Weather Observations AOS 101

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Weather ObservationsAOS 101 Section 302Ross
LazearJanuary 30, 2007
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What types of weather observations are made?
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What types of weather observations are made?

1. Temperature and Dewpoint

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What types of weather observations are made?

1. Temperature and Dewpoint

Both are measured with a thermometer in an
enclosed box, to shut out sunlight that may
contaminate the temperature. Dewpoint is the
temperature at which the water vapor in the
atmosphere condenses into liquid water. This is
why we get dew on calm, clear nights. Conversion
Tf(9/5)(Tc32) Tc(5/9)(Tf-32)
http//www.crh.noaa.gov/lot/coop/equipment.php
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What types of weather observations are made?
2. Barometric Pressure
Measured with a barometer Units hectopascals
(hPa), or millibars (mb). Also, inches of
mercury (in Hg) The barometric pressure
reported on station observations has been
adjusted to sea level.
http//www.ludolph.de/Handel20Barometer20262238.
jpeg
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What types of weather observations are made?
3. Wind Direction and Speed
Anemometer measures wind speed, and a weather
vane measures wind direction. Wind speed is
traditionally measured in knots 1 knot 0.514
m/s 1 knot 1.1507 mph A minimal hurricane has
maximum sustained winds of over 65 knots (75 mph)!
http//www.spl.org/images/branch/BAL_art/anemomete
r.jpg
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What types of weather observations are made?
4. Etc. . . . . .
http//en.wikipedia.org/wiki/Cumulus_humilis
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What types of weather observations are made?
4. Etc. . . . . .
http//www.extremeinstability.com
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What types of weather observations are made?
4. Etc. . . . . .
http//www.extremeinstability.com
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Upper air observations
Balloons with radiosondes attached are released
twice per day at 72 stations in the U.S. (900
worldwide) Measures temperature, dewpoint, wind
speed and direction and pressure as it rapidly
rises throughout the atmosphere Atmospheric
soundings are created from these observations.
These help meteorologists understand the vertical
profiles of temperature, dewpoint, etc.
http//www.gdargaud.net
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Why do we use station models?
They are concise! A very large amount of weather
data can be retrieved from a given weather
station -Temperature -Pressure -Dewpoint -Win
d direction -Wind speed -Sky condition -Weather
condition -Visibility and more!
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A sample of the continental U.S. stations
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Each station model has specific placement for
every observation taken
http//weather.cod.edu/notes/stnmodel.html
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Organization of a station model

• Temperature In U.S., expressed in degrees
  Fahrenheit. Most other countries, in degrees
  Celsius.
• Dewpoint Expressed in same units as temperature.

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Organization of a station model

• Wind Direction The line drawn represents the
  direction from which the wind is blowing.
• Wind Speed Represented as barbs on the line.
  Wind speed is measured in knots
• Short barb 5 kts
• Long barb 10 kts
• Triangle 50 kts

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Wind Barbs
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Organization of a station model

• Surface Pressure Adjusted to sea level. Units
  are in mb.
• If reported value is greater than 500, the
  initial 9 is missing. Place it on the left and
  divide by 10. Ie 827 982.7mb
• If reported value is less than 500, the initial
  10 is missing. Place it on the left and divide
  by 10. Ie 027 1002.7mb.
• Pressure Tendency Change in pressure over last
  three hours. Change in pressure is represented
  by a value and line indicating how the pressure
  was changing.

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Organization of a station model

• Cloud Cover Total cloud amount represents the
  fraction of the sky covered.

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Organization of a station model

• Visibility How far we can see from the
  observing point, expressed in units of miles.
• Present weather conditions Symbols are used to
  convey this information (rain, snow, ice, etc.).

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Now for some real life versions of these weather
observations . . .