Pineapple Express

Saturday, December 11, 2010
2:18 P.M.

Wait a minute...

There we go. :)

The word is out that we will likely see some of the biggest flooding since January 2009 on some rivers, and January 2009 was a record-breaking event for the Snoqualmie @ Carnation and saw major flooding on many other rivers. Some rivers are certain to flood, like the Skokomish, and others will probably flood also, like the Snoqualmie. Thankfully, the Green River doesn't look like it will quite reach flood stage, although with qpf (precipitation amount) forecasts going upwards over the last few model runs, we will have to keep a close eye on the situation there. 

We have a lot to talk about, and I'm sorry I couldn't get to it earlier. I was studying for the ACT, which I took this morning. Anyways, the leading edge of the warm front from this system is over us now and is bringing light to moderate rain to many areas, which will only increase in intensity as the weekend progresses. The radar below shows that a lot of rain has already spread over the area, and it will only get heavier as time goes on.

We also have some snow issues to deal with today. While this will mainly be a rain event, there is some cold air trapped in Eastern Washington and that cold air is causing snow from the passes eastward. Rocky Canyon, east of Cle Elum, is getting moderate snow right now.

Snoqualmie Pass is getting dumped on as well.

This cold air will work its way out as milder air from Hawaii starts to invade the area. Until then, expect heavy snows in and east of the Cascade passes. We could also encounter some sleet and freezing rain as well during the transition.

But the real story here will be the rain. Freezing levels will shoot up all the way to 8,000 feet with this storm, which means pretty much everything falling in the mountains will be rain, save the volcanoes and highest peaks. The new models showed generally 2-3 inches of rain in most parts of the lowlands in the 24 hour period between 4 P.M. tonight and 4 P.M. Sunday. You can see some areas of white in the graphic below, and those areas illustrate where there is the potential for over 10 inches of rain in 24 hours. 

This is a serious flooding event, but it isn't too out of the ordinary. We usually get a storm like this every year or so, and this one won't be as serious as the ones of November 2006 and December 2007, which caused catastrophic flooding on many rivers. However, I do expect major flooding on many rivers flowing off of the Cascades and Olympics for several reasons. The forecast models have been trending wetter and commonly underestimate precipitation amounts in Pineapple Express events, which is why I feel like we are going to get more serious flooding than the National Weather Service's hydrological center is predicting. 

Looking at the forecast model above, which is the 12z GFS, you can see an intense rain shadow northeast of the Olympics. While some areas of the Olympics will likely see a foot of rain in this period, some places 60 miles away might get only .01 inches. That is 1200 times less rain! Just goes to show how pronounced the Olympic rainshadow can be. So if you live north of Seattle, you'll start to feel the effects of the rainshadow, and if you live by Port Townsend, you'll probably be wondering what all this fuss about flooding is about. Because the winds in the middle atmosphere are traditionally very strong with Pineapple Expresses, they drop a ton of rain over the mountains via orographic enhancement, and then sink rapidly on the leeward sides, preventing much more precipitation from falling (at least until they hit the Cascades again).

We will have to be careful of urban flooding as well. While we won't have any convective downpours like we did that one morning last week, we will see a lot of rain in a fairly short period of time, and with all the leaves down, expect storm drains to get clogged up and large puddles to result.

Latest river forecasts can be found HERE: http://water.weather.gov/ahps2/forecasts.php?wfo=sew&view=1,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6

Stay dry, and stay safe :)
Charlie

Flooding?

Tuesday, December 7, 2010
5:44 P.M.

I know... I know... I haven't updated it in a while. Same story as always... I've been extremely busy. I thought senior year was supposed to be a breeze! Not with my class schedule... we will see if all my hard work pays off and I get into college. Hopefully I can at least get in somewhere.

Alas, this will be a short post, as there is more work to do in the homework department. However, I've been watching the models very intently for the past few days and they have been EXTREMELY consistent in showing a Pineapple Express event. The nature of the event, however, has been anything but consistent. Model runs have ranged from bringing all the rain to Oregon to a bulls-eye over Seattle to bringing the majority over Vancouver Island. They seem to be trending further northward. Things could change, and it will be wet around here, but I don't expect major river flooding issues in the Central and South Cascades. This means that the Green River will probably escape the flood threat, which is good news. The Olympics, North Cascades, and southern mountain ranges of British Columbia (Vancouver Island and the mainland) look to get a lot of rain, but we just aren't sure how much. The latest model runs don't stall the front as much either, which means more areas will get rain but less overall than if it stayed over one specific area.

In the meantime and in between time, it's raining heavily over the lowlands right now, and we could see an inch out of this storm system over the next couple days. The "Pineapple Express" over the weekend has the potential to give us even more significant rains, but the model runs as of now don't show a ton of rain for Seattle. It is a situation that bears watching.

And no snow in the foreseeable future.
Thanks for reading. :-)

Charlie

0:09 minutes

A Little Bit Of Light Snow This Morning, Then Changing To Rain

Thursday, November 25, 2010
8:59 A.M.

Hey ya'll, so we are seeing a little bit of light snow this morning. It's not that big of a deal because it is going to change to rain later in the afternoon and it will melt. I suspect some roads will still be slushy (especially sidestreets) but as time goes on we will warm up enough that that slush won't last too long either. I've gotten less than an inch so far at my house, and most other places will receive the same amount of snow before it changes to rain, save the hills and up north in Bellingham where you could see up to 2 and 3 inches respectively. A WINTER WEATHER ADVISORY is in place for all of Western Washington except the Cascades, where a WINTER STORM WARNING is in place for a foot of snow.

Other than that, there isn't too much to talk about. The DOT handled the roads nicely with salt, which of course, I didn't really like, but it was ok because I got school off anyways. Salt kills engines and the environment, but it works. Still, I like seeing the arterials white with snow. I went skiing down some back in 2008. THAT was fun.

We will be gradually warming up to "balmy" temperatures in the mid 40s with showers most of the time, except some drying during the weekend. No big storms look to be headed our way.

However, there could be another arctic outbreak on the horizon. It looks very unlikely at this point, but some models have been showing some arctic air spilling down. Right now, it is much too far to our east. We will see if we get some more Fraser River outflow. This would be in approximately one week. I'll keep you posted. LAWES level 1.

But it heads off much further east later. Still, an impressive arctic high!

Of course, the mountains are looking good for snow. Here's the Alpental base...

And here's Snoqualmie Pass...

So the lowlands are done with snow for a while, but the mountains will get some, and there is a possibility, albeit slim, that we could return to colder weather next week. Have a great day and give thanks for the snow we did have. :)

0:26 minutes

Visibility

Ok, visibility kinda sucks, at least right now. It may change. I'm not sure why. Maybe because the snow is giving off some moisture, maybe because there is more particulate matter. But it will get better throughout the day today. I might talk with Scott Sistek more about this. For those of you who don't know Scott, he's the man. Find him on "Scott Sistek Weather" on facebook. In addition to his insights, me and a bunch of weather nerds always post stuff on his wall. It's a really cool community, and those who are excited about weather should check it out.

Midnight Update

Monday, November 22, 2010
11:50 P.M.

So the snow has now largely come to an end. Don't be surprised if you see a flurry, but I doubt you will see any additional accumulation.

Generally, I've been hearing of about 5 inches of snow in the Seattle area. I have 5 inches at least. Very, VERY cool stuff. I'm pretty darn happy right now. And the mountains are getting tons too.

This has been pretty crazy. This much snow this early. Let's hope that it is a precursor of things to come. I think I already said this too, but Barrow, Alaska was warmer than Seattle today.

The big stories now are going to be cold and wind. First, let's look at some temperatures. This model below shows the 7:00 A.M. (generally coldest part of morning this time of year) temperatures for Tuesday morning. Seattle will likely get down to 20 degrees or so. Even areas near the water will still be below freezing.

By the way, tomorrow will feature SPECTACULAR visibility. The atmosphere is very dry, there is little air pollution, and it will be completely sunny. There will be a marked difference. When you don't have humidity or particulate matter clogging up the atmosphere, you can see a lot further. That is why deserts (except when they have dust storms) are often very good for viewing stars - very low humidities.

The day after tomorrow (haha) will be even colder. Here is the same chart 21 hours later (the morning low will occur earlier because the sun will be out).

Even colder for Seattle! You can already see warming off the coast - that is part of the high pressure that gave Barrow a high of 34 today coming in. Yeah, it's that big of a high pressure ridge. But in Seattle, lows will get into the mid teens. Outlying locations could get to 0 degrees.

This graphic shows how dry the air mass is by measuring the RELATIVE HUMIDITY of the atmosphere. It is for mid-morning tomorrow. See that orange around us? It means we have a relative humidity of 25 %. That is extraordinarily dry. And colder air masses hold less moisture (90 degrees 100% relative humidity is much more humid than 50 degrees 100% rh) so a subfreezing air mass with a relative humidity of 25 % is extremely dry.

Haven't shown the relative humidity graphic before. It's a cool one. :)

Now - winds! The saga never ends. The winds are blowing like crazy up north right now, as this graphic shows. This shows what was forecasted for 10 P.M., so it is actually an old graphic, but that is when the winds peaked and this is how fast they were. Note - these are SUSTAINED winds. Multiply by 1.5 to get gusts (approximation).

You can see a very localized, but intense, area of winds up north.

These winds will weaken, but winds will spread throughout Puget Sound Tuesday as this graphic indicates.

It will be cold and windy, especially in the sound. This graphic doesn't show Seattle getting real strong winds, but all you need to do is shift the gradient a little, so I would still be on the lookout for some gusts tomorrow. Places over water, however, will take the main beating. These winds, however, will be nowhere near as strong as the ones being witnessed right now over the San Juans. A high wind warning is in effect for those areas right now. Winds over most of the sound look to be below advisory level for most of the day (except in that dark band of blue and green).

One last graphic - the 1000-500mb level thickness model is regarded as "the" model to determine the true strength of an arctic outbreak. Simply put, it measures the temperature of the lower atmosphere. More complexly put, it measures the distance in decameters from the 1000mb air pressure level to the 500mb air pressure level in the atmosphere and calculates how cold it is based on the distance, with a lower distance being colder (cold air is denser, takes up less space) and a higher distance being higher. Heat waves generally have a value of above 580 decameters in Washington. You have to start thinking about snow when it gets to 522 dam (dam=decameters). Right now, it is like 507 dam. That is extremely low.

This is for tonight at 1 P.M. As I write this now it is 12:51 A.M. Yeah this has so far taken me one hour, but I enjoy doing it. I was watching the Bourne Trilogy but decided I'd rather write an update.
You can see that there is clearly a lot of arctic air in Western Washington. If this was in December or January, I would seriously be concerned about highs getting out of the teens. No joke. They might reach twenty. But we are gonna get an arctic blast that has not been diluted too much.

Wow! The models actually showed this 16 days ago. Not this exact scenario, but this idea. Pretty crazy. Then they shifted to highs in the 40s, believe it or not. There is not a lot of data over the arctic, so models commonly have problems with these situations. Given that it is a La Nina year, I expect that we will see more arctic outbreaks. This is definitely a good way to start. :).

To wrap it up - cold tomorrow and FRIGID Wednesday morning, before moderating while remaining mostly dry through Wednesday. A more active, typical storm track will return after a system affects us on Friday.

1 hour, 12 minutes (now I'm going to post how long I've worked on these. Hopefully someday I can count them all up. :)
Charlie