Weather Glossary


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100-year Flood A statistic that indicates the magnitude of flood which can be expected to occur on average with a frequency of once every 100 years at a given point or reach on a river. The 100-year flood is usually developed from a statistical distribution that is based on historical floods. This is also called a base flood.
100-year Flood Plain The flood plain that would be inundated in the event of a 100-year flood.
500 hPa Level of the atmosphere at which half the mass of the atmosphere lies above and half below, as measured in pressure units. This area is important for understanding surface weather, for upper air storms tend to be steered in the direction of the winds at this level and are highly correlated with surface weather.
88D Doppler Radar currently used nationwide by the National Weather Service.