Ed Hoffman, Publisher of The Baltimore Guide and Amateur Meterologist.
Will it rain on Sunday? There’s a chance it will.
If you’re mowing the lawn or working outside this weekend, you should get it done on Saturday. It won’t rain the entire day Sunday, but the chances increase from 20 percent in the morning to 40 percent in the afternoon that wherever you are, there will be a shower or even a thunderstorm.
Often a forecast will read “a 30 percent chance of scattered showers.” It is an odd choice of words. The chart below, from the National Weather Service, is an attempt to standardize the POP (percent of precipitation) with expressions used in verbal forecasts.
* 0% – No mention of precipitation
* 10% – No mention of precipitation, or isolated/slight chance
* 20% – Isolated/slight chance
* 30% – (Widely) scattered/chance
* 40% or 50% – Scattered/chance
* 60% or 70% – Numerous/likely
* 80%, 90% or 100% – No additional modifiers (i.e. “Showers and thunderstorms”)
That’s right they really take this stuff seriously. Next time you hear a forecast of isolated showers, don’t panic, it only means a 10% chance. These terms only apply to convective precipitation, that is, thunderstorms and showers caused by the local heating (rising air) and cooling (descending air) of the atmosphere causing condensation and rain or snow to occur. Did you ever wonder what the difference is between partly cloudy and mostly sunny? There is one, email me or visit my blog next week.
