Weather Instruments Temperature Atmospheric Pressure Relative Humidity Wind Speed Wind Direction Amount of Precipitation Thermometer Barometer Psychrometer Anemometer Wind (Weather) Vane Rain Gauge Atmospheric Property Instrument

Temperature Measured with a thermometer. Two temperature scales: degrees Fahrenheit, °F degrees Celsius, °C Temperature Scale Conversions °C  °F °F  °C

Examples of Temperature Conversions Convert 20°C to Fahrenheit Convert 98.6°F to Celsius

Temperature Records Record High Temperatures World: El Azizia, Libya, Sept. 13, °F US:Death Valley, Calif., July 10, °F Record Low Temperatures Contiguous US: Rogers Pass, Montana, Jan. 20, °F Alaska: Prospect Creek, Alaska, Jan. 23, °F World: Vostok, Antarctica, July 21, °F Sudden Changes in Temperature (US only) Drop: Browning, Montana, Jan, 23-24, F° in 24 hrs Rise: Spearfish, SD, Jan. 22, F°In 2 minutes! 7:30am = -4°F … 7:32am = 45°F

Mercury Barometer Units:mmHginHgmillibar, mb

Aneroid (without liquid) Barometer Standard Atmospheric Sealevel 760mmHg29.9inHg1013mb

Relative Humidity How does the relative humidity change as the temperature changes? As temperature increases, Absolute Humidity increases

Consider a classroom where the number of students allowed is determined by the number of seats available. The number of seats available is determined by the temperature, one seat for each F°. Suppose we begin with the room at 80°F and 40 students present. 80 seats, 40 students…the room is 40/80 = 50% occupied. Suppose we now cool the room to 70°F, 10 seats must be removed. 70 seats, 40 students…the room is now 40/70 = 57% occupied. Suppose we now cool the room to 50°F, 20 seats must be removed. 50 seats, 40 students…the room is now 40/50 = 80% occupied. Suppose we now cool the room to 40°F, 10 seats must be removed. 40 seats, 40 students…the room is now 40/40 = 100% occupied.

From this analogy we see that as a mass of air is cooled its relative humidity increases. When the relative humidity reaches 100% we say that the air is saturated. The temperature at which the relative humidity becomes 100% is called the dew point. If the air is cooled below the dew point some of the water leaves the air by condensing back into droplets of liquid water if the dew point is above freezing or ice crystals if the dew point is below freezing. If the water droplets/ice crystals condense above the ground a cloud forms. If the droplets/ice crystals condense directly onto the ground dew/frost is formed.

Measuring Relative Humidity Dry Bulb Temperature 85°F Wet Bulb Temperature 75°F Difference in Temperatures 10F°

Relative Humidity = 62%

Dew Point = 71°F

Anemometer measures wind speed Units:

A wind vane is used to measure the direction of the wind. A wind vane turns pointing into the direction of the wind. Wind (weather) Vane

Rain (snow) Gauge Units:inches Record Rainfall:Alvin, Texas July 25-26, inches in 24 hours!