Forecasting a trough is just like drafting a top football prospect to join your NFL team; there’s no guarantee that the player will turn out to be a star, but the probability is in your favor. In other words, you want to get the best players on your team so that your chance for success increases. And forecasting a trough increases our chances of seeing colder air and snow.
When meteorologists talk of “troughs” and “ridges”, they’re talking about the general storm track and the chances for precipitation. A ridge occurs when the storm track bulges north away from the equator, and this usually brings dry weather and warmer air. The opposite pattern is called a trough, which occurs when the storm track dips south and often brings cooler weather with more precipitation.
Looking at the forecast for the U.S. over the next week-plus, most computer models agree that we’ll see a trough develop over the country. Check out the lines dipping down (toward the south) across the U.S. in the graphic below. This is the broad trough that we’re talking about, and it might just make several skiers and riders quite happy across the country.
The longer-range weather forecast models show a dip in the storm track for most of the U.S. This is called a trough, and it should keep the nation colder—and with a better chance of snow—than we’ve seen in recent weeks.
Of course there are always caveats in every weather forecast, and this one relates to our analogy of drafting that promising player without the guarantee that he’ll turn into a star. In the same way, forecasting a trough gives us a great chance of seeing a lot of snow and colder air over the next week or two, but it’s no guarantee that all mountains will get dumped on. Within this broad trough—which might stretch from coast-to-coast—there will be individual storms that move across the country, roughly following the lines on the graphic. And I say ‘roughly following’ because each storm will take a slightly different path, and the details of this path will determine who gets snow and who doesn’t.
Long-range forecasts cannot confidently predict powder days or even the location of the heaviest snow. But with the forecast of a trough, it does look like we’re about to draft that great prospect. So here’s hoping that this player (or trough) turns into a snowy superstar over the coming weeks.
Check out this episode of Snow Science for more information about long-range forecasting and why it's not always correct.
Meteorologist Joel Gratz is the creator of opensnow.com and is based in Boulder, Colo.