It keeps happening. And it keeps killing people. If I may be blunt, it’s a highly reliable and effective killer. Looking at accident statistics, it’s the least survivable of the various flavors of general aviation weather-related aircraft accidents. Recent data from the AOPA Air Safety Institute puts the fatality rate for VFR flight into IMC at 75 percent.

Telling people, “Just don’t do it,” doesn’t seem to be working, so I have two operational tools for your consideration. The first one is to get real about the definition of marginal VFR (MVFR). Yeah, yeah, yeah, we know the “official” definition: a ceiling 1,000 and 3,000 feet and/or visibility 3 to 5 miles inclusive. But that’s beguiling. Permit me to say the same thing in another way: MVFR means that the ceiling could be one foot higher than the traffic pattern, while the visibility could be low enough that you can’t see the other side of the airport.

That said, you may be able to launch in MVFR if you know the area, have experience with low-altitude flight, and—most importantly— know that conditions won’t get worse. So how can you know that? The solution is right there in your electronic flight bag.

Pull up the weather for any airport that issues terminal area forecasts. If your departure or destination airport doesn’t issue TAFs, that’s OK, find one nearby. The kind of weather you’re after tends to be significant. Look for a forecast product called “MOS,” which stands for Model Output Statistics—a more finely tuned version of the classic TAF—that includes a gem absent from the TAF: the forecast dew point.

Every pilot should know that the closer the temperature and dew point, the lower the cloud ceiling and visibility. Now, MOS lets you not only peek at the current spread but also check the trend for your route and destination. If the forecast shows dropping dew points, flight conditions will deteriorate. If the ceiling and visibility are already at the ragged edge of safe and legal, would you launch knowing the forecast could worsen?

So be real about what MVFR is, and if you fly in it, use dew point forecasts to make sure you know which way the ceiling and visibility are going: up or down.