Weather by the minute

Those minute-by-minute forecast apps have become hot products in the weather marketplace, promising users exact starting and stopping times for precipitation for any location.

"It's really been changing the way in which people consume weather," said Jon Porter, a meteorologist and vice president at AccuWeather, who helped develop the AccuWeather version.

After acquiring Canadian minute-caster Sky Motion in late 2013, AccuWeather entered the market in a huge way, expanding the service to 13 countries.

The level of specificity of the two-hour forecasts, available on smart phones and computers, is astonishing, down to the minute, down to the street address.

The forecasts rely heavily on radar and what Porter describes as "a very sophisticated image analysis processing … that allows us to capture changes in precipitation."

We find it fascinating to monitor, to watch technology match wits with the atmosphere. But given the chaos of the atmosphere, be aware that the technology has its limits and that the meteorologists -- and AccuWeather has many excellent ones -- don't write the promo material.

What's more, the forecasts are moving targets, changing constantly. To paraphrase Mark Twain's famous observation, if you don't like the weather forecast, wait a few minutes.

If you decide to mow the lawn because the forecast says rain will hold off for an hour, by the time you start the mower, the forecast might have been updated two or three times. For that matter, it might even be raining.

"As with any product or service, if you use it properly, it has value, but it doesn't come with a user's manual," observed Penn State's Jon Nese, former meteorologist at the Franklin Institute and a Weather Channel alumnus.

We gave AccuWeather's a test-drive on July Fourth when we had to make life-changing decisions, such as when it was safe to take a walk, or when to fire up the grill.

We were impressed that it latched on to the general idea of the episodic nature of the precipitation and the short duration of the showers. However, the stop-and-start times kept changing with the updates.

At 1:51 p.m., for example, we were informed the rain would stop at our house in 13 minutes, so we viewed this as our window of walking opportunity. However, at 2:07 it was still raining, and the updated forecast said we'd have to wait 10 more minutes.

One thing that gave us pause was the fact that it was having some trouble with the "now." At 6:38 p.m., it said it was pouring rain at our house; it was raining only lightly.

At one point earlier in the afternoon, it said was raining when it wasn`t, at another point, not raining when it was.

"If an app can't get the current weather correct at my house, I have little faith in its predictions of future weather," said Nese.

"This is a forecast," said Porter, as opposed to direct, ground-truth observation. While the concept of a forecast for "now" might appear to challenge existential bounds, it isn't as though AccuWeather or anyone else could tell you precisely what is happening at any given moment at any given point in 13 countries.

We will keep watch. In fact, this afternoon is looking like a perfect time to see how the Minutecast is faring.

If you don't have the smart-phone app, just click here and plug in your home or work address, and keep score.