Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Modern Weather Forecasts Are Stunningly Accurate

theatlantic.com

Post reply on HN
Print view View original

111–120 of 120 posts

Re: Modern Weather Forecasts Are Stunningly Accurate

#111

Post by labster »

saltcured wrote: post #106
kevin_thibedeau wrote: post #98

Earlier quoted context omitted.

If you live near where the jetstream boundary usually lies, forecasts are generally less accurate because small, less predictable shifts can have a large impact on daily weather.

Yes! As a west coast native and sometime visitor to the midwest, I'd say that is true for the whole western US at least. If you learn to read the forecasts and maps you can actually start to grok it and intuit the mechanics. You can start to imagine the jet stream whipping like a hose and understanding that the exact rate of its swing might vary, causing weather fronts to sweep across the plains a little earlier or a…

Nah, midlatitude west coasts are worse because of the lack of good data over the oceans. Satellites can't tell you as much as you think, especially in the vertical direction. Knowing how much water is in a column of air is useful, but not as useful as if you knew precisely which layers it was in.

A considerable amount of data in models for California is from observations that were made in China and Japan, that flow with the wind across the Pacific. Or conversely, you can look at it as a data hole that advected across the ocean, too.

I'd like to note that of the few blown forecasts we get in Southern California, almost none of them have to deal with the jet stream. It's actually the cut-off lows offshore that don't have steering winds, which makes it difficult to predict where it will go next. The same is true with hurricanes.

Re: Modern Weather Forecasts Are Stunningly Accurate

#112

Post by labster »

tropo wrote: post #92
jacques_chester wrote: post #46

Many folks, when hearing forecasts have improved, will disagree. They can think of many times when the forecast was wrong, perhaps hilariously or disruptively so. This is textbook availability bias. You overestimate the failure rate because the failures were memorable, especially the major failures. But the far more frequent accurate predictions are not recalled, because they don't leave as much of an emotional impre…

Often I can't even say for sure if the forecast is wrong or not. For example, what is a 10% chance of rain at 10? That could mean 10% chance that rain will occur at some point from 10 to 11, 10% chance that it will be raining at a randomly selected point between 10 and 11, or 10% chance that it will continuously rain from 10 to 11. Also, it could be any of those three, except from 9:30 to 10:30. Also, it could be a 1…

What it really means in terms of exact timing is that an AWOS (weather station) will record measurable precip between the 1000 report and the 1100 report.

Sometimes percent means forecast confidence, sometimes it means that they can't predict what area will get hit with rain. Like synoptic conditions will say "this region will definitely get a few thunderstorms", but when you drop down to mesoscale then you can't tell which city will actually get the rain.

In longer-term forecasts, 10% usually means "I have no idea what's going to happen, so I guess precip is possible then." At mid range, like 3-5 days, it usually means "we haven't nailed down the timing of this thing yet".

If you actually want to know what the logic is, go read the forecast discussions.

Re: Modern Weather Forecasts Are Stunningly Accurate

#113

Post by labster »

brootstrap wrote: post #91
mannykannot wrote: post #80

Earlier quoted context omitted.

I get the feeling that this "hyper-local" mentality contributed to NYC and surrounding areas being caught flat-footed by the first-of-season snowfall at the end of last year. I have little understanding of meteorology, but it was clear, just from the forecast maps, that a small change in the location and timing of the rain/snow line would make a big difference to the outcome, and that something more than was forecast…

Your last statement is the so true. An amateur forecaster can spend ten minutes looking at the some big picture (synoptic scale) weather and know regional trends (this part of country is dry, these guys are wet, humid etc). This would be a pressure & wind map, showing location of high/lows, maybe some 850mb moisture charts too... But you are painting broad strokes. All of these dumbos on HN want to know exactly when…

It's not that, it's selective memory. Everyone remembers the blown forecasts. Even I do. Three or four years back NWS predicted a big Christmas storm in SoCal, but the damn cut-off didn't come on shore, and the resulting offshore flow made the day nice and warm.

And, Americans only: if you forecast temperatures of 99°F and the observed temperature is 97°, good job. But if the observed temperature is 100°, then you made a huge mistake. People need to know when you hit the century mark!

Re: Modern Weather Forecasts Are Stunningly Accurate

#114

Post by ggm »

Back in the seventies and eighties there were four sources of impetus for improvement in highly parallel supercomputing. Military/Nuclear, high energy physics, oil and gas exploration (seismic analysis) and weather.

The weather people were the nicest. They could talk to almost anyone about their work!

I remember somebody in csiro talking to me about models getting accurate at the 1km square granular scale for a day. I think we're well beyond that for both cell size and duration now.

Everyone loves to talk about the weather and Bob Dylan was wrong about not needing a weatherman to know which way the wind blows

Re: Modern Weather Forecasts Are Stunningly Accurate

#115

Post by ip26 »

jdietrich wrote: post #102
brootstrap wrote: post #81

Just a little knowledge to drop, as a bachelor degree meteorologist and also coder / HN'er. Dont use your built in phone app for forecasts. Dont expect hour by hour precision (maybe for the next few hours sure, but not 2,3,4,5 days out). Trust nobody expect the trained professionals at NWS. These people look at ALL the models, they watch things like a hawk. I work with some of these nerds and it's crazy. They are lik…

If you really care about short-term weather forecasts, learn to read surface pressure charts and rainfall radar. It's not particularly difficult and it gives you a huge amount of additional information. A summary forecast can only tell you so much, especially in changeable conditions and complex microclimates. Knowing the range of probable conditions is often much more useful than knowing the most probable condition.

How do you suggest really learning to read the surface pressure charts? I have gotten to the point I understand what I'm looking at, but can't really turn the factual knowledge of watching the highs and lows and winds moving around into real understanding & forecasting.

Re: Modern Weather Forecasts Are Stunningly Accurate

#116

Post by PopePompus »

travisjungroth wrote: post #89
brootstrap wrote: post #81

Just a little knowledge to drop, as a bachelor degree meteorologist and also coder / HN'er. Dont use your built in phone app for forecasts. Dont expect hour by hour precision (maybe for the next few hours sure, but not 2,3,4,5 days out). Trust nobody expect the trained professionals at NWS. These people look at ALL the models, they watch things like a hawk. I work with some of these nerds and it's crazy. They are lik…

Don't all those apps just get their data ultimately from the NWS?

Some commercial forecasters have a "wet bias" (https://en.wikipedia.org/wiki/Wet_bias). They intentionally overestimate the odds for precipitation on the theory that people are happier if it doesn't rain when they were planning on rain than they would be if it rained when they did not expect it.

Re: Modern Weather Forecasts Are Stunningly Accurate

#117

Post by Groxx »

brootstrap wrote: post #108
wenc wrote: post #90

Earlier quoted context omitted.

I bought the app because of its hyperlocal forecasting, but it's been known to predict precipitation where there's none, and vice versa. I wonder if it does better in some geographies than others (e.g. high pressure system areas where things are more stable)

hyperlocal is a joke, sorry to say it. Just because you can downscale your grid to a very small number doesnt mean good data. It just means you can do statistics and mathy stuff to interpolate. Everyone forecasts better in stable times such as a strong high pressure ridge. The tricky part is the edge areas between air masses, the transition zones. This is where all the juicy weather actually happens and it is the har…

Totally agreed on it being a marketing term, not a real prediction improvement - it's essentially the same as any other app in terms of "will it rain" / etc.

But they do a much better job of notifying about changes based on where I physically am, instead of for the city / region as a whole. Other weather apps I've used don't differentiate between "rain falling now 50 miles away" and "rain falling on my head", even though the radar map clearly gives them that info at a much finer level of detail.

Re: Modern Weather Forecasts Are Stunningly Accurate

#118

Post by mh8h »

If you're looking for a graph that shows more than a projected minimum/maximum for every day, take a look at Foreca's 15-day forecast page [0]. It shows percentile lines for the forecasted minimum and maximum, which give a much better idea of what to expect. It also forecasts global vs. local precipitation. Unfortunately it is only available in Finnish.

[0] https://www.foreca.fi/Canada/Vancouver/15vrk

Disclaimer: I used to worked for MSN Weather, where we used Foreca's feed as the source for our weather data.

Re: Modern Weather Forecasts Are Stunningly Accurate

#119

Post by brewdad »

moocowtruck wrote: post #2

why is my weatherman always wrong? :(

Being "wrong" can be no big deal (48F vs 50) or hugely significant. My town will be getting precipitation this weekend. If the temps stay at 36, it will be a typical cold, wet weekend. If temps fall to 33 or lower, my town will be shutting down for a day or two since we don"t have snowplows.

Re: Modern Weather Forecasts Are Stunningly Accurate

#120

Post by js2 »

chooseaname wrote: post #71
saagarjha wrote: post #4

> In 2009, a back-of-the-envelope study estimated that U.S. adults check the weather forecast about 300 billion times per year. That's every single adult in the United States checking the weather four times a day . A bit more than I would have expected…

Floridian. During the summer months I check more often (when I'm heading out) so that I know if a T-Storm will be developing in the next couple hours.

Wait what? I grew up in Miami: the answer is always yes.
Post reply on HN