DoNow Name 3-5 observations that are made for weather. (Hint: example = wind)

Weather Observations

Types of Observations Temperature Dewpoint Atmospheric Pressure Wind Speed and Direction Cloud Cover Humidity Precipitation Types/quantities

Observations Observations are taken by both weather instruments and individuals

Temperature and Dewpoint Both are measured with a thermometer that is shielded from direct sunlight Hygrothermometer Temperature around the world is recorded as oC Scientists use degrees Kelvin United States uses oF

Dewpoint (Td)

Dewpoint (Td) Air around us contains water vapor Warm air can hold more water vapor than cold air Dewpoint tells us the temperature at which the current amount of water vapor would saturate the cooler air and start to condense (form dew) on an object What is saturate?

Dewpoint (Td) If we have a little moisture in the air, we have to cool the air more to get it condense Can you think of when we see dewpoint not related to weather?

Dewpoint (Td) Soda Can A cold soda can from the fridge meets the warmer air and forms drops. Drops form on it because it is colder and cools the air coming in contact with it to below the dew point so it cannot hold the water it contains in vapor form. Water condenses out of the air and forms on the sides of the can.  Water vapor or water in the form of a gas exists in the atmosphere. If you listen to weather reports, you will hear a number called the dew point. That number is the temperature. When the temperature drops below that number, the water in the atmosphere condenses. It turns to dew. If you have a glass with ice in it, the temperature on the outside of the glass is below the dew point. When water vapor hits that glass, it turns to dew. In your case, it was a can of soda that became covered with dew. If the dew point had been below the temperature of the soda can, you would not have seen any dew form on the can of soda.

Atmospheric Pressure AKA Barometric pressure Units of pressure: Hectopascals (hPa) Millibars (mb) Inches of mercury (in Hg) NOTE: not same as pressure in other sciences (chemistry)

Atmospheric Pressure Reported values are adjusted to sea level

Wind Speed and Direction Speed measured in knots: 1 knot = 0.514 m/s 1 knot = 1.151 mph Weak hurricanes have wind speeds of over 65 knots (75 mph!) Why do we care about wind direction?

Wind Speed and Direction Help predict where a storm is heading (wind patterns) Most storms move east-west so look at weather to the east to determine if a storm may come Helpful for sailors because determines roughness of water

Clouds Cloud amounts and height Cloud type only done by sight

Humidity Amount of water vapor in the air What is the relationship between humidity and dewpoint?

Humidity and Dewpoint A high relative humidity indicates that dewpoint is closer to the current air temperature When humidity is 100%, dewpoint is equal to the current air temperature and the air is completely saturated

Humidity and Dewpoint

Precipitation Types What is precipitation?

Precipitation Types Definition – any product of the condensation of atmospheric water vapor that falls due to gravity Name 3 types of precipitation.

Precipitation Types In pairs, write one sentence to describe each type of precipitation

Precipitation Types Rain – drops of liquid that fall from clouds when water vapor condenses Diameter > 0.5 millimeters The drops become too heavy to hold so they fall Drizzle – rain with droplet diameter < 0.5 millimeters

Precipitation Types Hail – forms within thunderstorm clouds when upward air prevents frozen water pellets from falling They eventually become heavy and fall in large stone-like shapes Sleet – slush falling from sky Raindrops that freeze into ice as they fall

Precipitation Types Snow – ice crystals that form due to sublimation What is sublimation?

Precipitation Quantity Totality of fallen liquid or solid precipitation for a certain time interval Measured in mm per hour