A weather front is a meteorological term that describes the advancement of an air mass that will soon replace the existing air mass in a particular region. This boundary between two air masses brings differences in pressure, density, temperature, and moisture. There are four categories of weather fronts — and understanding how these fronts affect the weather, especially offshore, is important for the fishing industry, shipping industry, and coastline communities.
There are four types of weather fronts defined by which type of air mass is advancing over the other. These categories are:
1. A cold front: when a cold air mass advances over the boundary of a stationary warm air mass.
2. A warm front: when a warm air mass advances over the boundary of a stationary cold air mass.
3. A stationary front: neither air mass is advancing over the other. Both air masses are stationary, and so is the front.
4. An occluded front: a cold front moves faster than a warm front, and overtakes a warm front. This happens because cold fronts move faster than warm fronts.
What determines whether a front is warm or cold? And where do these air masses form, to begin with? Weather fronts are the result of air masses, large bodies of air of similar temperature and humidity across any horizontal direction. Air masses are formed when air stagnates over a uniform surface for a significant period of time. Air masses can extend hundreds, or even thousands, of miles horizontally.
Meteorologists differentiate between continental air masses (which form over land) and maritime air masses, which originate over the ocean. Continental air masses are dry air masses; maritime air masses are moist.
Air masses change as they move around Earth. “For example, in winter an arctic air mass (very cold and dry air) can move over the ocean, picking up some warmth and moisture from the warmer ocean and becoming a maritime polar air mass (mP) - one that is still fairly cold but contains moisture,” explained the NWS.
Air masses impact offshore weather forecasts, but their effect can sometimes be difficult to understand — until now.
What do all these different factors mean for offshore weather forecasts? Understanding how air masses form and move around the planet can help the shipping industry, fishing industry, and coastal communities prepare for bad weather. Weather fronts often signal what kind of weather is coming: Cold fronts, for example, bring heavier, more dense air, which pushes under the lighter warm front.
“As the cold front passes, winds become gusty. There is a sudden drop in temperature, and also heavy rain, sometimes with hail, thunder, and lightning. Atmospheric pressure changes from falling to rising at the front,” wrote the UCAR Center for Science Education. “After a cold front moves through your area, you may notice that the temperature is cooler, the rain has stopped, and the cumulus clouds are replaced by stratus and stratocumulus clouds or clear skies.”
Rain or shine, captains don't take weather fronts lightly. On the high seas, bad weather wastes fuel, time, and money. Tracking air masses and weather fronts helps seafarers avoid storms and reduce emissions. However, even the best marine weather forecasts are hindered by insufficient marine weather data. Accurately predicting weather fronts comes down to data: we don’t have enough of it, and the data we do have is often unreliable.
Using the world's largest fleet of open-ocean sensors, Sofar Ocean's Wayfinder product assembles real-time observational weather data to produce offshore weather forecasts that are up to 50% more accurate than NOAA and ECMWF. On top of tracking weather fronts, Wayfinder evaluated over 100 million routing options based on the latest weather forecast and the user's business needs.
For more on preparing for extreme weather, visit the Sofar Ocean blog.