• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Probability of Rain Math Question

J

JDawg1536

Golden Member
If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........
 
JDawg1536 said:
If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........
Click to expand...
% chance of rain has to do with % coverage for an area.

Re-worded, the question reads: If 20% of an area is covered with rain today, 60% is covered tomorrow, and 20% is covered the third day, what is the probability it will rain over the next 3 days.

The answer is 100%, ever day. Of course another acceptable answer is meteorologists are rarely accurate so you might as well flip a coin. 😀
 
This is what I have seen over the years

20% = partly cloudy
30% = maybe it will drizzle somewhere in the town
40% = definitely will see some wet weather
50% or more = you will get some good rain
 
JDawg1536 said:
If there is a 20% chance of rain today, 60% chance tomorrow, and 20% chance of rain in two days, what is the probability it will rain over the next three days? Anyone know how to figure that out? College stats seems like 20 years ago........
Click to expand...

.8*.4*.8= 25.6% chance it won't rain. 100-25.6 = 74.4% chance it will rain over those 3 days.
 
The problem with chance of rain numbers in a forecast....those usually deal with the % of your listening / viewing area getting rain. While us mathematical types think it is talking about the odds our house will get rain.

The forecast over your house could be near 100% but an hour south of you will remain dry.
 
NoTine42 said:
The problem with chance of rain numbers in a forecast....those usually deal with the % of your listening / viewing area getting rain. While us mathematical types think it is talking about the odds our house will get rain.

The forecast over your house could be near 100% but an hour south of you will remain dry.
Click to expand...

Very true. I was just looking for the easy answer on calculating a problem like the one above, though.
 
BoomerD said:
Well...I live a short distance away from Seattle. We've had about 1.75" of "drizzle" in the past 24 hours...:whiste:
Click to expand...

That you think under 2" of rain in 24 hours is notable sort of illustrates my point. Seattle rainfall per year is only about 37"
 
I think the way they express things and how they are interpreted by the unwashed masses (dirty fuckers) is that 20% chance of rain means for a given set of conditions assumed for the day in question the last five exact days of those conditions had one day rain.

So, for the next five days in the future where they forecast 20% chance of rain you can think of one of them getting the ground wet.
 
Here's a wrench in the system. I learned from a meteorologist some time ago that forecast accuracy drops by 15% per day.
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top