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feet is 190° at 10 knots with a temperature of -2C.
Wind speed between 100 and 199 knots are encoded,
so direction and speed can be represented by four digits.
This is done by adding 50 to the two-digit wind
direction; and subtracting 100 from the velocity. For
example, a wind of 270° at 101 knots is coded as 7701
(27 + 50 = 77 for wind direction and 101 – 100 = 0l for
wind speed). A code of 9900 indicates light and variable
winds (less than five knots). However, wind
speeds of 200 knots or more are encoded as 199.
It is important to note that temperatures are not forecast
for the 3,000-foot level or for any level within
2,500 feet of the station elevation. Likewise, wind
groups are omitted when the level is within 1,500 feet
of the station elevation. For example, the station elevation
at Denver (DEN) is over 5,000 feet, so the forecast
for the lower two levels is omitted.
TRANSCRIBED WEATHER BROADCASTS
A transcribed weather broadcast (TWEB) contains
recorded weather information concerning expected
sky cover, cloud tops, visibility, weather, and obstructions
to vision in a route format. This information is
transmitted over selected navigation aids such as very
high frequency omni-directional ranges (VORs) and
non-directional radio beacons (NDBs). At some locations,
the information is only broadcast locally and is
limited to items, such as the hourly weather for the
transmitting station and up to five adjacent stations,
local NOTAM information, the local TAF, and potential
hazardous conditions.
When a TWEB is available along a route of flight, it is
particularly useful for timely in-flight weather information.
At some locations, telephone access to the
recording is also available (TEL-TWEB), providing an
additional source of preflight information. The telephone
numbers for this service are listed in the A/FD.
A circled “T” inside the communication boxes of
selected NDBs and VORs on National Aeronautical
Charting Office (NACO) enroute and sectional charts
identifies the TWEB availability. In the regions where
there has been high utilization of TWEB, the FSS puts
the TWEB on a recording called Telephone
Information Briefing Service (TIBS). It can be
accessed prior to flight by calling 1-800-WX-BRIEF,
then choosing TIBS from the menu.
FD KWBC 151640
BASED ON 151200Z DATA
VALID 151800Z FOR USE 1700-2100Z TEMPS NEG ABV 24000
FD 3000 6000 9000 12000 18000 24000 30000
ALA 2420 2635-08 2535-18 2444-30 245945
AMA 2714 2725+00 2625-04 2531-15 2542-27 265842
DEN 2321-04 2532-08 2434-19 2441-31 235347
HLC 1707-01 2113-03 2219-07 2330-17 2435-30 244145
D
Figure 9-56. Winds and Temperatures Aloft Forecast.
9-40
APPENDIX A—KEY FOR TAF AND METAR
10-1
Soaring flight, maintaining or gaining altitude rather
than slowly gliding downward, is the reason most
glider pilots take to the sky. After learning to stay aloft
for two or more hours at a time, the urge to set off cross
country often overcomes the soaring pilot. The goal is
the same whether on a cross-country or a local flight—
to use available updrafts as efficiently as possible. This
involves finding and staying within the strongest part
of the updraft. This chapter covers the basic soaring
techniques.
In the early 1920s, soaring pilots discovered the ability
to remain aloft using updrafts caused by wind deflected
by the very hillside from which they had launched. This
allowed time aloft to explore the air. Soon afterward,
they discovered thermals in the valleys adjacent to the
hills. In the 1930s, mountain waves, which were not
yet well understood by meteorologists, were discovered
leading pilots to make the first high altitude
flights. Thermals are the most commonly used type of
lift for soaring flight, since they can occur over flat terrain
and in hilly country. Therefore, we will begin with
thermal soaring techniques.
As a note, glider pilots refer to rising air as lift. This is
not the lift generated by the wings as was discussed in
Chapter 3—Aerodynamics of Flight. The use of this
term may be unfortunate, but in reality it rarely causes
confusion when used in the context of updrafts. This
chapter refers to lift as the rising air within an updraft
and sink as the descending air in downdrafts.
THERMAL SOARING
When locating and utilizing thermals for soaring flight,
called thermalling, glider pilots must constantly be
aware of any nearby lift indicators. Successful thermalling
requires several steps: locating the thermal,
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Glider Flying Handbook(134)
