James WX Blog: Why flood warnings persist even though lake levels dropping

The NWS Buffalo has issued yet another Lake Ontario flood warning for Wayne County.

Currently the water level sits at 248.13’ and continues to drop. It has dropped at a significant pace over the past two months due to very high outflows. Unfortunately it is still at very high levels and that’s why we’ve got the warnings. Winds 20-30 mph will create waves 5+ feet at times that could cause erosion.

Check this out. This graph above represents outflow of Lake Ontario. The blue line represents this year and it’s at maximum flow for just as long as it was in 2017, about two months. According to IJC reports it will remain there through the rest of the month. This is about 366,900 cubic feet per second. Outflow is at the Moses-Saunders dam on the St. Lawrence well upstream.  Any higher and it would jeopardize shipping lanes and cost millions in trade. According to analysis done by the commission of both US and Canadian scientists, increasing flow much higher than this wouldn’t have much more of a significant impact on lake levels compared to the damage it would do to trade.

Above is net total supply into Lake Ontario. This is 80% what comes over Niagara falls from Lake Erie (PS Lake Erie was at record highs as well as many of the other lakes) as well as creeks, streams, rivers, and tributaries. For over a month through April, May, and June the flow into Lake Ontario was well above the maximum outflow.

Above is the forecast. A few things to note here. One is that we’ve been above the 2017 levels since mid May and might remain above those levels until the end of the year. Also note the dotted/dashed grey line that represents “Criterion H14 thresholds.” The water levels are normally between these two lines and Plan 2014 is used to regulate the levels. Once the level gets outside this mark (above or below) then Plan 2014 is “scrapped” for the time being and focus is getting the water levels where they need to be (up or down). Levels were regulated regardless of Plan starting in mid-May and continue to be that way until the forecast levels drop below the high criterion in early November. 

NOTE: According to the Army Corps of Engineers, Lake Ontario water levels are expected to drop by about a foot in one month’s time.

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