4. Wedge lines between the Greenwich Meridian and 110° longi- 

 tude are almost always migratory in character, moving from 

 west to east at 15 to 20 knots. 



5. In moving eastward with a high pressure wedge, barometic 

 tendency was successfully used to judge the speed necessary to 

 keep up with the wedge's eastward movement. A speed of 15 

 knots would almost always maintain a steady pressure trace and 

 indicate that exact pace was being kept with the wedge. 



CLOUDS 



1. Local forecasting for short periods can be handled adequately 

 by continuous observation of cloud conditions. The sequence of 

 clouds is similar to that experienced in midlatitudes. The clouds 

 associated with the Antarctic Front are very similar to those asso- 

 ciated with the Tropical or Equatorial Front. Alto-cumulus and 

 alto-stratus shields may be followed in 1 to 2 hours with moderate 

 to heavy precipitation and near zero conditions. Over the ocean 

 and ice packs, low stratus, which may obscure middle and high 

 clouds, exists for a large percentage of the time. When forecast- 

 ing for flight operations near the continent the appearance of this 

 stratus is very deceiving. Assuming a situation where the ship 

 is moored to land-fast ice with open water to the north, the follow- 

 ing situation often exists : southward, looking toward the conti- 

 nent, the stratus and snow will blend together, appearing very 

 white ; northward, the stratus appears very dark or nearly black 

 due to the reflection of the open water. When first observed this 

 water sky appears similar to an advancing roll cloud or squall line. 

 It is very dark and ominous and pilots will question the advisability 

 of flight operations at the time. 



However, after observing this phenomena for several hours it 

 will be found that there is very little change and everyone will soon 

 get used to it and, in fact, be glad to see a ivater sky, because it 

 indicates open water, which helps greatly in navigating the ice 

 pack. Another phenomena is ice blink. This is the reverse of 

 water sky and is light reflected from a field of ice on the low stratus 

 clouds. The clouds appear brighter or much whiter than the sur- 

 rounding clouds. When ice blink appears on the horizon it is a 

 sure indication that the ice pack will soon appear. When these 

 two situations exist it is most difficult to estimate a ceiling. In 

 some cases the estimate was as much as 4,000 feet in error when 

 checked by releasing a pilot balloon. 



2. The tops of most cloud formations can be reached at about 



215 



