The Truth About Snow

November 16, 2010
8:53 P.M.

Alright ladies and gents, it’s time to tell you the TRUTH about snow in the upcoming days. There have been a lot of rumors flying around. I don’t know if I’ve ever told you, but I hate rumors. But not weather rumors! Weather rumors create an exciting atmosphere (there’s a knee-slapper right there). However, I don’t want you guys to get your hopes up and then have a massive let down, because snow is a chance at best. However, I am becoming more optimistic about it after seeing the latest model runs.

Before, models were showing most of the cold air being shunted to our east, which is what usually happens. The location of the arctic high has to be just perfect to direct significant arctic outflow into our area. Why? Because we have not one, but two major mountain ranges ready to funnel air to our east. The air has to be just far west enough to avoid these mountain ranges, but if it is too far to the west, it will moderate over the ocean. It’s one of those classic situations in which even small changes in the models could have huge changes in the forecasts.

Let’s first discuss the most likely scenario, which, at this point, is a blend between the European (ECMWF – European Centre for Medium-Range Weather Forecasts, if you wanna impress your friends) and American models (mainly the GFS – Global Forcast System) as well as just common sense with what usually happens with predicted snow events (i.e. – one thing can completely screw it up). Most t.v. forecasting stations are predicting dry-ish conditions once the cold air sets in, which is correct, and they aren’t going all-out on the intensity of the cold air, which is what I am also forecasting.

Let’s break it down. Tomorrow, we will be wet and rainy. The mountains, however, will be very snowy. I have a feeling that the models are underdoing the precipitation for Snoqualmie Pass. They are calling for around 8 inches of snow there, but I’m expecting a foot. The orographics are very favorable for snow in the passes from the looks of it. The volcanoes will get pounded. Don’t be surprised if Paradise and Mt. Baker pick up 2-3 feet of snow from this storm. The below model shows the thickness of the atmosphere near the surface to the 500 millibar level (level in the atmosphere where the air pressure is 500 mb) and is measured in decameters. Don’t ask me why it is measured in decameters, it just is. But anyways, the brighter reds and yellows mean that the temperature in the atmosphere is higher because the number of decameters it takes to cross 500 mb in the atmosphere is greater, meaning the air is less dense (warm air is less dense than cold air). The blues, purple, and whites mean colder air. Once you get to around the 522 decameter level in our area, it’s time to start thinking about snow.

This image shows the low off Vancouver Island, and you can tell there is a front over us because of the large change in thickness (a front divides different air masses). This forecast is for tomorrow Wednesday at 1 P.M. PST. Now, watch what happens.

The low has weakened and moved to the southeast, right off of our coast. This is a crucial detail in the forecast. Dropping this low southward now gives us winds from the northeast. And there is a lot of purple to our northeast.

I don’t think that that low is going to be strong enough to pull in a whole bunch of arctic air. However, a reinforcing shot of arctic air might hit us early next week. The models are showing different things, but the GFS model (shown) has been consistent in showing this solution. Unfortunately, we also run out of moisture.

So the question remains: will we get snow?

There is a chance we might get a few isolated snow showers over the weekend, but I don’t think they will be heavy and widespread enough to close school. However, if a convergence zone forms over Seattle at night and dumps a whole bunch of snow, we may have a shot at a day off. One of the models was showing highs in the low 20s for Seattle and snow totals of 8-18 inches for us. I doubt that is going to happen, I’m just using it to illustrate how tough of a forecast this is. I think our best shot at snow is either with an arctic front with the reinforcing shot of cold air (and then it would freeze on the roads as the arctic air sets in) or an overunning event with a system off the Pacific “overunning” the cold air, producing snow. That is a very real possibility. But so many things could change. A couple things are for certain – it will get colder – the mountains will see snow – and the days will keep getting shorter until the winter solstice.

I HIGHLY recommend friending Scott Sistek and Steve Pool on facebook. Type in “Scott Sistek weather” and “Steve Pool komotv” and they will come up. They provide discussions, but their walls are also discussion places for me and other weather nuts to discuss what we see in the models. It’s a very fun place!

On the windstorm last night – it was very unique, I’ll talk about it some other time.
Pray for snow please. 🙂
Charlie