Air Masses and Fronts

What is an Air Mass? Air masses are large bodies of air which have similar temperature and moisture characteristics. Air masses form when air stays over a region (called the source region) for several days. Air masses that form over water will be moist. Air masses that form over land will be dry.

Latitude determines temperature Moisture determined by whether it forms over oceans or continents

c continental = dry m marine = moist A = Arctic P = Polar T = tropic

Continental Polar does not move west

Fronts – boundary that separates 2 air masses with different temperatures

Cold Front a. short-lived thunderstorms b. move faster than warm fronts

Warm Front – longer, steady precipitation

Stationary Front A stationary front occurs when the air masses on either side of the front are not moving toward each other.

Counter clockwise rotation into Low Storm moves northeast due to prevailing winds

How Mid- Latitudes Lows (occluded fronts) Form Counter- Clockwise rotation

OCCLUDED FRONT Warm air mass gets caught between 2 colder air masses and is forced aloft

Occluded Front

Winds spiral clockwise out of the High and counterclockwise into the Low Fronts are low pressure – lousy weather After the front passes – happy weather

Weather Changes after Fronts Pass 2 TOTALLY different air masses so a change in weather Temperature changes Wind direction changes Wind velocity changes Dew Point changes Barometer falls when front approaches and rises after it passes

BRRR!

WINDS FLOW COUNTERCLOCKWISE IN TO THE LOW PRESSURE SYSTEM – RISING AIR WINDS FLOW CLOCKWISE OUT OF THE HIGH PRESSURE SYSTEM – SINKING AIR

Hurricanes – counterclockwise low pressure systems (lousy weather)

Weather in a High Clockwise Rotation Bright, Clear Happy Weather

Box 9.2 LAKE EFFECT - SNOW

Thunderstorm Facts At any given time there are an estimated 2000 thunderstorms in progress, mostly in tropical and subtropical latitudes. - About 45,000 thunderstorms take place each day Annually, The U.S. experiences about 100,000 thunderstorms. About 16 million thunderstorms occur annually around the world! The lightning from these storms strikes Earth about 100 times each second

Lightning Within the thunderstorm clouds, rising and falling air causes turbulence which results in a build up of a static charge. The negative charges concentrate in the base of the cloud. This first, invisible stroke is called a stepped leader. As soon as the negative and positive parts of the stepped leader connect there is a conductive path from the cloud to the ground and the negative charges rush down it causing the visible stroke.

Tornadoes Area of quickly rotating air associated with a thunderstorm Some contain winds of over 300 miles per hour They can be as small as a hundred yards wide or larger than a mile wide

Development of a Funnel

Damage

Severe Weather Warnings Tornado, Severe Thunderstorm, and Flash Flood Warnings Severe weather is occurring If it is for your area, take shelter right away Don’t leave shelter until warning has expired

Severe Thunderstorm Warnings A thunderstorm with winds of 58 mph or greater Penny sized hail or larger Also contain lots of lightning Stay inside Keep off the phone Don’t take a shower or bath Stay away from windows

Tornado Warnings A tornado or funnel cloud has been detected Take shelter RIGHT AWAY!!! Get under something sturdy in your basement No basement? Go to a room that has no windows like a closet or bathroom In mobile homes, leave them and go to a storm shelter if available or lie flat in a ditch

Where we get data Weather Stations Radar Satellites

Doppler Radar

Next Generation Radar (Nexrad)