Anyone who’s planned a serious cross-country knows not to pay attention to any weather forecast until about 12 hours before the flight, not to take any forecast seriously until 2 hours before the flight, and not to rely on a forecast, ever. Nevertheless, we have to plan flights days or weeks in advance, and passengers want to know if we’ll be able to make a trip.

The regular, public forecasts have limited value for aviation. We need to know where the pressure systems and fronts will (supposedly) be, and what kind of moisture and winds we’ll be facing. The 48-hour U.S. prog charts (which also cover southern Canada) are a common stop, since they’re a lot easier for lay people to interpret than the Environment Canada GEM.

A 48-hour weather forecast is very likely to be completely wrong, but still, many pilots would like to torture themselves by looking even further ahead. For us, there is good (??) news: Unisys publishes U.S. (and southern Canadian) prog charts up to 5 days (yes, that’s 120 hours) ahead, not just for the surface but for higher altitudes like 700 mb (~10,000 feet) and 500 mb (~18,000 feet), with winds. So now you can agonize for five days about your flight — just don’t try to decide until two hours before, because the forecast will probably change.