Drier!

Monday, January 20, 2011
11:57 P.M.

This has to be a quick post, as I am doing tons of hw (I am SO excited for the semester to be over!) but it is mainly just an update to let you know I am still blogging. Although we have a couple flood watches now, it will get drier over the next week or so and possibly stay that way for quite some time as a blocking ridge of high pressure rests off of our coast. We should see partly cloudy skies and a few showers from time to time as weak storms attempt to break through the ridge. No snow in Seattle anytime soon.

I told you that would be quick! Three minutes to be exact :)
Charlie

A Note About Snow and looking ahead

Wednesday, January 12, 2011
4:29 P.M.

Hey everybody, I am going to try and update this blog more often, even if it is only for a little while. We saw more snow than what was expected last night, although not that much more. The reason? The models scoured out the cold air too quickly. This is something I have seen with the last three of these overrunning events. It takes a significant amount of energy to melt snow to rain, and it seems as though the models underestimate this amount. They seem to simply "swap in" milder, marine air without paying attention to the latent heat of fusion (energy required to melt ice). Next time, I will add in a note and forecast the snow to end a little later than what is forecast on the models. However, there are also times when the snow has ended and switched over to rain sooner than predicted. Just goes to show how hard it is to forecast in the Pacific Northwest!

Looking ahead, we have a fairly active week in front of us, with several moderately strong storms passing to the north of our region. The latest GFS model has a strong zonal flow over Oregon, which would give Oregon lots of rain and the mountains lots of snow. We will be mild, with highs getting up into the upper 40s/low 50s.

That's all for now, thanks for reading!
Charlie

Our Dilemma

Tuesday, January 11, 2011
8:26 P.M.

 

Thankfully I don't have this dilemma. Who would possibly want to go to college?

I have to make this quick, as additional homework warrants priority, but I just felt like I needed to have a quick note to explain what is going on and all the hype that we received earlier this week and how none of it is coming true. Before, the models were predicting a historic snow event. The biggest snow event in our lifetimes, possibly even in our parents lifetimes if everything panned out correctly. It could have been the snowiest week in Seattle history. This is not an exaggeration. That possibility seemed very real, and models were continuing to forecast it only 4-5 days out, which meant that it was well within the believable range of probability, though admittedly far from a slam dunk. 

Then, all of the sudden, the low pressure system was forecast to go to our north, and here I am at my house, distraught with "what could have been" with a measly .10 inches of snow on the ground, forecasting a changeover to rain in an hour or so. 

Here is the dilemma - should forecasters tell the truth to the general public about what they see in the models? Or should they wait before claiming there could be a gigantic snowstorm? Is it better to give the public advance notice of a serious event developing? Or is it better to wait until you are sure to prevent confusion from occurring and your tv ratings/reputation from going down if you are wrong?

I supported what the media did on this one - they went ahead and forecast a giant snowstorm and then changed when the models changed. Sure, it got super hyped up and nothing really happened, but if the original forecast was right and the media didn't let people know, people could become stranded. People could die. And I think that we can all agree that massive disappointment is better than death. 

What I feel like the general public and even some professional forecasters don't realize about forecasting is that is a field of probabilities. There are ensembles of models, and they all show something slightly different. There is a feature called "probcast" at the uw that gives a forecast of a probability of what things might occur based on averages of different models. It can be found at http://www.probcast.com/. Although it is not very specific and still has a lot of work to do with regards to development, it is a great start, and it is often very accurate for short range forecasting, particularly with weather events where the models vary wildly and you can't really pick a solution. When meteorologists make a forecast, they generally look at a model and interpret what it is saying. But all the models show different things, so wouldn't it make more sense to give a probability of what might happen? I think it would.

But the question is if this is friendly to the consumer. A lot of times, I'll be asked if we will get snow or not, and I'll start explaining convergence zones and wet bulb cooling and adiabatic warming/Chinook winds, and people will just interrupt me and say, "look, do I have to do my hw for tomorrow?" Do people want a probability forecast that is more accurate and gives a better glimpse of what truly goes on in the profession I plan to enter, or do people just want a simple number? I'm guessing they would just want a simple number with an icon (smiley face sun optional). There are meteorologists who are opposed to forecasting with probabilities because in their eyes, one thing is going to happen, and we are going to forecast the one thing we think is going to happen. Those opposed to probabilistic forecasting also point out the contradictions in National Weather Service forecasts. They might say "How can you have a 50 percent chance of snow, and still have it accumulate to 2 inches? Does that mean it will snow 2 inches if it doesn't snow at all?" Obviously, it means more like it will so 2 inches if it does snow, but the wording can be a bit ambiguous at best in NWS forecasts. Even though the NWS forecasts can be confusing sometimes, I still think that giving PoP (probability of precipitation) forecasts along with quantitative forecasts make the most sense.

So what should the commercial sector do in regards to these storms? Should they give a big heads up? Should they play it safe? My answer is that they should give a big heads up if it occurs in the models more than twice, and mention it if it has occurred at least once. But they absolutely NEED to stress the probability aspect of it. I actually wrote an essay about computer models for my computer science class (maybe I'll post it on here sometime for ya'll to read), but the bottom line is that forecasts are chances of what might happen, they are not what will happen. Commercial stations need to give larger warning times (as a safety measure) but STRESS UNCERTAINTY. They glaze over it, but when snow-crazy kids like you Garfield students read the forecasts, "there is a slight possibility of two feet of snow" becomes "Jeff Renner says there could be two feet snow," which becomes "Jeff Renner says it is going to snow two feet" which becomes "OMG!!!!!!!!!! IT'S A NEW ICE AGE!!!" Of course, King5 contradicts itself often because the forecasters explain that it might happen, and then all of the sudden Parka Boy (Jim Foreman) comes in and tells us how we could get devastated with two feet of snow, but nobody listens to the "could" part of it.

When I write these forecasts, I try to show you a little bit of my world in forecasting - I give models, I give probabilities, and I generally take more risks in forecasting and mention things further in advance than the tv stations and even the NWS or Cliff Mass. But I cannot stress enough that this is a field of probabilities, and while it is fun to look at models of crazy events happening (and beneficial to those who could be affected), nothing is certain and things are bound to change with each model run.

I would like to hear from you guys on this! Is it better to play it safe, or to give lead advance time? Would tv weather be more interesting if they showed computer models? Do you have a favorite tv station for weather? Do meteorologists stress enough that every forecast is a forecast of something that has only a chance of occurring? Post on this blog! I'd love to hear your opinions. Cliff Mass routinely gets 20 comments per post, often times more. Let's bring the ruckus and knock him off his top spot for once!!!

Charlie

0:50

To Be Or Not To Be?

Sunday, January 9, 2011 9:04 P.M.

As I try to memorize this stupid... er... wonderful passage, I am faced with an utterly more important question. Will we, or will we not, see a major snowstorm? 
And the answer is... I really have no clue. But it is looking less likely.
One thing meteorologists look for in models is run to run consistency and trends. The previous models, especially the one Americans use the most, the GFS, were all very, very consistent in bringing a historical snow event to at least some part of the Pacific Northwest. However, now all the models have shifted the storm track much further north. This means we would be on the warm side of the storm. As you can see in the map above, the low pressure center is now approximately over Ucluelet (Southern Vancouver Island). This would mean that instead of getting a cool northerly wind to cause snow to the area, we would get a warmer southerly wind that would change it all to rain. We may see 1-3 inches before the switchover, but compared to what the models were showing before, this is nothing.But there is a little bit of good news. I did save money on my car insur...Just kidding. But really, there is some good news. Models before had the storm even further north, up by the northern tip of Vancouver Island. Now, it is about 200 more miles south. If it is 200 miles more south, we WILL see a snowstorm of historic proportions. Precipitation is not the issue. The temperature is. And the mountains will see tons of snow regardless. Here is a 24 hour snowfall period forecast from 4 P.M. Tuesday to 4 P.M. Wednesday. The storm is also expected to get here sooner, Wednesday instead of Thursday.

Whether tis nobler to have a storm come in to our southOr to suffer the travesties of one to our northOk I give up. Gotta study.But listen closely. If this storm does come to our south, we will see a foot, perhaps more, of snow. So now is the time to prepare.You stay classy, planet Earth.Charlie

A Major Snow Event?

Friday, January 7, 2011
6:07 P.M.

This is what 2 feet of snow looks like

Hey everybody! It's been a while since I last posted. It has been all college apps... a word of advice to underclassmen... get them done early! But, I successfully sent all my January 1st deadline college applications, and I am ready to roll!

Thankfully the weather has been fairly benign lately, and there hasn't been much to talk about. But then I woke up this morning, and I saw this.

This is a map of predicted 24 hour snow accumulations from 4 P.M. Wednesday to 4 P.M. Thursday. At face value, this would mean a FOOT of snow in Seattle. To top it off, more snow comes pouring in later on this model, which would bring the storm total to over two feet in our area before it is all said and done.

Now, I don't want everybody to get excited. There are often events like this that show up on the models and everybody gets super excited only to have snow not fall at all. Out of three models, two are showing significant snow, and one is showing a snowy transition to rain. I'd say we have a pretty good chance of getting some snow. The question is if we get a switchover to rain, or if it stays all snow and we just get walloped (like above). First, you need to have cold air in place. Cold air will start to filter into the area this weekend, with highs in the mid 30s or so. While I would like to have the air be colder, it is cold enough for snow (air can be above freezing and the precipitation can still be snow, particularly if the air is dry or the precipitation is heavy). Now, take a look at the graphic below.

It is important to understand why we might have such a big snow storm, and what ingredients are needed to come together to deliver a potentially historical punch. The scenario shown above is the PERFECT scenario for gobs of snow for Seattle. We have a split jet stream in the upper atmosphere, with one branch coming into our area from Canada and one coming off the Pacific. You can see a developing low pressure system in the far left corner of the picture. This comes onshore just north of Astoria, as evidenced down below.

It is a little hard to make out exactly where the center of the low is, but it is near the mouth of the Columbia River in this diagram.

The crucial key here is that it goes close enough to us to provide us with ample moisture, yet it goes south so it draws in a cold northerly wind. That's why the models are going crazy with snow amounts. If this does verify, we could see the biggest snowfall we have seen in at least 15 years, going back all the way to December 1996.

But it is a big if.

I'll keep you posted. :)
Charlie

0:56