According to a new study from the University of Washington, many people don't understand a rainy weather forecast.
One example given is for a 20% chance of rain. Some people think it means that it will rain for twenty percent of the time, while others think it means that there will be rain for twenty percent of the area covered by the forecast.
450 Pacific Northwest college students were tested. The first experiment evaluated forecasts of either a low or a high percentage chance of precipitation accompanied by a series of icons, or "precipicons," that were visual representations of the chance of rain. The precipicons included the familiar cloud symbols used by many forecasting outlets, as well as pie charts and bar graphs. Each student only saw one icon and forecast, and filled out a questionnaire.
Two of the questions asked for how long it would rain and over what areas. Only 43 percent of the students correctly responded with the choice "can't tell from this forecast."
Those who responded incorrectly were more likely to say they'd wear a jacket or bring an umbrella, suggesting they thought it was definitely going to rain.
Full Story Here
My initial forecast for this week was off a little so here is a quick revision:
For the rest of the week, expect sunny skies, with highs in the mid to high 80s and lows in the 50s to 60s.
Here is a link to a story by NWS Ruskin. Some of the pictures are a bit funny.
UPDATE TO STORY ABOVE
To Quote a friend I sent the story to: (Easier to quote than try to give a better explanation myself, when I know I can't)
"The probability of precipititation is the probability of any particular point area within a forecast area receiving measurable precipitation in a given time period."
"The POP is determined by
two parameters: The probability that any precipitation will occur in forecast
area AND predicted areal coverage of precipitation if precipitation does occur.
Thus, areal coverage is just one aspect of POP. The chance that any measurable
precipitation will occur in the first place within the forecast area must also
be considered. When referring to POP it is most accurate to say, "There is a
___% POP that any particular measurement station in the viewing area will get
precipitation". For example, when averaged over many 30% POP days, a particular
station should have precipitation 30% of the time if the forecaster or computer
model is accurate.
For example, suppose during the course of a year that a Tampa measurement station has a 30%
POP on 100 individual days. If the POP prediction is fairly accurate over the
long term, it should have precipitated at the Tampa station on about 30 of those
days. Thus, think of POP in terms of a long term average prediction. All to
often, people assume a 20% chance of rain means 20% of forecast area will get
rain on that one day. This is often not the case for any one day. Often no
precipitation occurs at all in the forecast area on days with a 20% POP since
one component of POP is the chance that any precipitation will develop. "
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