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Questions About Station Plots

Q:  Why is the precipitation type displayed as "Unknown" for some stations and times?
A:  The precipitation type station forecasts are only plotted for times when GFS-LAMP is also forecasting the occurrence of precipitation (precipitation type is conditional on precipitation occurring). If the occurrence of precipitation is not being forecasted for a particular hour, the plotted precipitation type will appear as light gray for "NO PRCP." If the occurrence of precipitation is being forecasted at a station or time where the precipitation type forecast is missing, then a dark gray box will be plotted for "UNKNOWN PTYPE."

Q:  How are the flight categories defined?
A:  The flight categories represent aircraft regulations that occur under certain conditions. The following table details the ceiling height (Cig) and visibility. When one condition from two different flight categories is forecasted, the category with the highest threat level is chosen.

Flight Category Ceiling Height (Cig)   Visibility (Vis)
VLIFR Cig < 200 feet and/or Vis < 1/2 statute mile
LIFR 200 ≤ Cig < 500 feet and/or 1/2 ≤ Vis < 1 statute mile
IFR 500 ≤ Cig < 1000 feet and/or 1 ≤ Vis < 3 statute miles
MVFR 1000 ≤ Cig ≤ 3000 feet and/or 3 ≤ Vis ≤ 5 statute miles
VFR Cig > 3000 feet and/or Vis > 5 statute miles

Q:  Why can I sometimes see a station and click on it, but be unable to load its meteogram?
A:  This will happen for the new stations that have been added during the development of GFS-LAMP. A station label will display if you scroll the cursor over its location, but there will not be a plotted forecast or a corresponding meteogram. Click here for more information on the new forecast sites.

Questions About Meteograms

Q:  Why are the observations sometimes not shown?
A:  Possible explanations include:
  1. The observations are missing due to an outage at a station, a communication error, or a timing problem between receiving the observation and updating the website.
  2. The computer where GFS-LAMP runs operationally went down and the website could not update with the new observations for a period of time
  3. Some elements are not reliably observed at certain stations. For example, some sites only report at certain times of the day. Automated stations will not observe certain elements (e.g. obstruction to vision, precipitation type) if they do not have the necessary sensors or the sensors are currently not operating correctly.
Questions About Analysis Images

Q:  Why are the analysis images sometimes old?
A:  This can occur if there are no observations (see above), a computer job fails, or an image creation process fails. When this happens, the previously run images are not replaced with the most recent data. The looping controls on the analysis site will skip over these old images, but you can access these images by manually selecting them from the dropdown menu.

Forecast Quality
***These are issues that the GFS-LAMP team is aware of and working to resolve:
  • If the observed precipitation type is unknown precipitation (UP), a GFS-LAMP precipitation forecast of rain may sometims appear at an early projection when we would expect snow instead. This unexpected result is a consequence of how "unknown precipitation" reports are being dealt with in the GFS-LAMP system (both developmentally and in operationally).
  • An obstruction to vision forecast of "Blowing" can occur at a time when there is also a forecast of light winds.
  • In certain dynmaic meteorological situations (i.e. the passing of a strong cold front) the 25th projection temperature/dewpoint forecasts will steeply rise for no apparent reason. The source of this problem has been found and corrected, and these changes will be reflected in our next implemntation in April.

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Page Last Modified: September 05, 2007. 17:06  UTC