As Glenn Schwartz posted on Thursday, moisture from the remnants of Tropical Storm Bill is likely to douse the region during the weekend, when the astronomical summer arrives.
The National Weather Service has posted a flash-flood watch for the entire region from Saturday evening through Sunday evening with the potential for up to 4 inches of rain – that's about a month's worth.
As usual, expect rain totals to vary considerably from place to place. Once the weather turns warm and the more-organized storms of winter give way to showery rains, nature's caprice takes precedence.
One feature worth noting in Schwartz's forecast is the way he characterizes the precipitation probability, and we think it's something the weather service might consider.
He uses the expression "chance of rain at any one spot," which is the true definition of "precipitation probability." It means the chance of rain at any given point, rather than throughout a geographic area.
Rainfall totals in the last week constituted a clinic in the randomness of rainfall, according to the Middle Atlantic River Forecast Center's analysis of rain gauges in Philadelphia and the neighboring seven counties.
In Delaware County, a mere 0.2 inches was measured in the seven-day period that ended Thursday, or 18 percent of normal. Right next door, in New Castle County, the total was 1.1 inches, or 126 percent of normal.
Burlington, Camden, and Montgomery Counties all weighed in at way below averages, while the Bucks' total was well above.
Chances are that totals in all eight counties will be bumped up by the end of the weekend, but that's no guarantee.