Biblical flood.

Valid 05:00 am PDT Sat, 13 Oct 2012 - 48hr Fcst - UW 4km 12z WRF-GFS 24-hour precip ending 05:00 am PDT Saturday

This rain will make the roads quite slippery, because there is a lot of oil and dust on them that has accumulated and not been washed away for a very long time. The rain mixes with the oil and dust to create a very slippery lubricant. Also, there are likely people who have forgotten how to drive in even the slightest amount of rain. I remember when I was taking a calculus class last year that I had placed into because of AP testing at Garfield, but I couldn't even remember what the chain rule was, so I had to do a bit of catching up. That was a pretty long quarter for me.

But the great thing about this front is that it will open the door to a much stronger and wetter series of storms that will reach our area Saturday night and persist until Monday morning. These storms have tapped into some tropical moisture, and they will be centered right over our area in an "atmospheric river" type pattern, where the atmosphere flows in such a way that a moist air mass from the subtropics makes its way into the mid-latitudes in a "river-like" fashion and tends to flow over an area without moving too far away from it. Take a look at the picture below, which shows the "river" of moisture over our area.

Valid 11:00 pm PDT Sun, 14 Oct 2012 - 90hr Fcst - UW 36km 12z WRF-GFS Column Integrated Water Vapor

Most of our big flooding events come from atmospheric river events. Since the air has subtropical origins, snow levels are high, so the precipitation that does fall falls as rain. As I stated previously, they tend to stall over a region, leading to prolonged periods of heavy precipitation. And since the air is very moist, there are high rainfall rates associated with them. The good thing is that we will not see flooding from this atmospheric river event. The river levels are pretty darn low because of the lack of rain, so the rivers will have plenty of space to rise without reaching bankfull. The only exception is the Skokomish, which floods very easily, but even if it does flood, the flooding will be minor. 

So how much rain are we talking here? Take a look at the picture below.

Valid 05:00 am PDT Mon, 15 Oct 2012 - 96hr Fcst - UW 12km 12z WRF-GFS 24-hour precip ending 05:00 am PDT Monday

We are generally looking at 0.5-2.5 inches in the lowlands, 2-6 inches in the Cascades, and 4-8 inches in the Olympics, with the differences being due to different amounts of adiabatic forcing. Areas north of Seattle, particularly around Sequim, will see 0.1 to 0.5 inches of rain, and the areas marked in red on the Olympics and parts of the Cascades could see 8 inches of rain from this single storm. Folks, that's a lot of rain.

But it's not just rain that we will have to contend with. Some models, most notably the GFS (which is one of the ones the UW uses for their high-resolution forecasts), bring a strong low pressure center into Vancouver Island Monday morning. With lower pressure to our north and higher pressure to our south, we can expect some pretty breezy conditions in our area. As is usual, the highest winds will be over the coast and north interior.

Valid 05:00 am PDT Mon, 15 Oct 2012 - 96hr Fcst - UW 12km 12z WRF-GFS 10m Wind Speed

The model above shows a 977 mb low pressure center headed towards North Vancouver Island. The models differ on the timing and track of this storm, but a storm like this could give Seattle gusts of 40 miles per hour. Yeehaw!!! 

Tomorrow is the 50th anniversary of the famous (or infamous) Columbus Day Storm of October 12, 1962. I'm going to a presentation Cliff Mass is giving for free at 7:30 tonight at the UW's Kane Hall, so I'll have plenty of fresh information to relay back to you guys tomorrow. If you read this blog in time, you should try to make it, it should be an interesting lecture.



  1. Hey Charlie,
    Thanks for the link to Brian Schmits page and GFS extraction. Have you had a chance to validate how well the predicted precip totals track with actual rainfall? This tool seems like a great way to get a quick look at the models without clicking through individual outputs and adding the ranges, although I still like to do that.

  2. Hi Murdoch, the predicted precip totals are usually a bit high because the GFS has trouble picking up shadowing from the Olympics. It is also generally colder than normal because it filters in too much arctic air (when we do get arctic outbreaks) because it puts more air through the Fraser River gap than generally occurs.