A second cold front connected to the large low near the pole, crossed SHEBA ship in the morning before the flight arrived. This front brought extensive cloud cover up to 7 km altitude according to the ship's radar. Surface winds shifted to southeasterly on the previous night, and then shifted to northwesterly as the front passed in the morning. Some of the altostratus cloud may have been present when the aircraft started taking data. But after 22:40 UT, the radar no longer showed any clouds above 1 km. The 00 UT sounding also found the atmosphere to be very dry above this level.
The satellite images at 23:18 UT show the altostratus/altocumulus clouds had moved northeast of SHEBA ship. The low stratus also showed a clear boundary just south of the ship. This clearing was moving away from the ship to the east.
The trajectories to SHEBA ship show show the effects of the near station low pressure center near the pole. Most of the trajectories remained in the Arctic Ocean circling around the low center. Only the surface and 9 km trajectories show a slight difference going back into the Asian coast around western Siberia.
The trajectories to Barrow show a different pattern from SHEBA ship. The low level air, surface to 1.5 km, came from the west across the Arctic Ocean from the central Asian coast. The higher levels, 3-9 km came from the south - the Pacific Ocean. The first day of the higher trajectories came from the Chukchi Sea southwest of Barrow. Two to four days back in time the trajectories trace back to the Aleutian Islands and the north Pacific Ocean.
