Subj : Wx Terms (#)(1)
To   : All
From : Daryl Stout
Date : Mon Jun 26 2017 12:05 am

1-2-3 Rule
A means of avoiding winds associated with a tropical cyclone by taking
into account the forecast track error of the National Weather Service
over a 10 year period which is approximately 100 nm in 24 hours, 200 nm
for 48 hours and 300 nm in 72 hours. The forecast track error is added
to the 34 knot wind radii to compute the danger area. The wind radii may
be found within Tropical Cyclone Forecast Advisory (TCM) forecasts.

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.

30-30 Rule
If you hear thunder within 30 seconds after seeing lightning, you are in
danger of being struck by lightning. If 30 minutes has elapsed since the
last time you heard thunder, you can resume normal activities.

500 hPa
Pressure surface (geopotential height) in the troposphere equivalent to
about 18,000 feet above sea level. 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,
upper air storms tend to be steered in the direction of the winds at this
level and are highly correlated with surface weather.

500 mb
Pressure surface (geopotential height) in the troposphere equivalent to
about 18,000 feet above sea level. 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,
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.



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