last 101 code group. This allows other units to enter the
sounding into their TESS system and recreate an
accurate sounding profile.
What causes an upper-air sounding to be
automatically terminated by the MRS system?
What program in the MRS produces a printout of
the significant levels?
What does the letter "U" indicate next to a
significant level on the printout sheet?
What is the purpose of selecting significant
What is the criteria for selecting a significant
level wind based on direction?
Which activities in WMO Region IV do NOT
report fixed regional level winds?
What do the "RI" and "MRI" columns indicate
on the significant level printout sheet?
What is the purpose of the 101 indicator groups?
PILOT BALLOON (PIBAL) WIND
LEARNING OBJECTIVES: Identify the
procedures and equipment used to conduct
Identify the computer
software routinely used to evaluate PIBAL
Pibal observations during the 1940s through the
1960s were the primary method used to determine
atmospheric winds, and the balloons were tracked as
high as possible. Today, the primary application for
Pibal-observed winds is low-level wind measurements
for tactical fixed and rotary-wing aircraft operations,
and para-drop operations. Although most naval units
have little need to conduct Pibal observations, U.S.
Marine Corps observers attached to Mobile Weather
Support Teams and Recon Units routinely conduct
mobile-land station Pibal observations during field
operations and exercises. The collected information is
normally distributed locally in plain language, and
rarely encoded for electronic distribution.
A PIBAL is a balloon that is inflated with helium or
hydrogen to provide a fixed free lift, which, in turn,
produces a predictable ascension rate. It is tracked
visually with an optical theodolite (an instrument used
for measuring horizontal and vertical angles), with the
observed azimuth and elevation angles recorded each
The height (AGL) of the balloon at each
successive minute is based on a standard ascension rate
for the size of the balloon. These ascension rates are
listed in the FMH-3. When inflated properly to achieve
a set free-lift weight, balloons are assumed to ascend at
the standard rate, and true wind speed and direction are
computed from the change in the horizontal position of
The equipment and procedures required to conduct
a Pibal observation are thoroughly described in the
Federal Meteorological Handbook Number 3.
Guidance on encoding Pibal-observed winds by land,
ship, or mobile observers in International code (FM32-
IX PILOT, FM33-IX PILOT SHIP, AND FM34-IX
PILOT MOBIL codes) with the required Regional and
National coding practices are contained in the FMH-3.
Additionally, the basic International code is covered in
WMO Publication 306, Manual on Codes, Volume 1,
The equipment used to conduct a Pibal observation
is fairly limited. You will need an ML-474 shore
telescopic theodolite with an ML-1309 tripod (fig. 1-7)
30- or 100-gram balloons, a Universal Balloon Balance
(PIBAL) weight set or the MK-216/GM balloon
inflation nozzle and weight set, and a pressure-reducing
helium regulator with hose. To evaluate the data, you
will need either an appropriate calculator or computer
and Pibal evaluation program, or you may use the
manual method. The manual evaluation method
requires the use of the MF5-20 Winds Aloft
Computation Sheet, a set of Balloon Distance
Projected on a Curved Earth scales (Horizontal
Distance Out "HDO" scales) or a Horizontal Distance
Computer (FCW-19) or an 18-C-58 PIBAL-RAWM
calculator. An Aerological Plotting Board or Winds
Aloft Plotting Board with the appropriate wind speed
scale for the board, and a Winds Aloft Graphing Board
or Wind Aloft Plotting Chart could also be used. The
manual method is rarely attempted due to time
requirements and the quantity and weight of the
equipment. It has been replaced by the use of PIBAL
software for hand-held programmable calculators and