Multiple Storms Will Bring Significant Snow To Western Washington

Update 8:20 PM: Winter Storm Warning issued for King/Pierce County line southward. Alert below. This is for 1-3 inches of snow from 6 AM Thursday to 6 AM Friday.

Additionally, a Winter Storm Watch is in effect area-wide for the Friday/Saturday storm. Totals 6-13 inches possible. Stay tuned!

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Over the next few days, multiple weather systems will bring snow to Western Washington. There are currently 3 times to watch.

1. Thursday morning to Friday morning (weak system, not widespread)

2. Friday night to Saturday (widespread snowstorm possible)

3. Sunday and Monday (precipitation type and amount uncertain)

This blog post will examine the first two events and briefly preview the uncertain third event.

Snow will begin in the South Sound between 4 AM and noon Thursday. Below is the predicted snow forecast from NWS (National Weather Service) Seattle for Thursday morning to Friday morning. (Click to enlarge)

Expect 1-4 inches of snow with this system, ending by Friday morning. Isolated areas of more than 4 inches of snow are possible, but not likely, with this first system.

An important aspect of this first storm will be its weakness. This first storm is a cutoff low, which basically means it's a weak storm that's meandering its way onshore. Additionally, this storm will be battling dry air as snow moves north. The dry air won't entirely win the battle south of Seattle, but once you get into northern King County, snow totals dip under an inch to near nothing.

However, this first storm could be considered an "appetizer" to the second, more widespread snow event arriving Friday afternoon/evening.

A low pressure center will move onshore around the mouth of the Columbia River on Friday evening. With cold air in place, this storm will likely be near the "sweet spot" for a snowstorm in the Puget Sound area.

We'll look at multiple forecasts for this storm so that we can get the best idea of what to expect.

NWS Seattle predicts that areas south of Seattle will get 6-8 inches of snow. That's impactful snow, especially for our area. The heaviest snow is currently expected Friday night into Saturday morning. 

Below is the European forecast model, which has been consistently showing 8+ inches of snow in the Friday-Saturday system. The forecast below is valid through 4 PM Saturday, showing total snowFALL (what hits the ground), not snowDEPTH (what's left after settling, etc.)

Image from Cliff Mass Weather Blog and WeatherBell.

This forecast shows a total of 12-18 inches in the South/Central Sound! That will be enough to cause major impacts in the Puget Sound area! 

Before we pass this off as "certain" (which it isn't), we need to see the real probability of this happening. We can do that by examining the ensemble predictions. The ensemble predictions are many "members" of a forecast model coming together to make a prediction.

Below is the European Model's ensemble for SeaTac airport. Add a couple inches to these predictions if you live south of there.

Image from Cliff Mass Weather Blog and WeatherBell.

Nearly every member of the ensemble predicts a major snow event. The bottom half of the graphic shows the averages. Bottom line: the skillful Euro model is confident in at least 10 inches of snow at SeaTac (11-12 inches south of the airport).

Now, the slightly less skillful GFS (American) forecast model (also for SeaTac airport).

Image from Cliff Mass Weather Blog and WeatherBell.

The GFS model is also pretty confident in a major snowstorm, with at least 8 inches likely among the ensembles.

What does this mean?

Well...nothing is absolutely certain yet, but be prepared for a major snow event, with totals of 6-15 inches, starting Friday afternoon and ending on Saturday.

What happens after midday Saturday is still uncertain. A changeover to rain or rain/snow mix by Saturday afternoon is possible, but confidence isn't high enough to determine that yet.

The next system, slated for Sunday/Monday, is too far out for us to accurately know what will happen.

As far as impacts to roads go...the temperature will play a big part. In the forecast for Puyallup (below...from weather.com), we see that temperatures on Friday will stay near/below freezing, keeping the ground cold. That means that snow is more likely to accumulate on roads.

Similar, or colder, temperatures are likely around the area. Don't be surprised if either one of our 2 storms brings snow accumulating at least on side streets.

Please stay tuned for updates! I will have nightly updates until this event is over.

Significant Snow Event Possible Starting Thursday

It now appears increasingly likely that a significant snow event will occur starting Thursday morning. 

This event will likely bring 2-6 inches of snow from Seattle southward, with the most snow from South Seattle to Centralia.

A Winter Storm Watch (text below) has been issued for the blue shaded areas. 

Let's dive in to the data.

I want to stress that since last night, the GFS model has come into agreement with the Euro model on a snowstorm. This is a change from last night when the GFS wasn't forecasting much snow. Agreement among forecast models = better likelihood of event happening.

Below is the Euro model showing snow through 10 PM Thursday.

Image from Cliff Mass Weather Blog and WeatherBell.

This prediction gives approximately 4 inches of snow from SeaTac southward.

Keeping with the Euro model, here is its total snow by 10 PM Friday.

Image from Cliff Mass Weather Blog and WeatherBell.

Wow! If this prediction verifies, 8-14 inches of snow will have fallen. Remember that while 8-14 inches of snow will fall, less of that will accumulate (due to settling, melting, etc.).

Remember that this is just one forecast. A forecast isn't complete until we see multiple solutions.

To show a different forecast, below is a graphic from NWS Seattle, showing expected snow through 10 AM Friday.

The NWS forecast shows 2-6 inches of snow in the South Sound, including Puyallup.

Bottom Line: I would expect anywhere from 4-14 inches of snow in the South/Central Sound by Friday night. 

The question now is not if or when it will snow, but instead how much will it snow.

Here's a good way to visualize the Puyallup/Tacoma area snowfall:

Least Possible: 1-2 inches

Most Likely: 2-6 inches

Highest Possible: 10-14 inches

As if this isn't enough, another potentially larger and more widespread snow event is possible on Saturday.

Some forecasts have indicated Saturday being a major event, with large totals and big impacts. However, it is simply too early to tell what will happen on Saturday and beyond (so stay tuned).

Below is a great graphic from NWS Seattle showing what to expect for this upcoming winter weather event.

Wednesday morning temperatures will be 26-32 degrees. Just a preview of the potential 17-25 degree lows for Thursday-Saturday.

Additionally, cold wind chills, winds out of the Cascade gaps, and very cold temperatures Thursday-Sunday are all in the cards. Snow is NOT our only talking point in this event.

It is best to stay tuned as details will likely fluctuate. As a reminder, I will have daily updates as long as this event continues.

Monday Night Update: Certain Cold, Uncertain Snow

We are certain that Western Washington will be plunged into the freezer this week. However, with that cold comes the potential for lowland snow. The snow potential is uncertain right now. 

This graphic from NWS Seattle illustrates what we know, don't know, and what you should do.

Let's take a look at the temperature forecast. Below is the forecast for Puyallup from The Weather Channel.

Temperatures get progressively colder all week, bottoming out on Friday. It is important to note that temperatures can, and possibly will, get colder than this forecast indicates.

Do not rule out low temperatures of 17-23 degrees from Thursday to Saturday.

Additionally, brisk N-NE winds will bring very cold wind chills of 10-20 degrees from Thursday through Saturday. Even colder wind chills, down to the single digits, are possible in wind gusts. 

Expect N-NE winds of 10-15 mph, with gusts of 15-30 mph. The 20+ mph gusts combined with temperatures not exceeding freezing are what form these dangerous wind chills. Below is an informative graphic from the NWS about the science of wind chill.

Now for what you really want to know about...the potential of lowland snow later this week. The bottom line for current snow potential is that snow chances are uncertain. 

As of Monday night, there are 2 possible times for snow events.

Chance #1: Wednesday night/Thursday morning (smaller-impact event)

On Wednesday night, a modified arctic front will move through the Puget Sound area, bringing colder temperatures and a chance of snow. This snow chance is not very likely, but should it occur, expect an area of heavier snow (2-5") between SeaTac and Seattle (and eastward), with lesser amounts (0.5-1.5 inches) in the South Sound.

Chance #2: Thursday into Saturday (potentially larger-impact event)

In weather forecasting, forecasts are generally determined by forecast models, which are systems that predict upcoming weather. 2 major forecast models are the European Model (aka “Euro” or ECMWF) and the American Model (GFS).

Below is the Euro model ensemble forecast (many forecasts put together) for SeaTac airport. Most of the ensemble members show significant snow (5-18 inches) at SeaTac airport.

Image courtesy Cliff Mass Weather Blog and WeatherBell.

The Euro model gives an average of 10-14 inches of snow through Monday at SeaTac Airport. I’d add a couple inches to that prediction for the South Sound.

However, a forecast isn’t good unless you compare multiple predictions.

Below is another forecast ensemble, but instead from the GFS (American) Model.

Image courtesy Cliff Mass Weather Blog and WeatherBell.

Far less ensemble members show heavy snow, with an average at SeaTac airport of 5-7 inches. I’d expect about the same for the South Sound in this scenario.

Bottom line: The Euro says 10-14 inches, the GFS says 5-7 inches, and the GFS has been trending lesser on snow amounts across the Puget Sound area.

This all means that there’s A LOT of uncertainty. (Would it be a Seattle snowstorm without uncertainty??) 

Expect that through the next couple days we will see forecasts start to align a bit more on a solution...but until then, stay tuned. Lots will change.

I will be posting nightly updates on the blog as this winter weather situation continues. Be sure to check back each night!