AT 4897m is Mount Vinson the highest mountain IN Antarctica but from a global perspective this is not extremely high. But due to its position it is one of the coldest summits to reach. The combination of low temperatures, high winds and bad weather can turn the climb of this mountain into a dangerous adventure.

Therefore it is of GREAT importance for guides as well as for climbers to:
•    be informed about the meteorological and climatological characteristics of the Mount Vinson area.
•    keep ‘an eye on the sky’, which means that by observing the weather one can see the first signs of changing weather.
•    have the knowledge to give an accurate discription of the prevailing weather conditions

Quasi Stationary Polar Anticyclone
The climatological and meteorological conditions in the Ellsworth Mountains area  are determined by the quasi-stationary polar high. This high pressure system or anticyclone, being a part of the global circulation pattern, ALMOST CONSTANTLY covers MAJORITY of the Antarctic continent.

Formation of a strong Surface Inversion
The vertical motion in a high pressure system is pointing downward. This downward motion or subsidence has a few important consequences for the airmass covering the Antarctic interior:  as it moves downward the airmass heats up (due to compression) and dries out. As a consequence a strong temperature inversion near the surface is formed. This surface inversion prevents a vertical flux from the surface: it keeps all moisture and momentum in the near-surface layer or boundary layer: there is no vertical exchange.

Formation of Fog and Low Stratus on the Branscomb Glacier (base camp)
The boundary layer with a surface inversion is a favourable environment to have the formation of low cloud and fog, as the indispensable moisture is kept near the surface. The upsloping southwestern side of the Branscomb Glacier is exposed to a katabatic wind regime. The katabatic wind flows roughly from SSW to NNE (true wind direction), which is almost parallel to the orientation of the glacier. This has two important consequences:
•    The katabatic flow pushes the air upward on the sloping southwestern side of Branscomb Glacier. This upward sloping air is subject to cooling and, depending upon its moisture content it reaches saturation and hence condensation. This condensation results in the formation of local fog or low stratus. So it is obvious that these parts of the Ellsworth Mountans are prone for fog and stratus formation.
•    This kind of fog/low stratus is very persisting and can linger for a few days.

The picture below shows the Ken Borek Twin Otter, operating for ALE, on the surface of the Branscomb glacier near Mt Vinson Base camp.

Moisture content of airmasses in the interior of the Antarctic continent.
Normally an airmass that is being advected (WHAT DOES THIS MEAN?) from the South is very cold and dry as it originates from the high Antarctic Plateau. On certain occasions frontal systems or mesoscale cyclones can bring moisture into the interior of the Antarctic continent. The residual moisture of these decaying systems can be caught in the katabatic outflow, resulting in the formation of low cloud or fog, as explained above.

Frontal systems and mesoscale cyclones.
Dry katabatic airstreams prevail during a big part of the summer season. Nevertheless on A REGULAR BASIS frontal systems and ON OCCASSION, mesocale cyclones can penetrate far into the Antarctic continent and determine the weather over the Vinson area.

We can distinguish two different systems:
•    The frontal depressions coming in from the west. These systems originate from the Bellingshausen/Amundsen Sea and bring multilayered cloud on to the mountain range.  Usualy these systems are not very active and they produce only intermittent and slight precipitation.
Note: The first signs of these systems are high Cirrus-clouds on the western horizon. If the angle of these clouds grows increasingly larger and the clouds become thicker and veil the sun than this frontal band is coming your way (see picture 2). A gradual pressure drop could be a sign as well but this is not very big with ‘Amundsen/Bellingshausen’ systems