These thresholds delineate two boxes in the graphic of the exceedance function: a watch box and a warning box.
Watch Guidance
Whenever the probability of the river stage exceeding the flood stage
(green line) is greater than 0.3, the frame of the watch box turns yellow.
In the example, this probability is 0.61.
Flood Watch
Whenever a flood watch has been issued by the NWS, the inside of the
watch box on the Decision Rule page turns yellow. The intensity of the
yellow signifies the degree of urgency: the closer the exceedance
function to the upper right corner of the box, the greater the probability
of flooding, and the higher the level that will be flooded with a
given probability.
Warning Guidance
Whenever the probability of the river stage exceeding the flood stage
(green line) is greater than 0.7, the frame of the warning box turns red.
In the example, this probability is 0.97.
Flood Warning
Whenever a flood warning has been issued by the NWS, the inside of the
warning box on the Decision Rule page turns red. The intensity of the red
signifies the degree of urgency: the closer the exceedance function to the
upper right corner of the box, the greater the probability of flooding,
and the higher the level that will be flooded with a given probability.
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