Wednesday, January 11, 2012


Wednesday, January 11, 2012
11:14 A.M.

I don't have too much time here, but I thought I'd give you an update on the forecast for this weekend and beyond. It seems as though most forecasters are much more conservative as far as snow goes.

In fact, here's what the KOMO forecast had to say this morning.

A few thoughts about this snow chance:  It is marginal at best.  It won't be that cold and it isn't forecast to be that wet.  Any trend drier or milder will eliminate this snow chance entirely.  That said, if we get just a little more moisture, snow may in fact accumulate (I consider an 'accumulation' more than 1" on the ground) in the lowlands.

I disagree with this statement. I think we have more than a marginal chance of snow. Which leads me to my own snow scale rating!

For a refresher, it is printed below.

So, lets go through this scale.
LAWES level 0: You are on a planet that has the ingredients necessary for snow
LAWES level 1: Models are showing a chance of snow beyond a week out, 0-20% chance of snow
LAWES level 2: Models are showing a chance of snow within a week, 20-40% chance of snow
LAWES level 3: Models are all showing a scenario that would easily produce snow within a couple days, 40-60% chance of snow
LAWES level 4: Places around the area are already getting snow AND snow is forecasted for Seattle, 60-99 % chance of snow
LAWES level 5: Snow is occurring, 100% chance of snow (derp)

Now, notice how there are no measurements for how strong a Seattle snowstorm could be. But have no fear! That's what suffixes are for. 
Ending in:
.1 - 0-2 inches of snow
.2 - 2-4 inches of snow
.3 - 4-6 inches of snow
.4 - 6-8 inches of snow
.5 - over 8 inches of snow
.6 - board the next plane to Panama

I'm gonna go with a LAWES (Likelyhood of an Arctic Weather Event with Snow) 2.1 at this point. I'm pretty confident that some places in Western Washington will get snow, but I'm not quite sure that Seattle will get snow, so it would be around a 40% chance of snow in Seattle at this point. I'm not sure how much snow there will be yet (models are all over the place, so I'm going with a 0-2 inch estimate in Seattle for right now. Other places could get more. Still, I don't think we will be boarding the next plane to Panama anytime soon.

This probably won't be an event like 2008, but it has the potential to be major. It's really hard to tell this far out though. Heck, some forecasters around here can't predict snow 30 minutes in advance.

Valid 04:00 am PST Mon, 16 Jan 2012 - 120hr Fcst - UW 12z 12km WRF-GFS 24 hour snowfall

You can see some light accumulations in the Western Washington lowlands, with heavier amounts in the mountains. Remember, the GFS is showing the least snow of all the models, but it still gives Seattle a bit of snow. It's not much, but it's a good sign. 

The 180 hour frame is pretty exciting as well! Of course, you can't take this seriously, but it's fun to look at! Lots of snow to our south.

Valid 04:00 pm PST Wed, 18 Jan 2012 - 180hr Fcst - UW 12z 12km WRF-GFS 24 hour snowfall

Now, one more quick picture from the European model. 

Valid 04:00 am PST Sun, 15 Jan 2012 - 96hr Fcst - ECMWF 500bm thickness, SLP

You can see a big trough over the Pacific Northwest, giving us cold temperatures and some precipitation, especially in Oregon.

Gotta go! College calls.



  1. Hi Charlie! This is going to be fun to watch and hopefully it doesn't turn out to be a flop event! To get a good snowstorm around here you need a lot of frasher outflow to happen to get that real cold air in. Right now the GFS and other models are showing a trough bringing in some moderate cold air. If the trough of low pressure is situated just right - off the coast and to the south - it can start sucking in the cold air and also add some moisture to the mix creating some snow showers. This is what happen last year around thanksgiving. What will be interesting to watch as well is the jet stream to the south looks to be rather strong throughout the period as well. If any strong low pres forms and makes landfall to the south of the area, that would be the perfect recipe for a snowstorm. It’s perfectly plausible at this points too. There are so many details the models can’t pick up on yet…

    1. If high temperatures get down below freezing, there is usually a pretty good chance of snow in the area. Often, moisture is scarce during these times, but there are occasionally arctic fronts that form on the leading edge of these cold air masses which can be quite intense (like Novemer 2006). Also, if the air is below freezing, any precipitation falling will likely be snow (there is a slight chance it may be sleet or freezing rain) if a system comes into the area, even if it goes north. The difference is that a system going north of us will bring up southerly air, eventually turning the snow to rain. If a storm goes to our south, the precipitation stays as snow, and that's when we really get clobbered. :)

  2. hey charlie. big fan of your blog. I live in Bellingham and it looks like we may have a better shot than the metro area for significant snowfall! what do you think?