DataStreme Activity 1A:

SURFACE AIR PRESSURE PATTERNS


Mistakes happen! In Study Guide, Part B, Applications, the pre-printed portion of Activity 1A, Item #4 should read,

4. The letter "H" or "L" marks the center of closed isobars and signifies centers of relatively high or low pressure, respectively, compared to pressure readings in the surrounding area. On the map above, the pressure inside the 1004-mb isobar is lower than the pressure outside that isobar. Place an "L" about 1 centimeter in height inside the closed isobar. (Thanks to Brent Lothamer, Northern Indiana NWS Office, LIT member, for the notice.)


Note: This activity is the same as DataStreme Activity 1A from Preview Week. Participants only need to complete the activity once.

Do Now:

  1. Print this file.
  2. Print the Monday Image 1 File.
  3. Print (when available) the Tuesday, 12 September 2000, Daily Summary File.

Welcome to DataStreme. We hope the use of current weather information will become a pleasant and anticipated daily experience. We encourage your exploration of the DataStreme weather products from the homepage and the use of that material in your classroom or school.

To Do Activity:

  1. Read Chapter 1 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 1A.
  3. Return here (Monday Activity A File) when told to do so.

Go to Study Guide - Activity 1A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

The weather story at the end of the summer was one of a change to cooler weather with showers across the northern tier of states from the Dakotas to New England while the heat hung on in the Southern Plains. Showers also brought some relief from persistent dryness over the Southeast. The wildfires in the Northwest that had been assisted by earlier dry weather were finally starting to come under control.

  1. The Image 1 map acquired from the DataStreme homepage (identified across the top as "Pressures") displays atmospheric pressure values in millibars at ______ Z on __________________. This time is 8 a.m. EDT, 7 a.m. CDT, 6 a.m. MDT, 5 a.m. PDT, etc., on Monday, 04 September.

  2. The lowest reported air pressure on the map is _______ mb. This was located
    [(in south central Canada) (in the Southwestern US and also at Cape Cod, Massachusetts)].

  3. The highest reported pressure is _______ mb. This was located
    [(in south central Canada) (in the Southwestern US and also at Cape Cod, Massachusetts)].

  4. The isobars in the conventional series that will be needed to complete the pressure analysis on this map are: 1012, _____, 1020, _____, _____. An isobar may need to be drawn more than once if pressure values are located in several sections of the map area with values above and below the isobar's number.

  5. Follow the steps below to draw these isobars on this map to determine the pressure pattern that existed at the time the observations were made. Consider each pressure to be located in the center of the reported number.

    1. Let us start by arbitrarily choosing to draw the 1028-mb isobar. Let us begin where the pressure is "1028", such as Nagagami, Ontario (just northeast of Lake Superior). The 1028-mb isobar will go through the center of this number. Then extend the line to the next "1028" at Thunder Bay, Ontario, and on between reported pressures, keeping values higher than 1028 mb on the same side of the line, and lower values on the other side. That isobar will curve around the stations with the highest pressure values you identified above. Extend the ends of the 1028-mb isobar to the edge of the reported pressures. Because it is not an enclosed area of higher values (than 1028 mb), the 1028-isobar will begin at the edge of the map values and end at their edge to the west. Place the isobar value, 1028 as a label at the ends of the isobar line.

      NOTE: For helpful hints, refer to Tips on Drawing Isobars on page 1A-3 of the STUDY GUIDE, Part B: Applications.

    2. Next, draw the 1024-mb isobar to separate the highest pressure values you located on the map from the lower values around it. You can start the 1024-mb isobar by scanning the pressure field outward from the isobar you just drew to locate the positions of the 1024-mb isobar. This isobar line will also extend from one edge of map data to another where the plotted numbers end. Also label this isobar line at its ends with its value, 1024.

    3. Complete the pressure analysis across the map for the remaining isobar values listed in number 13 above. Be sure to label each isobar with its value at the end where it reaches a data boundary. [Individual values greater than an isobar value, such as the 1017 in northwestern New Mexico, should be encircled with the appropriate, labelled isobar value (1016 in this case). Single values exactly equal to an isobar value such as the 1012 at Brownsville, Texas, do not require the drawing of an isobar. However, multiple occurrences of that equal value do need a labelled isobar line.]

At map time, the 1024- and 1028-mb isobars provided evidence of the leading edge of a cooler air mass that was advancing into the north-central US. Lower pressures along the New England and Mid Atlantic Coasts were associated with widespread shower activity there. The relatively uniform pressures from the Florida panhandle to the Southwest resulted from the extended period of hot temperatures across the region.


The DataStreme Homepage routinely delivers unanalyzed ("Pressures") and analyzed ("Isobars & Pressures") surface pressure maps. Practice drawing isobars by calling up the unanalyzed version. Use the DataStreme analyzed map as your "answer key". If appropriate, try having your students make a pressure analysis. You might share with your teacher colleagues this "detective scheme" of analyzing surface air pressures to find storms or broad-scale air masses that are mentioned in the news.


Hold this activity until you have completed all applications for this week. Instructions for faxing your LIT mentor will appear at the end of this week's Wednesday Activity B. (If possible, take this activity to your first course group meeting.)


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