1. 1 n Weather Maps – –We use weather maps to give us a pictorial view of the weather when dealing with large amounts of data. – –We typically report: » »Temperature » »Sea Level Pressure » »Moisture » »Winds (Speed and Direction) » »Cloud Cover » »Precipitation

2. 2 Surface Station Model n A station model is a pictorial way of representing the weather data recorded at a specific site. A simplified station model This represents the typical data reported at a station. Some stations may report more or less.

3. 3 Surface Station Model A simplified station model T = Temperature (Fahrenheit) T d = Dew Point Temperature Vis. = Visibility (miles) Wx = Present Weather Press = Sea Level Pressure Precip. = Precipitation amount (Liquid Equiv. In inches) dd = Wind Direction (degrees) ff = Wind Speed (knots)

4. 4 Surface Station Model A station model EXAMPLE Temperature = 90 F Dew Point = 68 F Visibility = 10 Miles Present Weather = Rain Shower Press = 1001.0 mb Precipitation = 0.05 inches Wind Direction = North -- 00 Degrees Wind Speed = 24 knots Cloud cover = 9/10 Clouds

5. 5 Surface Closeup At Oklahoma City (OKC) Temperature = 82 FPressure 1001.0 mb Dew Point = 64 FWeather = Partly Cloudy Winds = Southeast at 3-7 knots.

6. 6 Surface Station Model n Comments on reporting pressure – –The pressure is reported in millibars (tens, units, and tenths -- the leading 9 or 10 is omitted) reduced to seal level. Examples 1014.7 mb 986.3 mb 147 863

7. 7 Surface Station Model n Comments on reporting wind – –The direction is reported, in degrees, from where the wind comes from. Examples North WindEast Wind Southwest Wind

8. 8 Surface Station Model n Comments on reporting wind – –The speed is indicated by the barbs or pennants attached to the “arrow”. – –Half barb represents 3-7 knots – –Full barb represents 8-12 knots – –Pennant represents 50 knots Examples Calm13 - 17 Knots58 - 62 Knots

9. 9 Surface Maps -- Pressure Systems n Low Pressure – –Typical Weather: » »Cloudy » »Windy » »Warmer » »Precipitation – –Flow around a low is cyclonic (counterclockwise in the Northern Hemisphere) – –Stronger pressure gradient » »Pressure changes more rapidly over a given distance.

10. 10 Surface Maps -- Pressure Systems n High Pressure – –Typical Weather: » »Clear » »Light Winds » »Cooler » »Dry – –Flow around a low is anticyclonic (clockwise in the Northern Hemisphere) – –Weaker pressure gradient » »Pressure changes less rapidly over a given distance.

11. 11 Surface Analysis n Warm Front – –Long periods of clouds, winds, and precipitation – –Warm, moist air after frontal passage – –Occasionally produces severe weather – –Denoted by a red line with red half-circles that point toward cold air. Fronts: Boundaries between large regions of air (air masses) with differing temperature, humidity, or both.

12. 12 Surface Analysis n Cold Front – –Shorter periods of clouds, winds, and precipitation – –Cold, dry air after frontal passage – –Often produces severe weather in spring – –Denoted by a blue line with blue triangles that point toward warm air. Fronts: Boundaries between large regions of air (air masses) with differing temperature, humidity, or both.

13. 13 Surface Analysis -- 12 Jan 98 High Pressure Low Pressure Rain Fog Warm Front Cold Front Snow Isobars: Lines of Constant Pressure

14. 14 Surface Analysis -- 20 Aug 98 Image from: The Weather Channel Low Pressure Isobars: Lines of Constant Pressure Cold Front High Pressure Tropical Depression

15. 15 Upper Air Station Model n A station model is a pictorial way of representing the weather data recorded at a specific site. A simplified station model This represents the typical data reported at a station. Some stations may report more or less.

16. 16 Upper Air Station Model A simplified station model T = Temperature (Celsius) DD = Dew Point Depression Z = Height of the constant pressure surface dd = Wind Direction (degrees) ff = Wind Speed (knots)

17. 17 Upper Air Station Model A station model EXAMPLE Temperature = -21 C Dew Point Depression = 10 C Height = 5460 m Wind Direction = North -- 00 Degrees Wind Speed = 50 knots

18. 18 Upper Air Station Model n Height of pressure surfaces – –850 mb » »1100 - 1800 m » »Recorded as 100 - 800 with the leading “1” omitted – –700 mb » »2700 - 3500 m » »Recorded as 700 - 500 with the leading “2” or “3” omitted

19. 19 Upper Air Station Model n Height of pressure surfaces – –500 mb » »4700 - 6000 m » »Recorded as 470 - 600 with the trailing “0” omitted – –250 mb » »9000 - 11000 m » »Recorded as 900 - 1110 with the trailing “0” omitted

20. 20 250 mb Upper Air