| Glossary and terminology |
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A brief explanation of the parameters shown in BOLAM model forecasts is given in the following: Sea Level Pressure: Contours indicate sea level pressure in hPa (or millibars). High pressure is shown in green and blue, low pressure is shown in yellow and red. Capital letters H and L denote centers of high and low pressure, respectively. High sea level pressure indicates calm weather. Low sea level pressure indicates cyclones or storms near the surface of the earth. Cloudiness: The gray shading denotes the presence of clouds. Darkest colors indicate overcast sky. 6-h Precipitation: The blue shading indicates 6-h accumulated precipitation, expressed in millimeters. In BOLAM forecasts over Greece, 3-h and 12-h accumulated precipitation is also given. 10-m wind:
Wind forecasts are shown
with barb notation. Wind
intensity is expressed
by the number and length
of barbs: one small barb
equals 2.5 m/s (or 5 knots)
one large barb equals
5 m/s (or 10 knots). A
10 m/s wind is shown with
two full barbs, a 12.5
m/s wind is shown with
two full and one half
barb and so on. Contours
indicate the wind intensity
in m/s. In the sailing
forecasts contours indicate
the wind intensity in
Beaufort scale. Snow: The blue shading in BOLAM maps indicate areas covered by snow. 850 hPa temperature: Contours indicate the air temperature at the 850 hPa level, in degrees Celsius. Temperature at this level is a very good indicator of warm and cold intrusions in the lower part of the atmosphere. The 0 °C contour line can be used as a divider between rain and snow in high terrain. Negative temperature is shown with dashed contours. 500 hPa Geopotential Height: Contours indicate the geopotential height of the 500 hPa surface, expressed in meters. Low geopotential height (compared to other locations at the same latitude) indicates the presence of a storm or trough at mid-troposphere levels. Relatively high geopotential height indicates a ridge and quiescent weather. 300 hPa Geopotential Height: Contours indicate the geopotential height of the 300 hPa surface, expressed in meters. This altitude is near the level of the core of the jet stream. The wind inside the jet stream is blowing parallel to the geopotential contour lines with the lowest heights on its left. 2-m temperature:
Shading indicates temperature
at 2-m height above ground.
Yellow and red colors
indicate high temperature,
green and blue shading
indicate low temperature. ------------------------------------------------------------------------------------------------------------------------------------ A brief explanation of the parameters shown in MM5 model forecasts is given in the following: Sea Level Pressure and cloud top temperature: Orange contours indicate sea level pressure in hPa (or millibars). High sea level pressure indicates calm weather. Low sea level pressure indicates cyclones or storms near the surface of the earth. Cloud top temperature is shown with gray shading. Light gray/white denotes high clouds while dark gray low clouds. 10-m wind: Wind forecasts are shown with barb notation. Wind intensity is expressed by the number and length of barbs: one small barb equals 2.5 m/s (or 5 knots) one large barb equals 5 m/s (or 10 knots). A 10 m/s wind is shown with two full barbs, a 12.5 m/s wind is shown with two full and one half barb and so on. Shading indicate the wind intensity in m/s (blue shading corresponds to strong surface winds). In the following example:
500 hPa Geopotential Height and sea level pressure: Shading indicate the geopotential height of the 500 hPa surface, in meters. Low geopotential height (compared to other locations at the same latitude) indicates the presence of a storm or trough at mid-troposphere levels. Relatively high geopotential height indicates a ridge and quiescent weather. White contours show sea level pressure in hPa (or millibars). 300 hPa Geopotential Height and wind speed: Green contours indicate the geopotential height of the 300 hPa surface, in meters. This altitude is near the level of the core of the jet stream, blowing parallel to the geopotential contour lines with the lowest heights on the left of the jet stream. Contours indicate the wind intensity in m/s at 300 hPa level (only values greater than 20 m/s are shown). The darkest shading corresponds to the core of jet stream. 6-h Precipitation: The blue shading indicate 6-h accumulated precipitation, expressed in millimeters. In MM5 forecasts over Athens, 2-h accumulated precipitation is presented. 2-m temperature: Shading indicates temperature at 2-m height above ground. Negative temperature is shown with dashed contours.
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