Excessive Rainfall Outlook Explained: Marginal, Slight, Moderate, and High Risk
How excessive rainfall outlooks describe flash flood potential, what the risk categories mean, and how to use them before heavy rain starts.
What it forecasts
The outlook is about rainfall capable of producing flash flooding, not just total rain. Terrain, soil moisture, urban drainage, and storm speed all matter.
A lower category can still produce serious flooding in a vulnerable spot.
Risk categories
Marginal and slight risks are common but still worth attention. Moderate and high risks are more serious signals that flooding may be more widespread or dangerous.
The category is a planning cue, not a guarantee of what will happen at one address.
How to use it
If your area is highlighted, avoid low-water crossings, check drainage, and plan around routes that flood easily.
At night, take flash flood warnings especially seriously because water depth is harder to judge.