DataStreme Activity 1B:

AIR PRESSURE AND WIND


Mistakes happen! In Study Guide, Part B, Applications, Monday's 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.)


Do Now:

  1. Print this file.
  2. Print the Wednesday Image 1 File.
  3. Print (when available) the Thursday, 7 September 2000 Daily Summary File.

To Do Activity:

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

Go to Study Guide - Activity 1B Now


WELCOME BACK: Procedure continued from STUDY GUIDE.

  1. The Image 1 "Isobars, Fronts, Radar & Data" map acquired from the DataStreme homepage is the depiction of weather conditions at stations across the contiguous US at 12Z 05 SEP 2000. This is 24 hours later than the map you analyzed in Activity 1A. Weather data at individual locations are plotted in a coded format called the "station model". The station model will be explained in Activity 2A.

    The Image 1, 12Z 05 SEP 2000, map shows a high pressure center (H) just north of the Great Lakes. This is the location of the center of the cool air mass that entered the northern US bringing record low temperatures to the Northeast. The highest pressure in that area at 12Z on the 5th was 1035 millibars as shown by the bold number beneath the H.

    Air pressures are plotted on surface map station models to the upper right of the station circle representing the station location. The pressure is plotted in a three-digit code to the nearest tenth of a millibar. On the 12Z 05 SEP 2000 map, Kansas City, Missouri, has the digits "234" plotted to the upper right. This signifies a pressure of 1023.4 mb. The isobar just to the north of that station circle is the [(1023) (1024) (1027)] -mb isobar.

  2. The wind directions at reporting stations on the map are shown by the line (which can be thought of as an arrow shaft) which depicts the air flow into the station locations (circles). Wind at a station is named by the direction from which the air flows, i.e., air coming towards the station from the south is a south wind. The wind direction at Kansas City was from the [(west-northwest) (east-southeast)], so it was a(n) [(west-northwest) (east-southeast)] wind.

    The wind speed is given by a combination of long and short "feathers" on the direction shaft. Details for deciphering station data are given in your Homepage User's Guide (linked from the DataStreme Homepage). At map time, Kansas City, MO, had a 10-knot wind. [A circle or double circle without a direction shaft signifies calm winds, and a shaft without feathers denotes 1-2 knots. A knot is a nautical mile per hour. A nautical mile is about 1.2 statute (land) mile.]

  3. The wind at Midland, Texas, (pressure 1014.0 mb) was from the [(southwest) (northwest)] at 5 knots (half feather).

  4. Apply the hand-twist model of a High to infer the wind directions in the broad high-pressure area centered just north of the Great Lakes. Wind directions at stations in the states and provinces around the high-pressure center show that, as seen from above, the air spiraled generally [(clockwise) (counterclockwise)] around the high-pressure center.

  5. The observations around the high-pressure area also indicated that the air generally spiraled [(inward toward) (outward from)] the high-pressure center. This pattern is [(consistent with) (contrary to)] the hand-twist model of a High.

  6. The low-pressure center in southeastern Montana (marked by two closely spaced L's in the computer pressure analysis) shows winds that are typical of the flow around a Low. The wind directions in the several state and southern Canadian area surrounding the low-pressure center show the air spiraling generally [(clockwise and outward) (counterclockwise and inward)]. This pattern [(is) (is not)] consistent with the hand-twist model of a Low.

  7. Your isobar analysis on the Monday, Activity A map showed highest pressure values at that time in western Ontario, to the west of the position of the H on this surface map. Lightly place an "H" on this 12Z 05 SEP 2000 surface map at the location of the highest pressure values that were plotted on the 12Z 04 Pressures map. Between 12Z on the 4th and 12Z on the 5th of September, the high-pressure center moved generally toward the [(southeast) (southwest)].

    The position of lower pressures on 04 SEP that became the Montana Low of 05 SEP was depicted by a distortion of the 1012-mb isobar in northeast Utah. Over the 24-hour period, this Low moved generally northeastward.

When the centers of fair weather Highs or stormy Lows are near your location, you might try having students fit your local wind direction (as shown by the school flag, for example) with map circulations and the hand-twist model of weather systems. (One note: the hand-twist model must be applied cautiously, in the western US where mountainous terrain can be a predominant factor affecting wind directions, or when wind speeds are low.)


Record your responses to items in Activities 1A and 1B on the Activity Response Form for transmission to your course mentor.

Faxing Instructions:

After completing this week's applications, fax the following pages to your LIT mentor by Monday, September 11, 2000, or as coordinated with your mentor:

  1. Chapter 1 Progress Response Form from the Part B: Applications binder, Week 1, or the DataStreme Homepage
  2. Activities 1A and 1B Activity Response Form , the DataStreme Homepage
  3. STUDY GUIDE, Part B: Applications, pages:
  4. Your drawing of isobars on the Activity 1A Image 1, Pressures map for 12Z 04 SEP 2000

Notice for Local Implementation Team (LIT) members - recall that the week's answer key will be available to mentors each Friday after 12 noon, Eastern time. Check with your LIT Manual or your LIT leader for answer key.


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