What do you believe weather forecasters mean when they say "40% chance of rain"?
1) It will rain for 40% of the day. 2) There's a 40% chance it will rain at some point.I googled it and apparently it depends on the forecaster? 1) and 2) are completely different meanings.
I think it means 2
So pretty useless then. I have no idea if it will be for 20 minutes or the entire day.
I've taken it to mean that the chance of rain within the forecast area is
40%, which is subtly different.In the last month, the Met Office has issued 3 48 hours weather warnings for rain for my area. However, the chance of rain each time never exceeded 5%.
I cynically suspect that whatever methodology is being used, it allows a retrospective "we got it right" approach.
The politically correct uncertainty principle.
The more technically correct a statment is, the less use it is.
Yesterday Accuweather MinuteCast was showing no rain for at least
120mins - I only looked at the site because it was raining and I hadn't noticed a forecast for it.
The best forecast I've found (if I'm already where I'm going to be and haven't moved in the last day) is my watch. It takes a pressure reading every minute and draws a graph of the next 12 hours of weather. Basically I look out the window and look at the graph, if it's going down then I know the weather will end up worse than it already is.
I suspect that also.
Meteox showed no thunderstorms within about 50 miles of us, when we were in a thunderstorm.
When they explained it on the TV durign a weather documentary they said it wass the chance of rain andn showed how they calculated it. In waether there';s a few things that can happen due to changign Highs and lows and various 'gulf' type streams the forcaster can guess which will effect which but it's a probabilty rather than a known outcome, so they use the % term. I suppose they could use odds like bookies.
whisky-dave expressed precisely :
I was wondering about that yesterday, reading the local forecast. It was showing various percentages for each hour, 20%, 30%, 40%, 70%. Even threats of thunderstorms. Does the first 20% mean that there is a 20% risk of some rain within that hour, or something else?
In fact what happened was someone 2 miles away saw some brief and light rain, hardly worth a mention. We had cloudy, no rain fell at all, no thunder, the sun came out when it was supposed to be 70% and it was hot and very humid.
Given that it includes the word "chance" (ie probability) I'd interpret it as the second meaning: if (hypothetically) you replayed the day many times (Groundhog Day!) then approx 40% of the occurrences of the day would have some rain.
I guess that what it means, perhaps some may think that it means there's a 20% chance of rain in their lifetime, how anyone would come to that conclusion escapes me, but there's some on here that think the new doctor who is a women ;-)
Unless there is high pressure stuck over us you can go to 7 UK forecast sites and get seven different percentages or timings. They all claim to get their information from the Met Office. I don't believe that all seven have in-house meteorologists so who makes it up?
Which is of no use to me whatsoever. Pouring with rain all day is nothing like spitting for half an hour. Yet they don't distinguish between the two. There should be a measurement where 0% means no rain at all, and 100% means rain all day.
Gardening and DIY are 100% related to weather.
And I'm not a new entity. I've asked about 4 gardening questions in the gardening group over the last year, and I'm in the DIY group a lot.
If I've been in the same place for 12 hours, and am going to be there for another 12, my watch's barometer is a better guide than the internet forecasts. It takes a reading every minute, so I get a graph of the next 12 hours ish. It doesn't say exactly what the weather'll do, but it's a very accurate guide that it'll get worse or better throughout the day.
I've seen the Met Office get yesterday's forecast wrong!
We know but aren't you only taking notice of a part of the information on offer?
They do, but not by using the single variable you mention in isolation.
0% is just that, no rain at all that'There is a 100% chance of rain' (as the definition of that prediction) means that it *will* happen (as a prediction) at some time during that 24 hour period (say) and the *additional information* will generally determine how hard and for how long it will (is likely) rain during that same interval.
So, whilst 'There is a 100% chance of rain today' wouldn't be of use to you in isolation, it would be of use to anyone thinking of watering their garden or painting their shed 'that day'.
It could rain heavily ... it could rain all morning ... there may just be light shower in some places ... are examples of the additional information you weren't considering?
Cheers, T i m
Prick.
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