Ensemble Forecast System at AER
What is an ``ensemble''?
Due
to the chaotic nature of the atmosphere, very small changes to the
initial conditions of a numerical weather forecast can produce very
different outcomes in 2-10 day forecasts. An ensemble of forecasts
for a given day is generated from small perturbations to the initial
conditions. Positive and negative perturbations are applied at
locations in the atmosphere which are most sensitive to initial
condition errors. Each perturbed initial condition is used to produce
a forecast. Each forecast is called an ``ensemble member''. The
range of outcomes in the ensemble forecasts should be a reflection of
the uncertainty of the forecasts. If all members forecast similar
conditions, the ``spread'' of the ensemble members is small and the
forecast is reliable. If the members forecast a wide range of
possible weather forecasts for a given day, the spread of the ensemble
members is large and the forecast is less reliable.
How are ensemble members used to predict
average daily temperature?
TBD
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Last modified: Mon Oct 22 10:45:00 US/Eastern 2001
