With certainty
A 98% chance is dramatically different than a 100% certainty.
Certainty isn’t on the spectrum of chance. It’s a different thing altogether. If the weather report says the chance of precipitation is zero, one should never walk outside into the rain.
When you leave yourself a few points of wiggle room, you can build more trust. Low chance of rain is fundamentally different than a slight chance of rain.
At the same time, if it actually is certain, say so.