How Accurate are 14 Day Forecasts?

Brooks

Brooks

Filing Flight Plan
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BellancaGuy
I have a XC trip that I am planning to fly in two weeks. I looked today at a 14 Day Forecasts, and different websites are saying different things. For example, one website says it's supposed to be clear and sunny on the day, and the other one says it's going to be rainy and cloudy.

So, how accurate are these 14 day forecasts? How many days in advance do forecast models start to become accurate?

Thanks
 
At 2:30 pm today we were supposed to get heavy snow starting at 5pm. It's almost 9 and haven't seen anything yet. I don't put too much faith in extended forecasts.
 
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Three day forecast are not as accurate as one would like. There have been times when the in flight weather changed and I was only going a few hundred miles.

14 days is an eternity in weather ... o_O
 
Racerx said:
At 2:30 pm today we were supposed to get heavy snow starting at 5pm. It's almost 9 and haven't seen anything yet. I don't out too much faith in extended forecasts.
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At some point did it go from Sunny to Cloudy? if so, they had great success. If not, wait a couple days and ask yourself the same question....
 
Other than listing the 14 days, nothing can be relied upon.

Just for laughs, take a look at TAFs. They incorrectly forecast 30 hours out, every 6 hours. If they can't get that right, how can we ask for 14 days out?
 
I'm a meteorologist and I wouldn't use a 14 day forecast to wipe the oil off my dipstick even.

Other than to maybe look at a long wave pattern trend. i.e. is it trending warm or cold 2 Mondays from now? That might be somewhat useful.
 
I'll go even one step farther. Any service providing a 14 day forecast is likely trash. Nobody reputable will put their name to that.
 
Todd82 said:
I'll go even one step farther. Any service providing a 14 day forecast is likely trash. Nobody reputable will put their name to that.
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Yeah, I see what you are saying there. Hence why big names do not really offer 14 day outlooks. I always see the smaller, kinda sketchy websites doing that.
 
Brooks said:
I have a XC trip that I am planning to fly in two weeks. I looked today at a 14 Day Forecasts, and different websites are saying different things. For example, one website says it's supposed to be clear and sunny on the day, and the other one says it's going to be rainy and cloudy.

So, how accurate are these 14 day forecasts? How many days in advance do forecast models start to become accurate?

Thanks
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In my experience that’s a typical forecast. One source being the opposite of the other makes that one 50% accurate. The only purpose a 14 day forecast serves is to maybe give you a little hope. I wouldn’t schedule my work around a fourteen day forecast. I believe that anything beyond about 72 hours is useless as far as flying goes.
 
Not. 8-14 day forecasts are good for very general trends only, like regional temperature and circulation changes. For clouds and precip, it's just too far out to get specifics or timing right. Even 7 days out the timing of systems could be off by 24 hours, and intensity of certain systems like rapidly developing noreasters, could be way off.
 
14 hour forecasts aren't even reliable here in the great lakes area.
 
EdFred said:
14 hour forecasts aren't even reliable here in the great lakes area.
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Yep. Downwind of Lake Ontario the weather can change rapidly with a 10 degree wind shift. Usually a 285 wind direction at my home airport is deadly in winter. Ten degrees away from that, it might be sunny and clear. Darn Lake effect.
 
I look at how the long range forecast changes over time. If it stays mostly the same, the the models are probably working well and I MIGHT belive the mid-range forecast 3-5 days out. If they're changing a lot, then the weather pattern is unstable and uncertain.

That also factors into how much I believe in tomorrow's forecast. So I guess I care more about trends and less about absolute numbers.
 
ja_user said:
At some point did it go from Sunny to Cloudy? if so, they had great success. If not, wait a couple days and ask yourself the same question....
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Nope. Overcast all day. Still waiting.
 
I find forecasts to be remarkably poor in their accuracy. How we can have all these radar and satellite tech and such a keen understanding of the airmass yet be so awful at predicting weather is a mystery to me. Look at the barometer, look out the window, take a look at a satellite map, and make your own intelligent guess
 
I could make little airplane plans 14 days out, but I tell anyone involved in the plan that everything is weather dependent, and the initial go/no-go 'feeling' comes 48 hours prior, and even then the plan is still very much subject to change. Most people get that.
 
EdFred said:
14 hour forecasts aren't even reliable here in the great lakes area.
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hell 14 minute ones in our area couldn’t be relied on! When you are a 15 minute flight from me and I was on skis while you had grass showing... lol
 
Tantalum said:
I find forecasts to be remarkably poor in their accuracy. How we can have all these radar and satellite tech and such a keen understanding of the airmass yet be so awful at predicting weather is a mystery to me. Look at the barometer, look out the window, take a look at a satellite map, and make your own intelligent guess
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Crappy weather modeling, awful journalism, and 1950s engine tech. No wonder I don't watch the news.
 
We occasionally say that little boys who lie...

Well, we really do appreciate the effort, but it's quite "fun" trying to schedule things on forecasts in the photography business.
 
Brooks said:
Haha, same... I also don't like to feel down all the time either. In lieu of the news I hangout on these forums and at the airport.
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Down all the time, world is imploding, stocks are soaring, people are unemployed and struggling. The news has become too sensationalistic to have any meaningful value...like social media. Hell, look at the weather. They make up terms to sensationalize. "Bomb cyclone", "Polar Vortex", "Arctic blast". Are Any of these phrases useful? Or do we just come up with it to try to make weather a headline? Btw, it's 11:30 and my front steps maybe have a dusting. The 8-12 is at least 7 hours from a report 9.5 hours ago. Well done!
 
Weather idiots here can barely predict 2 hours away, much less 14 days.
 
It's just adding ammunition for those of us who call them "weather guessers".
 
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I suspect too many people here trust what they read on weather.com as gospel (it’s one of those trash sites...)

Try going to pivotalweather.com and poke around through the weather model data. They are usually pretty close 5-6 days out, at least out here in the west.
 
The big systems (hurricanes, winter storms) they’re pretty good at up to 3 days...but local weather (like today they didn’t predict fog, and that’s a 3 hour forecast).
14 days is a complete guess...like the farmers almanac.
 
I weatherman's only concern is his customer. The one that pays him. The advertiser of the show. If the weather forecast is accurate 3 days out, the viewer would not need to look at it again for 3 days. And the viewer would not see more advertisements.
 
I've read weather forecasting has improved recently. The article stated the 5 day forecast is now as accurate as the 3 day forecast used to be. The cynic in me says that maybe that improvement is no big deal b/c maybe the 3 days forecasts have historically not been all that accurate. The few times I've had something important on the calendar and started watching the forecast 14 days out, the weather was nothing like the original 14 day forecast.
 
Brooks said:
how accurate are these 14 day forecasts
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As accurate as your instrument rating.

kyleb said:
The sunrise and sunset times are both something you can count on
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Someone will find a way to argue this point. I predict by the first four posts of page 2, someone will have a case against sunrise/sunset times being reliable.
 
Brooks said:
I have a XC trip that I am planning to fly in two weeks. I looked today at a 14 Day Forecasts, and different websites are saying different things. For example, one website says it's supposed to be clear and sunny on the day, and the other one says it's going to be rainy and cloudy.

So, how accurate are these 14 day forecasts? How many days in advance do forecast models start to become accurate?

Thanks
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14 day forecast are not accurate at all. I have used 10 Weather Channel forecasts for a general indicator with generally good results in some parts of the US. Other parts of the US the 7 day forecast is iffy at best.
 
Weather forecasting is another casualty of COVID. With fewer airliners flying and automatically reporting weather all over the world, weather input is less complete. Reductions in ocean liner reports has also reduced oceanic information. Technology has improved markedly, but without data to analyze, the forecasts are suffering.
 
I'll admit if I have a trip coming up I'll start watching the long range forecast, if for nothing else to get a sense of the trends. It can show a forecasted low or high system a week out, although the track may vary. Sometimes a shift of 50 miles in the center of a low is the difference in a blizzard or a sunny day, and I've seen that happen in a 14 day window numerous times.
 
For those who remember the best weather forecast. It was more accurate 3 days out than local weather for the day.
A.M. Weather[1] was an American weather news program that ran from October 30, 1978 to February 3, 1995. and was broadcast on PBS member stations throughout the United States. The 15-minute daily program
Funding was provided by various aviation-related companies and government agencies, including the Federal Aviation Administration, the Aircraft Owners and Pilots Association (and its Air Safety Foundation arm), Phillips Petroleum Company, Gorman-Rupp pumps, Hilton Hotels Corporation, the National Business Aviation Association
 
To be honest weather products are pretty good for temps, cloud cover, and precip predictions for 48 to almost 72 hours. Highly localized conditions like lake-effect precipitation are more difficult to predict exactly for location, that should be expected. The granularity of weather models is in the many km range, not at the km level. The last few times I did flight planning, the weather predictions for ceilings and cloud tops were reasonably accurate en route. It's been pretty rare that tops en route are say, forecast to be 7000 and they turn out to be 14,000. Beyond 48-72 hours the granularity grows exponentially and the timing is increasingly uncertain, but the general sequence of weather features, like frontal passages and temperature changes, are generally correct. Just not certain enough in location and timing to necessarily be useful for specific route planning far into the future. But maybe useful enough to know that in the next week the weather will be likely to be frequently unfavorable for VFR flight, let's say. Or that a stretch of clear weather is likely to take hold.
 
I think some places have more accurate forecasts than others. I have watched the forecast change six times in six hours for a time eight hours away.. One thing I wish I had done when I started flight training was tracking forecasted weather against actual conditions. The short-term forecasts are so bad around here, my instructor and I have resorted to only cancelling flights after checking the current weather in all the surrounding areas just before I leave (so about 2 hrs before lesson time). So, I tend to think most, if not all, forecasts are pretty much guesses that may or may not be educated. :D
 
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I’ll start looking a week out, see if forecast is staying stable, trying to be flexible. Two days prior, check MOS. One day out check the TAF.’s along the route. Always prepared to leave a day early or later if there is a big difference in the weather TAF. Flexibility is a must. IFR rating really helps with the go/no go decision, even if one flies with high personal minimums, above freezing temps or vfr on top, and around convective areas, not thru them.
 
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