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Course Syllabus can be found at: http://www.wx4sno.com/portfolio/BSU/Fall_2011/

This lecture will be posted AFTER class at:http://www.wx4sno.com/portfolio/BSU/Fall_2011/Lectures/

Lesson 17Weather Maps

Hess, McKnight’s Physical Geography, 10 ed. A13 - A18

Station ModelsIn lesson 13 we introduced

station models with an emphasis on temperature and air pressure.

We will now cover station models in-depth and discuss the symbology associated with different weather conditions

Station Models, cont.Temperature

◦Located in the upper-left corner ◦Given in degrees Fahrenheit

◦For example, 64°F in the example above

Station Models, cont.Dew Point Temperature

◦Located in the lower-left corner ◦Given in degrees Fahrenheit

◦For example, 58°F in this example

Station Models, cont.Wind Direction

◦ Indicated by a shaft or “wind barb” protruding from the station model

◦ Can be positioned anywhere around the station The direction it points toward is the direction from

which the wind originates

In this example, the wind is coming from the southeast (SE)

Station Models, cont.Wind Speed

◦Wind speed is provided along the wind barb

◦To determine wind speed, simply add the barbs No barb = calm winds ½ barb = 5 knots 1 barb = 10 knots 1 pennant = 50 knots

◦ Recall: 1 knot = 1.15 MPH 1 knot = 1.9 KM/HR

Station Models, cont.Wind Speed, cont.

◦For example, what would be the wind speed from our example?

Answer: 15 knots

Station Models, cont.Sea Level Pressure

◦ Located in the top-right corner◦ As we’ve already covered, this number is

the last three digits of the observed pressure reading in millibars (mb)

In this example, the pressure is 1002.7 mb

Station Models, cont.Sea Level Pressure Change

◦ Located directly below the pressure reading◦ Given in tenths of a millibar◦ Simply add a decimal point between the two

numbers◦ “+” means the pressure has increased x-amount

over the past 3 hours◦ “-” means the pressure has decreased over the

past 3 hours

In this example, the pressure change is an increase of 2.8 mb

Station Models, cont.Weather Conditions

◦ Current weather conditions are listed between the air temperature and the dew point temperature

For our example, fog was reported at this weather station

Station Models, cont.Weather

Conditions, cont.◦ There are various

symbols for different types of weather phenomenon

◦ You are not expected to know these…a few are given here for general reference:

Weather Maps from the NWShttp://

www.hpc.ncep.noaa.gov/dailywxmap/index.html

These maps provide both surface conditions, upper-air conditions, precipitation, and high & low temperatures

Let’s discuss each of the maps given…

Surface Weather MapSurface maps

provide a weather “snapshot” taken at 7:00 AM EST

Locations of high and low pressure systems

Locations of frontal systems, as well as precipitation (green)

Isobars show surface pressure (mb)

Dashed isotherms are plotted for 32°F and 0°F

Surface Weather Map

Some General RulesGenerally, weather systems move

from west to east with timeAs a frontal system or low pressure

system approaches an area, air pressure decreases and clouds/precip increase

As a frontal system or low pressure system moves away from an area, air pressure begins to increase which results in clear skies and no precipitation

Remember, high pressure near an area results in fair/clear skies and low pressure near an area results in clouds and precipitation

Surface TemperaturesHigh and low

surface temperatures for the previous 24 hours are given

Precipitation over the past 24 hours is also plotted

500 mb Height ContoursThe last map provided illustrates the

conditions of the upper atmosphere at 500 millibars

The 500 mb height (or elevation) above sea level is plotted across the U.S.◦ Given in dekameters (1 dkm = 10 meters)◦ Height values change with fluctuations in pressure

High 500 mb elevations indicate high pressure below that region

Low 500 mb elevations indicate low pressure below that region

For reference, the 500 mb average elevation is 5600 meters.

Lesson 20Faulting

Hess, McKnight’s Physical Geography, 10 ed. pp. 405 - 408

Types of FaultsFaulting occurs when stresses

forcibly break apart and displace rock structure

This displacement can be horizontal, vertical, or a combination of the two

Several different kinds of faults, but generally can be separated into four categories

Types of Faults, cont.

Normal FaultsMovement is primarily verticalNormal faulting is the result of

extensional (tensional) stress◦This stress pulls apart the landscape

(shown with arrows) creating a steep fault plane

Reverse FaultsMovement is primarily verticalReverse faulting is the result of

compressional stress◦This stress pushes the landscape

together (shown with arrows), eventually creating a steep fault plane

Thrust/Overthrust FaultsMovement is also primarily verticalThrust faults are also caused by

compression, but the overthrust block overrides the downthrust block at a low angle

Strike-slip FaultsMovement is primarily horizontalStrike-slip faults are produced by

sheering stresses◦Think of the stress exerted when you

press your hands together and try to move them parallel to one another

Landscapes from FaultingDifferent landscapes are created

from different types of faultingNormal faulting results in such

areas as the Basin and Range region of the western U.S.

Landscapes from Faulting, cont.Thrust faulting uplifted

sedimentary rocks millions of years ago creating the Appalachian Mountains◦Erosion has resulted in the

mountains being warn-down

Landscapes from Faulting, cont.The San Andreas region of

California is characterized by strike-slip faults◦The sudden movement of these

faults result in the earthquakes common to Southern California

Landscapes from Faulting, cont.The Sierra Madre Mountains of

Mexico were created by reverse faulting◦Compressional stress forces the

landscape to rise, creating mountains or a mountain range