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Unformatted text preview: U .S . D E P A R T M EN T O F COM M E R C E-N O A A N A T IO N A L WE ATHE R S E R V IC E JetStream - An Online School for Weather Weather Map Symbols 77 998 5-03 71 20 A D B B E F H I B J 1 2 3 G C Along the center, the cloud types are indicated. The top symbol is the high-level cloud type followed by the mid-level cloud type. The lowest symbol represents low-level cloud over a number which tells the height of the base of that cloud (in hundreds of feet) In this example, the high level cloud is Cirrus, the mid-level cloud is Altocumulus and the low-level clouds is a cumulonimbus with a base height of 2000 feet. Cu Ci As Moderate Cu Dense Ci Dense As a/o Ns Cb no anvil Dense Ci from Cb Ac; semi- transparent Sc from Cu Ci invading sky Ac Standing Lenticularis Cs below 45 Ac invading sky Sc NOT from Cu Cs above 45; not overcast Ac from Cu St Overcast Cs Ac with As / Ns Stfra or CuFra of bad weather Cs not ovcercast; not increasing Ac congestus Cu ans Sc different heights Cc Ac of chaotic sky Cb w/anvil B 1 2 3 A In the upper left, the temperature is plotted in Fahrenheit. In this example, the temperature is 77F. On the second row, the far left number is the visibility in miles. In this example, the visibility is 5 miles. D The number at the lower left is the dewpoint temperature. The dewpoint temperature is the temperature the air would have to cool to become saturated, or in other words reach a relative humidity of 100%. H At the upper right is the atmospheric pressure reduced to mean sea level in millibars (mb) to the nearest tenth with the leading 9 or 10 omitted. In this case the pressure would be 999.8 mb. If the pressure was plotted as 024 it would be 1002.4 mb. When trying to determine whether to add a 9 or 10 use the number that will give you a value closest to 1000 mb. C C This number and symbol tell how much the pressure has changed (in tenths of millibars) in the past three hours and the trend in the change of the pressure during that same period. In this example, the pressure was steady then fell (lowered) becoming 0.3 millibars LOWER than it was three hours ago. Pressure lower than three hours ago Rising, the falling Rising, then steady; or rising, then rising more slowly Rising steadily, or unsteadily Falling or steady, then rising; or rising, then rising more quickly Steady, same as 3 hours ago Falling, then rising, same or lower than 3 hours ago Falling, then steady; or falling, then falling more slowly Falling steadily, or unsteadily Steady or rising, then falling; or falling, then falling more quickly Pressure higher than three hours ago G G These lines indicate wind direction and speed rounded to the nearest 5 knots. The longest line, extending from the sky cover plot, points in the direction that the wind is blowing FROM. Thus, in this case, the wind is blowing FROM the southeast. The shorter lines, called barbs, southeast....
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- Summer '10