Winters in Western New York are generally cloudy, cold and snowy...but are changeable and include frequent thaws and rain as well. Snow covers the ground more often than not from Christmas into early March, but periods of bare ground are not uncommon. Over half of the annual snowfall comes from the "lake-effect" process and is very localized. Lake-effect snow occurs when cold air crosses the relatively warm lake waters and becomes saturated, creating clouds and precipitation downwind. The location of these snowbands is determined by the direction of the wind. Due to the prevailing winds, areas south of Buffalo receive much more lake-effect snow than locations to the north. The lake snow machine can start as early as mid November, peaks in December, then virtually shuts down after Lake Erie freezes in mid to late January. The area does not experience many heavy general (synoptic scale) snows, because large scale storm systems usually pass well to the east.
Spring comes slowly to the Buffalo area. The ice pack on Lake Erie does not usually disappear until mid April and the lake remains chilly through most of May. As the prevailing flow is southwesterly, areas near the lake are often as much as 20 degrees colder than inland locations. Fortunately, the cool lake waters act as a strong stabilizing influence, so areas near the lake shore, including the city of Buffalo, experience more sunshine and fewer thunderstorms than inland areas. The cool air from the lake also retards the growing season, but this diminishes the threat of damaging late spring frosts. The average date of the last frost is near the end of April in the Buffalo metro area, but in mid May well inland.
Summer is pleasant in the Buffalo area. Sunshine is plentiful, temperatures are warm, and humidity levels are moderate. Rainfall is adequate, but it shows an overnight maximum, so it is seldom a problem for outdoor activities. The stabilizing effect of Lake Erie continues to inhibit thunderstorms and enhance sunshine in the immediate Buffalo area through most of July. The lake also modifies the extreme heat that approaches from the Ohio Valley. There usually are periods of uncomfortably warm and humid weather during summer, but an average of only three 90 degree readings makes conditions more bearable than at most other locations. August usually turns a bit more showery and humid as the lake is warmer and loses its stabilizing influence. In fact, a good nighttime thunderstorm or two is often a feature of late summer in Buffalo. Overall though, Buffalo has the sunniest and driest summers of any major city in the Northeast, with enough rain to keep vegetation green and lush.
Autumn on the Niagara Frontier is pleasant, but rather brief. September is usually quite tame, as is much of October. The first frost can be expected in late September over interior sections, but not until mid October in the Buffalo metro area. During some years, the warm Lake Erie water can extend the growing season into early November adjacent to the lake shore. Cold fronts from Canada become common in late October, and as the cold air passes over the warmer Great lakes, cloud cover increases drastically. This heralds the start of the Lake-Effect season. The first measurable snow usually occurs in mid November, but snow cover is sporadic until mid December. However, many of Buffalo's greatest snowstorms have occurred in late November and early December, due to the lake-effect phenomenon.