How Weather Modeling Gets Better 43
Dr_Ish writes: Bob Henson over at Weather Underground has posted a fascinating discussion of the recent improvements made to the major weather models that are used to forecast hurricanes and the like. The post also included interesting links that explain more about the models. Quoting: "The latest version of the ECMWF model, introduced in May, has significant changes to model physics and the ways in which observations are brought into and used within the model. The overall improvements include better portrayal of clouds and precipitation, including a more accurate depiction of intense rainfall. The main effect of the model upgrade for tropical cyclones is slightly lower central pressure. During the first 3 days of a forecast, the ECMWF has tended to have a slight weak bias on tropical cyclones; the new version is closer to the mark."
Re:Weather forecasting has a way to go (Score:5, Interesting)
I can understand why they get predictions about the future wrong, that bit is hard. What gets me is when the prediction for right now is at odds with what is actually happening. It seems like there is a significant delay between sensors on the ground taking a reading and the models being updated.
Apart from it being slightly comical when the guy on TV says sun is out but looking through the window I can see rain, it makes short term predictions useless. If they say it will rain this evening when I want to go out but the forecast for right now is wrong, what am I supposed to do with that information?
At best you get a vague prediction of the weather in the next few days, but the exact timing of events tends to vary quite a bit from what they say. It doesn't help that in the UK TV weather forecasts are delivered in the most confusing way possible, but fortunately we have the internet now.
Re: Weather forecasting has a way to go (Score:4, Informative)
Weather often varies dramatically over small distances. It may be sunny at the studio and raining 1/2 a mile away where you are. Rain predictions are not 50% chance that a given spot will get an inch of rain. The prediction is that 50% of a large area will get a inch of rain. Big difference between those.
Re: Weather forecasting has a way to go (Score:4, Interesting)
My experience has been that the predictions are usually quite accurate about what will happen, but is less precise about when. When they predict a front moving in, you can count on those thunderstorms, but don't always count on the storms starting exactly at 5pm.
The article mostly talks about predicting tropical storms, and for this the modelling of exactly what the path of the storm is going to be is critical. It does see that the predictions of storm tracks is getting better.
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Really?
I check 4 websites for the weather in my city [forecast.io, theweathernetwork.com, weather.gc.ca, accuweather.com], and they regularly will all have totally different weather. One will be 'sunny', one will be '5-10 cm of snow', one will be 'rain', and one will be 'overcast'.
It seems like they all get together, decide on the 4 most extreme possibilities, then randomly assign each one to a site.
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I wasn't considering even a week in the future. These were next day forecasting.
One of them will nail it. I just don't know which one.
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Part of the problem with UK forecasts is that they don't give the percentage chance, they just say it will it will not rain. I've always thought that was ridiculous.
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Weather often varies dramatically over small distances. It may be sunny at the studio and raining 1/2 a mile away where you are. Rain predictions are not 50% chance that a given spot will get an inch of rain. The prediction is that 50% of a large area will get a inch of rain. Big difference between those.
Not exactly. From the wikipedia Chance of Precipitation page:
if there is a 100% probability of rain covering one half of a city, and a 0% probability of rain on the other half of the city, the POP for the city would be 50%. A 50% chance of a rainstorm covering the entire city would also lead to a POP of 50%. The POP thus usually expresses a combination of degree of confidence and areal coverage.
Note that the Storm Prediction Center uses a different method when they give percentages for tornadoes and other severe weather. A 25% for tornadoes on a SPC convective outlook graphic means there is a 25% chance of a tornado within 25 miles of any given point in the area outlined on the map. As an aside, 25% using this method is pretty damn high, so if you ever see that indicated for your area you should really pay attention.
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I can understand why they get predictions about the future wrong, that bit is hard. What gets me is when the prediction for right now is at odds with what is actually happening. It seems like there is a significant delay between sensors on the ground taking a reading and the models being updated.
I'm not a Met, but I do have some understanding of the processes involved in model forecast runs.
Both the ECMWF and the US's GFS V2 (which, incidentally, is normally trounced by the ECMWF when it comes to predictive qualities) rely on a global network of real-time pressure and temperature sensors. Every six hours, that data is assembled into the databases needed for the ECMWF (and GFS, GEM, JAMSTEC etc) to run. They crunch the numbers and spit out a forecast, starting 6 hours out from the initialization c
Re: (Score:2, Interesting)
I am a meteorologist and I disagree with a lot of what you're saying. I'm not on TV. I'm a researcher.
Yes, a lot of forecasting now involves looking at numerical models. But you're getting a lot of things wrong here.
Yes, the ECMWF was once far better than the GFS. Over the past decade, the GFS has dramatically improved and the difference is much, much less. The GFS is criticized for its forecast of Hurricane Sandy eight days out, but there are plenty of times when the ECMWF is also dead wrong. The GFS isn't
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I can understand why they get predictions about the future wrong, that bit is hard. What gets me is when the prediction for right now is at odds with what is actually happening. It seems like there is a significant delay between sensors on the ground taking a reading and the models being updated.
Most regional models are run at least once an hour and make use of data from sensors up to a few minutes before the model is run. Even if a weather model was perfect, it would still produce incorrect results because models are always started with conditions that do not reflect the true state of the atmosphere. Weather models use other models or earlier runs to produce a best guess at the current state of the atmosphere. The atmosphere model is "adjusted" using the latest sensor, sounding, radar and satell
The late, lamented Weather Underground... (Score:2)
I just wish Weather Underground hadn't been taken over by The Weather Channel and, more to the point, their Web dev team. WU was an outstanding source for quick, concise reports on current weather, weather history, and news. Apparently they still post interesting content from time to time, but it just isn't worth my while to go slogging through the "new, improved UI" to get to it.
I still do pull it up for local conditions and radar; if I'm not in a hurry, it gives me the info I need, at least when I'm on my
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I haven't been running public-facing Web projects lately, but if I go back to it, I'll insist that we test on something other than a fast LAN connection and giant screen. The current team at WU obviously doesn't do that.
It seems to me like low-resolution displays are becoming rare on PCs, and like they expect you to use a mobile site or an app on your more portable devices. I have some of those poky old PCs with little screens too, and it's become a bit frustrating using them. Maybe they have a more noble purpose, like becoming part of an art project. Pip-boy, anyone? :p
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And even with all that AJAX and screen real estate, they still dumbed it down to the point of near-uselessness. Try finding the conditions graphs for the past, even just yesterday. Try finding tide info.
There ought to be an open weather project for people to submit personal weather station feeds to. I would have been happy to contribute to independent Wunderground, but TWC? No way.
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Ditto. I miss their classic designs. Now, if we could get accurate readings from all these weather sites. They all say different things!
PDEs (Score:1)
Isn't weather forecasting just solving PDEs?
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Isn't weather forecasting just solving PDEs?
...in four dimensions, with complex boundary conditions.
It would be hard even if partial differential equations were not chaotic.
http://arxiv.org/abs/0909.0910 [arxiv.org]
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Well that sort of thing seems typical of many HPC computations, which are a well studied topic.
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Yes, but it's not that simple.
The partial differential equations you're referring to are the Navier-Stokes equations, which have no known analytical solution. Instead, they're solved numerically with atmospheric data on a three dimensional grid. There are still a few problems here:
1) Although dx, dy, dz, and dt are pretty small these days, an order of magnitude lower than a couple of decades ago, we don't have in situ observations every dx, dy, and dz. You might have a few grid points in each county of the
5 day forecast (Score:2)
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Numerically simulating hurricanes is HARD (Score:1)
Dr. Masters' article is about numerical models that are used for hurricane forecasting. There is nothing simple about hurricane forecasting.
1) The atmosphere is a chaotic system. Small errors in the initial state grow exponentially as the model is integrated forward. There aren't many in situ observations over the oceans, so the initial state of the model is generally less accurate there than over land. Forecasts produced will also have larger errors.
2) A wide range of models are discussed here ranging from
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I'm trying to read Dr. Masters's article. It's very annoying that as I'm reading something down the page a bit, the page suddenly reloads on me, I assume because the ad at the top is refreshing. I'm bumped back to the top of the page and lose my place.
Why is advertising so much more important than the information on the page?
Why do companies have so much money they spend it on nefarious, intrusive advertising tricks? Obviously we have plenty of production capacity and the real problem companies are trying t
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I just closed the page linked in the article, which I think was Dr. Masters's blog, because it started playing an audio ad. I guess I should look into AdBlock. The proliferation of intrusive advertising is becoming intolerable. Anyway thanks for your comments (if you are the same AC who posted the original post I responded to), I learned something and the page didn't jump around on me or start yelling at me to buy something as I was reading.
Weather Underground was better at domestic terror (Score:1)
https://en.wikipedia.org/wiki/... [wikipedia.org]
Too bad some idiots stole the domain from the original group back in 90's that wanted it as an archive.
Open source weather (Score:1)
Now open source weather prediction is possible, these days. You can download the required weather initialisation files and the prediction engine. The only problem is noone has made open source for it. There is free RASP (see http://www.drjack.info and http://www.drjack.info/cgi-bin/rasp-forum.cgi and http://www.drjack.info/twiki/bin/view/RASPop/WebHome ) but it is not open and has maintenance issues. The hard part is validating and tweaking for a region.
A RASP operator (I can't even install it...).
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Open source weather prediction involves obtaining the data and running a numerical model.
There are a lot of acronyms for weather models in the comments such as the HWRF, HRRR, RAP, and NAM. All of the those models are actually various configurations of the Weather Research & Forecasting (WRF) model. Other models like the GFS, UkMet, and ECMWF are different and aren't based on the WRF. You can download WRF and compile it yourself. It's actually not that hard. The site is http://www2.mmm.ucar.edu/wrf/user [ucar.edu]