Saltier Seas Mean More Rain for the Midwest
By Dan Symonds. US researchers have reported that the saline content of the ocean surface provides a far more reliable indicator of whether or not heavy summer rains will fall in the US Midwest compared to sea surface temperatures.
Seasonal weather in the Midwest is atmospherically connected to the Pacific and Atlantic Oceans, with wind patterns delivering heat and moisture to the region at different times in the year. The report states that scientists have long relied on sea-surface temperatures to predict how those wind patterns will behave and what the weather will be thousands of kilometers away from the ocean.
Sea surface temperature however is highly variable, especially as oceans warm, so rainfall predictions based on temperature can be hit-or-miss. Adding data about surface salinity improves predictions for overall seasonal rainfall by telling meteorologists how much water has been supplied to the atmosphere.
When water evaporates from the ocean, it leaves its salt behind, so the surface ocean gets a little bit saltier. That evaporation is driven by large-scale atmospheric patterns that are connected to weather over the continental USA, so saltiness works as an indicator for the amount of moisture carried by the atmosphere and patterns in where it will rain out.