Frequently Asked Questions
|When does the NCWF forecast show the most skill?
The NCWF forecasts are based on storm extrapolation. The forecasts
are LIMITED to extrapolation of regions of existing storms.
Therefore, areas of storm initiation, growth, and decay are NOT
captured. Regions of short-lived isolated storms are often not well
forecast. Forecast skill is best for long-lived linear
multi-cellular storm systems. The quality of the forecast can be
accessed in real-time by using the "performance" option. A
complete set of documentation is available under "product
Why don't all storms have forecast?
The NCWF algorithms only provide forecasts for storms that meet
specific criteria. These criteria are primarily based on area
coverage. An elliptical filter (designed by MIT/Lincoln
Laboratories) is used to remove perishable scales. The concept is to
1) only forecast for storms that are likely to persist for an hour
and 2) not to fill an image full of small polygons that don't add
meaning to the product.
Occasionally a large storm will not contain a forecast. This may be
due to insufficient storm history (an isolated storm has to be
identified and tracked for 40 min before a forecast is shown) or a
poor motion vector. The algorithm automatically checks to make sure
that motion vector is not too fast and that the direction of motion
is reasonable. Poor motion vectors are eliminated and a nearest
neighbor motion vector is used. However, when the storm is isolated
and a nearest neighbor motion is not available then the storm will
not contain a forecast.
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