DataStreme Activity 5A:

AIR PRESSURE CHANGE

Do Now:

  1. Print this file.
  2. Print the Monday Image 1 and Image 2 Files.
  3. Print (when available) the 10 October 2001 Tuesday Daily Summary File.

To Do Activity:

  1. Read Chapter 5 in STUDY GUIDE, Part A: Narrative.
  2. Go to STUDY GUIDE, Part B: Applications. Start Activity 5A.
  3. Return here (Monday Activity A File) when told to do so.

Go To STUDY GUIDE - Activity 5A Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. The major weather maker for the eastern two-thirds of the nation over this past weekend was an expansive cool air mass. This continental polar air mass dove south and east from the northern Plains to the southeastern states over the weekend setting low temperature records and forcing the issuance of frost and freeze warnings over a large area of the country. The advancing edge of this air mass was a strong cold front that brought a quick turnaround from balmy temperatures that were the norm earlier in the week. Details of these events are in the Monday, 8 October, Daily Weather Summary.

    Highs (Hs) and Lows (Ls), the pressure systems routinely plotted on surface weather maps, identify local values of atmospheric pressure that are relatively the highest or lowest in a region. These systems generally move from west to east across our midlatitude portion of the globe so that pressure values at locations in their paths fall as a Low approaches or a High departs, and pressures rise with approaching Highs or departing Lows.

    Image 1 is the surface weather map for 12Z 06 OCT 2001 (8 AM EDT Saturday morning). At map time the primary low-pressure center with central pressure of 992 mb was located [(in central Oklahoma) (on the Vermont-Canada border)]. A cold front curved southwestward near the Atlantic coast and then westward across northern Mexico before becoming a stationary front in Arizona and Utah. The center of the cool air mass was marked by a high-pressure center of 1027 mb [(in central Oklahoma) (on the Vermont-Canada border)].

  2. At 12Z 06 OCT Charleston, South Carolina, had a temperature of _____ °F, dewpoint _____ °F, wind from the [(south-southwest) (northeast)] at about 5 knots. (The pressure value was not plotted). Nashville, TN, behind the front to the northwest, had a pressure of 1021.1 mb, temperature _____ °F, dewpoint _____ °F, wind from the [(south) (north)] at about 5 knots and it was partly cloudy.

  3. Temperatures behind the front were [(lower) (higher)] than ahead of the front (as at Charleston). Note Dulles International Airport (IAD), just west of Washington, DC, where the temperature was 59 °F, dewpoint 55 °F, overcast, with radar precipitation echoes, and a wind from the northwest at about 10 knots. These data and the position of the front drawn on the map indicate the front [(had already passed) (not yet reached)] Dulles Airport.

  4. Image 2 is the meteogram for Dulles Airport for the 24-hour period from 0100Z 06 OCT 2001 to 0000Z 07 OCT 2001. Label the time line of the meteogram in local EDT time along the bottom to show local time, starting with 01Z being 9 PM EDT. Draw a vertical line on the figure at 8 AM (12Z), the time of the surface map. Compare the atmospheric conditions reported on the surface map for 12Z at Dulles with those on the meteogram at 12Z. They are [(the same) (very different)].

  5. From 01Z through 10Z 06 OCT , temperatures for Dulles Airport (top panel of the meteogram) were near [(55) (70)] degrees Fahrenheit with winds (second panel) generally from the [(south) (northwest)] and pressure (bottom panel) [(rising) (falling)]. The dewpoints during this period (top panel) were [(rising) (falling)].

  6. This time period was [(during the day) (overnight)]. Usually, temperatures gradually fall during this part of the day. The steady temperatures during this time period were likely the result of [(warm) (cold)] air advection.

  7. The meteogram shows that, between 11Z and 12Z, the change of wind direction, the decrease of temperature and dewpoint, and the subsequent occurrence of precipitation all suggest the cold front [(had) (had not)] passed Dulles Airport.

  8. The atmospheric pressure values were [(rising steadily) (steady) (falling steadily)] from the beginning of the reporting period until 10Z. This pressure tendency also indicated that the front was probably moving [(toward) (away from)] Dulles Airport during this time. At 11Z the pressure began to [(rise rapidly) (remain steady) (continue falling)].

  9. After passage of the cold front, winds suddenly shifted to northwesterly. From 11Z onward for the period of the meteogram, the dewpoints generally [(rose steadily) (remained steady) (fell steadily)]. The temperatures fell from 11Z to 14Z, then rose [(a few) (more than ten)] degrees.

  10. As the air mass shown on the Image 1 surface map proceeds eastward, the air pressures at Dulles Airport would be expected to [(fall) (rise)] until the center is nearest.

The clear skies and light winds of the air mass allowed extreme nocturnal outgoing radiation, dramatically heralding the coming of fall and end of the growing season for much of the eastern two-thirds of the U.S. over the weekend!

When weather changes or passing storm systems influence your weather, print out meteograms for a city near you. If you have local recording instruments, or have plotted local weather conditions such as those reported hourly by NOAA Weather Radio, have your students compare their values with those of the meteograms. (A blank meteogram for plotting purposes may be printed from the DataStreme homepage.) Also relate the view of weather conditions from meteograms with those of a sequence of weather maps. Post these meteograms and maps in your classroom.


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 Activity B.


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