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People don't like it when 14 inches is forecast and the actual snowfall is 2 inches, but they aren't going to like hearing forecasts of 2-16 inches. That sort

People don't like it when 14 inches is forecast and the actual snowfall is 2 inches, but they aren't going to like hearing forecasts of 2-16 inches. That sort of wide confidence interval is more accurate, but it's also basically useless. How does a 2-16 inch forecast help a parent or school district or mayor plan for anything?

mikeash 12y ago
Yes, it's hard to plan for 2-16 inches. But that's a fault with reality, and not a reason to give bad forecasts. It's really hard to plan for hurricanes, so let's just give a forecast of "it's going to miss us"! That's much easier to plan for! Sometimes life is uncertain. The answer is to account for the uncertainty when planning, not insist that the information indicate certainty when it's not actually there.
ScottBurson 12y ago
You make contingency plans for both ends of the range, and most importantly, you know you have to check for updates frequently.
saalweachter 12y ago
A single 9x% confidence interval like 2-16 inches gives the impression of a continuous bell-curve distribution, when you might have a multiple peaks based on a couple of simple factors. I wonder if it would be useful to give out a couple of probability buckets. If people heard "20% chance of 10 or more inches, 60% chance of less than 2 inches", would then know to be ready for a lot of snow, but not be surprised if it doesn't happen, or would they ignore the considerable chance of a heavy snowfall?
adamtj 12y ago
I disagree. When forecasters know with certainty that there will be 14 inches, that's what they should say. It's definitely more accurate. However, when they only know that it might go either way, they should say "2-16 inches", which is more useful and accurate in the face of real uncertainty. Even better would be "2-16 inches, probably 14". A school administrator who sees a forecast of "14 inches" may simply cancel class the evening before, giving people time to prepare with certainty. That's nice, but not at the cost of a lost school day and calendar disruptions. A forecast of "2-16 inches, probably 14" might cause that same administrator to wait and see. TV and radio would broadcast the news about possible school closings the evening before, so parents could prepare. They might have a bit more difficulty planning, but that's worth it if the school day can be saved.
itafroma 12y ago
> but they aren't going to like hearing forecasts of 2-16 inches. The NWS provides probabilistic accumulation guidance: http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=48&ptype=snow http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=48... Similar to what this article suggests in its postscript, you wouldn't have to merely say 2-16 inches. Instead, you could say, "there's a 50% chance it'll be between 4-6 inches, and a 15% chance it'll be between 14-16."

mikeash 12y ago

Yes, it's hard to plan for 2-16 inches. But that's a fault with reality, and not a reason to give bad forecasts. It's really hard to plan for hurricanes, so let's just give a forecast of "it's going to miss us"! That's much easier to plan for! Sometimes life is uncertain. The answer is to account for the uncertainty when planning, not insist that the information indicate certainty when it's not actually there.

ScottBurson 12y ago

You make contingency plans for both ends of the range, and most importantly, you know you have to check for updates frequently.

saalweachter 12y ago

A single 9x% confidence interval like 2-16 inches gives the impression of a continuous bell-curve distribution, when you might have a multiple peaks based on a couple of simple factors. I wonder if it would be useful to give out a couple of probability buckets. If people heard "20% chance of 10 or more inches, 60% chance of less than 2 inches", would then know to be ready for a lot of snow, but not be surprised if it doesn't happen, or would they ignore the considerable chance of a heavy snowfall?

adamtj 12y ago

I disagree. When forecasters know with certainty that there will be 14 inches, that's what they should say. It's definitely more accurate. However, when they only know that it might go either way, they should say "2-16 inches", which is more useful and accurate in the face of real uncertainty. Even better would be "2-16 inches, probably 14". A school administrator who sees a forecast of "14 inches" may simply cancel class the evening before, giving people time to prepare with certainty. That's nice, but not at the cost of a lost school day and calendar disruptions. A forecast of "2-16 inches, probably 14" might cause that same administrator to wait and see. TV and radio would broadcast the news about possible school closings the evening before, so parents could prepare. They might have a bit more difficulty planning, but that's worth it if the school day can be saved.

itafroma 12y ago

> but they aren't going to like hearing forecasts of 2-16 inches. The NWS provides probabilistic accumulation guidance: http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=48&ptype=snow http://www.wpc.ncep.noaa.gov/pwpf/wwd_accum_probs.php?fpd=48... Similar to what this article suggests in its postscript, you wouldn't have to merely say 2-16 inches. Instead, you could say, "there's a 50% chance it'll be between 4-6 inches, and a 15% chance it'll be between 14-16."