Weather

Weather... You can’t see me, but you feel me, you can’t touch me, but I can touch you. I have been called the “Breathe of the Gods”, or the killer and giver of life, gentle and fierce, friendly and enemy, angry and happy. The Native Americans called me Moriah, and Snow Eater (Chinook). The Japanese call me Kaze and in Russia I am called Veter. I can shatter homes, or wake a child from a peaceful sleep or bring relief in times of need. I can spread the most dreaded diseases or bring a welcome freshness. What am I?

Weather is.... The current state of the atmosphere...what is happening right now BUT… Climate is different Climate – longer time scale (the average conditions , temperature, humidity, rainfall, winds, and other meteorological elements over a long period of time

Main points to remember as we learn about weather: The sun warms the earth’s surface and therefore all the air above the surface The earth is warmed most at the equator and least at the poles---why? The air above land is warmed more quickly than air above water. Warm air expands and rises, creating an area of low pressure; cold air is dense and sinks, creating an area of high pressure

What are weather variables? Temperature Barometric (air) pressure Wind speed/ Wind Direction Humidity (Relative humidity) Precipitation

The Station Model

Weather Factors Weather: The state of the atmosphere at a specific time and place TEMPERATURE= the average motion of molecules ↑ TEMP= ↑movement of molecules= feels hot ↓ TEMP= ↓movement of molecules= feels cold

Instruments to measure weather variables Temperature Measured with a thermometer 2 common scales are Farenheit*** and Celcius

Air Pressure- the force exerted by a column of air at a given point Warm air= expanding or rising air= leaves behind L pressure Cold Air=sinking air= leaves an area of H pressure The higher the altitude… the lower the pressure

Air Pressure Units of pressure: millibars and inches of mercury Air pressure (H or L) is measured with a device called a barometer Units of pressure: millibars and inches of mercury

Air pressure rules When air pressure is noted on station model as greater than 500, we place a 9 in front of the number and a decimal point at the tenths place. Ex 506 = 950.6 mB of air pressure When the air pressure is noted as less than 500, we place a 10 in front of the number and a decimal at the tenths place Ex 467 = 1046.7 mB of air pressure

Trends in Atmospheric Pressure If the pressure is falling… stormy weather lies ahead If the pressure is rising… clear skies are coming

Wind -moving air Direction and speed are needed to describe the wind Wind direction is the direction that wind is blowing from Wind moves from High Pressure to Low Pressure Large pressure gradient= strong winds The knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph

What causes winds? A wind is a horizontal movement of air from a area of high pressure to an area of low pressure It is this difference in pressure that makes the air move=wind Winds are measured by direction and speed The anemometer is the tool we use to measure this Wind chill=↑ cooling the wind causes

Wind speed Wind speed is measured using an anemometer. Speed is measured in mph or knots (1.15 mph = 1 knot) Feathers are used to show wind speed on a station model

Wind direction Wind direction is found by using a wind vane. Wind direction is always described as the direction FROM which the wind moved

Local Winds The land cools and heats faster than the ocean. Water holds heat longer than land, and takes longer to heat or cool. SEA BREEZE During the day, the land gets hotter faster than the water. The heated air rises, leaving behind an area of low pressure. Wind from the cooler sea blows in to take the place of that warmer air. These happen during the day!

Land Breezes At night the lands cools off faster than the sea. Cool air sinks creating an area of high pressure. Wind blows from the land to the sea.

Wind Speed and Isobars Isobars- Isolines of equal pressure The larger the pressure gradient the faster the The closer the isobars the faster the wind

Coriolis deflects winds to the right in the northern hemisphere

Wind speed (con’t)

Draw the tail feather on a station model A. A 5 knot wind blows from the N B. A 10 knot wind blows from the N C. A 15 wind blows from the N D. A 20 knot wind blows from the N E. A 30 knot wind blows from the N F. A 35 Knot wind blows from the N G. Repeat A-F for a Southerly Wind, a North Easterly Wind and a South Westerly Wind

Humidity -the amount of water vapor in the air (mass of water vapor/total mass of air) The hotter the air… the more water vapor it can hold

Relative Humidity -the amount of water vapor in the air compared to what the air can hold (before the air is saturated) Relative humidity is defined as the ratio of the water vapor compared to the amount of water vapor that the water could hold. Relative humidity is expressed as a percentage High relative humidity= muggy feel or rain

Relative Humidity Relative humidity is described as the amount of water vapor in the air compared to the total it can hold. (ex. sponge) Measured with a sling psychrometer

Relative Humidity -the amount of water vapor in the air compared to what it could hold Dry air= 0% Saturated = 100% The hotter the air… the more water vapor it can hold

Dew Point -the temperature at which water vapor condenses out of the air - the temperature at which air is saturated Dew in the moring The hotter the air… the more water vapor it can hold

Dry air is more dense than moist air Humid air is less dense than dry air because a molecule of water (mass =1+1+16 ≈ 18 ) is less massive than a molecule of nitrogen (mass= 14 +14 ≈ 28) and a molecule of oxygen (16+16 ≈ 32). Pressure and Moisture also have an inverse relationship

Review As altitude, temperature and moisture increases, density and pressure decrease

Cloud Formation Clouds form when water vapor condenses on aerosols (dust, salt particles in the air) Factors needed for cloud formation… The temperature in which condensation begins is called the dew point

TYPES OF CLOUDS Cirrus Clouds: wispy, feathery clouds Form only at high levels, therefore are made of ice crystals

Types of Clouds Cumulus Clouds: are puffy white cotton ball looking clouds

Cumulonimbus Clouds These are thunderstorm clouds

Types of Clouds Stratus Clouds: clouds that form in flat layers- cover all or most of the sky and are low level clouds

Precipitation FALLING LIQUID OR SOLID WATER FROM CLOUDS (RAIN, DRIZZLE, SNOW, SLEET FREEZING RAIN, HAIL)

Precipitation A rain gauge is used to measure the amount of precipitation over a period of time

Types of precipitation Rain- Falls from clouds above Freezing and air above freezing Drizzle- Small precipitation <0.5 mm Snow- Falls from clouds below freezing and air below freezing Sleet- Falls from clouds above freezing but air below freezing Hail-up and down movement of rain in clouds multiple freezing as altitude goes up and down Freezing Rain-Hail-Falls from clouds and air above freezing but ground below freezing

Haze, Fog and Smog are NOT forms of PRECIPICATION

Problem Set 3 Identify the forms of precipiation

Reading a weather map ISOBAR= connects areas of equal pressure BAR comes from BARometric pressure

Reading a weather map... Isotherm: Connects areas of equal temperature; therm means temperature

Aim Masses & Source Regions Air Mass is an extremely large body of air whose properties of temperature and moisture content (humidity), at any given altitude, are fairly similar in any horizontal direction. Source Regions are simply geographic areas where an air mass originates. Should be: uniform surface composition - flat light surface winds

Air Mass Classification 4 general air mass classifications categorized according to the source region. polar latitudes P - located poleward of 60 degrees north and south tropical latitudes T - located within about 25 degrees of the equator continental c - located over large land masses--dry marine m - located over the oceans----moist

Types of Air Masses cP continental polar cold, dry, stable cT continental tropical hot, dry, stable air aloft--unstable surface air mP maritime polar cool, moist, and unstable mT maritime tropical warm, moist, usually unstable

Air Masses Air masses are masses of air that have the same characteristics of the surface over which it develops Pressure Systems descending (going down)=H pressure ascending (going up)=L pressure

Fronts: Fronts: the boundary between 2 air masses This is the symbol on a map for a warm front Warm Front: warm air slides over departing cold air- large bands of precipitation form

This is the symbol for a cold front Cold Fronts Cold air pushes under a warm air mass. Warm air rises quickly=narrow bands of violent storms form

This is the weather map symbol for an occluded front 2 air masses merge and force warm air between them to rise quickly. Strong winds and heavy precipitation will occur

This is the weather map symbol for a stationary front Warm or cold front stops moving. Light wind and precipitation may occur across the front boundary

Problem Set What type of weather is associated with each type of front Draw the symbol for each front

Wind blows from high pressure areas to low pressure areas

The pressure gradient and coriolis force cause low’s to spin counter clock-wise and highs to spin clockwise