Lab: Intro to Observations 1

Objectives

  • Overview of meteorological observations (lecture).
  • Tour of rooftop.
  • Introduction to sky, visibility, and present weather observations.
  • Filling out the MF1-10 observation form.

Resources, Materials, and Equipment

Deliverables

  • Two weather observations, one taken at approximately 9:50 AM, the second at approximately 10:30AM. These will be recorded on the standard observation form (MF1-10) used by the National Weather Service.
  • On a separate page, turn in your two observations encoded in METAR format.

Procedure

  1. Fill out the top line of the MF1-10 form. Take the station altitude as 1,074 ft. (327.5 m), corresponding to the height of the pressure sensor on the roof. Latitude is 43.07N, longitude is 89.41W. Conversion from LST to UTC is currently +5. For the station, enter Madison, WI. Leave SID blank.
  2. All times will be entered in UTC, so check the UTC box in Column 2.
  3. At the time of your first observation, go to the roof. Enter the time in UTC as four digits, no punctuation, using a 24-hour clock. For example, 9:30 LST would be entered as 1430. Recall that during Daylight Savings Time (DST), UTC is 5 hours later than local time.
  4. Evaluate and enter the sky condition, present weather, and visibility in columns 7a, 9 and 10. Be sure to use the appropriate METAR abbreviations and values as discussed in class.
    1. Visually evaluate and record the prevailing visibility in statute miles, using any available landmarks that have been pointed out to you by the instructor. The most likely standard visibility values at this location include 1, 1-1/2, 2, 2-1/2, 3, 4, 5, 6, 7, 10, 15, 20.
    2. If the visibility is 6 miles or less, you will need to record an obstruction to vision (e.g., fog, haze, smoke, precipitation) in column 9, using standard abbreviations from the handout. You will also record any precipitation even if the visibility is 7 miles or more.
    3. Evaluate the number of cloud layers and the cumulative fraction in oktas covered by each one. 1
    4. Identify the cloud type(s) associated with each layer and attempt to assign a reasonable altitude based on those types. This is something that requires considerable experience to do accurately, but you should be able to at least judge whether you’re looking at low, mid, or high clouds.
    5. Based on your sky observation, record all significant cloud layers (an okta or more each) in column 10 using standard abbreviations and heights in 100 ft increments (see examples on handout). Also fill in column 17 with a number of oktas from 0 to 8.
  5. Return to the classroom to determine the entry in the wind speed and direction columns:
    1. Open a browser on your computer. Go to http://metobs.ssec.wisc. edu/aoss/tower/. Click on the “meteorogram” button and wait for it to load (if you run into an error related to the use of Java, please see the instructor).
    2. Using the applet controls, display the 10-minute period starting with the time recorded on your MF1-10 form. Specifically, change “Realtime Update” to “Set range below. . . ”. Then set the start and end times. Choose the smallest available interval. Then click on the “Plot graph” button.
    3. Using the values at the beginning of the 10-minute interval (i.e., the one corresponding to your observation time), enter the temperature and dewpoint in degrees Celsius rounded to the nearest degree (columns 11 and 12). Do the same for the station pressure in inHg, rounded to the nearest 0.01” (column 22)
    4. Using the first full minute of the displayed data, estimate the average wind speed in whole knots and direction to the nearest 10 degrees and enter it columns 3 (two digits, drop the final zero) and 4. If the wind is calm, use ’00’ for the direction; otherwise use ’36’ for due north.
    5. Now scan the entire 10-minute record for wind speeds that are more than 10 kts. greater than the average wind speed you reported in the previous step. If there are none, then there are no gusts. Otherwise report the highest observed value (whole knots) in column 5.
  6. Write your initials in column 15, and either ‘M’ or ‘S’ in column 1. The ‘S’ signifies that you’re taking the observation at a non-standard (“SPECI”) time. ‘M’ is reserved for standard METAR reports on or shortly before the hour.
  7. Take a complete second observation following the above steps at the later time during the lab period. If necessary, you can fill in the data from the tower at a later time, but you will need to make at least the sky and visibility observation “live”.
  8. On a separate sheet of paper, encode your observations in standard METAR format, following the examples on the handout.