OGIMET

Versión española

Meteosat-9/metar

GFS world weather maps

Summary

• About the data
• Synop reports
• Metar reports
• Taf reports
• Meteorological parameter used
• Temperature
• Maximum temperature
• Minimum temperature
• Daily mean temperature
• Dew point temperature
• Heat index / Wind chill
• Relative humidity
• Air pressure
• Precipitation amount
• metar's color
• About forecast maps
• Surface maps
• 850 Hp maps
• 500 Hp maps

1.- About the data

Database at Ogimet stores alphanumeric meteorological reports, i.e. alphanumeric text data, no graphic formats. Most important of them are synop reports and metar reports. These reports are from meteorological services around the whole world. They are released using specific lines for international interchange proposes. Remember that weather don't know about country borders. Some servers or Institutions in the Internet, most remarkable NOAA, selects a subset of free data and made it available in the Net. Ogimet collects these reports and use them to display the data in a easy and professional way

About forecast maps, Ogimet downloads a selection of data from GFS (Global Forecast System). Data are in grib format. Then some maps are plotted. Ogimet plots maps daily from 00 and 12 UTC runs. The maps cover all the world, some areas more detailed. They became available about 8 hours after initial model run time, (about 08 and 20 UTC)

2.10.- Metar's color

Metar's color is a color which intend to give an easy whole code about horizontal visibilty and cloud ceil in a station or airport. Horizontal visibility is the distance from where certain objects and bodies are visible. Cloud ceil ia an aeronautical term that means the level over ground with more than half sky covered by clouds. In other words, a plane flying over the cloud ceil will see less than half ground surface. Cloud ceil term is different to cloud top, which is the top level of a cloud layer

Then, taking into account horizontal visibility and cloud ceil, the color is assigned to an airport according with the following rules

• Blue. Visibility greater or equal to 8000 meters and ceiling equal or over 2500 feets.
• White. Visibility greater or equal to 5000 meters and ceiling equal or over 1500 feets, not being blue
• Green. Visibility greater or equal to 3700 meters and ceiling equal or over 700 feets, not being white or blue
• Yellow. Visibility greater or equal to 1600 meters and ceiling equal or over 300 feets, not being blue, white or green
• Amber. Visibility greater or equal to 800 meters and ceiling equal or over 200 feets, not being blue, white, green or yelow
• Red. Visibility less than 800 meters or cloud ceil below 200 feets
• Black. Closed by meteorological reasons not visibility nor cloud ceil, as example because of snow over the railway

3.- About forecast maps

As commented above, basic data is in grib format. It is downloaded from nomad3 server at NOAA. This format stores the results of meterorological fields in a very compact and efficient way. This fields in grib format are contourned and plotted with de aid some free packages, as GMT, the one used at Ogimet. Currently, there are three kinds of maps at ogimet. Projection used is orthographic. There are generic maps for Polar, Medium Latitude and equatorial zones. They covers all the world. Some specific zones are plotted with some more details. You can ask for some zone to be included freely in the named zones

3.1.- Surface maps

In this kind of map, there are plotted 5 fields or meteorological variables:

• First is the air Pressure contour at mean sea level, units in HectoPascal (Hpa) or millibar (mb). Solid black line, at 2 or 4 Hpa interval, depending on resolution, former for named zones
• The thickness of air layer between 500 and 1000 Hpa is contourned with discontinued color lines. It is a way to visualize the mean temperature of about the half lower part of atmosphere (first 5.5 Km over sea level). Lower thickness are lower temperature. A 60 meters thickness increment is about 3 °C mean 500-1000 Hpa layer temperature rise. The thickness unit is geopotential decameter. A geopotential meter is almost a geographic meter, just a constant gravity is take to compute the potential energy. It can be take as standard meter for practical proposes. Standard atmosphere thickness for 500-1000 layer is 5520 m. This thickness is marked with a solid blue line. Lesser thickness, lower than normal temperatures, otherwise higher.
• Cloud cover. It is ploted the cloud cover in grey scale when it is over 50%. Cloud cover plotted summarizes the cloud during 6 prevous hours. You can check the cover amount with the aid of lateral scale.
• 6 hours precipitaction amount. When the forecasted precipitaction during previous 6 hours is over 0,2 mm, it is plotted the area according with the color scale you can see at the right of plot. It overplots the cloud field. The zones where the expected precipitation is snow are aditional contourned with a light red line
• In named zones, the 10 m over ground level wind is plotted. For clarity proposes, only winds over 15 Knots are plotted. Isotachs lines (lines with the same wind intensity) are contoured with dashed dark line, every 15 kts. The size of wind sticks are proportional to the intensity. You can see the size of a 50 Kts wind stick in the lower right conner of the map

3.1.- 850 Hp maps

Here, 3 meteorological variables are plotted. First one is geopotencial (altitude) of the 850 Hpa Pressure Surface. Units are geopotential Decameters (see prior paragraph about geopotential units). They are plotted at 6 ó 3 Dm intervals with a solid white line, depending on the scale of maps, the former for named zones. This is the Flight level 050 (FL050). Lower geopotential is the same that would be lower pressure at sea level. When the wind intensity is over 20 Knots threshold, it is plotted with sticks sized depending of the intensity of wind. You can see the size reference in the right of map area. Finally, the temperature at this pressure surface is plotted with colors according to the lateral scale. The temperature contour lines are black dashed lines

3.1.- 500 Hp maps

The interpretation of this kind of maps is the same that the 850 Hp ones. This is now the 500 Hpa Pressure surface, or the Flight Level 180 (FL180). The wind threshold is 30 Knots