WEATHER STATION MODEL
Much information is needed to interpret what is happening with the atmosphere.
Need to condense this information in a small space
Need to show the geographic characteristics of this data
Weather maps can both display this data and summarize the patterns
Station Model--Allows the data to be plotted in a condensed and usable format
weather data are plotted either as a series of numbers or as symbols plotted on a map
From this plotted data, more accurate weather forecasts can be made.
The detailed information is coded and systematically positioned to communicate it all in a small amount of space.
The position of the station on the map is indicated by the central circle.
A name or airport abbreviation may be indicated.
Temperature is given in degrees Fahrenheit or Celsius
Dew point temperature is given in degrees Fahrenheit or Celsius
To show wind direction, a staff is rotated around the station circle
Remember, winds are identified as where they are FROM. The example above would be a west northwest wind or about 290°.
Attached to the staff are symbols to show the wind speed in miles per hour or knots. Knots are easily interpreted from the symbols.
A half staff is about 5 knots. A half staff is not at the end of the wind direction staff.
A full staff is about ten knots.
These are additive for the total amounts.
A flag is about 50 knots.
The current barometric pressure is very important.
Remember that average barometric pressure at sea level is 1013.25 millibars.
Current barometric pressure is reported to the nearest tenth of a millibar.
To conserve space, pressure is abbreviated.
Barometric pressure varies above and below 1013.25 millibars.
A range of 30 millibars includes most of the pressures routinely experienced.
If it is 30 millibars higher than average, the pressure would be 1043.25.
If it is 30 millibars lower than average, the pressure would be 983.25.
To conserve space, the leading number(s) are not printed.
To conserve space, they also do not print the decimal point and report to the nearest tenth.
If the pressure is average, it would be written as 133. No leading 10 or no decimal point.
So, from the three numbers, the value must be made to be that which is nearest to 1013.3.
Either a 9 or a 10 precedes the three digits. It is which ever makes it most realistic.
Thus, to decode the pressure value, add the decimal point before the rightmost number, and add to the front either a 9 or a 10, which ever makes the value nearest to 1013.3 millibars.
084 —> 08.4 —> 1008.4 (only 4.9 mb away from 1013.3)
962 —> 96.2 —> 996.2 (only 17.1 mb away from 1013.3)
281 —> 28.1 —> 1028.l (only 14.8 mb away from 1013.3)
875 —> 97.5 —> 997.5 (only 15.8 mb away from 1013.3)
332 —> 33.2 —> 1033.2 (only 19.9 mb away from 1013.3)
Not only is the pressure itself important, but so is the way the pressure has been changing.
So more information must be given and must be coded.
The trend tells whether the barometer NOW higher (+) or lower (-) than in the past.
The amount the pressure has changed in the past three hours is given and reported in tenths without printing the decimal point.
More detail is given by graphically depicting the pattern of the change in the past three hours.
These can be broadly decoded from the line shapes. For example, / is rising, \ is falling, and – is steady.
These can be combined to show patterns such as rising and then steady or rising a little and then falling more.
The total percentage of sky covered by clouds is graphically depicted inside the circle for the station location.
Again, these are easily generalized. No filling of the circle is clear. A vertical line in the circle adds about 10% coverage. Each quarter of the circle filled in is about 25% more coverage. Complete overcast is filled in. Sky obscured is just an X in the circle.
Cloud types tell much about the weather conditions. The cloud types are identified by symbols, and classes as high, middle, or low clouds.
How much of the sky is covered by low and middle clouds together is reported in tenths and coded with the percentage closest to the printed number.
What is the present weather is reported. This current weather is very important. A detailed set of symbols provides weather descriptions. Understanding some of the basic symbols allows general interpretation of this detailed information without reference to the coding table.
100 different symbols provide detail about the present weather.
Visibility is especially important for pilots and generally given in miles and fractions.
The past weather uses symbols that are simplistic adaptations of the current weather symbols. The basic symbols are fog, drizzle, rain, snow, showers, and thunderstorm.
The time the precipitation began (if it is current) or ended (if it is history) is coded in hours. The coding is close to the number shown. (Again, familiarity with the real coding charts are needed to completely decode these data.)
The height of the cloud base, important for pilots, is coded.
The amount of precipitation is plotted in inches to the nearest hundredth of an inch. The decimal may or may not be shown.