As you’ve probably seen over the last few days on TV and across social media, we do the dance with snowfall potential starting midday Superbowl Sunday, and it continues through midweek. The purpose of this blog is to break down the possibilities, and explain the how’s/why’s/what’s about the forecast. Let’s start by saying that this is one of the most difficult forecasts many of us have ever seen. There are so many factors that go into potential snow events like this, and many of them are right on the fringe for this particular event. As we get into this blog, we will talk about what those factors are and how they could affect the snow potential both positively and negatively. For now, disregard any model images you have seen floating around over the last few days with varied snow totals. At this point, this looks to be an event that we won’t be able to nail down until it’s practically already here.

Starting out at about midday tomorrow, we may some snow showers around the Sound, although the bulk of the moisture looks to stay toward the south end, Tacoma southward. Cold air will begin being pushed down from Canada through the Fraser River Valley (Fraser Outflow) and some gusty winds up north with push those winds southward into Washington. Temperatures will be marginally cold enough, so this means that those closer to sea level may see cold rain while a few hundred feet higher up might see some snow showers.  During the daytime hours, it looks as if the snow level will hang out around 1,000ft for most areas, except those in the south part of the state. Will these showers amount to much in terms of accumulation? Probably not too much, unless you are in the south sound where that more abundant moisture could be hanging out. However, this is important regardless because of the Superbowl and traffic before and after the game. A heavier shower could also drag the snow level down to sea level temporarily. That said, tomorrow’s dance with snow is going to depend a lot on where the moisture goes and if we are cold enough. Many of the models have pushed the moisture further south, sending the bulk of it more toward Portland versus southwest Washington, say Kelso through Olympia. As the cold front moves northeastward, there will be showers around and this where the forecast becomes difficult. Each of the models have painted different solutions as to where the front goes and who gets larger accumulation amounts.

The models however sometimes have a hard time with marginal temperatures like what we will likely see. Sometimes they overdo the cold, or overdo the warmth, and struggle with taking into account additional factors like elevation and how that relates to the temperatures. We also get what is called mountain bleed, where sometimes the models overdo snow accumulation totals because of how close the Puget Sound lowlands is to the mountains. Ultimately, the big thing to know is that if we don’t get the right combo of cold and moisture, that obviously means no snow, or very little snow.

Overnight Sunday into Monday, that Fraser River Outflow will continue to push colder air into the area. By Monday morning, we will most likely be cold enough to see all snow in most places. However, that’s when the moisture could become a problem. There may not be too much to work with, and that’s where the track of the cold front makes a huge difference. A hundred miles one direction, north or south, could have a huge impact on how much or how little snow we see here in the Seattle area. Many of the models have sent the front into Oregon, aiming the bullseye between Vancouver and Salem, nailing Portland, providing their temperatures support snow versus cold rain. This could mean areas over 1,000 feet in Portland see a foot plus of snow, while the valley floor sees none if the temperature hovers just above freezing. The same sort of concept could go for us if the front tracks more northward, with the bulk of the moisture falling between Olympia and Kelso. We would need our temperatures to be cold enough to support snow. That is why this is a very complicated forecast, since we are really sitting right on the fence, between cold enough and not cold enough.

Let’s take a look at a few of the model images. But before we start, take the accumulation amounts on these with a grain of salt. Why? Because it’s still a day out and there is plenty of model disagreement. That said, the reason I’m showing these models is purely to show the big differences in model runs and WHY there is so much uncertainty with this forecast.

This first model is the European Model, courtesy of WeatherBell. It shows the 24 hour snowfall totals through Monday. This model shows the bulk of the moisture heading right between Olympia and Kelso. As you can see, the heavier totals fall from about Renton southward, with the eastside getting a decent amount as well. The further north you go (save for the Cascades), the less snow we begin to see.

This second model is the University of Washington’s model, the WRF-GFS. This one shows the 72 hour snowfall totals through Tuesday evening, so a bit longer range. Looking at this model shows that again, the bulk of the moisture heads further southward, leaving the north end areas with little to no snow. Seattle metro still sees a decent amount over the course of the 3 days, as do some of the communities east of I-5 and west of Olympia.

This third model is the GFS, the Global Forecast, courtesy of Tropical Tidbits. This one shows the 24 hour snowfall totals through Monday evening. It’s a bit of a wider view, but if you can zoom in, you can see the bulk of the moisture is a little more north, painting a bit of a snowier picture for the Seattle area. This is also one of the first afternoon runs (the 18z, running on Universal Time), while the first two were this morning’s model runs, the 12z.

This last model is the NAM, the North American Model. This shows the 24 hour snowfall totals through Monday. With this model, you can see the bulk of the moisture stays in the Cascades and to the south. This particular model has painted an incredibly snowy scenario for the Southwestern Washington area and Portland, providing temperatures stay cold enough. On the other hand, it leaves Seattle with almost nothing.

So what’s the takeaway from all these crazy models? That there is currently a LOT of uncertainty on where exactly this front is going to go. And that one factor is HUGE when it comes to who gets the most snow, or the least snow, just as much as temperature is a huge factor as well. It’s hard to look at one particular model and say, “Oh look, we will get, say, 10 inches through Monday!” Unfortunately, it just doesn’t work that way. As a forecaster or meteorologist, this is where studying the models and a variety of other sources comes into play. Another key factor is knowing terrain influence, and other influences such as the Fraser Outflow, or the effects of a cold front versus a warm front. When temperatures are just marginally cold enough, it’s really hard to say for sure what will happen. A degree or two difference is all it takes to push it one way or the other, or a lack of moisture even if the temperatures support snow.

Another method forecasters use to look at potential scenarios is by looking at the model ensembles. The ensembles take many different models for a given time and put them all into a graph or chart, with an ensemble mean, which is the average of all the models. Here is an example:

This GEFS ensemble shows 19 out of 20 model members showing some amount of snow for KSEA, which is Seatac Airport’s code, so the Seattle area. Only 1 model member shows no snow at all. The ensemble mean shows anywhere between 3-4 as a best average. But again, we are looking at marginally cold temperatures and a huge variance in where the cold front brings the moisture. So ultimately, it’s still incredibly hard to say with any confidence exact totals for the area.

If I absolutely had to pick a ballpark range for Sunday into Monday’s event, as if my life was on the line if I didn’t, I would say we have a shot for 1-3 inches around most of the Seattle area. This is still up in the air, however. We very well could see nothing at all. Higher hills could likely see the higher amounts. The next model run is currently starting, so we will get to take a look at the trends and see what direction things are headed again. After that, the last model runs of the day begin later this evening. Ultimately, our best bet for knowing what will happen is to wait until the storm starts to arrive. This may be an inconvenience to some who need to know ahead of time, but it’s very difficult to say for sure and with any confidence what the potential snow totals look like at this time. It is possible that the National Weather Service in Seattle will issue a Special Weather Statement this afternoon regarding the event, or a Winter Weather Advisory after looking through this next model round. A few people have asked why there hasn’t been anything issued yet, and I suspect that the NWS is being cautious after numerous forecast busts this winter and past fall. That is also why I’m very hesitant to say anything with any certainty. It does look as if we will see some amount of winter weather tomorrow through Wednesday, but as of right now, the details are still up in the air.

Your take-away today as a weather information “consumer”?
As of this moment, the potential for winter weather conditions is there. It would be wise to prepare for a winter event just in case. Worst case scenario (or as I said on the facebook page, best case scenario for those who aren’t snow fans) is that we don’t see any major snow accumulations, and roads/commutes remain normal with only cold rain. Best case scenario (worst case for non-snow fans) is that we see a decent snow event for the Seattle metro area and commutes are affected come Monday morning. In my personal opinion, as someone who advocates for emergency preparedness, it is always best to be ready for the worst just in case. If nothing happens, you’re ready for the next potential event.