Training Guide in Surface Weather Observations - Multiple Choices

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The conversion from ice to water can be made easily with the psychrometric calculator. Find the dew point with respect to ice on the T i scale (A in Figure 6-4), then read the dew point with respect to water directly opposite it on the DP ( or Tw,DP) scale (B in Figure 6-4). Figure 6-4. Conversion of Dew Point. As a check on dew-point calculations, remember that the dew point will always be equal to or less than the dry-bulb and wet-bulb temperatures. If the dry- and wet-bulb temperatures are the same, the dew point will also be the same unless the conversion from ice to water is involved. One final word of caution. Psychrometric calculators are not all the same. Each calculator is designed for use in a certain range of pressures. Table 6-1 shows which calculator to use depending on the elevation of the station. Station Elevation (Feet) 6-7 Computer Pressure Base (Inches of Mercury) 531 to +392 30 393 to 1341 29 1342 to 2316 28 2317 to 3836 27 3837 to 5976 25 Above 5976 23 Based on ICAO Standard Atmosphere Table 6-1. Psychrometric Calculator on Basis of Station Elevation 6.6 Obtaining Temperatures from Hygrothermometers. 1. Read the dry-bulb temperature and dew point to the nearest degree Celsius. If readings are in Fahrenheit, convert to Celsius.
2. If the hygrothermometer is not working, or either the dry-bulb or dew-point temperature is outside the operating limits of the system, use the psychrometer to determine the missing data. Always use the hygrothermometer dry-bulb temperature, if within limits, even though the dew point temperature is determined by means of a psychrometer. 3. Record the temperature in column 11 and the dew point in column 12 of MF1M-10. 6.7 Liquid-In-Glass Minimum and Maximum Thermometers 6.7.1 Minimum Thermometer - How It Works The minimum thermometer (see Figure 6-5) has an alcohol-filled bulb, graduated at 1° intervals. It is exposed in a slightly lower than horizontal position. The alcohol is often colored to make it easier to read. The bore contains a dark dumbbell-shaped object called an index. As the temperature rises, the alcohol expands and flows around the index without displacing it. As the temperature falls the alcohol column retreats until the top of the column just touches the index; with further cooling, the retreating column moves the index nearer the bulb. As the temperature rises again, the alcohol column moves toward the right without moving the index. 6.7.2 Maximum Thermometer - How It Works The maximum thermometer (see Figure 6-5) has a mercury-filled bulb (sensing element). It is exposed in a nearly horizontal position. Graduations at 1° intervals are etched on the stem. The bore is constricted between the graduated portion of the stem and the bulb. As the temperature rises, some of the expanding mercury in the bulb is forced to pass through the constricted portion into the graduated portion. When the thermometer is lowered for reading, the top of the mercury column indicates the highest temperature reached. Figure 6-5. Maximum and Minimum Thermometers. 6-8
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Training Guide in Surface Weather O
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PREFACE METAR/SPECI is the internat
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CHAPTER 7 - PRESSURE ..............
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1.2 Content and Format of the Manua
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1.6 Report Modifier - COR An observ
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1-6
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12. A METAR observation contains se
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25. At no time shall an observation
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2.1.4 Estimated Winds Though winds
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2-4
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Code the following wind situations
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19. Which of the following wind par
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3.1 Visibility 1 CHAPTER 3 VISIBILI
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3.2.3 Surface and Tower Visibility
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SUR- FACE VISIBILITY PRESENT WEATHE
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3.3 Visibility Chart As an aid for
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OUTLINE DETERMINING VISIBILITY From
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REVIEW QUESTIONS Select the best an
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11. 12. At the time of observation,
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23. Weather conditions being equal,
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38. Visibility of 2 3/8 miles is re
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When more than one type of present
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4.1.2 Descriptors Descriptors are q
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Obscurations that stand alone, i.e.
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Page 82 and 83: layer aloft will be considered as m
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Page 88 and 89: Select the correct answer. REVIEW Q
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QUALITY CONTROL EXERCISE Each of th
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21. METAR KKKK 282045Z E29006KT 7SM
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42. METAR KFFF 302250Z 03008KT 40SM
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16. a. METAR 17. b. second 18. d. f
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11. - a change in wind direction of
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...unfocused lights of moderate int
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22. b precipitation occurring not a
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52. b. decreasing dominance. 53. b.
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24. 8 VV 25. 8 OVC 26. 7 BKN 27. as
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A-14
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A-16
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A-18
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18. 1200 UTC or other time modified
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9. Lower layer has 1 /8ths coverage
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16. METAR KFFF 312148Z 36005KT 1 1/
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43. METAR KGGG 052145Z 05009KT 4SM
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WET BULB TEMPERATURES 31 32 33 34 3
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WS Form B-11 (12-96) Pres. by WSOH
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C-3
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. If an altimeter setting indicator
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Training Guide in Surface Weather Observations - Multiple Choices

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