Description of Surface Observations of Visibility Reducing Weather
Synoptic surface weather reports are operationally received and decoded at
the Fleet Numerical Meteorological and Oceanographic Center (FNMOC) and the Naval Research
Laboratory (NRL) in Monterey, CA. These observations contain information about
aerosols, either directly (eg. Current and past weather) or indirectly (eg. horizontal
visibility). We have developed a
old station model, used previous to October 24, 2004
for plotting these observations that
highlights areas where visibility has been degraded by aerosols.
The convention results in aerosol-affected areas appearing cyan, precipitation-affected
areas appearing green, and other areas appearing either red (no interesting weather) or blue
We estimate extinction based on the surface weather parameters.
When the necessary parameters are available at a station, the extinction is calculated and
displayed using a circle with a diameter proportional to the extinction. So a large circle means
high extincion, or low visibility. The color of the circle is chosen using the same convention
as for the current weather [see above].
Conficts occur when visibility is low (plotted in cyan) in the
presence of precipitation (plotted as green). In these cases the reduced visibility
is most likely due to the precipitation. Coding and decoding errors can produce
unexpected results: Give low confidence to a single station and high confidence
to an area where many stations are reporting similar weather. Decoding errors also
occur for the current weather received from automated stations. We presently do not
have the information to discern one from the other and assume a manual station as
the default. If the station were an automated one, then the wrong table is used.
For example, a report of fog from an automated station in Sweden will be decoded
as dust. These uncertainties and errors will be eliminated in the future.