2What are Fronts?A boundary between two air masses is called a __Front_________The shape of the _Front_______ depends on the density of the air masses and their speed
3When a front forms:Pressure falls when a front approaches (low pressure edges of air masses move in)Changes in wind direction occur. High pressure air moves Clockwise, low pressure air moves CounterclockwiseTemperature changes occurPrecipitation occurs and can be in the form of strong storms
4Low pressure is associated with the formation of clouds and precipitation. Warm air rises and when it reaches a certain elevation it cools and become saturated.Clouds form and when they are saturated, it precipitates
6Warm Front:Warmer air invades a cold air mass and is lifted over and replaces cooler air.Cirrus and stratus clouds are associated with warm frontsGentle rain for days, slow clearing, and rising temperatures follow
7Cold FrontCooler air invades a warm air mass and moves under the warm air and replaces itCumulus clouds and thunderstorms produce HEAVY RAIN for a short period of timeCooler temperatures andclear and fair weather invade the area once the storms have passed
8Stationary FrontOccurs when pressure differences cause a warm front or cold front to stop movingIt may remain in the SAME area for a few days.Weather conditions include light winds and precipitation across the entire frontal region.
9Occluded FrontResults from two cool air masses merging and forcing warmer air between them to riseStrong winds and heavy precipitation may occur
10How do weather systems move? Weather systems move across North America from West to East.
11Weather forecastingMaking predictions about future weather based on weather data.
12Weather Maps Provide data from stations all over the earth Help meteorologists forecast weatherData included:Temperature, air pressure, change in air pressure during the last three hours, wind speed, direction, dew point, visibility, cloud cover, cloud types and precipitation.
18Technology and Weather Forecasting Satellites photograph sections of the earth’s surface and show cloud coverage
19Air MassA large body of air that has the same properties as the surface over which it developsAn air mass over the GULF of MEXICO would be warm and moistAn air mass over CANADA would be cool and dry
20Air masses Cool and dry --> high pressure, low humidity CANADA Warm and moist --> low pressure, high humidity GULF of MEXICO
21Thunderstorms Occur inside warm moist air masses and fronts Result when warm moist air rises quickly and cools and condenses rapidlyHeavy raindrops fall, dragging air with them, creating strong windsProduced by cumulonimbus clouds
22LightningAtoms of air which are caught in the strong winds lose and gain electrons, creating cloud regions which are positively or negatively chargedCurrents flow between these regions resulting in lightning
23ThunderRapid heating and cooling of air due to lightning (rapid expanding and contracting)
24Tornado Forms along fronts Wind at different heights blows in different directions and at different speedsThis along with a strong updraft produces a rotation
25HurricanesA low pressure area develops where the ocean water is very warmTrade winds blowing in opposite directions meet causing a swirl of air that is rotatingAs moist air rises over the low pressure system, it cools and condenses and begins to descendThis pattern is repeated over and over
26Clouds - condensed water vapor Recipe for a Cloud:Water vaporCondensation nuclei (dust, smoke, ice, salt)Relative humidity of 100% - saturation point or dew point
27Types of Clouds: Stratus fair weather or precipitationLayers of sheets of clouds, can be dull gray blanket of cloudsLow altitude cloudsSee pages
28Types of Clouds: Cumulus White puffy clouds with flat basesFormed when moist air risesFair weather or thunderstormsSee pages
29Types of Clouds: Cirrus WispyHigh altitudeContain ice crystalsFair weatherSee pages