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AOS 101

AOS 101. Weather Observation. Jan 29 (302), Jan 31 (304). Background. Observations allow meteorologists to assess the current state of the atmosphere Synchronized : taken at same time at every location Standardized : all measurements taken the same way Two main types:

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AOS 101

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  1. AOS 101 Weather Observation Jan 29 (302), Jan 31 (304)

  2. Background • Observations allow meteorologists to assess the current state of the atmosphere • Synchronized: taken at same time at every location • Standardized: all measurements taken the same way • Two main types: • SURFACE and UPPER AIR

  3. Surface Observations • Taken hourly at thousands of sites around the world • Originally was manual, but now mostly automated • Mostly at airports • Stations identified by four letter code • KMSN = Madison • KORD = Chicago O’Hare ASOS station

  4. Spaced very close together, 48 stations in Wisconsin alone = Ave. spacing of 60 km.

  5. Upper Air Observations • Radiosondes (weather balloons) measure the atmosphere aloft. • Released twice daily at the same time globally. • 6 AM and 6 PM CST • Can reach 90000 feet • 900 stations globally • 72 in the continental U.S. Radiosonde

  6. Measures temperature, moisture and wind direction/speed to attain vertical profile of atmosphere

  7. Other data types • Ships • Commercial Aircraft (ACARS) • Satellite • All this data goes into forecast models.

  8. 7 important measurements • 1. Sky Cover • How much sky do clouds cover? • Partly cloudy, mostly cloudy, etc. • 2. Current Weather • Is there precipitation falling? What type? • Is it foggy? Thunder?

  9. 3. Wind • Speed • 1 mph = 0.869 kts = 0.447 m/s • Anemometer • Direction • Measured from a direction • Either cardinal direction or degrees • Examples: 0o = N, 225o=SW • Wind vane Cup anemometer

  10. 4. Temperature • oF = (9/5 * oC) + 32; oC = (oF - 32) * 5/9 • Thermometer • 5. Air pressure • Units: hectopascals (hPa), millibars (mb) or inches of mercury (“ Hg) • hPa = mb • 1000 hPa = 29.53” Hg • Falling pressure = stormy weather is on the way (usually). • Barometer Barometer

  11. 6. Dewpoint • Related to amount of moisture (water vapor) in the air except in temperature units. • The temperature to which the air must be cooled for condensation to take place • Example: Morning Dew • If dewpoint is close to temperature (within 3o), expect fog, haze or precipitation. • 7. Visibility • How far one can see horizontally. • Clear day visibility more than 10 miles • Fog or heavy snow can cause visibilities of less than one mile

  12. 26 181 +14 3 23 Station Model • Combines all seven measurements into a readable figure

  13. N = Sky Cover • Quarters of sky that are cloud covered

  14. RAIN SNOW • ww = current weather • Symbols representing certain weather conditions • Omitted if no current weather DRIZZLE FRZ. DZ. SLEET T’STORM FOG HAZE

  15. D = Wind direction • Line (wind barb) drawn in direction wind is from.

  16. S = Wind speed (in knots) • Lines drawn at end of barb • Full line = 10 kts • Half line = 5 kts • Flag = 50 kts • Calm = circle around station

  17. TT = Temperature • In Fahrenheit • dd = Dewpoint • In Fahrenheit

  18. PPP = Pressure (in hPa) • If PPP>500, place a 9 in front of PPP and divide by 10, example 876 = 987.6 hPa • If PPP<500, place a 10 in front of PPP and divide by 10, example 181 = 1018.1 hPa • app = Pressure Tendency (in hPa) • Change in pressure over last 3 hours in tenths of hPa (ALWAYS with a + or -), also a symbol describing how it has changed (see handout).

  19. vv = Visibility (in miles) • can have a fraction • Several station models can be plotted on a map and analyzed to find fronts, high/low pressure systems, cold/warm areas, and areas of cloud cover…

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