On Saturday, November 8, 1457, a low pressure weather system formed in the southwestern portion of Equestria; its edge rangeing from Ponyville, across Filledelphia to Canterlot. The system moved eastward at a steady pace, pulling with it cold air from the Rocky Mountains. As it moved over Appleoosa, its air rotating counterclockwise, the system pulled in moisture from the Southern Sea and warm air from Las Pegasus. Storm Clouds formed and the Equstria Weather Service predicted rain.
On that same day, a low pressure system in Stalliongrad began moving eastward across the southern edges of the Snowy Wastes and the northern third of Equestria. The system pulled frigid arctic air in its wake, setting off forecasts for snow in the north central part of Equestria.
Such weather patterns are not uncommon during the "transition month" of November, when Jet Streams and upper-air patterns create strong and sometimes unpredictable weather systems. By the time the low-pressure system in southern Equestria had reached the center of the country, at seven o'clock on the morning of November 9, the Equestria Weather Service was confident in forecasting "a typical November storm" for much of Central Equestria and the upper Great Lakes. The storm would move north and east at a rapid pace, pass over Lake Celestia, and wind up in Starswirl Bay. The Griffin system continued its eastward trek, bringing down more cold air from the Wastes. The Equestria Weather Service kept a close watch on this system, concerned about what might happen if it slammed into the system moving up from the southwest.
There really wasn't much room for speculation. History dictated the forecast: in the vernacular, if the two systems met, all hell was going to break loose.
A/N My first shot at a seafaring tale. In this story, Equestria is shaped like North America. Las Pegasus is where Las Vegas would be, Ponyville is on the Great Plains, etc.