Upwind lakes do not always lead to an increase of precipitation downwind. Vorticity advection aloft and large upscale ascent help increase mixing and the convective depth, while cold air advection lowers the temperature and increases instability. Typically lake-effect precipitation will increase with elevation to the lee of the lake as topographic forcing squeezes out precipitation and dries out the squall much faster. As a lake gradually freezes over, its ability to produce lake-effect precipitation decreases for two reasons. Firstly, the open ice-free liquid surface area of the lake shrinks. This reduces fetch distances. Secondly, the water temperature nears freezing, reducing overall latent heat energy available to produce squalls. To end the production of lake-effect precipitation, a complete freeze is often not necessary. Even when precipitation is not produced, cold air passing over warmer water may produce cloud cover. Fast moving mid-latitude cyclones, known as Alberta clippers, often cross the Great Lakes. After the passage of a cold front, winds tend to switch to the northwest, and a frequent pattern is for a long-lasting low-pressure area to form over the Canadian Maritimes, which may pull cold northwestern air across the Great Lakes for a week or more, commonly identified with the negative phase of the North Atlantic Oscillation (NAO). Since the prevailing winter winds tend to be colder than the water for much of the winter, the southeastern shores of the lakes are almost constantly overcast, leading to the use of the term "The Great Gray Funk" as a synonym for winter. These areas allegedly contain populations that suffer from high rates of seasonal affective disorder, a type of psychological depression thought to be caused by lack of light. Cold winds in the winter typically prevail from the northwest in the Great Lakes region, producing the most dramatic lake-effect snowfalls on the southern and eastern shores of the Great Lakes. This lake effect results in much greater snowfall amounts on the southern and eastern shores compared to the northern and western shores of the Great Lakes. The most affected areas include the Upper Peninsula of Michigan, Central New York, Western New York, Northwestern Pennsylvania, Northeastern Ohio, southwestern Ontario and central Ontario, Northeastern Illinois (along the shoreline of Lake Michigan), northwestern and north central Indiana (mostly between Gary and Elkhart), northern Wisconsin (near Lake Superior), and West Michigan. Tug Hill in New York's North Country region has the 2nd most snow amounts of any non-mountainous location within the continental U.S., only trailing the Upper Peninsula, which can average over of snow per year.