page_title: United States rainfall climatology
section_title: Warm season
hierarchical_section_title: United States rainfall climatology / Great Lakes / Warm season
caption_attribution_description: English: NOAA false-color image of a tornadic supercell approaching Siren, Wisconsin, USA on June 19, 2001.
context_page_description: The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Late summer and fall tropical cyclones bring precipitation which falls across the Gulf and Atlantic states. During the winter, and spring, Pacific storm systems bring Hawaii and the western United States most of their precipitation. Low pressure systems moving up the East coast bring cold season precipitation to the Mid-West and Northeast states, as well as Great Salt Lake and the Finger Lakes region. The snow to liquid ratio across the contiguous United States averages 13:1, meaning 13 inches of snow melts down to 1 inch of water.
  During the summer, the North American monsoon combined with Gulf of California and Gulf of Mexico moisture moving around the subtropical ridge in the Atlantic Ocean bring the promise of afternoon and evening air-mass thunderstorms to the southern tier of the country as well as the Great Plains.
context_section_description: Weather systems in the westerlies that cause precipitation move along jet stream, which migrates north into the region by summer.  This also increases the likelihood for severe weather to develop due to stronger upper-level divergence in its vicinity.  Mesoscale convective complexes move into the region from the Plains from late April through mid-July, with June the peak month for the western portions of the Great Lakes.  These systems contribute about 2% of the annual precipitation for the region.  Also, remnants of tropical cyclones occasionally move northward into the region, though their overall contribution to precipitation across the region is minimal.  From the spring through the summer, areas near the shores of the relatively cooler Great Lakes develop sea breezes, which lowers rainfall amounts and increases sunshine near the immediate coastline. The eastern Great Lakes are significantly drier during the summer.
caption: Satellite view of a supercell near the Great Lakes
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