Surely the Current Weather Forecast is Wrong!

RedRedemption · Apr 13, 2015

solid said: ↑

I live in Eastern Texas, and our weather forecast is for seven days and seven nights of "thunderstorms." Most days and nights have a 80% or higher chance. I just don't see the weather maps supporting that. Your forecast in Houston is very similar. What do your "weather guys" think?
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What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?
The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.
How do forecasters arrive at this value?
Mathematically, PoP is defined as follows: PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.
So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)
But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )
In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.
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http://www.srh.noaa.gov/ffc/?n=pop

Say what you will about the forecaster being right or wrong, but they aren't just flat out lying to you on TV. :grin:

solid · Apr 13, 2015

The forecasts are starting to back off the "great flood" prediction. Sunny all day today up here with a 90% chance of rain. Didn't happen.

SmeggySmeg · Apr 14, 2015

loads of rain this morning, got drenched on my run with Behad

solid · Apr 14, 2015

Another essentially clear day where I live. Their predictions are off. I couldn't understand what weather dynamics they were looking at.

Rocketman95 · Apr 15, 2015

solid said: ↑

Another essentially clear day where I live. Their predictions are off. I couldn't understand what weather dynamics they were looking at.
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Most of Houston got drenched yesterday.

PhiSlammaJamma · Apr 15, 2015

Guys, we need to sign free agents. Hush.

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Surely the Current Weather Forecast is Wrong!

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