Tuesday, May 21, 2019

Verification of Yesterday's Heavy Rainfall Forecast

This is what meteorologists are trying to prevent by advance forecasting of where floods will occur and advice like "turn around, don't drown."

Because of (tiny) controversy on Twitter yesterday pertaining to my flash flood forecast versus the NWS's and because I generally publicly validate my forecasts, here it is:
The black outline is my forecast. You'll recall it called for "Widespread 5", maximum 13inches." The darkest red color is 5 inches. The dark purple is 8 to 10 inches.

I would judge the geographic accuracy an "A." The quantitative precipitation forecast (a/k/a how much rain fell?) would be a B. I over-forecasted the maximum amount but the widespread nature of the 5+" largely compensated (e.g., the runoff would be about the same).

Here is another, perhaps better, way of judging the quality of the forecast which is, "How did it translate into river levels?"
Purple is "major flooding." With the exceptions of the Missouri River (outside the scope of this forecast) and the two gages in Reno County, Kansas, the forecast appears to be excellent.

Throughout this event, I tried to emphasize the flooding was just as important as the tornadoes. Very serious flooding is going to occur in many areas. If the Salt Fork of the Arkansas River reaches the forecast level, Interstate 35 will be closed in northern Oklahoma as an example. Please follow the advice of your local emergency managers/law enforcement if you live in one of the affected areas.

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