Wednesday, February 23, 2011

Snow Still Be Comin'

Wednesday February 23, 2011
11:15 A.M.

Hey everybody! Just a quick morning update. It still looks like some places are gonna see six inches of snow, except the band has shifted a little northward into Snohomish county. Seattle still looks to receive at least three inches or so. We won't really know until later this afternoon. I am still going higher than the NWS forecasts, so I'm leaning towards 4-5 inches or so, but I'm a little tentative to put 6 after these latest models came out. As always, convergence zones are notoriously hard to predict. The forecast will change, I can guarantee you that. And I will keep you updated when it does!


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. :)

Wednesday, February 2, 2011

Tranquil Weather

Wednesday, February 2, 2011
6:24 P.M.

While the eastern half of the country is getting clobbered this winter, we have actually had a pretty tranquil and quiet winter, especially for a La Nina year. Sure, we've had some close calls (models were calling for 3 feet of snow in Seattle a couple weeks ago) but this winter has certainly not lived up to even my expectations, which (no offense) are based on tons of research as opposed to those of the general public who simply believe it because the tv stations hype it up. But this has taught me an important lesson. La Nina and El Nino increase the probability of certain weather patterns occurring, but they don't set anything in stone. The most startling thing, for me, is the amount of snow in the Cascades. The last time we saw a La Nina this strong, Snoqualmie Pass set an all-time record for snowfall, with 821 inches falling in one season, 150 more inches in a season than has ever fallen. This year, we are below average. It's a bummer for ski enthusiasts like me, but it is also an indicator of the nature of climate forecasting. Climate forecasts are forecasts that highlight the chances of something occurring in the long range, like above average snowfall, or a greater frequency of storms. But just like weather forecasts, they are not always right.

Meanwhile, the eastern half of the nation has had a classic La Nina winter. They are just recovering from a massive snowstorm, and they have seen several more already this past winter. I think New York has already received about 5 times the amount of snow this winter compared to last winter. As you can see, climate forecasting is often a crapshoot, as is weather forecasting. Sometimes things pan out the way we expect, and sometimes they don't, and we don't know why. As research continues, hopefully we can find reasons why certain things occur the way they do, giving us better seasonal forecasts and a greater understanding of the weather.

Now, let's talk weather. Frankly, there isn't much to talk about. If you looked at the satellite pictures yesterday of the nation's developing storm, you could see that there is a large ridge of high pressure over the Pacific Northwest. And it looks like that ridge will hang around for some time. Long range models are hinting at breaking it down in about 10 days, but that is super far away, and it should go without saying that if forecast models often have trouble 4 days in advance, 10 days is a whole different world entirely. Meanwhile, arctic highs will drop down from Canada to our east, pushing cold air through the rest of the country and offering to respite from the snow they have seen as of late.

Thanks for reading,


Tuesday, February 1, 2011

Huge Midwest Storm!!!

Tuesday, February 1, 2011
11:05 P.M.

Hey everybody! I am now a second semester senior, so I'm sure you know what that means. It means, of course, that I will be writing a lot more weather forecasts because I now have some additional time to do so! I want to thank everybody who has been reading this blog even though I haven't been updating it lately, it really means a lot to me. You guys inspire me and let me know that people truly appreciate this blog, and you encourage me to share my knowledge with the rest of the world. I commend you for that.

For those who haven't been reading this blog, that's ok too! Now that I am updating it more, you can check back and be assured that there will be a new post. Perhaps I can even revitalize your interest in weather if reading my blog helped you develop one but it faded away as my blog posts started becoming less and less frequent.

Anyways, the focus of this blog post is to focus on the gigantic storm that is effecting the nation's heartland. Our weather is currently pretty boring right now (unless you are fascinated by fog and partly cloudy skies) and I expect it to remain fairly mundane for some time, although I'll keep you updated if things change. This storm in the Midwest, however, is shattering records left and right. My aunt lives in Kansas City, and she said she had already gotten 16 inches of snow, with 6 to 8 more hours of snow expected. 

Let's look at some satellite imagery. The most amazing thing about this storm is how much it has developed in such a short time. This intense storm development is called "explosive cyclogenesis," or, as many scientists around here call it, "bombing." At Tuesday 12 A.M. PST, the storm was just some moisture down south being fed by a strong jet stream. It is the swath over Oklahoma, northern Texas, Kansas, Missouri, and parts of the adjacent states to them.

Six hours later at 6 A.M. PST, you can see a swirl developing as well as an intense squall line marking the storm's cold front.

At 12 P.M., the storm has gotten even bigger and shifted eastward. A bent-back occlusion is now very apparent, the trademark characteristic of a rapidly-developing cyclone. Although it is more complex in reality, the northeast parts of the storm are generally seeing snow and the southwest parts are seeing rain. In other places, it could go either way depending on the situation.

At 6 P.M., the storm has gotten even larger. Explosive cyclogenesis is no longer occurring, but the storm is still very strong and is dropping very heavy precipitation, particularly further east.

By the time I am writing this, at 11:46, the event is mostly confined to the Eastern Seaboard, although it is still snowing in the bent-back occlusion of the storm, which stretches over the upper Midwest.

Wow! Pretty intense huh? Aside from being huge amounts of snow where it is cold enough, extremely cold air has started to filter in behind the front and the low pressure center is bringing windy conditions to many areas. This storm even brought thundersnow (a thunderstorm with snow) to some places. I have heard of at least one report of it from Chicago. Thundersnow is a rare phenomenon as thunderstorms are most common when there is a lot of heat energy in the atmosphere.

It is amazing how much this storm has progressed and how much it has moved in the past 24 hours. It started out with some sections in New Mexico and now some parts of it are way out over the Atlantic! Truly phenomenal.

I'll discuss the local weather later, there really isn't that much going on right now. The rest of the country, as you can see, is a different story.

Have a good one,