collection of ridge wind maps
A complement to TherMap
Using a relatively
simple model, these maps have been computed to reveal the effect of
ridge winds. Numerous validations with actual flight records have revealed
that the maps reflect the real situation quite well, provided that the
underlying wind direction correspond to the locally prevailing wind.
A particular advantage of this approach is that the maps also show the
thermal potential of less visited regions.
© The utilization of the maps for noncommercial
purposes remains free. For commercial uses, quotations, as well for
further publication, written
copyright permission must be obtained via the mail address mentioned
at the end of this site.
During the last years long
distance mountain flights have demonstrated the often underestimated
potential of ridge winds. Due to this, and following the positive experiences
with TherMap, the meteorological section of OSTIV also expressed an
interest in ridge wind maps. WindMap is an attempt to provide an answer
Position the cursor on
the picture on the left and you can see a map extract of WindMap, a
tool for glider pilots, to visualize the local potential of ridge winds
for a given wind direction, assuming no other meteorological
interferences or mountain waves. The WindMap picture also contains an
actual flight track showing the flight phases with climbing (blue) and
sinking (white) phases.
For every multiple of
15 degrees (e.g. wind from 195° in the case of the example), ridge
wind maps may be downloaded from this site for numerous regions.
Before the flights WindMap
allows you to study the best itineraries, or to explain them to less
experienced pilots, particularly across less known regions. After the
flight, you may superimpose your flight tracks on these maps, typically
IGC-files (or kml-files with Google Earth), to find out where you might
have followed more promising paths. The maps may also be imported as
raster maps into some other flight analysis applications.
ridge wind maps
b. Maps considering channelled ridge wind
a. Simple ridge wind maps
Digital elevation models (DEM), such
as the worldwide 90m SRTM satellite models, provide a relatively detailed
topological profile of the surface of the earth. Extracts of these
files can be used to determine the special orientation of each surface
cell of about 90 meters. If wind from a given direction blows against
such a surface field, it will usually be diverted by the latter, basically
in the direction of the intersection between the plane of the surface
field and the plane determined by the original wind vector and its
mirror on the surface plane. This is of course only applicable where
the wind vector meets a surface element from above. The vertical component
of the diverted wind is used as a measure of the upwind potential
at the location of each surface field. A further factor of importance
is the downwind area behind obstacles within which no upwinds can
be expected. Based on empirical analyses WindMap assumes these areas
to be determined by a shadow declining by 10 degrees in the direction
of the wind. Despite its simplicity this model already leads to fairly
realistic ridge wind maps, as illustrated on the sample map shown
b. Maps considering channelled
In the simple model the wind deflection
is calculated independently for each surface element. In practice
this is only partly valid, namely when adjacent surface elements have
the same spacial orientation. However if wind blows up a narrowing
valley, the air flow tends to be compressed and hence the wind normally
accelerated. In the present, refined model, such compression effects
have been considered over a local distance of about 400 meters. This
has led to more pronounced maps, as can be seen when moving the cursor
over the picture of the simple model below. The refined method has
therefore been used for all maps offered on this site.
Region east of lake Walensee,
for wind from 195°, generated by the simple model.
Moving the cursor over the picture reveals the refined map with channelled
a. Selecting the right maps
b. Limitations of the WindMap approach
c. How to read the maps
d. Preflight use of maps
e. Post-flight analysis using the maps
a. Selecting the right maps
Depending on the extent of your flight you may
have to select the maps of more than one country or region
48° 00'’ N /
05° 30’ E
45° 30'’ N /
11° 00’ E
48° 00'’ N /
09° 30’ E
46° 00'’ N /
16° 20’ E
47° 30'’ N /
05° 00’ E
43° 00'’ N /
07° 30’ E
43° 20'’ N /
03° 00’ W
42° 00'’ N /
02° 30’ E
45° 00'’ N /
07° 30’ E
43° 30'’ N /
12° 30’ E
43° 30'’ N /
11° 30’ E
41° 00'’ N /
15° 00’ E
Wind direction :
offers 24 maps per region, with 15° increments for the wind
directions from 15° to 360°. Select the maps showing the
main wind directions of your flight. The wind directions are included
in the file name.
b. Limitations of the WindMap approach
of radar maps: Radar reflection signals
are not perfectly precise when scanning altitudes. They are rather
unreliable when reflected by water or ice. This it why it is difficult
to automatically identify lakes on the basis of radar scan data. In
the present TherMap version many lake outlines have therefore been
imported separately, but these imports had to be limited, due to the
manual effort involved, and hence not all lakes are displayed. Ice
covered surfaces may appear blurred. Fortunately neither of these
limitations is of real importance for the use of the TherMap maps.
Changing wind direction:
WindMap is based on a simple local model and each map is calculated
for one single wind direction. Wind directions and strength can however
change with the altitude and the geographical position. This can lead
to atmospheric interactions not covered by the WindMap model and which
the users must therefore interpret accordingly.
Whilst one part of a distance flight may be determined by ridge winds
another part may be dominated by thermals, with a blurred transition
zone in between. In such cases it is advisable to study the corresponding
maps for both, WindMap and TherMap. On the other hand during days
with strong winds it is possible to meet upwinds at locations having
no potential according to WindMap. This can be due to mountain waves
or large scale channelling effects, none of which are considered in
the WindMap model..
c. How to read the maps
The maps should be zoomed at least to 100 percent. Original maps may
contain around 20 megapixels, which corresponds to about 25 standard
screens. The maps are worthwhile to be studied in detail, if necessary
by zooming above 100 percent, due to their huge information content.
For your convenience it is recommended to use viewers (e.g. MS Picture
Manager®) permitting to maintain the zooming level and the selected
window frame while paging between different images.
As a backdrop WindMap uses simple topographic maps illuminated more
realistically from South-West. A basic wind speed of 6 m/sec
has been assumed. Its vertical component must reach at least 25 percent
of this, i.e. 1.5 m/sec, allowing a glider with a sinking speed of
0.75 m/sec to climb at about the same rate. Above this level the maps
are coloured as follows: Zones with a moderate climbing potential
are coloured from dark to light red (net climbing rates of 0.75 to
1.75 m/sec), whilst regions above this are coloured from beige to
yellow. This is illustrated by the following colour diagram:
At regular intervals the maps show white lines in the direction of
the wind . These lines only appear in downwind areas where no updrafts
are expected. Slopes facing the wind are hatched
if they are expected to be in the windshade of upwind terrains.
3D visualisation: Importing
the corresponding TherMap maps into Google Earth® (KML Ground
Overlays) or SeeYou® (raster maps) takes a few minutes, but this
can facilitate the preparation or the retrospective analysis of flights,
particularly when using the 3D mode. The advantage of Google Earth
is that "flight" routes can be freely chosen, which is useful
for flight preparations. For flight analyses the IGC records are frequently
extracted via SeeYou, but can easily be converted to KML-format of
Google Earth, which does not require importing the maps, but offers
less possibilities for illustrating the flight path.
South Foehn wind near Innsbruck, Austria: WindMap
3D-view für 195° wind, with Variometer flighttrack (reproduced
The picture also illustrates the high coincidence between the WindMap-potential
coloured on the surface and the recorded variometer values shown by
the track colour
d. Preflight and in-flight use of maps
Meteorological wind maps show that wind direction and strength change
with time, location, and altitude. WindMap shows a different map
for each wind direction and its use is only indicated if ridge winds
predominate thermal updrafts. This requires the judgement of the
user. Under these conditions the maps of WindMap can be a useful
complementary tool to the meteorological forecasts.
Pre-checking planned flight
paths: WindMap is best used before the flight to check
ridge wind situations at the expected time of overflight.
In-flight use of WindMap:
Consulting a map printout during the flight must not interfere with
the necessary observation of the flight space. Tests with mobile
navigation tools, into which TherMap hotspots had been imported,
have shown that distraction from flight observation remains a critical
issue, besides the limited readability of most navigation devices.
Future devices may one day offer better readability. However even
then, the mobile tools should be designed to automatically show
the hotspots depending on the actual wind direction at a given location,
to avoid distracting the pilot when manually selecting of the map
file of the local wind direction.
e. Post-flight analysis using the maps
The wind direction of the maps
used must be the same as that of the flight segment investigated.
Digital flightlogs provided by IGC-files are very precise and may
therefore permit to identify more easily where better itineraries
might have been followed. In order to minimize their size. TherMap
files are in JPG format.
As already mentioned, solution
providers like GoogleEarth ® and SeeYou® offer functions
to import WindMap files and to view them from above or in 3D. Goggle
does not need to convert the files into another format. Where possible,
it is also recommended to show the flight path in variometer option,
in order to visualize the climbing and sinking phases of the flight.
When importing the raster maps you have to enter the positions of
the country maps used (NW and SE corner coordinates), as indicated
under section a.
Example with foehn blowing from the
South near Innsbruck. For better contrast flight phases with significant
ridge winds are shown in blue.
The picture shows once again how well the WindMap model can represent
the updraft potential.This map has been produced with WindMap.
Select for the desired country region (Switzerland,
French Alps, Austria, Pyrenees, North Apennine, Central Apennine) the
field with the wind directions nearest to those of the flight (about
4-6 Mb per JPG map). Then either
double-click on the corresponding
field to open, analyse and, if desired, save the corresponding map
right-click on the same field and
request the target to be saved directly in a directory of your computer.
© Wafer:All maps of this collection
are provided by the copyright holder solely as an informational tool for
the planning of the best course of soaring flights. In particular, airports
and landing places are indicated mainly for geographical reference without
guarantees about their exact location and/or their operational conditions.
These maps are not intended to be used for navigation. Pilots should independently
confirm all information regarding airports and landing places and other
information required for navigation, and obtain an official briefing before
flight. In no event shall the copyright holder or the contributors be
liable for any direct or consequential damages caused by incorrect, obsolete
or missing graphical or written content.
The copyright holder: Beda Sigrist,
maps in Google Earth
A 3D view may facilitate the perception of a given wind
situation, as illustrated by this example.
Users having installed Google Earth©
on their PC (not on tablets or smartphones) can generate such perspectives
themselves. WindMap is based on the same topographic data (SRTM) as
Google Earth. You can view the WindMap files also in Google Earth, provided
that you have installed this application on a desktop (not yet possible
on Google Earth running on Android). This can be done as follows:
download the kmz-file of Windmap
by right-clicking here
and then saving the file on your computer.
upon clicking on the downloaded
kmz-file Goggle Earth will open, showing the links to the WindMap
files available on Google Earth.
Note that in order to avoid a significant loss of image
resolution, the original charts have been cut into tiles of 2 square
degrees which are referred to at the lowest level of the Google selection
tree. Therefore the selection hierarchy looks as follows
WindMap-3D > Region > Region+Wind
direction> Tile (coordinates of lower left corner)
It is crucial to avoid making selections
above "Region+Wind Direction", to prevent Google to superimpose
pictures with different wind direction. The selctions appear as overlays
on the Google screen. Picture transparency is set at 35 percent, but
may be adjusted manually (right click on selection tile field > click
on "Properties" > use transparency slider on top).
Who is behind WindMap?
WindMap is a private initiative of Dr. Beda Sigrist, a senior Swiss glider
pilot with a scientific background. Following the success of TherMap,
Dr. Hermann Trimmel and Olivier Liechti encouraged him to find out whether
it was not possible to also generate sensible ridge wind maps. Several
models were tried together with experienced competition pilots until the
present map collection was established. On this occasion, their invaluable
contributions are acknowledged, particularly those
of Stefan Leutenegger.
Can the application behind TherMap be purchased?
It would of course be interesting to have available directly the source
code needed to generate the maps. If the application itself was distributed,
the product would have to be wrapped up as a professional package and
update management procedures introduced to ensure that the users would
always have available the latest version. The resulting costs would require
a commercial approach. Apart from the much bigger effort, this would be
in conflict with the conditions set by SRTM, the distributor of the satellite
data, which is basically only made available for non-commercial use.
Can WindMap be extended to other regions, e.g. outside
The development of WindMap, like TherMap, has also been the result
of intensive information exchange with experts and experienced pilots,
because the models represent only partly physical processes, the
other part being rather models of the perception of experienced pilots.
For any new region to be addressed it would therefore be crucial to have
such competent and experienced counterparts to properly adjust and validate
the models, if necessary. With such help from colleages of new territories
it would however be a pleasure to extend the scope of WindMap beyond the
But even then, it cannot be guaranteed that the resulting
maps would be of practical use. For instance using the WindMap model,
ridge wind maps have also been tested for the fameous Appalachian ridges
in the USA. Although it turned out that the maps reflected the updraft
conditions quite well, it turned out that the skills of the most experienced
pilots were mainly due to their ability to judge where and whether it
was safe to "jump" between the usually low ridges. This skill
appeared to be far more important for long distance flights than the ability
to simply follow a given ridge. Since WindMap could not provide reliable
guidance for ridge jumping, it has been decided not to publish WindMap
for this region.
A website offering also forecasted
wind maps: Meteoblue
Meteorological panel of OSTIV
If you have any comments, suggestions, or questions, you are
welcome to directly contact the author Beda Sigrist by e-m@ail.