Thursday, December 29, 2011

A higher mathematics?

The online weather forecasts never seem to work out all that well for China, and especially not for Beijing. The 5-day forecasts are, of course, particularly unreliable; but even the 24-hour ones go bizarrely astray at times.

And then, sometimes, even the 'current' news seems to be completely up the spout. This morning, for example, Weather Underground is assuring me that there is a "0% chance of precipitation" today, even though it is already snowing.

I wonder if there can be some mathematical justification of this apparent aberration: when the likelihood of precipitation tends toward infinity, does it somehow flip back to zero?

Or is it more of a semantic thing? When snow has become an actuality, there's no more 'likelihood' about it?

Enquiring minds want to know.


JES said...

Here y'go.

The bottom line -- especially for a fairly large geographic area, like an entire large city -- seems to be that the "chance of precipitation" is useful only if you're going to be everywhere in the city for every second within the particular 6- to 12-hour window of time for which the chance was calculated. And even then, it's only an average. So "0%" probably is never the same thing as true zero, but more like a 0 with some tiny fraction of an actual probability.

I think meteorologists need a new term. Or, maybe better -- simpler for sure -- would be eliminating the whole 100-point scale, replacing it with a binary, carry-or-don't-carry-an-umbrella guideline.

A guy named Mark Hurst, a user-experience expert, recommends this "umbrella storage system" (it's on p. 13 of that PDF): Here's how to ensure you always have an umbrella on hand when it's raining. Buy two umbrellas, and keep one at home and the other at work or school. (Perhaps store another in the car.) Then grab an umbrella whenever it's
raining, and -- this is the only hard part -- remember to put the umbrella back in its place afterward.

That actually works for me. The complication, of course, is that it's not JUST me. It doesn't make any difference how faithfully I "remember to put the umbrella back" if I'm not the only one who needs to make use of the umbrella, especially the one in the car. If you follow my drift.

Froog said...

It snowed - at least thinly, intermittently - across most of Beijing on Thursday morning.

When I made this observation, it was snowing moderately heavily in the area of Beijing where Weather Underground's main city centre recording station is.

However, large the area is, you can't get to zero percent, when it's already 100% in parts of it.

Froog said...

That comma bothers me, but I'm not going to change it.

I think that's a positive achievement for me - in a Zen/Tao sort of way.