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

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: 0 o = N, 225 o =SW –Wind vane Cup anemometer

10. 4. Temperature – o F = (9/5 * o C) + 32; o C = ( o F - 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 3 o ), 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. Station Model Combines all seven measurements into a readable figure 26 23 3 181 +14

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

14. ww = current weather –Symbols representing certain weather conditions –Omitted if no current weather RAIN SNOW DRIZZLEFRZ. DZ.SLEET T’STORMFOGHAZE

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…