Page 64 - AFMAN 15-111, 12 MAR 2019

64 AFMAN15-111 12 MARCH 2019

Chapter 12

TEMPERATURE AND DEW POINT

12.1. Introduction. This chapter describes the observing and reporting standards for
temperature and dew point. Temperature is a measure of the average kinetic energy of air
molecules. Dew point is the temperature that a parcel of air at a constant pressure and water vapor
content must be cooled, in order for saturation to occur.
12.2. Temperature/Dew Point Group (T'T'/T'dT'd). The temperature and dew point are
encoded as two digits rounded to the nearest whole degree Celsius. Subzero temperatures and dew
points will be prefixed with an M. (T-0).
12.2.1. Temperature is separated from the dew point by a slash (/). For example, a temperature
of 4C with a dew point of -2C is encoded as "04/M02." A temperature of -0.5C is encoded
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as "M00." Exception: On the electronic (Excel ) AF Form 3803, use a minus sign (-) rather
than an M to indicate below zero temperature/dew points. The form macros will automatically
convert the minus sign to an M on the form while retaining the numerical value of the
temperature/dew point for calculations.
12.2.2. If the temperature is not available, the entire temperature/dew point group will not be
encoded. If the dew point is not available, the temperature is encoded followed by a slash (/)
and no entry will be made for dew point. For example, a temperature of 1.5C and a missing
dew point would be reported as "02/". (T-0).
12.3. Temperature/Dew Point Algorithms. The FBWOS continuously senses and measures
temperature and dew point and provides a report in degrees Celsius every minute. The 24-hr
maximum and minimum temperatures are based on the highest and lowest average temperatures
during the period of evaluation. Note: The AN/FMQ-19 stops reporting dew point when the
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temperature is ≤ -34 Celsius.
12.4. Standards and Reporting. Temperature and dew point are primarily determined using an
FBWOS or other approved digital instrumentation. If no digital method is available, use any
backup means available.

12.4.1. All measurements are reported in degrees Celsius (C). Reports are to the nearest whole
degree in the body of all observations. Reports are to the nearest 1/10th of a degree in the
summary of the day section of the AF Form 3803 and the remarks section of an observation.
Reports are to the nearest whole degree on the JET Form 3813 due to system.
12.5. Manual Observing Methods.

12.5.1. The primary method to obtain temperature and dew point are by directly reading the
sensor output from an FBWOS. If using back-up equipment, follow the procedures in the
applicable T.O. or user’s manual.

12.5.2. The maximum and minimum temperatures are the highest and the lowest temperature
values respectively for the time period (hourly, 6-hr, 24-hr). Determine maximum and
minimum temperatures from a digital readout or temperature recording equipment. If no other
record is available, use the temperature entries recorded in the observations (24-hour observing
locations only).