# Atmospheric Moisture and Precipitation

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Atmospheric Moisture and Precipitation

More Weather _______________________- The condition of the atmosphere at a certain place and time. When talking about weather, you are actually describing what is happening in the_________________________________. Weather is constantly changing. Without the_______________________, there would be no weather!

Factors Of Weather These are the most important factors that influence weather ____________________________________

________________________
Remember the water cycle, the sun causes_________________________________, which bring moisture to the air. The amount of water vapor in the air is___________________________________. This varies from day to day. The amount of water vapor the air can hold depends on the temperature of the air.

Expressed as a _____________________:
Humidity _________________________________: compares the amount of water vapor present in the air to the maximum amount that the air can hold at that temperature Expressed as a _____________________: At 100% relative humidity, air is saturated.

Relative Humidity changes when:
Atmosphere gains or loses water vapor Evaporation Temperature changes __________________________________ relative humidity rises __________________________________ relative humidity decreases Thus, warmer air can hold more water vapor than cooler air.

_________________________
Example: If you hear a meteorologist say that the relative humidity is ________________,that means that the air on that day is only holding 50% of the water vapor is capable of holding. When air is holding all of the moisture it possibly can- that means it is said to be saturated . Thus, saturated air has 100% humidity.

Relative Humidity We are very sensitive to humidity. _____________________________________keeps our body cool and maintain its current temperature. If the air is at 90% relative humidity, ____________________________will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is_______________, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling the body.

Relative Humidity How relative humidity (RH) is measured?
Wet- and Dry Bulb__________________________ It consists of two identical _______________________thermometers, one of which has a wet cotton or linen wick around its bulb. Evaporating water from the wick absorbs heat from the thermometer bulb, causing the thermometer reading to drop. The difference between dry-bulb and wet-bulb temperatures is compared on psychrometric charts.

Relative Humidity How relative humidity (RH) is measured?
Wet- and Dry Bulb ________________ Wet - and Dry Bulb Psychrometer

Relative Humidity How relative humidity (RH) is measured?
Wet- and Dry Bulb Psychrometer Psychrometric Chart. If the difference between wet and dry bulb is 6º F and the temperature is 72º F (dry bulb), then the RH is 54%.

The “Dry Bulb” Don’t let it fool you. It is just a thermometer.
It measures the _________________temperature. Duh! 20°C

The “Wet Bulb” Has a little wet booty tied to the bottom.
Gets cool when water evaporates. 12°C Wet Booty

Dry-bulb temperature is your air temperature.
The formula for calculating Relative Humidity is as followed: ________ Temperature _ ________Temperature = Difference Between Wet and Dry Bulb Value. Then compare results on the chart First, look for the Dry Bulb Temperature on the left. Example= 20 °C

14 °C

4 °C

Subtract (the difference) between the dry bulb and wet bulb

20°C 14°C 20-14=6

18°C 16°C 18-16=2

Put it all together 20°C 8°C 20-8=12 Relative Humidity = 11%

14°C 10°C 14-10=4 Relative Humidity = 60%

Humidity ______________________: temperature at which air with a given humidity will reach saturation when cooled without changing its pressure. The dew point temperature is the ________________________for really measuring the amount of moisture in the air. It tells you the temperature in which “dew” will start to form. Meaning its saturation point.

The Dew Point Chart works the same way
14-10=4 Dew Point = 6°C

______________________
Think about the water cycle again, clouds form has humid air is cooled to its dew point and condense. The condensing water vapor forms tiny drops of water around dust particles in the atmosphere. When millions of these drops form together, a cloud forms.

________________________
Yes, there is a classification system to identify clouds. This system though, helps tell you what kind of weather is going to occur. In addition this system classifies clouds based on shape and altitude.

Cloud Types Guess What? There are actually different cloud types.
These clouds can help you determine what kind of __________________you are going to have.

Clouds Clouds are divided into categories, in fact 4 of them
______________________500-18,000 meters _____________________above 6,000 meters __________________2,000 to 6,000 meters ____________________below 2000 meters

Vertical Clouds 500-18,000 meters Two Types
____________________________________

__________________________
These are towering clouds, they spread out to top to form an anvil shape. Associated with thunderstorms, heavy rain, and hail. A.K.A “____________________________”

_______________________
Dense, _______________________clouds Associated with fair weather, but may produce precipitation.

High Clouds Above 6,000 meters ___________________________________

_______________________
*These are the ______________________clouds. *They are made of____________________, not water. They are associated with fair weather. They are thin wispy clouds. Feather – like.

Middle Clouds 2,000 to 7,000 meters
_____________________________________

Mid-Level Clouds “______________" Clouds
Clouds with the prefix "alto" are middle level clouds that have bases between 2000 and 7000 m (6500 to 23,000 ft.). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough.

Low Clouds Below 2,000 meters or below.
____________________________________ _____________________________________

_________________________
Thick layer or dark clouds that block the sun. Associated with steady precipitation.

__________________ *Thick, clouds that cover the sky.
*Associated with __________________ systems. *They bring precipitation. They act as a blanket- it keeps in_________. They are usually low level clouds.

__________________________
Fog is simply __________________clouds right next to the ground. This caused by air that is cooled to its dew point near the ground and condenses.

Fog is a cloud layer at or close to Earth’s surface
Clouds Fog is a cloud layer at or close to Earth’s surface ______________________formed when temperature of the air at ground level falls below dew point ______________________forms when warm moist air moves over a cold surface Common over oceans (“sea fog”)

__________________________
Precipitation is a step in the water cycle. It occurs when the clouds cannot hold anymore moisture. all precipitation occurs because of condensation Precipitation occurs in different forms based on the temperature of the air. _________________________ __________________________ ___________________________

___________________________________
The rain shadow effect is when on the___________________ side of a mountain/mountain chain receives a lot of precipitation due to the fact that the air ( usually rich in moisture) is forced to be lifted up the side of the mountain. As the air is cooled, it condenses, clouds form and then it rains/snows. After the air is lifted over the peak of the mountain, the air has to go down. As the air goes down, it is warmed, and the clouds break and usually ___________precipitation. Thus, on the _____________________side of the mountain, it is very dry due to little precipitation.

Orografic effects in orogens

____________________________
Hail forms when__________________of water in layers around a small nucleus of ice. Hail forms in_______________________. They grow larger as they are tossed up and down by rising and falling air currents in a storm.

_________________________!!
Coffeyville,___________________, in The largest hailstone ever documented, it weighs 0.75 kilograms (1.67 pounds), and spans 14.4 centimeters (5.67 inches).

_____________________
Sleet forms when ________________passes through a layer of warm air, melts and then ________________________near the ground. It requires a deep layer of cold air near the ground.

How Does Sleet Form?

Freezing Rain

_________________________
*It causes a glaze on objects. *Cause for most____________________. *As snow falls from the clouds, it melts ____________________________and there is a shallow layer of cold air at the surface and causes it to______________________________.

______________ *_____________________is a function of subfreezing temperatures through out the atmosphere and the surface. * It does not _____________________at all as it falls from the upper atmosphere.

LAKE-EFFECT SNOW

Overview of the Lake-Effect Process
Occurs to the____________________ of the Great Lakes during the cool season Polar/arctic air travels across a lake, picks up heat and moisture, and is destabilized.

Lake-Effect-type Phenomena in Other Regions
Lake-effect (Finger Lakes, NY) Bay-effect (Chesapeake, Delaware, Massachusetts Bays) Ocean-effect (Gulf Stream, Sea of Japan)

LAKE-EFFECT Occurs during the unstable season when mean lake temperatures exceed mean land temperatures…aka, the __________________is warmer than the land. Mean annual snowfall exceeds 100 inches in the snowbelts to the lee of the lakes, and exceeds 200 inches in the Tug Hill Plateau in New York, to the lee of Lake Ontario and on the Keweenaw Peninsula of northern Michigan, to the lee of Lake Superior. Occurs heavily in____________________________, on lee of_________________________. from Eichenlaub (1979)

Basic Concepts of Formation
The warm water provides thermal energy and moisture to the overlying cold air – remember that thermal energy transport is from warm to cold.

Basic Concepts of Formation
The rising air condenses to form precipitation, and snow falls downwind of the shore line. The greater the air-water temperature contrast, the heavier the snowfall

Review On How Lake Effect Happens.
Cold Outbreak: Frigid air flows over warm water and is warmed from below. Moisture evaporates into the air. Heavy Snow: Warmer more moist air rises downwind of the lakes and often forms heavy snow squalls.

Effect of Orography

Snow ___________________……
Sometimes lake-effect snow clouds develop enough up and down motion to create "thundersnow" - a snow storm with ________________________________________________.

__________________________
_____________________ measure air temperature. Thermometers work because matter expands when heated. Most thermometers are closed glass tubes containing liquids such as alcohol. When air around the tube heats the liquid, the liquid expands and moves up the tube. A scale that shows the temperature is on, or attached to, the tube.

__________________________
A ___________________measures air pressure. An Italian scientist named Torricelli built the first barometer in People still use mercury barometers based on Torricelli's design to measure air pressure.

Glass tube from which the air has been removed is inserted into a dish of mercury. The air pressing down on the mercury in the dish forces some of the mercury up into the glass tube. At the Earth's surface, air pressure pushes the mercury about 30 inches up into the tube - give or take close to a couple of inches.

_________________________
An instrument used for measuring the water vapor content of the atmosphere. A psychrometer measures relative humidity

Sling Psychrometer It consists of two glass thermometers containing a liquid, usually mercury. One thermometer measures the air temperature while the other one measures the wet-bulb temperatures. After the wick is dipped in distilled water, a weather observer whirls the sling psychrometer around, using the handle. As the instrument is whirled, water evaporates from the wick on the wet-bulb thermometer and cools the thermometer.

_________________________.
The lowest temperature that can be obtained by evaporating water into the air at constant pressure. The name comes from the technique of putting a wet cloth over the bulb of a mercury thermometer and then blowing air over the cloth until the water evaporates. Since evaporation takes up heat, the thermometer will cool to a lower temperature than a thermometer with a dry bulb at the same time and place. Wet bulb temperatures can be used along with the dry bulb temperature to calculate dew point or relative humidity

Sling Psychrometer

__________________________
Is an instrument that measures wind speed.

__________________________
Measures Wind Direction!!!

Combined-Wind Vane and Anemometer
Most weather stations combine these two instruments.

_______________________
The most common rain gauge used today by official forecasters and airports was invented over _________________________ years ago. it consists of a large cylinder with a funnel and a smaller measuring tube inside of it. The official rain gauge has a 50 centimeter high cylinder with a 20 centimeter in diameter funnel that collects water into a measuring tube that has exactly one-tenth the cross sectional area of the top of the funnel.

_________________________measure the upper air!!!
Weather balloons carry instrument packages called _______________________________high into the atmosphere that gather essential upper-air data needed to forecast the weather. These instruments are launched twice a day at ____________________ sites around the world. Temperature, ______________________and air pressure are measured at various altitudes and transmitted via radio waves to a receiving station. Radio navigation supplies wind speed and direction at each altitude.

Up and Away: Balloon lifts a milk carton-sized box of instruments 20 miles into the atmosphere. The Descent: The balloon pops and the radiosonde floats back to earth by a parachute. Radiosonde: Instruments in the box measure three things: _________________, _________________ and _________________