Wednesday, February 23, 2011

Snow is coming!!!

Tuesday February 22, 2011
11:46 P.M.

Yay! I'm back on this blog. In retrospect I should have put an update that I just needed to take a break from it to work on some academic and college stuff and get all that stuff up and running, but now I am on mid-winter break. And of course, there is some exciting news on the way too. :)

We saw some pretty interesting weather today. We saw heavy showers with sun in between. But these weren't snow showers. They weren't rain showers. They weren't even hail showers. Or sleet.

Look familiar?

They were graupel showers! Graupel is not a term many people are familiar with, but ya'll in the Puget Sound region should be familiar with it because we get it fairly frequently, perhaps even more frequently than snow. It is kind of halfway between snow and hail. Snow forms when supercooled water droplets find a particle to condense on and then freeze, creating a hexagonal crystal lattice structure. Hail occurs when supercooled water droplets freeze but don't form that same structure for reasons I will not explain quite yet because frankly I don't know. Graupel is a combination of the two. First, there is a snowflake, and then supercooled water droplets condense on the outside of it, giving it the appearance of a "snow pellet." Hail and graupel are often associated with areas of convergence and instability in the atmosphere, which is exactly what happens with convergence zones here. The huge thunderstorms that the plains will see in the upcoming months can produce some spectacular (and destructive) hail that can reach the size of baseballs, grapefruits, or even softballs. Although I'd love to witness some, I'm kind of glad we don't have any here. Besides, I'm not a huge fan of putting shingles on roofs.

Over the past week or so, models have hinted at snow, but have been pretty inconsistent. That is why the tv stations have not hyped up the snow chances much. And obviously you can reason why. Snow forecasts this year have been particularly inaccurate (and that is saying something!). However, I can say with near 100 percent certainty that Seattle may see up to 6 (that's right, half a foot) of snow, with some places having higher amounts. In fact, if things plan out in a certain way, Seattle could see a FOOT of snow before it is all said and done. It is unlikely, but it could happen. Of course, on the flipside, we could only see a inch or two. But at this point, I think we will see around 6.

Who is responsible? Can you take a guess? I'll give you a hint... it kind of sounds like a band name...

 Convergence Zone earlier today (taken from Cliff Mass' blog, thanks Professor Mass)

That's right folks! It is our trusty ole Puget Sound Covergence Zone! Most convergence zones usually form a little bit north of us in southern Everett. However, this one is forecast to be right on top of us, leaving Everett with a relatively paltry 3 inches as opposed to our 6. Why is it further south, you say?

When we get a convergence zone, it is because air comes from the northwest, splits around the Olympics through the Chehalis Gap and the Strait of Juan de Fuca., and meets up again over Puget Sound, causing convergence and precipitation. The wind orientation is typically so that the convergence zone occurs somewhere between Edmonds and Mukilteo. However, if it is further west, it can meet all the way up near Mt. Vernon, and if it is mostly north, it can meet all the way in Kent, though the latter is particularly rare. However, when we get cold, our wind coming off the Pacific has a more northerly component than usual. Hopefully I don't have to go into detail why our ocean is warmer than Canada in the winter. But you get the idea. When there is more of a northerly component, the northern branch of the converging wind has farther to travel and the southern branch has to travel less, and they meet at a certain spot. In fact, downtown Seattle seems to be a local hot spot for this. A similar setup once brought a foot of snow to Seattle in 1990 while leaving Sea-Tac with 3 inches.

This convergence zone may produce some areas of graupel, but once it really starts to get going, it will be a mainly snow event. Here are the predicted snow totals in Seattle for 4 A.M. Wednesday to 4 A.M. Thursday. Generally six inches of snow, with an 8 inch bullseye over downtown.

So in retrospect, I think Seattle will see approximately 6 inches of snow with locally higher amounts, because that is where I think the convergence zone will form. However, other forecasts  had the convergence zone further north, with Seattle only getting an inch or two, and consequently, other forecasters are forecasting less for the Seattle area.. We won't really know how things will plan out until the convergence zone actually forms. The snow will start to fall in Wednesday afternoon as the convergence zone ramps up, and as the low pressure center slides south along the coast and draws in northerly winds, it will shift down to Seattle and has the potential to drop quite a bit of snow. Eventually, it will taper off to the south. All the while, the winds will be blowing like crazy up near Bellingham in the Fraser River Valley. Wind chills will reach dangerous lows, and freezing spray will be an additional concern for seagoing vessels up there. It could even get a little breezy down here too after the convergence zone passes.

Where do we go from here?
We get COLD. But not super cold. Our highs will be above freezing, but only barely so. However, we will have problems with snow really freezing on the roads like it did back in November. The temperatures will be higher, but they will still likely be below freezing when the snow is falling. Be prepared. And please, if you are a bus, don't try to go up a hill.

This storm could bring Seattle its greatest snowfall since December 2008, and it will certainly be the largest regionwide snowstorm since then. Winter storm warnings are up for nearly all of Washington from 4 A.M. to 10 P.M. for 2-6 inches of snow in Seattle, with me leaning towards the higher amounts.

We could see some additional snow Sunday as a moist Pacific storm overruns our cold air, but at this point it doesn't look to be too serious.

Thanks for reading, and I'm sorry I haven't posted in so long!

1 hour and 7 minutes. Phew. :)

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