The term freshet is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting. A spring freshet can sometimes last several weeks on large river systems, resulting in significant inundation of flood plains as the snowpack melts in the river's watershed. Freshets can occur with differing strength and duration depending upon the depth of the snowpack and the local average rates of warming temperatures. Deeper snowpacks which melt quickly can result in more severe flooding. Late spring melts allow for faster flooding; this is because the relatively longer days and higher solar angle allow for average melting temperatures to be reached quickly, causing snow to melt rapidly. Snowpacks at higher altitudes and in mountainous areas remain cold and tend to melt over a longer period of time and thus do not contribute to major flooding. Serious flooding from southern freshets are more often related to rain storms of large tropical weather systems rolling in from the South Atlantic or Gulf of Mexico, to add their powerful heating capacity to lesser snow packs. Tropically induced rainfall influenced quick melts can also affect snow cover to latitudes as far north as southern Canada, so long as the generally colder air mass is not blocking northward movement of low pressure systems. In the eastern part of the continent, annual freshets occur from the Canadian Taiga ranging along both sides of the Great Lakes then down through the heavily forested Appalachian mountain chain and St. Lawrence valley from Northern Maine and New Brunswick into barrier ranges in North Carolina and Tennessee. In the western part of the continent, freshets occur throughout the generally much higher elevations of the various west coast mountain ranges that extend southward down from Alaska even into the northern parts of Arizona and New Mexico. The term can also refer to the following: A flood resulting from heavy rain or a spring thaw. Whereas heavy rain often causes a flash flood, a spring thaw event is generally a more incremental process, depending upon local climate and topography. A stream, river or flood of fresh water which empties into the ocean, usually flowing through an estuary. A small stream of fresh water, irrespective of its outflow. A pool of fresh water, according to Samuel Johnson and followed in Thomas Sheridan's dictionary, but this might have been a misinterpretation on Johnson's