blue-sky flood

The problem with the blue-sky flood is that everyone thinks the worst is over.  It has probably been raining hard for some time. People have been dealing with the turmoil of storms. Possibly a flood has already gone through and they are cleaning up from that. But the clouds have gone away, the sun has come out, the skies are blue.  What confronts them now is the mass of water that is continuing to move downstream, causing the waters to rise and floods to peak in a sequence all down the river. It may take days for the flood peak to reach a particular town, days in which the sky is blue.

In America blue-sky flooding has referred to tidal flooding along a coastline which can occur in low-lying areas during exceptional high tides. Our SES use of the term smacks of coincidental re-invention in a different context in their attempts to keep communities alert to the danger of moving flood peaks.