A flood is not just a flood, especially if you are with the National Weather Service. Here is a breakdown of flooding situations you may encounter and the terms used to describe the advisories, watches, and warnings.
Flash flooding lives up to its name, flooding that happens in a flash. When you get very heavy rain in a short period of time you get these types of warnings issued for precise areas. What also has to be accounted for in addition to the heavy rain is what will happen to the rain once it falls. How quickly will the water be absorbed into the ground if at all. What is the area around where the rain is falling and where will all that water go. Radar can estimate the amount of rain that falls so when the National Weather Service issues a warning it is typically for a particular area that will likely be affected by the flooding. The biggest danger with a flash flood is that it happens in a very short period of time. If you are in a warned area then you need to take immediate action to protect yourself from immediate flooding. Know where to go to be safe and how to get there without traveling though any flood waters.
The urban and small stream flood advisory is issued when there is expected to be minor flooding that does not pose an immediate risk to life or property. You may have to avoid minor flooding or encounter some water ponding on roadways, but normally with this advisory it is just a nuisance and not life threatening. These advisories are often issued after a period of rain and are mostly specific to areas that typically flood or poor drainage areas.
The areal flood product is fairly new and is not to be confused with aerial (up in the air) or Arial (The Little Mermaid). When a particular area is expected to flood in at least 6 hours or later after the rainfall begins then you may find yourself in an areal flood warning. This differs from a flash flood in that the flooding will take a longer time to develop, but may still pose a serious risk to life and property. You may need to take actions but will have a period of time to prepare since this type of flooding develops over a longer time frame than a flash flood.
Finally there is river flooding or just a basic flood warning. While flash flooding and areal flooding are issued for particular areas, river flooding is issued for a particular point. Major rivers and larger creeks contain flood gauges that are monitored during periods of heavy rainfall over that river’s basin. River flooding is a much slower process and affects a particular area depending on what flood stage is predicted. What is important to note is that a river can flood with no rainfall at all. Knowing how much rain is falling over a river basin a forecast can be made for the particular river gauge downstream. This can lead to flood warnings issued days in advance for particular points. The good news is there is plenty of time to evacuate the area, the bad news is that the flooding will still occur.
