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Lesson 17 Weather Maps Hess, McKnight’s Physical Geography, 10 ed. A13 - A18

Station Models In 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 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 NWS /index.html /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 Map Surface 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 Rules Generally, weather systems move from west to east with time As 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 Temperatures High and low surface temperatures for the previous 24 hours are given Precipitation over the past 24 hours is also plotted

500 mb Height Contours The 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 20 Faulting Hess, McKnight’s Physical Geography, 10 ed. pp

Types of Faults Faulting 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 Faults Movement is primarily vertical Normal faulting is the result of extensional (tensional) stress ◦ This stress pulls apart the landscape (shown with arrows) creating a steep fault plane

Reverse Faults Movement is primarily vertical Reverse faulting is the result of compressional stress ◦ This stress pushes the landscape together (shown with arrows), eventually creating a steep fault plane

Thrust/Overthrust Faults Movement is also primarily vertical Thrust faults are also caused by compression, but the overthrust block overrides the downthrust block at a low angle

Strike-slip Faults Movement is primarily horizontal Strike-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 Faulting Different landscapes are created from different types of faulting Normal 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