CWS 8A

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SURFACE WEATHER MAPS AND FORCES

Do Now:

Print this file.
Print the associated Curr= ent Weather Studies A Image 1 File.
Print the Daily Summary and/or Supplemental Information Files, if directed by your instructor.=

To Complete Investigation:

Reference: Chapter 8 in t= he Weather Studies textbook.
Complete Investigation 8A= in the Weather Studies Investigations Manual as directed by your instructor.
Complete this Monday online-delivered Current Weather Studies 8A activity if directed by yo= ur instructor.

Image 1 is the surface weather map (Isobars, Fronts, Rada= r & Data) for 12Z 25 OCT 2009, Sunday morning. At map time cool, fair wea= ther associated with high pressure covered much of the eastern third of the nati= on while a frontal boundary in the central U.S. marked the leading edge = of another wave of cooler air moving in from the Northwest. That northwestern = cool air accompanied the high pressure centered in the northern Idaho area. Details of these systems a= re found in the Monday Daily Weather Summary.

1= . The wind at Glasgow, in northeastern Montana, where the temperature was 37 °= ;F and the dewpoint 31 °F, showed the air was = moving generally toward the [(east-southeast)(south-= southwest)(north-northwest)(north-northeast= )] at about 10 knots. (You might wish to make a small compass cross at Glasgow showing north parallel to the north-south Saskatchewan bor= ders to assist determining directions.)

2= . Draw a short, straight line through Glasgow that is perpendicular to the nearby 1020-mb isobar. Extend the line to the adjacent isobars (1024 and 1016). Place an arrow head on the end of the line toward lower pressure. Your arrow represents the direction of the [(Coriolis)(pressure gradient)(friction)] force acting on the air at <= st1:City w:st=3D"on">Glasgow.

3= . This force acting on the wind flow at Glasgow was directed generally toward the [(west-southwest)(west-northwest)(east-northeast)(south-southeast)].

4= . The wind direction at Glasgow was [(parallel)(at an ang= le)] to the force arrow you drew perpendicular to the isobars.

5= . Draw a small arrow at a right angle to the wind flow to represent the Coriolis effect acting on = the wind flow at Glasgow. It was directed generally toward the [(east-southeast)(south-southwest)(north-northwest= )(east-northeast)].

6= . The force acting toward the west-northwest in the direction opposite to the air flow at Glasgow was the local [(Coriolis)(pressure gradient)(friction<= /i>)] force.

7= .      Considering the Glasgow conditions as part of the circulation about the northwestern Hi= gh, the pressure gradient, Coriolis and friction fo= rces combine to direct surface air flow around Northern Hemisphere high-pressure centers that is [(clockwise and outward)(countercloc= kwise and inward)], consistent with the hand-twist model.

8= .      Now consider Huron, in eastern So= uth Dakota. Huron had a north-northwest wind of 10 kn= ots and a temperature of 41 degrees. Huron was influenced by the Low's circulat= ion. Huron's pressure gradient force (perpendicular to the isobar) was directed generally toward the [(south)(<= /span>north)(east)(west)].

9= .      The Coriolis force at Huron was directed generally = toward the [(south-southeast)(no= rth-northwest)(north-northeast)(west-southwest<= /u>)].

1= 0. The friction force at Huron was toward the general direction of [(sout= h-southeast)(north-northwest)(north-northeast= )(west-southwest)].

1= 1. Consi= dering the Huron conditions as part of the circulation about the Midwestern Low and frontal system, the pressure gradient, Coriolis= and friction forces combine to direct surface air flow around Northern Hemisphe= re low-pressure centers that is [(clockwise and outward)(<= u>counterclockwise and inward)], consistent with the hand-twist model.

1= 2. The pressure gradient force is the primary determiner of wind speed. Generally higher wind speeds are located where the pressure gradient is stronger. The spacing of isobars on the map imply the strength= of the pressure gradient with closer spacing associated with stronger gradient= s. The stronger pressure gradients at this early morning map time were located= in the region centered over the [(Utah= )(= Pennsylvania)] area.

The mountainous region in the West often hind= ers winds reaching a balance with large-scale pressure gradients. The Monday Da= ily Weather Summary mentions the forecasted development of high wind speeds as strong pressure gradients develop with the High later over the northern pla= ins.

The pressure patterns, including the pressure gradients they produce, are major determiners of local weather conditions including wind speeds and directions. However, local conditions can also influence winds, particularly when the broad-scale pressure patterns are not dominant. For example, light= pressure gradients allow sea breeze winds to flow onshore from late mornings to early evenings while the flow can be offshore late evenings. And, wind may be channeled by local terrain independently of isobar orientations.

Critical Thinking and Diversity Component: The Week 8 Critical Thinking/Diversity Component, located in the Learning Files section of the course homepage, applies the skill of transferring understandings to new contexts and the attribute of being insightful to the critical thinking activity of examining changes in upper-air weather patterns and to the diversity component, which describes a model for intercultural sensitivity.=

If directed by your instructor, place the answers to Investigation 8A and Current Weather Studies 8A on the A Answer Form linked from the AMS Weather Studies website.

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