Final answer:
When the polar-front jet stream is south of a location in the Northern Hemisphere, the weather is typically colder due to the influence of frigid polar air being steered into the region.
Step-by-step explanation:
In the Northern Hemisphere, when the polar-front jet stream is south of a locality, the weather at that location is relatively cold.
The polar-front jet stream is a significant weather feature that separates the cold polar air from the warmer air of the middle latitudes. When this jet stream dips south of a particular location, it allows the frigid polar air to descend into the region, resulting in colder weather. This is because the jet stream acts as a boundary, and its position can influence weather patterns by steering cold and warm air masses.
Hence, the presence of the jet stream to the south heralds the arrival of colder conditions for areas north of its path. Conversely, when the jet stream lies to the north of a location, warmer air from the south can move in, leading to higher temperatures.