Presentation on theme: "Weather Elements Know basic facts and general principles of the elements of weather. 1. Identify types of clouds. 2. Identify types of air masses and fronts."— Presentation transcript:
1Weather ElementsKnow basic facts and general principles of the elements of weather.1. Identify types of clouds.2. Identify types of air masses and fronts.3. Describe terrain factors that affect weather.4. Describe types of turbulence.5. Identify normal weather patterns.Lesson Objective: Know basic facts and general principles of the elements of weather.Samples of Behavior/Main Points:1. Identify the types of clouds.2. Identify the types of air masses and fronts.3. Describe terrain factors that affect weather.4. Describe the types of turbulence.5. Identify normal weather patterns.
2Overview 1. Clouds 2. Air Masses and Fronts 3. Terrain Factors 4. Turbulence5. Normal Weather PatternsOVERVIEW: In this lesson we will discuss:1. Clouds2. Air Masses and Fronts3. Terrain Factors4. Turbulence5. Normal Weather Patterns
3Types of CloudsClouds-The three general types of clouds are cumulus, stratus, and cirrus. All other types come from these three and are usually referred to as low, middle, and high.
4Low Clouds Stratus Sheet - like cloud. No turbulence. May be risen fog.Light drizzle or snow.Close to Earth’s surface.Can hide danger.Low - Beginning at the lower altitudes, between 300 and 6,500 feet.StratusLow, gray, uniform, sheet-like cloud with a smooth appearance.Indicates accurately to aviators that no turbulence is associated with the cloud.May be fog that has developed and risen a few hundred or so feet above the Earth's surface.If precipitation does occur, it will be a light drizzle or in the form of snow grains during the wintertime.A simple stratus produces little precipitation because it is relatively thin. A cloud must be at least 4,000 feet thick to produce significant precipitation.Can cause problems to aviators because it can lie close enough to the Earth's surface that it could close airports to aircraft and pilots who are not equipped and/or qualified to penetrate such cloud formations.Can hide the fact that pilots are flying into or toward unfavorable or dangerous situations.
5Low Clouds Stratocumulus Rolls or global masses. Bulbous protrusions. Heavy rain and snowVarying turbulence.Masks higher severe cloud buildups.StratocumulusGray or blue, individual rolls or global masses with similar layering characteristics as stratus clouds.Has bulbous protrusions on the upper side and usually is rather thick.Heavier rains and snow can be expected from this type of cloud.Turbulence of varying intensity can also be expected near the base of the layer.To aviators the appearance of stratocumulus ahead is a warning that flight under the formation most likely will encounter "zero-zero" visibility and probably strong turbulence.The stratocumulus can mask higher and more severe cloud buildups.
6Low Clouds Cumulonimbus Vertical growth group. Top has anvil shape. High winds, snow, hail, rain, lightning, and tornadoes.Extreme turbulence.CumulonimbusBelonging to the clouds with vertical growth group and is also known as thunderstorm clouds.Can grow to heights that reach the tropopause. At these heights, the top of the cloud is flattened out into an anvil shape by high winds.High winds, snow, hail, rain, lightning, and tornadoes are associated with these clouds.Storms developed in this cloud are more likely to occur in the afternoon and early evening because of the effects of the Sun's heating.The chief danger it offers all aircraft, particularly light aircraft, is extreme turbulence inside the cloud.
7Low Clouds Nimbostratus Shapeless, low-level, moderate precipitation. Fog and precipitation found beneath.Visibility restricted.Calm to light winds.NimbostratusDark gray, thick, shapeless, low-level clouds that produce light to moderate falling precipitation including ice particles and snow if temperatures are cold enough.The Sun and Moon are not visible through the cloud.Fog and precipitation are found beneath and around the cloud causing the determination of the base to be difficult.Visibility is greatly restricted by the precipitation.Calm to light surface winds are associated with the nimbostratus cloud.
8Middle Clouds Altostratus Relatively thin. Sun may be seen through veil.Ice crystals and super-cooled water.Light precipitation.Poor surface visibility.Middle - Starting at 6,500 feet and extending to 20,000 feet, the stratus and cumulus shapes are found, but at this altitude they are known as altostratus and altocumulus.AltostratusThe simple altostratus usually is relatively thin.It produces a gray or blue veil through with the Sun may be dimly seen.Due to its altitude, its condensate may be ice crystals and super-cooled water.If precipitation is produced, it will be very light.Usually associated with poor surface visibility with smooth air and moderate surface winds.
9Middle Clouds Altocumulus Wavy solid clouds with rounded outline. Light intermittent rain or snow.Commonly followed by thunderstorms.Poor visibility and moderate surface winds.AltocumulusWhite or gray layers, rolls or patches of wavy solid clouds with a rounded outline.Normally produces light intermittent rain or snow.The presence of altocumulus clouds on a warm humid morning is common followed by a thunderstorm late in the day.Turbulence is normally found in the altocumulus cloud with generally good surface visibility.
10High Clouds Cirrus Thin feathery clouds. No precipitation. Sign of approaching bad weather.High - Found at 20,000 feet and higher, cirrus, cirrostratus, and cirrocumulus types of clouds appear.CirrusWhite, thin feathery clouds found in patches or bands. They are commonly called "mares' tails."Precipitation doesn't fall from these clouds because of the high altitude.Usually a sign of approaching bad weather.
11High Clouds Cirrostratus Thin, resembles a sheet or veil. No precipitation.Nearly transparent.Often sign of approaching bad weather.CirrostratusWhite; thin cloud layers that resemble a sheet or veil.Precipitation doesn't fall from these clouds because of the high altitude.Because of the thin surface (nearly transparent) the Sun/Moon can easily be seen through them.Often a sign of approaching bad weather; surface winds bring overcast skies.
12High Clouds Cirrocumulus Thin clouds. Indicates high-level instability.Similar to cirrostratus but they have a slightly “bumpy” appearance.CirrocumulusThin clouds in sheets; individual elements look like tufts of cotton.Indicates high-level instability.Similar to cirrostratus but have a slightly "bumpy” appearance.
13Fracto and Lenticular Fracto Lenticular Broken and/or ragged. Cumulus fractos.LenticularLens-like shape.Tells turbulence, visibility, precipitation.Fracto and LenticularAnother term associated with the various cloud types is "fracto". Meaning "broken and /or ragged".Combine fracto with stratus to describe a broken stratus layer, fracto-stratus.There is a special type of cloud, which frequently forms as strong winds sweep up and over the tops of high mountains.It is called a lenticular formation and its name is the result of its lens-like shape.A lenticular can, and does, form over areas other than mountain areas.These clouds tell what can be expected with regard to turbulence, visibility and precipitation.Fracto and LenticularAnother term associated with the various cloud types is “fracto”. Meaning “broken and/or ragged”.Combine fracto with stratus to describe a broken stratus layer – fracto stratus.There is a special type of cloud, which frequently forms as strong winds, sweeps up and over the tops of high mountains.It is called a lenticular formation and its name is the result of its lens-like shape.A lenticular cloud can form over areas other than mountain areas.These clouds indicate what can be expected with regard to turbulence, visibility, and precipitation.
14Cumulus with Vertical Growth Fair weather cumulusA puffy, cottonball appearance.Develops from thermal updrafts.Flights below can be bumpy and choppy.Cumulus with Vertical GrowthFair weather cumulus.A puffy, cottonball appearance with a horizontal dark base.It develops from thermal or updrafts of heated air containing a relatively small amount of water vapor.Flights below fair weather cumulus can be bumpy and choppy because of updrafts beneath the clouds.
15Cumulus with Vertical Growth Vertical growth, or building cumulusProduce strong rain and moderate to severe turbulence.Very strong updrafts.With further building and increase in intensity, it becomes a thunderstorm.Cumulus with vertical growth, or building cumulus.These clouds produce strong rain showers with moderate to severe turbulence and probably will develop into a thunderstorm.Very strong updrafts are characteristic of these clouds as they build higher and larger. This type of growth continues until the cloud becomes cumulonimbus.With further building and increase in intensity, it becomes a thunderstorm.
17Fog Types Radiation Fog Formed at night when land surfaces radiate much of the heat absorbed from the Sun back into space.The cool land surface cools the air near it to below the dew point and fog is formed.Fog TypesNOTE: Fog is actually a cloud because it is developed within the atmosphere, but is considered as a separate classification because of the conditions under which it is formed.Radiation FogFormed at night when land surfaces radiate much of the heat absorbed from the Sun back into space.The cool land surface cools the air near it to below the dew point and fog is formed.
18Fog Types High Inversion Fog A low fog. Formed by condensation of water vapor at or near the top of cool air, which is overlain by a warmer air layer.High Inversion FogA low fog.Formed by condensation of water vapor at or near the top of cool air, which is overlain by a warmer air layer.
19Fog Types Advection Fog Formed when wind blows moist air over a cold surface.When the surface cools the air to its dew point temperature, fog is formed.Advection FogFormed when wind blows moist air over a cold surface.When the surface cools the air to its dew point temperature, fog is formed.
20Fog Types Evaporation Fog Also called steam fog, may occur when cold air moves over warm water.The water’s normal evaporation process saturates the cooler air with water vapor and the dew point is reached.Evaporation FogAlso called steam fog, may occur when cold air moves over warm water.The water's normal evaporation process saturates the cooler air with water vapor and the dew point is reached.
21Fog TypesUpslope FogResults when wind carries moist air up to a mountain slope or sloping land.The air cools to its dew point as it rises and water vapor then condenses into fog.Upslope FogResults when wind carries moist air up to a mountain slope or sloping land.The air cools to its dew point as it rises and water vapor then condenses into fog.
23Air MassA large body of air (usually extending over an area 1,000 or more miles across) which has generally the same temperature and moisture content within the entire mass.An air mass is a large body of air (usually extending over an area 1,000 or more miles across) which has generally the same temperature and moisture content within the entire mass.
25Air Mass Type and Origination Air masses are identified by letter symbols.A polar air mass (P) is cold.A tropical air mass (T) is hot.A maritime air mass (m) forms over water and is humid.A continental air mass (c) forms over land and is dry.Air mass type and originationAir masses are identified by letter symbols.A polar air mass (P) is cold.A tropical air mass (T) is hot.A maritime air mass (m) forms over water and is humid.A continental air mass (c) forms over land and is dry.
26Air Mass Type and Origination Aviators and meteorologists in the continental United States are chiefly concerned with air masses origination at two sources.Masses that move southward from Polar Regions.Masses that move northward from Tropical Regions.Aviators and meteorologists in the continental United States are chiefly concerned with air masses origination at two sources.Masses that move southward from Polar Regions.Masses that move northward from Tropical Regions.
27Air Mass Type and Origination Cold air massesContinental polar (cP)Maritime polar (mP)Arctic (A)Cold air massesContinental polar (cP)Maritime polar (mP)Arctic (A)
28Air Mass Type and Origination The principle warm air mass is maritime tropic (mT)The principle warm air mass is maritime tropic (mT)
29Temperature Classification of Air Masses Based upon its temperature in relation to the surface over which it passes.A cold air mass (k) is cooler than the Earth’s surface over which it is moving.A warm air mass (w) is warmer than the Earth’s surface over which it is moving.Temperature Classification of Air MassesBased upon its temperature in relation to the surface over which it passes.A cold air mass (k) is cooler than the Earth's surface over which it is moving.A warm air mass (w) is warmer than the Earth's surface over which it is moving.
30Temperature Classification of Air Masses Continental polar cold (cPk) - originates in the polar zone and moves south over a warm surface.Maritime tropical warm (mTw) - originates over the Gulf of Mexico and moves toward the north over a cold surface.An air mass originating in the polar zone and moving toward the south over a comparatively warm surface is identified by the symbol (cPk); continental polar cold.An air mass originating over the Gulf of Mexico and moving toward the north over a comparatively cold surface is identified by the symbol (mTw); maritime tropical warm.
31Characteristics of Air Masses Air masses originating in the tropical and equatorial areas move toward the northeast.Air masses originating in the arctic and polar area move toward the southeast.Characteristics of Air MassesDepends upon the surface over which it forms, the season, the surface it travels over, and the length of time away from the source.Air masses originating in the tropical and equatorial areas move toward the northeast.Air masses originating in the arctic and polar area move toward the southeast.
32Characteristics of Air Masses Cold air masses move more rapidly than warm air masses.The weather generally depends on the nature of a prevailing air mass or the interaction of two or more air masses.Cold air masses move more rapidly than warm air masses.The weather generally depends on the nature of a prevailing air mass or the interaction of two or more air masses.
33Characteristics of Air Masses As an air mass moves away from its source, its original characteristics are changed because of the surface it passes over. It may:Become warmer or colder.Absorb or lose moisture.Be lifted up by mountains or subside into valleys.As an air mass moves away from its source, its original characteristics are changed because of the surface it passes over.It may become warmer or colder.It may absorb or lose moisture.It may be lifted up by mountains or subside into valleys.
34FrontsThe boundaries between air masses are called frontal zones or fronts.This boundary or front moves along the Earth’s surface as one air mass displaces another.If a cold air mass replaces a warmer air mass, the boundary is called a cold front.If a warm air mass replaces a cold air mass, the boundary is called a warm front.FrontsThe boundaries between air masses of different characteristics are called frontal zones or fronts.This boundary or front moves along the Earth's surface as one air mass displaces another.If a cold air mass replaces a warmer air mass, the boundary is called a cold front.If a warm air mass replaces a cold air mass, the boundary is called a warm front.
36Fronts Cold Fronts Northwest to southeast. Cold fronts travel very far south.Amount of energy depends on amount of cold air in high-pressure cell.Formed at the junction of the high-pressure. cold air with low-pressure warm air.Cold air forces the warm air upward.Cold FrontsIts general direction of travel is from northwest to southeast.Cold fronts travel very far south, even in the summertime.The amount of energy depends on the amount of cold air that comprises the high-pressure cell behind it.The front is formed at the junction of the high-pressure cold air with low-pressure warm air.Since cold air is denser than warm air, it forces the warm air upward.
37FrontsCold FrontsMovement depends on condition of the warm air it collides with.In western states, the noticeable change is shift of wind, temperature, and blowing dust.In southern and eastern states it causes problems for aviators.The weather associated with a cold front's movement depends on the condition of the warm air with which it collides.In the western states, the air is often dry. As the front moves through, the only noticeable change is a shift of wind, cooler temperatures, and possibly blowing dust.As the "typical" cold front approaches the southern and eastern states, it encounters warmer vapor-laden air, which causes problems for aviators.
38FrontsCold FrontsAs warm air is forced upward, it cools, condenses into clouds, creating thunderstorms.If movement is rapid, with an abundance of water vapor, violent weather takes place.Squall lines develop ahead of the front.As warm, humid air is forced upward, it cools and water vapor condenses into clouds that create thunderstorms.If the movement of the cold air mass is rapid and there is abundant water vapor ahead of it, very violent weather takes place.Lines of thunderstorms (squall lines) develop ahead of the front (from 50 to 150 miles).
39FrontsCold FrontsAlong the cold front there will be a low-pressure cell where the weather is at its worst.Almost any type of clouds can be found near the cell.Poor visibility, low ceilings and rain in summer.Freezing rain and snow in winter.Along the cold front there will be a low-pressure cell where weather will be at its worst.Almost any type of cloud can be found near the cell because of highly concentrated water vapor and the temperature and dew points are very close.In the summer aviators can expect very poor visibility, low ceilings, and a lot of rain.In the winter it causes freezing rain and snow.
41FrontsWarm FrontsConnected to a low-pressure cell, travels northeastward.If cell did not move, the front would dissipate.Front slips upward over cool air and forms a wedge.Rises slowly which delays condensation.Warm FrontsThe usual warm front is connected to a low-pressure cell, extends "eastward" from it, and travels northeastward.If the low-pressure cell did not move, the warm front would travel counterclockwise around the cell until it dissipated.Since warm air is less dense than cool or cold air, the leading edge of a warm front slips upward and over the cooler air, forming a wedge shape.The warm air rises slowly and its rate of cooling (lapse rate) is slow, which results in "delayed" condensation of the water vapor.
42Fronts Warm Fronts Front is announced by cirrus clouds. As front approaches other clouds, skies darken.Near the frontal boundary, clouds are low, gentle rain falls and visibility is poor.Warm rain falling into cooler air causes fog.The approaching warm front is announced by the appearance of cirrus clouds. The cirrus may be as much as 1,000 miles in advance of the front.As the front approaches other types of clouds appear, and the sky grows darker. Eventually rain falls.Very near the frontal boundary, clouds usually are low; gentle rain falls and visibility is poor.Often the falling of warm rain into the cooler air near the surface produces fog.
43FrontsWarm FrontsAfter front passes, there is a rise in temperatures, general clearing and change in wind direction.In winter a warm front causes icing conditions at low altitudes.In northern latitudes snow may also be produced.After the front passes, there is a further rise in temperature, general clearing, and change in wind direction.In the winter months the passage of a warm front usually causes icing conditions at very low altitudes which may extend downward to the Earth's surface.In more northern latitudes snow may also be associated with the warm front.
45Fronts Stationary Front When air masses stop, a stationary front develops.Weather can be bad for aviation along the front.About every form of weather can be found.Stationary FrontWhen air masses stop moving, a stationary front develops.The weather along a stationary front can be very bad for aviation.In parts of the country where there is a large amount of moisture, just about every form of weather can be found along the stationary front.
46Front Stationary Front Toward the trailing edge of the any front there will be a stationary-front condition.The trailing edge stationary fronts are a great distance from the parent cell.As the distance become greater the front no longer exists.Toward the trailing edge of any front there will be a stationary-front condition, because a frontal zone cannot go on forever.These "trailing edge" stationary fronts are a great distance from the parent pressure cell that continues to move.At some point the distance becomes so great that the identity between cold and warm air is lost, and the front in that area no longer exists.
48FrontOccluded FrontThere is a tendency for a horizontal bend or wave to occur along the front.After a frontal bend starts, cold air moves ahead of a warm front.The cold section moves faster than the warm section.Occluded FrontUnder certain conditions there is a tendency for a horizontal bend or wave to occur along a front.After the frontal bends start, cold air moves in such a way that it retreats ahead of a warm front in an adjacent section.The cold front section moves faster that the warm front section and it overtakes the warm front. The warm air mass between the fronts is lifted above the surface by the two colder air masses.
49FrontOccluded FrontThe resulting front is called occluded or occlusion.Air pressure becomes less at the wave or bend than at other points.The weather that results is a combination of cold and warm front weather.The resulting front is called an occluded front or an occlusion.The air pressure becomes less at the wave, or bend, than at other points within the surrounding areas, the frontal surfaces tend to whirl together and a "low" has been created.The type of weather that results from an occluded front is usually a combination of cold front and warm front weather.
51Terrain FactorsThe presence of mountain ranges change the characteristics of a front.As air masses enter the United States the mountains cause them to rise.Along many seacoasts there is a breeze from the sea by day. This moist, relatively cool air rises and heats as it passes across land.Convectional clouds form and bring afternoon showers.Terrain FactorsThe presence of mountain ranges in the path of a weather front can change the characteristics of the front greatly. Gentle rolling hills also contribute to the manufacturing of weather.As air masses enter the United States, the mountains cause them to rise.As the air rises, it cools and loses practically 100 percent of its moisture on the windward (facing the wind) slope.The leeward slopes remain dry.Along many seacoasts, there is a breeze from the sea by day. This moist, relatively cool air rises and heats as it passes across land.Convectional clouds form a short distance inland and may bring afternoon showers.
52Terrain FactorsAt night the land cools and the breeze blows toward the sea.Wind blowing toward land formations and condensation will occur.The reverse can happen if the wind forces clouds downward into warmer air.Terrain FactorsAt night the land cools more rapidly than the sea, the current is reversed, and the breeze blows from land to sea.Wind blowing toward land formations that slope gently upward can carry moisture-laden air to the altitude where its dew point temperature is located and condensation will occur.The reverse can happen if the wind forces clouds downward into warmer air. The clouds will again become water vapor.
54Turbulence Thermal Turbulence Intense surface heating causes convection currents.More intense convection currents occur over dark-colored ground.Less convection currents will be over light-colored ground.Because velocity varies turbulent conditions are expected.TurbulenceThermal turbulence - caused by intense surface heating.Intense surface heating will create columns of rising air called convection currents or thermals.More intense convection currents will be present over dark-colored ground such as a black asphalt highway.Less intense convection currents will be present over light-colored ground such as wheat fields.Because the velocity of these currents varies according to the nature of the underlying surface, turbulent conditions should be expected.
55Turbulence Thermal Turbulence Presents the biggest problem for aviators during landing.To eliminate during normal flight, climb above clouds.Not confined to summer months.When cumulus clouds are present, convection currents and thermal turbulence exists.Thermal turbulence presents the biggest problem for aviators during the landing portion of the flight due to the increased tendency to either overshoot or undershoot the runway.To eliminate thermal turbulence during normal flights, climb above any cumulus clouds present.Thermal turbulence is not confined to only summer months.Anytime cumulus clouds are present, convection currents exists and thermal turbulence exists.
56Turbulence Mechanical Turbulence - Low Level Results from strong wind gusts over rough terrain or manmade features.Produces turbulent eddies below 500 feet.Mechanical turbulence - caused by friction, the interaction of the air with another surface.Low level mechanical turbulence.Results from strong, gusty winds flowing over rough terrain or manmade features.This flow will produce turbulent eddies making flight conditions poor in the atmospheric layer below 500 feet.
57Turbulence Mechanical Turbulence - Wake Turbulence Caused by aircraft flying through air.Presents a major hazard to another aircraft following too close.Most hazardous during landings and takeoffs.Wake turbulenceCaused by aircraft flying through the air; disrupts the airflow.This strong, cone shaped, rotational flow trailing behind aircraft wings is referred to as wingtip vortices and presents a major hazard to another aircraft following too closely.This condition is most hazardous during landings and takeoffs.
58Turbulence Mechanical Turbulence - Mountain Wave Caused by wind speeds of 25 knots or stronger.Produces a large-scale wave motion.Extends from ground level to tropopause and 300 nmi downwind.Most intense turbulence will occur within the first two or three waves.Mountain wave turbulenceCaused by wind speeds of 25 knots or stronger flowing perpendicular to a line of hills or mountains.These conditions will produce a phenomenon in which a large-scale wave motion develops downwind from the mountain range.The turbulent effects of this wave motion can extend from ground level to the tropopause and downwind as far as 300 nmi.Normally, the most intense turbulence will occur within the first two or three waves.
60Turbulence Wind Shear - Low Level Wind Shear (LLWS) Occurs below 10,000 feet.Primarily caused by frontal systems, low level jet streams and thunderstorms.Occurs rapidly.Wind Shear - caused by a sudden change in wind direction, wind speed or both for a short distance.Low level wind shear (LLWS).Occurs at altitude below 10,000 feet.Primarily caused by frontal systems, low level jetstreams, and thunderstorms.Low level wind shear occurs quite rapidly; therefore, a pilot should anticipate turbulence and be prepared to respond when conditions are present or forecasted.
61Turbulence Wind shear - Clear Air Turbulence (CAT) Occurs above 15,000 feet.Not restricted to clear skies.Turbulence occurs in vicinity of upper level jetstream.Clear Air Turbulence (CAT)When turbulence occurs above 15,000 feet and is not associated with thunderstorms, it is CAT.Not restricted to clear skies, but may also occur in a solid cloud deck.As long as the clouds are not associated with thunderstorms, the turbulence frequently occurs in the vicinity of the upper level jetstream.
64Normal Weather Patterns Superhumid ProvinceLies along the north Pacific coast.Precipitation from 30 to 150 inches per year.Temperatures are mild and summers dry.Cloudiest part of the country.Normal Weather PatternsSuperhumid Province - The wettest in the nationLies along the north Pacific coast inland to the Cascade Mountains of Washington, Oregon, and northern California.Precipitation (rain and snow) ranges from 30 to 150 inches per year, most of it falling during the winter as a result of cyclonic storms and the movement of air up the mountains.Temperatures are mild in this area and summers are mostly dry.Cloudiest part of the country where fog is sometimes a problem.
65Normal Weather Patterns Humid ProvinceArea east of a line form Texas Gulf Coast to Lake Superior.30 to 50 inches of rain annually.Average temperature from 40o F in north, 70o F along the Gulf of Mexico, 75o F in Florida.Cold waves in winter, heat waves in summer.Hurricanes are common.Humid ProvinceThe area east of a line from the Texas Gulf Coast to Lake Superior.Has inches of rainfall annually, most of it in the summer.Rainfall comes as a result of convectional showers, cyclonic storms, and thunderstorms.The average temperature ranges from 40o F in the north to 70o F along the coast of the Gulf of Mexico and to 75o F in southern Florida.Arctic and polar air masses may swoop easily into this area, bringing cold waves with them in the winter.Warm, moist air masses may move up from the Gulf in the summer, bringing heat waves.Hurricanes are common in this province.
66Normal Weather Patterns Subhumid ProvinceBelt miles wide just west of humid province.Average rainfall 18 to 30 inches.Cold in winter, hot in summer.Quick and severe temperature changes.Tornadoes in most of southern part of this area.Subhumid ProvinceA belt miles wide that lies just west of the humid province.Average rainfall of 18 to 30 inches, most of it coming in the late spring, early summer.Temperature is continental, cold in the winter and hot in the summer.Quick and severe temperature changes occur in the winter when arctic air masses funnel into the area, bringing blizzards and cold waves.Tornadoes are not unusual over most of the southern part of this area.
67Normal Weather Patterns Semiarid Provincemile wide area west of subhumid province from Canada to Mexico.Precipitation ranges from 12 to 25 inches.Warm, dry air masses common in winter.Hail frequent in spring and early summer.The Great Valley of California is geographically separated from rest of province.Semiarid ProvinceA mile-wide high country area west of the subhumid province and extends from Canada to Mexico. Most of this province is over 3,000 feet above sea level.This area does not get much rainfall since it is beyond the range of most of the moist winds of the Gulf and the Atlantic Ocean, and is cut off by mountains from the moisture of the Pacific breezes.Precipitation ranges form 12 inches in northern Montana to about 25 inches in southern Texas.In the Great Plains, months may pass with no rain. Then, up to a third of the annual rainfall may occur in one day.Warm, dry air masses called chinooks come sweeping down the eastern slope of the Rocky Mountains fairly frequently in the winter.Hail is frequent in spring and early summer.The Great Valley of California is geographically separated from the rest of the semiarid province.It is semiarid because of its annual rainfall.It gets the same amount of rain as the Rocky Mountain and Great Plains area, but almost none from May to September.In the winter, rain results from cyclonic storms and the ascent of Pacific air up the mountains.Fog is frequent in winter, but snow, hail, and thunderstorms are very rare at low altitudes.
68Normal Weather Patterns Arid ProvinceIncludes parts of California, Texas, Arizona, New Mexico, Nevada and Utah.Less than 10 inches of rain annually.Hot and dry summers, winters above freezing.Clear dry air and plenty of sunshine.Arid ProvinceIncludes part of southeast California, southwest Texas, Arizona, New Mexico, Nevada, and Utah.Rainfall amounts to less than 10 inches per year.Summers are very hot and dry, and winters well above freezing.Clear, dry air and plenty of sunshine are usual in this area.
69Normal Weather Patterns HawaiiTwo major factors determine weather.Dramatic heights and contours of land areas.Prevailing northeast trade winds.Pleasant temperatures.Little distinctions between summer and winter.HawaiiTwo major factors determine the weather in the Hawaiian Islands.One is the dramatic heights and contours of the land areas.The other is the prevailing northeast trade winds that blow over cool ocean currents.These factors combine to provide typical Hawaiian weather, which is pleasant temperatures (usually in the 70's), plenty of sunshine, and very few tropical storms.Very little distinction is seen between summer and winter except for additional rainfall in the winter.
70Normal Weather Patterns AlaskaHas several different kinds of weather.No great extremes in southern part of state.Arctic slope lies in northern part of state.Broad valley and low mountain ranges.Continental weather.Temperatures from -70o F in winter to 90o F in summer.AlaskaUnlike Hawaii, Alaska has several different kinds of weather, influenced by the varying terrain features.Mountains and warm ocean currents combine in the southern part of the state to make a climate with no great extremes of temperature.Rainfall is heavy, but varies from one section to the next depending on local geography.High mountains in the south intercept Pacific Ocean winds and wring out much of the moisture, which freezes and supports the glacier fields in the area.In the Aleutian Islands, the weather ranges from cool to cold and is always rainy. Fog is also present.Beyond the mountains in the northern section of Alaska lies the Arctic slope, an area exposed to winds from the Arctic Ocean.Temperatures are relatively mild in midsummer and early autumn.Ice stops shipping movements for up to 10 months of the year.Between the oceanic area of the south and the arctic area of the north lies a large area of broad valley and low mountain ranges.The interior section has continental weather comparable to the Great Plains of the western United States.Temperatures can drop to -70o F in the winter and can climb to 90o F during the long sunlight hours of the summer.
71Summary 1. Clouds 2. Air Masses and Fronts 3. Terrain Factors 4. Turbulence5. Normal Weather PatternsIn this lesson we discussed:1. Clouds2. Air Masses and Fronts3. Terrain Factors4. Turbulence5. Normal Weather Patterns